Guillermo Valenzuela-Venegas

Francisco Henríquez

Ludovic Montastruc

Marianne Boix

Felipe A Díaz-Alvarado

Toulouse Archive Ouverte

Keywords: Indicator, Resilience, Security, Eco-industrial parks

An Eco-Industrial Park (EIP) is a community of businesses that seeks to reduce the global impact through material sharing.

Even though an EIP presents an environmental improvement when compared with a set of stand-alone industrial plants, the established connections among the industrial participants can propagate failures, and become in a source of risk. For this reason, this work proposes an indicator to follow the resilience of EIPs, which is constructed to be applied on the design phase of eco-industrial parks, by means of an optimization problem. This indicator is based on two aspects of an industrial network: its topology and its operative flexibility. These aspects are measured by two respective sub-indicators, Network Connectivity Index (NCI) and Flow adaptability index (φ ). Both sub-indicators are integrated to compose a global resilience indicator. Finally, we apply the resilience indicator over five illustrative cases in order to analyze its applicability, obtaining consistent results.

Introduction

An Eco-industrial park (EIP) is a community of businesses located together on a common property, sharing materials, energy, or infrastructures. An EIP is motivated by the economic, environmental, and social improvements achieved through the collaboration among the firms within the park [START_REF] Boix | Optimization methods applied to the design of eco-industrial parks: a literature review[END_REF]). These relationships foster the implementation of Industrial Symbiosis (IS), which seeks to transform wastes, byproducts or products of a firm into inputs of another one taking advantages of their own connections [START_REF] Chertow | INDUSTRIAL SYMBIOSIS: Literature and Taxonomy[END_REF]).

An optimization problem can be formulated to design an EIP [START_REF] Boix | Optimization methods applied to the design of eco-industrial parks: a literature review[END_REF]). This formulation can back up decisions during the design phase of an EIP, formalizing the industrial planning to make the industrial development more sustainable.

In this context, there are several works regarding to propose a mathematical formulation in order to design an EIP [START_REF] Boix | Optimization methods applied to the design of eco-industrial parks: a literature review[END_REF]). Even though EIPs are largely studied in the literature, they suffer of reluctance from industries. Indeed, the potential industrial participants are often hard to convince due to security issues when connecting processes, because failures are also propagated through a network.

In computer science, a security or resilience factor is considered when defining a network so as to reduce its vulnerability. This measure takes into account the topology of the network, quantifying the damage done to the whole network when the most critical element (e.g. the element with the maximum number of connections) is removed [START_REF] Matta | Comparative Resilience Notions and Vertex Attack Tolerance of Scale-Free Networks[END_REF]).

In the context of EIP design, if we obtain an optimal configuration on the basis of the three sustainability dimensions, the question is what would happen if a participant is removed from the park. A pending issue in this field is to plan the connections of a single plant considering the stability of the other participants and their flow requirements, specially during failures within the network. In consequence, a new objective can be defined during the design phase to improve the security of the network by increasing its resilience. [START_REF] Chopra | Toward a network perspective for understanding resilience and sustainability in industrial symbiotic networks[END_REF] propose four metrics to apply over EIPs, all of them sustained on a network theory approach [START_REF] Chopra | Toward a network perspective for understanding resilience and sustainability in industrial symbiotic networks[END_REF]). The goal of these metrics is to measure the impact of a disruptive event of a park, focusing on their most affected nodes. These metrics are related with two aspects of the resilience of an industrial network: its connectivity and its efficiency. The first one establishes how necessary is to use a node to connect with others, and the second one, measures the changes in the efficiency of the park when a disruptive event occurs. Even though the authors obtain good results when apply these measures over an example, they propose to work on the resilience or adaptability of a network. In this context, an important lack of this metric is the quantification of the minimum performance of the network to be functional.

The novelty of this work is to create an indicator to measure the resilience of an industrial network based on its topology and operative aspects. The main difference with previous efforts is the orientation of the proposed indicator to operative changes after a disruption. The construction of this indicator relies on graph representation and is developed to be used in an optimization problem oriented to design an eco-industrial parks. To illustrate the use of this index, we apply it over five application cases. Accordingly, the objectives of this paper are to propose a resilience metric over EIPs and to illustrate its use.

Resilience indicator

We adopt the definition from [START_REF] Fiksel | Designing Resilient, Sustainable Systems[END_REF], where the authors define this concept as "the capability of the system to absorb disruptions before it changes its properties that control its functionality. This property allows an IS network to endure the impact of unforeseen event".

In this work, we consider a disruptive event as when a participant interrupts completely its activity. Therefore, if a disruptive event involves a participant, its associated connections (edges) disappear. In addition, since the network must continue operating, the other participants must modify the magnitude of their inputs and outputs to compensate the losses without important changes in its configuration (e.g. entering of a new participant).

Therefore, a resilience indicator must be focused on two aspects: (i) if the connections in the park are enough to withstand a disruptive event, and (ii) if the remaining participant can compensate the lost flows when a firm interrupts its activity.

For this purpose, the proposed resilience indicator measures two aspects of a network through the combination of two metrics: Network Connectivity Index (NCI) and Flow adaptability index (φ ). The first one measures the number of connections among participants and the second one measures the capacity of the participants of the network to compensate the flow demand when a firm suffers a disruptive event.

To define the metrics, and to support its application the design phase of EIP though an optimization problem, we use a graph representation of the park [START_REF] Aviso | Designing eco-industrial water exchange networks using fuzzy mathematical programming[END_REF]). Accordingly, each participant of the park is represented by a node, and the connections by oriented edges. Based on this representation, we define the following terms and sets: The goal of NCI is to measure if there are enough connections in a network to endure a possible disruption. In this sense, the more connections in the park, the better for the stability of the network, and NCI increases its value. The risk of isolation of the participants decreases with the grow of NCI.

The general idea of this metric is to set a maximum and a minimum number of connections of the network, and to establish its level of connectivity according to these values. We define the maximum number of connections as the maximum possible number of edges among participants (Eq. ( 1)); and the minimum number of connections, as the minimum number of edges to maintain the identity of the park (Eq. ( 2)). We assume that an EIP maintains its identity when each node has one connection at least. We define the corresponding NCI value associated to the maximum and minimum number of connections of a park. Then, if the network has C max m connections, NCI(C max n ) = 1. Otherwise, if the network has C min m connections, NCI(C min n ) = 0. With these values, and to simplify the calculation, we establish a linear function between both cases (Eq. ( 3)).

C max n = n(n -1) 2 (1) C min n = n - n 2 (2) NCI(n,C) = 2(C -n + ⌊ n 2 ⌋) n 2 -3n + 2⌊ n 2 ⌋ (3)
On the other hand, the goal of φ is to quantify the necessary flow to sustain the operation of the park by modifying the remaining flows after a disruption. In this sense, if the flow magnitudes in the park can change to compensate the activity interruption of a firm, the other participants can maintain their operation. Therefore, φ measures the flexibility of the park when a participant interrupts its activity and to determine if the other members can compensate this event through changes in their inputs and outputs.

Let k be the reference to a specific material being shared in the network. To determine the capacity of the park participants to absorb disruptive events (changes in the network), we consider that every plant has a security range for inlets and outlets, i.e. a maximum and minimum flow to operate. We define the maximum inlet and outlet capacity of a participant k ∈ N as Q max,in k and Q max,out k , and the minimum inlet capacity of a participant k ∈ N as Q min,in k . Since we need to measure the change over the park when a participant interrupts its activity, we define the "total lack of flows related to a disruption in k", L k , as:

L k = ∑ i∈OUT k max 0, Q min,in i -∑ m∈IN i ;m =k F m,i -∑ m∈IN i ;m =k Q max,out m - ∑ w∈OUTm;w =k F m,w + ∑ j∈IN k max 0, F j,k - ∑ l∈OUT k ;l =k Q max,in l -∑ v∈IN l ;v =k F v,l ∀k ∈ N (4)
As NCI, we define the worst and the best cases to compensate the loosed flow, and establish a linear function between them. The worst case is defined when each participant is operating at full capacity: L k is maximum. On the other hand, the best case is when the network can totally compensate the activity interruption of their participants: L k is minimum. Establishing both cases, we define φ k for the network affected by the interruption in the activity of the participant k (Eq. ( 5)). Accordingly, if the park is working at the worst case, φ k (L max k ) = 0; and if the park is working at the best case, φ k (L min k ) = 1. Finally, we apply φ k over each participant and calculate its average, in order to simplify the calculation, obtaining the Flow adaptability index φ of the whole park (Eq. ( 6)).

φ k (L k ) = 1 - L k ∑ j∈IN k F j,k + ∑ i∈OUT k Q min,in i k ∈ N (5) φ = 1 n ∑ k∈N φ k (6)
Finally, we define the resilience indicator as the average of NCI and φ .

Results and discussions

To analyze the applicability of the proposed indicator, we create four illustrative cases, where the connections among the participants are different in each of them (Table 1). Finally, to demonstrate the applicability of the proposed indicator to reality, we compose a new case considering all the previous examples, so as to address a new scenario with a higher complexity.

Table 1: Illustrative cases and their values of NCI, φ , and resilience indicator.

Example Configuration Results

Example Configuration Results

1

φ 1 = 0 φ 2 = 0 φ 3 = 0 φ 4 = 0 φ con f ig. = 0 NCI = 0.25 Resilience = 0.125 3 φ 1 = 0.667 φ 2 = 0.5 φ 3 = 0.125 φ 4 = 1 φ con f ig. = 0.573 NCI = 0.25 Resilience = 0.441 2 φ 1 = 0 φ 2 = 0 φ 3 = 0 φ 4 = 0 φ con f ig. = 0 NCI = 0.5 Resilience = 0.25 4 φ 1 = 0 φ 2 = 0.25 φ 3 = 0 φ 4 = 0.2 φ con f ig. = 0.112 NCI = 0.25 Resilience = 0.181 5 (Park) Resilience = 0.249
The first sub-indicator, NCI, considers the topology of a network, measuring the existence of connections in the park using the number of connections among the firms. Accordingly, if a network obtains a high NCI value, there are a lot of connections in the park, and therefore, the network does not loose connectivity when a disruptive event occurs. In contrast, if a network obtains a low NCI value, the park is weakly connected, and thus, the network has isolated participant during disruptions. This behavior can be seen on examples 1 and 2 (Table 1), where as the number of connection grows, the NCI increases its value. In the first example, if one participant interrupts its activity, it is highly probable that the network has isolated nodes. For instance, if the participant 2 interrupts its activity, participant 1 will loose connectivity. Conversely, in the example 2, since all participant have two connections, forming a closed loop, they will be always connected if any of them suffers a disruptive event. For example, if participant 2 interrupts its activity, the network maintains its connectivity. For this reason, the last configuration has the highest NCI value.

The second sub-indicator, φ , considers the performance of an industrial network, measuring the magnitude of the sharing flows and the feasibility of their substitution during disruptions. Therefore, if a network obtains a high φ value, the participants can endure the activity interruption of any of them, and therefore, the network can continue working.

We can observe on example 1, 3, and 4 (Table 1) the performance of this indicator, where the number of connections is kept constant (NCI = 0.25 for both of them), but the connected participant are changed. In the example 1, since all the participants obtain φ k = 0, they cannot be replaced, and therefore, the network cannot endure any disruptive event. In the example 4, the connection between participant 2 and 4 is changed for the connection between 1 and 4. This change makes modify the φ value of the network, suffering a little increase compared to the previous example. In this new configuration, participant 2 and 4 can be partially replaced for the other members when they suffer a disruptive event. In the example 3, the connection between participant 1 and 4 of the example 4 is changed for the connection between 1 and 3. In this new configuration, all the participant can be partially replaced by the other members, then φ of the network grows. This is because as some participants have more than one inputs or outputs, they do not depend just on one of them.

On the other hand, it is worth to note that the Flow adaptability index depends on the capacity of each firm to change the magnitude of its inputs and outputs, and on the connectivity of the participants. In consequence, φ depends on NCI.

An eco-industrial park is composed by a set of firms sharing different type of materials (e.g. water, biomass, oil, etc.). Each of these exchanges can be analysed through different sharing layers belonging to the same park, or by unconnected subsets within the park. In this context, two known examples in the literature are Kalundborg [START_REF] Knight | A rebirth of the pioneering spirit[END_REF]) and Ulsan [START_REF] Behera | Evolution of 'designed' industrial symbiosis networks in the Ulsan Eco-industrial Park: 'research and development into business' as the enabling framework[END_REF]). In the first case, the industrial network is composed by different sharing layers, where the same set of firms share water, sludge, steam, among others; in the latter, there are different unconnected subsets of firms sharing different type of materials, as steam, waste oil, and zinc powder, among others. An illustrative example is provided with this logic. It considers a park composed by all the previous examples, sharing different type of material at once. We can estimate the resilience value in this context as the average of the individual resilience values of each sub-network (Table 1).

A better estimation of the resilience value of the whole park is proposed for further works, because the integration of multiple sharing layers or subsets can evolve from an average to another function, so as to improve the assessment of real industrial parks.

Conclusions

We propose an indicator to measure the resilience of an EIP and to support future application in optimization problems in the design phase of eco-industrial parks. This indicator is based on two characteristics of an industrial network: its topology and its operation. These aspects are measured by two sub-indicators: NCI and φ , respectively. The first one measures the number of connections in order to maintain the connectivity of the participants during a disruption event. The second sub-indicator measures the capacity of the participants to modify their flows and to replace the loosed ones when a disruptive event occurs. Both sub-indicators are integrated, composing a global resilience indicator.

The resilience indicator has been applied over five examples, where the number of connections and the orientation of them are modified. We obtain consistent results regarding both sub-indicators and the resilience indicator. It is important to remark the need to construct a good estimation of the resilience of a whole park, where different type of material is exchanged among the participants. Besides the number of connections conditions the resilience, their orientation has significant effects on the resilience indicator. It is important to remark that there is a dependence between φ and NCI, since the existence of a flow requires the existence of connections. In consequence, further work can be done to integrate φ and NCI so as to compose a resilience indicator.

•

  N: Set of park participants. • C: Number of connections among park participants. • n: Number of participants in the network. • IN k : Set of participants that have an input into k ∈ N. • OUT k : Set of participants that have an output from k ∈ N. • Q min,in i : Minimum input needed capacity for the participant i ∈ N to operate. • Q max,in l : Maximum input capacity of the participant l ∈ N. • Q max,out m : Maximum output capacity of the participant m ∈ N. • F i, j : Magnitude of the flow between i ∈ N and j ∈ N. • φ k : Flow sensitivity of the participant k ∈ N in a network. • NCI: Network Connectivity Index of a park. • φ : Flow sensitivity of a park.

Antonio Espuña, Moisès Graells and Luis Puigjaner (Editors), Proceedings of the 27 th European Symposium on Computer Aided Process Engineering -ESCAPE 27 October 1 st -5 th , 2017, Barcelona, Spain

Acknowledgments G. Valenzuela-Venegas: This work was funded by the CONICYT-PCHA/Doctorado Nacional/2014-21140400. Felipe A. Díaz-Alvarado wants to thank the FCFM grant Apoyo a la Inserción Académica 2016; University of Chile.


B Courivaud

N Nolhier

G Ferru

M Bafleur

F Caignet

Novel 3D back-to-back diodes ESD protection

A 3D technology is used to design ESD protection devices. Based on back-to-back diodes, these devices are dedicated to first stage, external ESD protection. The main feature consists in using deep trenches, usually employed to build capacitors, to design 3D diodes. Specific trench configuration improves cumulative ESD stress robustness.

I. Introduction

Usually external ESD protection doesn't require a high surface area optimization as IC's ESD protection. But for applications where the protection and the device are reported on the same substrate, surface area should be minimized. The main goal of this study is to demonstrate the functionality of 3D diodes as ESD protection and to estimate the impact of surface reduction regarding conventional diodes. The technology process is based on an existing one developed by IPDIA [START_REF] Murray | Silicon based system-in-package: a passive integration technology combined with advanced packaging and system based design tools to allow a breakthrough miniaturization[END_REF] [START_REF] Gaborieau | 3D Passive Integrated Capacitors Towards Even Higher Integration[END_REF] for the design of high values capacitors. During an etch step, some holes are drilled in the silicon and then filled with polysilicon. In this particular case, the deposited polysilicon is doped with high phosphorus active concentration. After a thermal diffusion, we obtain a three dimensional diode including several holes connected in parallel. Back-to-back diodes are obtained by duplicating the 3D diode as depicted in Figure 1. The clamping voltage could be tuned in the range of 10V to 80V by changing technological parameters.

II. Layout parameter variations

In order to optimize ESD protection robustness we have studied two layout parameters (Figure 1): the distance (DIP) between holes and the distance between the two diodes (DID). As we decided to keep the same active surface area for each diode, the smallest distance between holes increases their quantity per diode (from 310 to 5700). A first study was carried out to determine the impact of this parameter on the breakdown voltage. From Figure 3, we can see that regardless of the number of holes, the leakage current is very steady and the breakdown voltage is roughly the same ( l9V).

The second parameter variation is the distance DID which has been varied from 35 to 165µm. We assumed that a trade-off has to be found between the current homogeneity during an ESD discharge and the device density impacted by a larger distance between diodes. As in the previous case, for all these devices no significant breakdown voltage variations have been found.

III. TLP results

To study the device ESD robustness, we performed a Transmission Line Pulsing characterization (TLP). The TLP stresses are increased until the device exhibits a leakage current equal to lµA, corresponding to I T2 . From the measured results presented in Figure 4, we can observe that I T2 increases with the number of holes. For large DIP distance, each hole can be considered as an elementary diode, so when more and more holes are used, the current density in each hole is lowered, and the ESD robustness is improved. This behavior saturates when we reach 2100 holes because the holes diffusions touch each others, creating a mega junction. The results demonstrate that the interdiode distance DID is also impacting the structure ESD robustness. When DID is increased, the intrinsic resistance of the device is increased too which should degrade ESD robustness in terms of power dissipation. But, as this added resistance acts as a ballast resistance, the resulting on-resistance of the device during ESD is lowered because current flow distribution is more uniform. DID have an optimum value. A good tradeoff between ESD robustness and surface area is found for a device formed by 5700 holes with a 95µm DID length. I T2 is 22A, corresponding roughly to 33kV HBM robustness. Total layout area of the structure is 160,000µm 2 . The hypothesis regarding the creation of mega junction has been verified. Cross sections of the devices have been prepared with a FIB setup and after a revelation step, the phosphorus diffusion behavior have been highlighted. On the picture 5, the DIP distance is sufficiently large to form separated holes. But for lower DIP distance we found lower limit before holes touch each other. This distance is approximately twice the width of a hole. However in a specific combination of DID and DIP values, the device exhibits a surprising behavior. Figure 6 shows that at high current stress of l0A, a first hole is damaged. But as the holes are in parallel, this latter fuses, and the rest of the structure is still functional up to 16 A with a reasonable leakage current (below lilA). So, if the maximum leakage current allowed by the protected power ICs, is below 100µA, the device has a good reliability regarding cumulative ESD stress.

IV. TCAD Analysis

To understand the behavior of the device investigated, a study has been carried out with TCAD simulation tools. Several assumptions were chosen for the simulator parameters. Thermal models have been neglected. In case of evaluating thermal breakdown this assumption should be critical but, in our case, we want only to highlight the difference in current distribution from a device to another. The purpose of the simulations is not to find I T2 . The benefit is to provide a good simulation convergence and avoid the limited thermal validity (600K-800K) of the impact ionization models [START_REF] Salamero | Accurate prediction of the ESD robustness of semiconductor devices through physical simulation[END_REF]. During TLP measurements, the I-V curve is constructed by extracting, for a given pulse, the current and voltage of device under test between 70 and 80 ns. We consider that during this time slot stationary regime is achieved. Based on this assumption high current simulations are performed using ACS technique [START_REF] Galy | Numerical evaluation between Transmission Line Pulse (TLP) and Average Current Slope (ACS) of a submicron gg-NMOS transistor under Electro-Static Discharge (ESD)[END_REF]. A single current ramp (10A, l00ns) is applied to the device rather than using several TLP pulses. The numerical calculation exhibits a better convergence and a great computational time speed-up. The major drawback of this method is a possible overvoltage during device triggering that could not be detected [START_REF] Delmas | Transient voltage overshoots of high voltage ESD protections based on bipolar transistors in smart power technology[END_REF]. The third assumption has been chosen regarding the structure geometry. A complete structure description is very complex and would lead to a huge structure mesh. We chose to perform bi-dimensional simulation with a limited number of holes (10) for each diode, as shown on Figure 7. For the total current calculation, an area factor has been tuned to fit the real device configuration.

A. DC Analysis simulations

A first simulation set has been performed in DC analysis to extract the breakdown voltage and calibrate the simulator. The impact of DID distance have been also studied. As reported in Table 1 the breakdown voltage is roughly the same irrespectively of the DID distance. Its value is slightly higher than the DC measurement. This can be explained by a little mismatch on doping profile description.

B. High current simulations

The measurement results in Figure 4 have shown that the ESD robustness is dependent on the DID distance between the two back-to-back diodes. When this distance increases, IT2 increases too but exhibits saturation for DID largest values. Even if it is not possible to extract IT2 from the simulations, the impact of DID values on the current distribution in all the holes have been studied.

Figure 8 shows the current distribution in each hole of the reversed biased diode for a total current of 10A. For the shortest DID distance, it is clear that the anode connected to the first hole, A I, carries the major part of the current because it is the closest hole to the forward biased diode that acts as a cathode, or an emitter if we consider the total device as a bipolar transistor with a floating base. This behavior remains for higher DID value but is attenuated. A higher DID distance induces, between the diodes, a higher serial resistance t h a t tends to attenuate the added current path from hole A1 to hole A10. This latter exhibits a surprising behavior. Even if it is located farther from the cathode, simulations show an increase of the current for this hole compared to neighboring holes (A9 or A8). This is due to the cylindrical junction created by the last trench. The current will predominantly flow towards the front anodes but will also be better distributed to the rear ones. This phenomenon must be taken into account to optimize the ESD robustness. High current versus voltage curves are presented in Figure 9. It shows that the on-resistance of the device in high current mode is increased with the DID distance, as discussed before. We can also notice that there is for each curve two different slopes. Roughly the device has two on-resistance values. Considering the lowest DID value, 35µm, the I-V curve presents a negative resistance between 200 mA and 600 mA. It is a snapback effect caused by impact ionization generated by the high electric field in the high concentration P layer. Due to this high electric field the electron hole pairs are drifted apart of the other direction. Consequently, the potential barrier height is reduced and the voltage drops too. This phenomenon appears when the P concentration is higher than 10 17 at/cm3 [START_REF] Bin | Punchthrough transient voltage suppressor for EOS/ESD protection of low voltage IC's[END_REF]. If the DID distance increases, the higher series resistance between diodes compensate this snapback effect. Of course, a trade-off must be found between ESD robustness, device surface area and ESD protection design window. As shown in Figure 9, if the DID distance is large, the sustained voltage for high current is very high, and the ESD protection would not be efficient.

V. Layout optimization strategy

A. Trench optimization

With the aim to optimize ESD structure robustness, a novel layout of our device has been designed. As seen previously, a specific DIP distance leads to holes touch each others with diffusion. Consequently, the emerging first idea has been to replace the holes by trenches along the length of the diode. The main advantage of trench is that we can benefit of more degrees of freedom for etching process. Then, with this particular feature, etching is deeper. Further, in the trenches, the doping concentration is the same at all point of this plan junction length and there is no more resistance variation. Figure 11 shows the cross section of trench diode. All these trenches have the same depth. One can observe that the trenches are not completely filled with polysilicon. Actually, the top of the trench is filled faster than the middle, and a cavity is formed along it. But we assume that there is no electrical impact because the doping diffusion is continuously present from the top to the bottom of the trench. Furthermore, these cavities should not pose a reliability issue for the device because they are totally encapsulated.

B. Width trench modulation

We have observed in paragraph III that the weakness of the previous device is the first line of holes. TCAD results in paragraph IV have also shown for high current density, that the major part of current flow through first holes. All current is carried by them and consequently device is failed. This phenomenon is exactly the same for trench structure and a new design has to be found in order to achieve a better current homogeneity in the diode. To have a better current distribution along the width of the diode, we need to decrease progressively the resistivity of each trench and adapt it as a function of the distance. This can be done by gradually increasing the trenches width. This width modulation offers another benefit. During the etching step, chemical species have an easier condition to penetrate in trenches. Consequently trenches are deeper in silicon substrate as we can see in the figure 12. This depth modulation of trenches will result in silicon intrinsically by a decrease of on-resistance. Indeed, as trenches are deeper at the rear, the distance traveled by the current is smaller in comparison with last trench device and the on-resistance in substrate is reduced. The particularity of this component resides on the self-compensation of the resistance of the substrate as shown in Figure 13. Figure 14 shows a cross-section of a device with a trench modulation of 300nm. As expected last trench is deeper than the first one. But this variation of 5 urn is not very significant. However we can imagine that if we take larger trenches, the corresponding depth is significant. We cannot define a fixed step of this depth modulation because the relation between the trench width and depth is not linear.

C. High current simulations

To confirm the previous hypothesis on current distribution in the structure, a TCAD simulation was performed under the same condition as explained in paragraph IV. The number of trenches has been limited to 10 for mesh consideration as depicted in Figure 15. The current distribution in the trenches has been plotted in figure 16 vs several DID distances. The simulation offers a trench width modulation of 0.5µm between two adjacent trenches. The injected TLP stress is fixed to l0A. We can compare TCAD results between figure 8 and figure 15. For the same total current injected in the component, a major part of the current is also carried by the first anode. However, for trenches A6 to A l0 we can see a different behavior. Whatever DID distance, the phenomenon is the same. The trench width modulation technique leads to a current distribution. If we look closely to DID 165µm curve, current in first anode is reduced (30%) and the current level in the rear trench is almost the same. The combination of ballast resistance due to large DID distance and the conductivity modulation induces current levels upstream and downstream positions in structure to be approximately the same.

VI. New TLP measurements

To demonstrate the efficiency of width modulation on ESD protection devices robustness, a study was carried out for different topology. For the same surface diode area (S-diode) of 4032µm 2 , three DID distance 55µm, 75um and 95um allow to have three corresponding total surface area (S-total) as above on the figure 17. This clearly shows that 3D technology is more robust than 2D's. Whatever DID distance Well3D robustness is approximately twice of Planar2D configuration, which is about 6kV HBM. If we focus now on 3D technology, we see directly than our first hypothesis on using simple trenches to improve surface junction area was a sound idea. We obtain a better robustness compared to well topology. I T2 is 13.7A corresponding of 20.5kV HBM robustness against 13.6kV for Well3D device. This increase is about 50%. The homogeneous doping concentration of first trench representing the main junction area gives a better current conductivity at on state. However, like Well3D we wanted to know in the same figure, the impact of DID distance on IT2 for Trench3D device. The change curve slope indicates us there is also a limit of this distance where IT2 stop to increase. The phenomenon is exactly the same for Well3D structure but this time, for a different current level. As previous seen on simulation, it would appear that the trench width modulation has also non-neglect impact. The current density must be more homogenous along trenches and should increase ESD robustness. Furthermore, increased trench width with the distance should also improve on-state resistance RON thanks to the change of depth trench. In the results shown below we wanted to quantify the impact of this modulation for different modulation width step. This step goes 100 nm to 300 nm but does not at the moment permit to give information on corresponding depth. From Figure 19, we see that a larger trench gives even better results in terms of ESD robustness. It is important to detail that V T2 is similar for all configurations (VT2=37 to 38V).

As seen on the Figure 20, for the same step width modulation about 100nm, doubling surface diode area gives better results. It's interesting to see that the evolution of robustness is the same whatever DID distance. This phenomenon should be kept up to a certain value of DID. When DID is 95um we can see there are not a large variation between the two diode's area. This hypothesis seems to be true.

VII. Conclusion

This work presented a novel 3D back-to-back diode ESD protection in a technology process dedicated to manufacturing high value capacitor. An etch step, necessary to form the capacitor, is used to produce three-dimensional elementary diodes. These elements are combined to form the back-to-back diode. This structure is appropriate to external, first stage, protection for high voltage ICs. Combining in the same component, high capacitors for filtering or decoupling, and efficient ESD protection, is a great challenge in system-level consideration. This study is based on experimental measurement on several test vehicles but also on TCAD simulations to better understand the device behavior in high current regime. The impact of layout variations on ESD robustness is also studied. The study has separated in three parts: first, 3Dwell back-to-back diode are investigated and two major parameters have been analyzed: the distance between the holes, and the distance between the two diodes. For a silicon surface area about 160 000um2, the best trade-off provides 33kV HBM robustness for the targeted ESD protection design window. For a surface silicon area of 30,000um2, Planar2D back-to-back diode robustness is low and doesn't exceed 6kV HBM robustness. Secondly, a new device configuration which replaces well by trench polysilicon has been investigated. This preliminary study has shown that for the same silicon surface area, device provides 20.5kV HBM robustness against only 13.6kV for Well3D device corresponding to an increase about 50%. Finally, to optimize this ESD protection device, a new emerging idea has been explored consisting to modulate trench width with many stepwise. The best configuration permits to have 22.7kV HBM robustness.

Figure 1 :

 1 Figure 1: Scheme of 3D back-to-back diodes. The back-to-back configuration deviates the E S D current when the voltage at the protection electrode

Figure 2 :

 2 Figure 2: Typical implementation of external 3D back-to-back diode protection.

Figure 3 :

 3 Figure 3: DC curves for several DIP lengths.

Figure 4 :

 4 Figure 4: TLP curves: IT2 versus number of holes for different DID values.

Figure 5 :

 5 Figure 5: Cross section of holes with phosphorus diffusion view.

Figure 6 :

 6 Figure 6: showing small impact of failed holes on the increasing leakage current.

Figure 7 :

 7 Figure 7: Doping concentration distribution of studied device.

Figure 8 :

 8 Figure 8: Anodes current distribution for several DID lengths.

Figure 9 :

 9 Figure 9: High I-V curves for several DID lengths.

Figure 10 :

 10 Figure 10: Scheme of 3D back-to-back Trench diodes.

Figure 11 :

 11 Figure 11: Cross-section with uncompletely filled trenches.

Figure 12 :

 12 Figure 12: Scheme of 3D back-to-back trench diodes with width and depth modulation.

Figure 13 :

 13 Figure 13: Schematic of conductivity compensation resulting into modulation of trench width.

Figure 14 :

 14 Figure 14: Cross section of trench diode with 300nm step width.

Figure 15 :

 15 Figure 15: TCAD current density calculation in a 3D device for a fixed l0A TLP stress.

Figure 16 :

 16 Figure 16: Anodes current distribution for several DID lengths.

Figure 17 :

 17 Figure 17: Layout view with the different surface diode.

Figure 18 :

 18 Figure 18: IT2-VT2 curves for Planar2D, Well3D and Trench3D back-to-back diode and for several DID lengths

Figure 19 :

 19 Figure 19: Bar-chart of I T2 for several step trench modulation width.

Figure 20 :

 20 Figure 20: I T2 versus S-diode for 100 nm step width modulation and three DID distance.

Table I :

 I DC curves simulation for several DID distances.


Bertrand Courivaud

Nicolas Nolhier

G Ferru

Marise Bafleur

Fabrice Caignet

Fabrice Caignet Novel

Novel 3D back-to-back diodes ESD protection

I. Introduction

Close to the application where external ESD protection is integrated, its surface aera should be minimized. The main goal of this study is to demonstrate the functionality of 3D diode as ESD protection and to estimate the impact of surface reduction regarding conventional diodes. The technology process is based on an existing one are developed by IPDIA company [START_REF] Murray | Silicon based system-in-package: a passive integration technology combined with advanced packaging and system based design tools to allow a breakthrough in miniaturization[END_REF][2] for the design of high values capacitors. During an etch step, we can make some holes in the silicon and after filling them with polysilicon. In this particular case, the deposed polysilicon is doped with high phosphorus active concentration. After a thermal diffusion, we obtain a three dimensional diode including as several holes connected in parallel. Back to back diodes is obtained by duplicate the 3D diode as depicted in Figure 1.

II. Layout parameter variations

In order to optimize ESD protection robustness we have studied two layout parameters, the distance (DIP) between the holes and the distance between the two diodes (DID). As we decided to keep the same active surface area for each diode, lower the distance between holes, involve an increase of their quantity (310 to 5700). A first study was carried out to determine the impact of this parameter on the breakdown voltage. Then, observing Figure 3, we can see that regardless of the number of holes, the leakage current are very steady an the breakdown voltage is slightly the same (19V).

The second parameter variation is the distance DID. As shown in Figure 4, DID have been ranged between & 35 to 165µm. Even if enlarge this distance consume more silicon surface area, we assume that an impact on current homogeneity could be found.

III. Results

To study the device ESD robustness, we perform a Transmission Line Pulsing characterization (TLP). The TLP stresses are increased until the device exhibits a significant leakage current, corresponding to I T2 . From the measured results presented in Figure 5, we can observe that the I T2 point increases with the number of holes. For large DIP distance, each hole can be considered as a elementary diode, so when more and more holes are used, the current density in each hole is lowered, and the ESD robustness is improved. This behaviour is saturating when the number of holes becomes important because the hole's diffusions touch themselves, creating a mega junction. The results demonstrate that the inter-diode distance DID is also impacting the structure ESD robustness. When DID is increased, the intrinsic resistance of the device is increased too, which should degrade ESD robustness in terms of power dissipation. But, as this added resistance acts as a ballast resistance, the resulting on-resistance of the device during ESD, is lowered because the triggering of the device is more uniform. DID value has an optimum. A good trade-off between ESD robustness and surface area is found for a device formed by 5700 holes with a 95µm DID length. I T2 is 22A, corresponding for a rough estimation of 33kV HBM robustness. Figure 6 shows that at high current stress of 10A, a first hole is damaged. But as the holes are in parallel, this latter blows-up, and the rest of the structure is still functional up to 16A with a reasonable leakage current (below 1µA). We are investigating this phenomena regard for cumulative ESD stress robustness.

Figure 6: showing small impact of failed holes on the increasing leakage current.

Figure 1 :

 1 Figure 1: Scheme of 3D back-to-back diodes.

Figure 1 :

 1 Figure 1: Typical implementation of external 3D back-to-back diode protection Clamping voltage requirement is tuned in the range of 10 to 80V regarding technological parameters.

Figure 3 :

 3 Figure 3: DC curves for several DIP lengths.

Figure 4 :

 4 Figure 4: Layout of device with DID variation As previous case, for all these devices no significant breakdown voltage variations have been exhibited.

Figure 5 :

 5 Figure 5: TLP curves : I T2 versus number of holes for different DID values. However in a specific combination of DID and DIP values, the device exhibits an amazing behaviour.Figure6shows that at high current stress of 10A, a first hole is damaged. But as the holes are in parallel, this latter blows-up, and the rest of the structure is still functional up to 16A with a reasonable leakage current (below 1µA). We are investigating this phenomena regard for cumulative ESD stress robustness.


Sandyanto Adityosulindro

Laurie Barthe
email: laurie.barthe@ensiacet.fr

Katia González-Labrada

Ulises Javier

Jáuregui Haza

Henri Delmas

Carine Julcour

Sonolysis and sono-Fenton oxidation for removal of ibuprofen in (waste) water

Two sonochemical processes were compared for the removal of ibuprofen in different water matrixes (distilled water and effluent from wastewater treatment plant). The effect of various operating parameters, such as pH (2.6-8.0), ultrasound power density (25-100 W/L), sonication frequency (12-862 kHz), addition of radical promoters (H 2 O 2 and Fenton's reagent) or scavengers (n-butanol and acetic acid), was evaluated.

Sono-degradation of ibuprofen followed a first-order kinetic trend, whose rate constant increased with ultrasound density and frequency. For this hydrophobic and low volatile molecule, a free-radical mechanism at the bubble interface was established. Coupling ultrasound with Fenton reaction showed a positive synergy, especially in terms of mineralization yield, while adding H 2 O 2 alone had no significant beneficial effect. Dedicated experiments proved this synergy to be due to the enhanced regeneration of ferrous ions by ultrasound.

Efficacy of the sonolysis process was hampered in wastewater matrix, mainly as the consequence of higher pH increasing the molecule solubility. However, after convenient acidification, sono-Fenton oxidation results remained almost unchanged, indicating no significant radical scavenging effects from the effluent compounds.

Introduction

Ibuprofen (IBP) (2-[4-(2-methylpropyl)phenyl]propanoic acid) is a common drug used to treat fever, pain, inflammation or minor injury, its annual consumption being about 200 tons/year [START_REF] Ineris | Données technico-économiques sur les substances chimiques en France: Ibuprofène[END_REF]. IBP can enter the environment through domestic, farming (intensive livestock production and aquaculture) and industry routes [START_REF] Rivera-Utrilla | Pharmaceuticals as emerging contaminants and their removal from water. A review[END_REF]. Several studies reported the presence of IBP in effluents from wastewater treatment plants (0.002-95 µg/L), in surface water (0.01-0.4 µg/L) and in drinking water (0.0002-0.0013 µg/L) [START_REF] Ziylan | The occurrence and fate of anti-inflammatory and analgesic pharmaceuticals in sewage and fresh water: Treatability by conventional and nonconventional processes[END_REF][START_REF] Azzouz | Influence of seasonal climate differences on the pharmaceutical, hormone and personal care product removal efficiency of a drinking water treatment plant[END_REF], proving the inability of actual treatment processes to completely remove this compound, as well as its persistence in the environment. Notwithstanding its medicinal use, IBP was shown to significantly affect the growth of several fishes, microorganisms, algae, bacterial and fungal species [START_REF] Feng | Removal of residual anti-inflammatory and analgesic pharmaceuticals from aqueous systems by electrochemical advanced oxidation processes. A review[END_REF][START_REF] Pomati | Effects of a complex mixture of therapeutic drugs at environmental levels on human embryonic cells[END_REF]. Furthermore, partial degradation of IBP might be dangerous since its transformation products can be more toxic [START_REF] Rizzo | Bioassays as a tool for evaluating advanced oxidation processes in water and wastewater treatment[END_REF]. Therefore, the development of water treatment processes for the conversion of IBP into innocuous compounds (small organic acids and/or CO 2 and H 2 O) is needed.

To date, advanced oxidation processes (AOPs) are among the most efficient treatments for the elimination of pharmaceutical contaminants in water [START_REF] Rivera-Utrilla | Pharmaceuticals as emerging contaminants and their removal from water. A review[END_REF]. AOPs are characterized by the formation of highly reactive and non-selective hydroxyl radicals ( % OH) which are able to mineralize almost all organic compounds. Among these, Fenton oxidation is very appealing due to its simplicity in generating % OH. Homogeneous Fenton oxidation (Eq. ( 1)) is based on the reaction between ferrous ions (Fe 2+ ) and hydrogen peroxide (H 2 O 2 ) under acidic condition [START_REF] Fenton | Oxidation of tartaric acid in the presence of iron[END_REF]. This reaction is characterized by a rapid degradation of organic compounds in the early stage of the process involving ferrous ions, followed by a much slower oxidation by Fe 3+ /H 2 O 2 [START_REF] Wang | A Comparative study of Fenton and Fenton-like reaction kinetics in decolourisation of wastewater[END_REF]. (1)

+ ↔ + = × + + + - Fe H O Fe-OOH H { K 3.1 10 [11]} 3 2 2 2 3
(2)

% → + = × + + -- s Fe-OOH OOH Fe { k 2.7 10 [11]} 2 2 3 1 (3)
Its main limitation is indeed due to the uneasy regeneration of Fe 2+ (Eqs. ( 2) and ( 3)) that may cause wastage of expensive H 2 O 2 reagent [START_REF] Navalon | Heterogeneous Fenton catalysts based on clays, silicas and zeolites[END_REF]. Furthermore, high iron salt concentrations (10-500 mg/L) -well above discharge limit (2 mg/L) -are normally needed to gain appreciable conversion and mineralization [START_REF] Babuponnusami | A review on Fenton and improvements to the Fenton process for wastewater treatment[END_REF][START_REF] Bagal | Wastewater treatment using hybrid treatment schemes based on cavitation and Fenton chemistry: a review[END_REF]. Such high concentrations can lead to techno-economic issues related to the formation of excessive Fe(III) hydroxide sludge and continuous loss of iron especially in large scale operation.

Ultrasound (US) is another promising AOP because it does not require any chemical addition and it is able to degrade organic pollutants through direct thermolysis (Eq. ( 4), in case of volatile compound) and/ or % OH attack (Eqs. ( 5) and ( 6)). Sonication generates compression and rarefaction cycles, thus cavitation bubbles are formed from nuclei and then collapse violently producing localized shock waves (temperature of around 5000 °C and pressure of 500 atmospheres during a few microseconds) [START_REF] Pilli | Ultrasonic pretreatment of sludge: a review[END_REF]15]. Such phenomenon gives rise to a pyrolytic cleavage of the molecules (including water) inside the bubble and to chemical reactions with the generated radicals at the bubble interface and/ or in the liquid bulk.

+ → Pollutant )))
degradation products (4)

% % + → + H O ))) OH H 2 (5) % + → Pollutant OH degradation products (6)
where))) refers to the ultrasound irradiation However, a low mineralization efficiency and a high energy consumption are the main drawbacks when US is used as single treatment [START_REF] Liang | Improvement in sonochemical degradation of 4-chlorophenol by combined use of Fenton-like reagents[END_REF]. Thus, it is more interesting to combine US with another AOP, for instance Fenton reaction [START_REF] Bagal | Wastewater treatment using hybrid treatment schemes based on cavitation and Fenton chemistry: a review[END_REF]. Theoretically, coupling US irradiation and Fenton oxidation (in the so-called sono-Fenton or US/Fenton process) can promote faster pollutant conversion/mineralization due to (i) higher generation of % OH (Eqs. ( 1) and ( 5)) [START_REF] Neppolian | Sonolytic degradation of methyl tert-butyl ether: the role of coupled Fenton process and persulphate ion[END_REF], (ii) improved mixing and contact between % OH and pollutant [START_REF] Bagal | Wastewater treatment using hybrid treatment schemes based on cavitation and Fenton chemistry: a review[END_REF][START_REF] Liang | Improvement in sonochemical degradation of 4-chlorophenol by combined use of Fenton-like reagents[END_REF], and (iii) enhanced regeneration of ferrous ions (Eq. ( 7)) [START_REF] Jih-Gaw | Oxidation of 2-chlorophenol in water by ultrasound/ Fenton method[END_REF].

% + → + + + Fe-OOH ))) Fe OOH 2 2 (7)
Several works have investigated the coupling of ultrasound and Fenton oxidation for the elimination of various organic compounds such as dyes, phenolic compounds and pesticides [START_REF] Bagal | Wastewater treatment using hybrid treatment schemes based on cavitation and Fenton chemistry: a review[END_REF][START_REF] Siddique | Synergistic effects of combining ultrasound with the Fenton process in the degradation of Reactive Blue 19[END_REF][START_REF] Chakma | Physical mechanism of sono-Fenton process[END_REF], and more recently pharmaceuticals [START_REF] Cruz-González | Enhancement of paracetamol degradation by sono-Fenton process[END_REF][START_REF] Lastre-Acosta | Ultrasonic degradation of sulfadiazine in aqueous solutions[END_REF][START_REF] Rayaroth | Degradation of pharmaceuticals by ultrasound-based advanced oxidation process[END_REF]. However, to our knowledge, this latter mechanism (Eq. ( 7)) was not fully established.

The aim of this work is to investigate IBP removal by sonolysis, Fenton oxidation and coupled ultrasound/Fenton oxidation process. The effects of sonication parameters and Fenton's reagent dosage are also addressed, as well as the influence of real water matrix.

Material and methods

Chemicals and solvents

IBP (C

Experimental set-up

Experiments were performed in a 1 L glass reactor, whose jacket was connected to a cooling thermostat in order to maintain the temperature (25 ± 2 °C). The reactor was stirred by a pitched-blade impeller. US probe was mounted at the bottom of the reactor (cup horn type) and direct continuous sonication of the solution was applied. Several ultrasonic devices were used in this study (Table 2). However, as shown in literature, calorimetric power can be used as reference for comparison of their results [START_REF] Liang | Improvement in sonochemical degradation of 4-chlorophenol by combined use of Fenton-like reagents[END_REF][START_REF] Goel | Sonochemical decomposition of volatile and non-volatile organic compounds-a comparative study[END_REF][START_REF] Mason | Quantifying sonochemistry: casting some light on a "black art[END_REF]. In addition, most of the experiments were carried out with equipment 1 since 20 kHz is a most common US frequency, which had already been successfully applied for such purpose [START_REF] Babuponnusami | A review on Fenton and improvements to the Fenton process for wastewater treatment[END_REF][START_REF] Bagal | Wastewater treatment using hybrid treatment schemes based on cavitation and Fenton chemistry: a review[END_REF]. It is also worth mentioning that a preliminary study indicated same sonochemical performance with various probe diameters (51 mm vs 35 mm). 20 mg/L IBP aqueous solution was prepared by dissolving IBP under vigorous stirring for 10 h in either distilled water or effluent from a municipal wastewater treatment plant (cf. Section 3.3). As abovementioned, concentration of IBP in water bodies of the environment is usually of tens of ng/L to tens of μg/L. However considering that application of AOPs is more economical for high contaminant loadings [START_REF] Miralles-Cuevas | Combined nanofiltration and photo-Fenton treatment of water containing micropollutants[END_REF][START_REF] Andreozzi | Advanced oxidation processes (AOP) for water purification and recovery[END_REF], as well as to achieve enough analytical precision, 20 mg/L of IBP (just below the molecule solubility) was used as initial concentration. For the Fenton-related experiments, the pH of the solution was adjusted to 2.6 with H 2 SO 4 (1 M solution), prior to the simultaneous addition of iron salt and H 2 O 2 to start the reaction. For the US-related experiments, sonication was applied from the starting of the reaction. During the experiments several samples were withdrawn (of 1 and 8 mL for HPLC and TOC analyses, respectively) and were immediately treated by 1 mL of phosphate buffer (mixture of KH 2 PO 4 0.05 M and Na 2 HPO 4 •2H 2 O 0.05 M) before HPLC analysis or 3 mL of quenching solution (mixture of phosphate buffer, KI 0.1 M and Na 2 SO 3 0.1 M) before TOC analysis to stop the reaction by precipitating dissolved iron (buffer) and/or reducing remaining oxidant (KI/Na 2 O 3 mixture) [START_REF] Haddou | Dégradation de dérivés de l'acide benzoïque par les procédés d'oxydation avancée en phase homogène et hétérogène: procédés Fenton, photo-Fenton et photocatalyse[END_REF]. The iron precipitate was removed on a 0.45 µm RC syringe filter prior to analyses of pollutant concentration.

Several experimental runs were duplicated to check for the reproducibility of concentration-time profiles of IBP and Total Organic Carbon (TOC) and the experimental errors were estimated by pooled standard deviations. The observed deviation was less than 5% for IBP and TOC concentration.

Analysis

IBP concentration was measured by liquid phase chromatography with UV detection at λ = 222 nm (PDA detector, Thermo Finnigan). Separation was performed on a C18 reverse phase column (ProntoSIL C18 AQ 5 μm, 250 × 4 mm) maintained at 40 °C. The mobile phase consisted in a mixture of acetonitrile and water (acidified with phosphoric acid at 0.1% v/v) fed in isocratic mode (60/40) at 1 mL/min. Samples were readily injected in the chromatograph after buffer treatment and filtration. Injection volume was set to 20 µL.

Total organic carbon (TOC) concentration was obtained from the difference between total carbon (TC) and inorganic carbon (IC) measured by a TOC analyzer (TOC-L, Shimadzu Corp.). In this case, samples were diluted by twofold with ultrapure water after addition of the quenching solution and filtrated. Injection volume was set to 50 µL and 400 µL for TC and IC, respectively.

Residual concentration of H 2 O 2 was determined by titanium tetrachloride method [START_REF] Chakma | Investigations in synergism of hybrid advanced oxidation processes with combinations of sonolysis + Fenton process + UV for degradation of bisphenol A[END_REF].

Results and discussion

The first series of experiments, described in Section 3.1 and 3.2, were performed using IBP solutions prepared in distilled water (DW). The matrix effect is addressed in Section 3.3.

Sonolysis (US)

Mechanism of IBP degradation under sonication

Under ultrasound irradiation (sonolysis), organic compounds can be degraded in three different zones, i.e. inside cavitation bubbles by thermolysis (Eq. ( 4)) and/or in the bubble interface and/or in the bulk solution by free radical attack (Eqs. ( 5) and ( 6)), depending on the volatility and the hydrophobicity of the molecule [START_REF] Goel | Sonochemical decomposition of volatile and non-volatile organic compounds-a comparative study[END_REF][START_REF] Gültekin | Ultrasonic destruction of bisphenol-A: the operating parameters[END_REF]. According to its low volatility and low water solubility (see Table 1), IBP degradation mechanism may correspond to a radical attack at the bubble surface. In order to confirm this hypothesis, two types of radical scavengers, namely n-butanol and acetic acid, were added to the IBP solution before 20 kHz sonolysis: n-butanol is a short chain alcohol with only partial solubility in water (log K ow = 0.88) known to be an effective % OH scavenger for the gaseous region and/or the interfacial region of the collapsing bubble [START_REF] Lastre-Acosta | Ultrasonic degradation of sulfadiazine in aqueous solutions[END_REF][START_REF] Quesada-Peñate | Sonolysis of levodopa and paracetamol in aqueous solutions[END_REF], while fully miscible acetic acid (log K ow = -0.17) reacts with % OH in the solution bulk [START_REF] Xiao | Using pulsed wave ultrasound to evaluate the suitability of hydroxyl radical scavengers in sonochemical systems[END_REF]. As shown in Fig. 1, addition of n-butanol and acetic acid (at 50 mM or 500 times the molar concentration of IBP) reduced the pollutant conversion from 48% after 3 h to 8% and 40%, respectively. Therefore, sono-degradation of IBP is mainly due to % OH attack at the liquid-bubble interface.

pH effect

The pH of IBP solution, initially at 4.3, was also adjusted before sonolysis to 2.6 and 8.0 with H 2 SO 4 and NaOH (1 M solution), respectively. The aim was to mimic pH condition of the Fenton reaction on the one hand, and pH of the wastewater effluent on the other hand. Lowering the pH did not modify IBP degradation rate, but a significant reduction (from 0.0035 min -1 to 0.0020 min -1 ) was observed at the alkaline value (Fig. 2). It can be explained by the different forms of IBP at a given pH. As the pKa of its carboxyl group is 4.9, IBP is in molecular form at pH 2.6 and 4.3, but fully deprotonated at pH 8.0. In ionic form, IBP should be less accumulated at the surface of the cavitation bubbles, where radical attacks mainly occurred. This result is also in agreement with previous studies on the sonolysis of ibuprofen [START_REF] Méndez-Arriaga | Ultrasonic treatment of water contaminated with ibuprofen[END_REF], diclofenac [START_REF] Güyer | Degradation of diclofenac in water by homogeneous and heterogeneous sonolysis[END_REF], dicloxacilin [START_REF] Villegas-Guzman | Enhancement and inhibition effects of water matrices during the sonochemical degradation of the antibiotic dicloxacillin[END_REF], paracetamol [START_REF] Cruz-González | Enhancement of paracetamol degradation by sono-Fenton process[END_REF][START_REF] Villaroel | Ultrasonic degradation of acetaminophen in water: effect of sonochemical parameters and water matrix[END_REF] and sulfadiazine [START_REF] Lastre-Acosta | Ultrasonic degradation of sulfadiazine in aqueous solutions[END_REF] conducted at high sonication frequency (300-862 kHz), that showed a reduction of the degradation rate at a pH value higher than the pKa of the molecule.

Effect of H 2 O 2 addition on sonolysis

The stoichiometric amount of H 2 O 2 required for IBP mineralization was calculated according to Eq. ( 8):

+ → + C H O 33H O 13CO 42H O 13 18 2 2 2 2 2 (8)
Under silent conditions, addition of two times (2×) the stoichiometric amount of H 2 O 2 did not result in any measurable IBP and H 2 O 2 conversion within 3 h at pH 4.3 or 8.0 and did not modify pH.

However, H 2 O 2 is expected to be decomposed by US and/or to react with % H generated by water sonolysis (Eq. ( 5)) thus generating additional % OH (Eqs. ( 9) and ( 10)) [START_REF] Gogate | Treatment of wastewater streams containing phenolic compounds using hybrid techniques based on cavitation: a review of the current status and the way forward[END_REF][START_REF] Pang | Review on sonochemical methods in the presence of catalysts and chemical additives for treatment of organic pollutants in wastewater[END_REF].

% + → H O ))) 2 OH 2 2 (9)
% % + → + H O H OH H O 2 2 2 ( 10
)
Formed % OH can degrade organic compounds (Eq. ( 6)), but also react with H 2 O 2 (especially when in large excess) (Eq. ( 11)) [START_REF] Lastre-Acosta | Ultrasonic degradation of sulfadiazine in aqueous solutions[END_REF][START_REF] Chakma | Investigations in synergism of hybrid advanced oxidation processes with combinations of sonolysis + Fenton process + UV for degradation of bisphenol A[END_REF][START_REF] Gogate | Treatment of wastewater streams containing phenolic compounds using hybrid techniques based on cavitation: a review of the current status and the way forward[END_REF] or recombine with different radicals (Eqs. ( 12)-( 16)) [START_REF] Rayaroth | Degradation of pharmaceuticals by ultrasound-based advanced oxidation process[END_REF][START_REF] Méndez-Arriaga | Ultrasonic treatment of water contaminated with ibuprofen[END_REF][START_REF] Neyens | A review of classic Fenton's peroxidation as an advanced oxidation technique[END_REF].

% % + → + H O OH OOH H O 2 2 2 (11) % % + → OH OH H O 2 2 (12) % % + → OH H H O 2 ( 13
) % % + → + OH OOH H O O 2 2 (14)
% % + ↔ + OOH OOH H O O 2 2 2 ( 15
) % % + → OOH H H O 2 2 (16)
At natural pH, addition of two times the stoichiometric amount of H 2 O 2 (6.4 mM) did not modify IBP sono-oxidation rate, while a slight decrease was observed at seven times (7×) the stoichiometric amount of H 2 O 2 (22.4 mM) of oxidant (Fig. 3A). These results confirmed those of some previous studies reporting no effect [START_REF] Chakma | Investigations in synergism of hybrid advanced oxidation processes with combinations of sonolysis + Fenton process + UV for degradation of bisphenol A[END_REF] or even a detrimental effect of H 2 O 2 [START_REF] Frontistis | Sonodegradation of 17α-ethynylestradiol in environmentally relevant matrices: laboratory-scale kinetic studies[END_REF] for hydrophobic compounds and low frequency US.

The existence of different reaction zones for IBP (bubble surface) and H 2 O 2 (bulk solution) could be hypothesized to explain why H 2 O 2 did not help the pollutant degradation under US irradiation [START_REF] Frontistis | Sonodegradation of 17α-ethynylestradiol in environmentally relevant matrices: laboratory-scale kinetic studies[END_REF], while its scavenging effect at high concentration (Eq. ( 11)) could explain the results observed at 22.4 mM. However, no decomposition of H 2 O 2 was measured at the lowest concentration, excluding the first mechanism.

On the other hand, at alkaline pH, H 2 O 2 sonolysis did occur (5% conversion) and accelerated the pollutant oxidation (Fig. 3B), although not reaching the degradation yield observed at pH 4.3.

3.1.4. Effect of ultrasound operating parameters 3.1.4.1. Effect of ultrasound power density (D US ). Three levels of ultrasound power density (D US ) -25, 50 and 100 W/Lwere tested during 180 min, corresponding to a specific energy (E US ) of 270, 540 and 1080 kJ/kg, respectively. As shown in Fig. 4A, the degradation rate of IBP increased with increasing D US in the investigated range. This is the consequence of higher number of collapsing bubbles that enhanced the formation of % OH. An optimum value of D US should be expected, due to bubble cloud formation on the emitter surface absorbing or scattering the sound waves above a critical value [START_REF] Gogate | Sonochemical reactors: important design and scale up considerations with a special emphasis on heterogeneous systems[END_REF], but due to the limitation of our ultrasonic equipment could not be attained. Calculated first-order rate constants were as follows: k 25W/L = 0.0024 min -1 (R 2 = 0.992), k 50W/L = 0.0035 min -1 (R 2 = 0.996), k 100W/L = 0.0048 min -1 (R 2 = 0.994), showing however that the positive effect of D US already levelled off (Fig. 4B).

Effect of sonication frequency (f US )

. The influence of frequency on sonochemistry is complex. Cavitation threshold increases and cavities appear to release less energy upon collapse at high frequency (> 100 kHz), but fewer acoustic cycles are required for the bubbles to reach their resonant size (which means more cavitation events) [START_REF] Beckett | Impact of ultrasonic frequency on aqueous sonoluminescence and sonochemistry[END_REF]. Moreover, more radicals should escape before being recombined due to a more rapid collapse [START_REF] Petrier | Ultrasonic degradation at 20 kHz and 500 kHz of atrazine and pentachlorophenol in aqueous solution: preliminary results[END_REF]. Therefore, high frequency is usually preferred for sonochemistry applications. Indeed, according to Fig. 5, IBP removal after 180 min was increased from 48% to 87% when increasing f US in the 20-862 kHz range. Degradation rates followed a first-order kinetic trend with: k 20kHz = 0.0035 min -1 (R 2 = 0.996), k 580kHz = 0.0084 min -1 (R 2 = 0.984) and k 862kHz = 0.0102 min -1 (R 2 = 0.959). Close values obtained at 580 and 862 kHz could be explained by similar % OH effective production rate (evaluated from H 2 O 2 concentration monitoring), as reported by Güyer and Ince with analogous equipment [START_REF] Güyer | Degradation of diclofenac in water by homogeneous and heterogeneous sonolysis[END_REF]. An optimal frequency for radical-mediated sonolysis was also observed by these authors as a consequence of abovementioned antagonist effects at high frequency.

Interestingly, audible frequency (12 kHz) was also able to slightly degrade IBP (16% after 3 h, k 12kHz = 0.0008 min -1 , R 2 = 0.968). Corresponding H 2 O 2 generation rate was 0.18 µM/min (R 2 = 0.928) with respect to 0.45 µM/min (R 2 = 0.940) for 20 kHz irradiation, confirming the similar evolution of H 2 O 2 generation and IBP degradation rates.

In all cases, TOC removal was low: 2%, 7%, 10% and 11% under 12, 20, 580 and 862 kHz irradiation, respectively. It could indicate that more hydrophilic degradation products were formed during sonication, as for instance n-hydroxyl-ibuprofen (log K ow = 2.25) [START_REF] Michael | Proposed transformation pathway and evolution profile of diclofenac and ibuprofen transformation products during (sono)photocatalysis[END_REF][START_REF]INERIS, 1-hydroxy-ibuprofene[END_REF]. [START_REF] Babuponnusami | A review on Fenton and improvements to the Fenton process for wastewater treatment[END_REF][START_REF] Bagal | Wastewater treatment using hybrid treatment schemes based on cavitation and Fenton chemistry: a review[END_REF].

Under silent conditions, the Fenton reaction (F) proceeded in two distinct steps (Fig. 6A): first a fast oxidation yielding up to 60% conversion of IBP within 5 min; then, a much slower degradation rate until the end of the reaction, which cannot be fitted either with first or second order kinetics. This behavior is consistent with that reported in previous studies on homogeneous Fenton oxidation of IBP [START_REF] Sabri | Chemical oxidation of ibuprofen in the presence of iron species at near neutral pH[END_REF][START_REF] Marković | Application of non-thermal plasma reactor and Fenton reaction for degradation of ibuprofen[END_REF]. At higher iron concentration (0.5-1 mM Fe), the authors observed 90% of IBP degradation in the first 5 min. The initial reaction stage corresponded to the fast % OH generation from reaction between ferrous ions and H 2 O 2 (Eq. ( 1)). Then, formation of stable ferric complexes, such as Fe-OOH 2+ (Eqs. ( 2) and ( 3)), hindered Fe 2+ regeneration and further radical generation. In the low concentration range investigated, increasing Fenton's reagent was found beneficial (no scavenging effect from H 2 O 2 or Fe 2+ ).

Coupling Fenton reaction with 20 kHz ultrasound (US/F) led to a clear enhancement of IBP degradation rate after the first 5 min of reaction (Fig. 6A). At low reagent concentration, full abatement of IBP was observed in US/F(-) process after 3 h vs. only 62% in F(-). At high reagent concentration, application of US reduced the time needed for 95% IBP degradation from 180 to 60 min. TOC removal was also significantly improved by the process coupling, but a much slower reaction rate indicated that more refractory degradation products were formed during the oxidation (Fig. 6B). At best conditions, US/F(+) achieved 40% TOC conversion within 180 min, vs. 10% or less for each of the separate process (cf. Section 3.1.4 for sonolysis).

Moreover, H 2 O 2 consumption at the end of Fenton (F(+)) and sono-Fenton (US/F(+)) oxidation was 13% and 44%, respectively. Higher amount of residual oxidant confirmed a lower overall activity of the Fenton catalytic system under silent conditions. Indeed, beyond additional radicals generated from water sonolysis (Eq. ( 5)), positive synergistic effect observed in the combined process could be ascribed to the sono-regeneration of ferrous ions, as illustrated by Eq. ( 7) [START_REF] Jih-Gaw | Oxidation of 2-chlorophenol in water by ultrasound/ Fenton method[END_REF].

In order to confirm such effect, a complementary experiment was conducted. Same amounts of H 2 O 2 and ferrous salt as in F(+) experiment were mixed into 100 mL of acidic distillated water (pH 2.6) during 60 min to pre-form the expected Fe-OOH 2+ complex. Fenton oxidation was then started by addition of this solution into 900 mL of IBP solution. The system was let under stirring for 180 min (silent Fenton oxidation), then sonication was applied for another 180 min period (sono-Fenton oxidation). In this case, only 4% of IBP was converted within 5 min (Fig. 7) vs. 60% for the standard Fenton oxidation procedure (Fig. 6A). The time-concentration profile of the pollutant also exhibited two different stages, with an IBP removal yield almost plateauing at 20-25% after 90 min. Ultrasound application at t = 240 min immediately accelerated IBP oxidation, the first-order rate constant (k = 0.0102 min -1 , R 2 = 0.978) being three times higher than for the sole sonolysis (cf. Section 3.1.4, k = 0.0035 min -1 ).

Effect of ultrasound operating parameters

To achieve appreciable TOC removal, the highest concentration of Fenton's reagent was applied for the study of ultrasonic parameters: [H 2 O 2 ] = 6.4 mM (twice the stoichiometric amount) and [Fe 2+ ] = 0.134 mM.

Effect of ultrasound power density (D US ).

As abovementioned, high ultrasound power density (D US ) promotes higher formation of % OH and thus improves degradation rate and efficiency of sonolysis process (Section 3.1.4). Nonetheless, the effect of D US on sono-Fenton oxidation process has been scarcely investigated. Siddique and coworkers [START_REF] Siddique | Synergistic effects of combining ultrasound with the Fenton process in the degradation of Reactive Blue 19[END_REF] reported that degradation of dye by homogeneous sono-Fenton oxidation increased from 60% to 75% with increasing ultrasonic intensity from 4 W/cm 2 (40 W/L) to 8 W/cm 2 (80 W/L). In the present study, the effect of ultrasound power density on sono-Fenton oxidation process was evaluated at 25 W/L, 50 W/L and 100 W/L (figure not shown). Time-concentration profiles of IBP were found similar on the whole D US range. Conversely, varying D US from 25 to 50 W/L improved TOC removal from 29% to 39%, but further increase to 100 W/L did not show additional benefit. This observation suggests the existence of optimum D US for sono-Fenton process.

Effect of ultrasound frequency (f US ).

Despite growing interest for sono-Fenton process in the literature, information about optimum US frequency is still scarce, because previous studies [START_REF] Babuponnusami | A review on Fenton and improvements to the Fenton process for wastewater treatment[END_REF][START_REF] Bagal | Wastewater treatment using hybrid treatment schemes based on cavitation and Fenton chemistry: a review[END_REF][START_REF] Rayaroth | Degradation of pharmaceuticals by ultrasound-based advanced oxidation process[END_REF]] usually operated at a single value (in the 20-40 kHz range). Sonochemical effects being suspected in the enhanced ferrous iron regeneration, two high US frequencies (580 and 862 kHz) were investigated. An audible frequency (12 kHz) was also applied since this frequency is rarely used in sono-Fenton process. Experimental operating conditions were set to 20 mg/L IBP, 6.4 mM H 2 O 2 , 0.134 mM Fe, pH 2.6 and temperature 25 °C.

Fig. 8 revealed that degradation rate of IBP increased with increasing sonication frequency, but the differences were mostly marked between 12 and 20 kHz. Likewise, TOC abatement was also favored at high frequency: 25% at 12 kHz vs. 48% at 862 kHz (after 3 h of reaction). The mineralization results are comparable to that obtained in previous studies on sono-Fenton oxidation of IBP (55% in 240 min) performed with high frequency ultrasound (300 kHz) and low molar ratio of H 2 O 2 /Fe (0.3) [START_REF] Méndez-Arriaga | Mineralization enhancement of a recalcitrant pharmaceutical pollutant in water by advanced oxidation hybrid processes[END_REF], and on sono-enzymatic degradation of IBP (37% in 60 min) using low frequency ultrasound (37 kHz) and horseradish peroxidase enzyme [START_REF] Chakma | Investigations in sono-enzymatic degradation of ibuprofen[END_REF].

Effect of real water matrix

Sonolysis and homogeneous sono-Fenton oxidation processes were shown to be promising methods for the removal of IBP in water. However, all the experiments that have been done so far were conducted in distillated water (DW). In order to investigate the efficiency in real application, some experiments with a real wastewater matrix (WW) were performed. Wastewater consists in a complex mixture of organic and inorganic compounds, such as nutrients, salts and many substances that could influence the outcome of advanced oxidation processes [START_REF] Giannakis | Ultrasound enhancement of near-neutral photo-Fenton for effective E. coli inactivation in wastewater[END_REF]. For instance, the presence of organic (humic acid, fulvic acid, etc.) and inorganic compounds (chloride, carbonate, bicarbonate, and phosphate ions) in WW may hamper Fenton reaction by scavenging % OH and/or forming iron complex [START_REF] Xiao | Sonochemical degradation of ciprofloxacin and ibuprofen in the presence of matrix organic compounds[END_REF][START_REF] Tokumura | Comprehensive study on effects of water matrices on removal of pharmaceuticals by three different kinds of advanced oxidation processes[END_REF]. On the other hand, phenolic compounds that WW may contain could reduce ferric ion to ferrous ion and thus enhance Fenton reaction [START_REF] Tokumura | Comprehensive study on effects of water matrices on removal of pharmaceuticals by three different kinds of advanced oxidation processes[END_REF].

According to recent reviews on hybrid processes [START_REF] Oller | Combination of advanced oxidation processes and biological treatments for wastewater decontamination-a review[END_REF][START_REF] Ganiyu | Coupling of membrane filtration and advanced oxidation processes for removal of pharmaceutical residues: a critical review[END_REF], AOPs are recommended in combination with membrane filtration as post-treatment of biological process for destruction of refractory organics in concentrate stream. Such hybridization allows the AOPs to reach appreciable mineralization level in relatively short oxidation time, and to save chemicals and energy.

In this study, water samples taken after biological treatment of a municipal wastewater treatment plant located in Nailloux village (France) were used to prepare the IBP solution (at 20 mg/L). Table 3 shows the physicochemical characteristics of this effluent. After addition of IBP, TOC concentration increased to 25 mg/L, IBP being the major organic compound in this matrix. The amount of carbonate and bicarbonate was evaluated from inorganic carbon (IC) analysis and the measured concentration level (29.4 mg/L) could be high enough to scavenge % OH at neutral and alkaline pH [START_REF] Zhang | Degradation of CI Acid Orange 7 by ultrasound enhanced heterogeneous Fenton-like process[END_REF]. On the other hand, the initial iron concentration (< 0.05 mg/L) appeared too low to effectively contribute to Fenton oxidation mechanism.

Matrix effect is evaluated for sonolysis (US), homogeneous Fenton (F) and sono-Fenton (US/F) oxidation in Fig. 9. The treatment efficiency in distilled water (DW) was also recalled for comparison purpose. As usual, the initial pH of DW and WW was set to 2.6 (using H 2 SO 4 ) for the Fenton and sono-Fenton oxidation runs, while the pH of WW was not adjusted for sonolysis. Degradation of both IBP and TOC by ultrasound was significantly hampered in WW. Lower IBP removal in WW (24% vs. 48% in DW after 180 min) could be mainly explained by a pH effect, the initial pH of the IBP solution varying from 4.3 to 8.0 whether prepared with DW or WW, respectively. As abovementioned (see Section 3.1.2.), pH value of 8.0 indeed reduced the sono-degradation of IBP to 31% in DW by increasing the molecule solubility. Competition or scavenging effects from organic and/or inorganic compounds of WW thus seemed to have only a minor effect.

After preliminary acidification to 2.6, time-concentration profiles of IBP during Fenton oxidation were almost superimposed for the two matrixes, while a slight decrease was observed for sono-Fenton process when in WW (Fig. 9A). Therefore, it seems to confirm that IBP didn't strongly compete for radicals with the organic molecules present in WW, and that iron complexation and free-radical scavenging were not significantly increased in this matrix. In particular, inorganic carbon content was almost totally converted into carbonic acid and CO 2 .

Moreover, overall TOC removal by Fenton oxidation was improved in WW (25% vs. 9%, Fig. 9B). Fenton oxidation test without IBP proved this result to be mainly the consequence of more readily oxidized organic compounds in WW (50% TOC removal). However, similar behavior was not observed in sono-Fenton oxidation. This might due to selective effect of acoustic cavitation towards specific organic molecules [START_REF] Torres | Sequential heliophoto-Fenton and sonication processes for the treatment of bisphenol A[END_REF] and complex interplay between iron and WW compounds (and/or their oxidation intermediates) somewhat hampering sono-regeneration of Fe 2+ .

All these results showed Fenton and sono-Fenton oxidation as promising post-treatment processes for pharmaceutical containing wastewaters.

Conclusion

The objective of this work was to study ibuprofen removal by sonolysis and sono-Fenton process. % OH-mediated oxidation at the bubble surface was proved as the main degradation mechanism in the pollutant sonolysis. Combination of homogeneous Fenton oxidation with US irradiation was found to be more effective than the sum of individual processes, especially in terms of mineralization yield. The sono-regeneration of ferrous ions from ferric complex could explain this positive synergy, which yielded up to 50% of TOC removal in 3 h with a low concentration of Fenton's reagent (especially an iron concentration below 10 mg/L). In real wastewater effluent, sonolysis was hampered mainly due to alkaline pH conditions increasing the pollutant solubility. Preliminary acidification could maintain the efficiency of Fenton and sono-Fenton oxidation.

Fig. 1 .

 1 Fig. 1. Effect of radical scavenger on IBP sonolysis. ([IBP] 0 = 20 mg/L in DW, pH 0 = 4.3 (natural), T = 25 °C, f US = 20 kHz, D US = 50 W/L, [scavenger] 0 = 50 mM).

Fig. 2 .

 2 Fig. 2. Effect of the solution pH on IBP sonolysis. ([IBP] 0 = 20 mg/L in DW, pH 0 = 2.6-8, T = 25 °C, f US = 20 kHz, D US = 50 W/L).

Fig. 3 .

 3 Fig. 3. Effect of H 2 O 2 addition on IBP removal under US irradiation: (A) pH 0 = 4.3 and (B) pH 0 = 8.0 ([IBP] 0 = 20 mg/L in DW, T = 25 °C, f US = 20 kHz with D US = 50 W/L under sonication, [H 2 O 2 ] 0 = 0-22.4 mM).

Fig. 4 .

 4 Fig. 4. Effect of ultrasound density on IBP sonolysis: (A) concentration-time profile and (B) first-order rate constant ([IBP] 0 = 20 mg/L in DW, pH 0 = 4.3, T = 25 °C, f US = 20 kHz, D US = 25-100 W/L).

3. 2 .

 2 Homogeneous sono-Fenton oxidation process 3.2.1. Effect of Fenton's reagent concentration and 20 kHz US In order to evaluate the effect of ultrasound irradiation on homogeneous Fenton oxidation, Fenton experiments were first conducted under silent conditions. Two concentration levels of Fenton's reagent were applied with molar ratio of H 2 O 2 /Fe set to 48: [H 2 O 2 ] = 3.2 mM and [Fe 2+ ] = 0.067 mM (referred to as F(-)), [H 2 O 2 ] = 6.4 mM and [Fe 2+ ] = 0.134 mM (F(+)). It is worth noting that iron concentrations used in this study (3.75-7.5 mg/L) were below the classical range (between 10 and 500 mg/L)

Fig. 5 .

 5 Fig. 5. Effect of sonication frequency on IBP sonolysis: (A) concentration-time profile and (B) first-order rate constant ([IBP] 0 = 20 mg/L in DW, pH 0 = 4.3, T = 25 °C, f US = 12-862 kHz, D US = 50 W/L).

Fig. 6 .

 6 Fig. 6. Fenton (F) and sono-Fenton oxidation (US/F) of IBP: evolution of (A) pollutant and (B) TOC concentration ([IBP] 0 = 20 mg/L in DW, pH 0 = 2.6, T = 25 °C, f US = 20 kHz with D US = 50 W/L under sonication, (-): [H 2 O 2 ] = 3.2 mM and [Fe 2+ ] = 0.067 mM, (+): [H 2 O 2 ] = 6.4 mM and [Fe 2+ ] = 0.134 mM).

Fig. 7 .

 7 Fig. 7. Effect of sonication on Fenton catalyst regeneration. ([IBP] 0 = 20 mg/L in DW, pH 0 = 2.6, T = 25 °C, f US = 20 kHz with D US = 50 W/L under US, [H 2 O 2 ] = 6.4 mM and [Fe 2+ ] = 0.134 mM).

Fig. 8 .

 8 Fig. 8. Effect of sonication frequency on sono-Fenton oxidation of IBP: evolution of pollutant concentration ([IBP] 0 = 20 mg/L, pH 0 = 2.6, T = 25 °C, f (U)S = 12-862 kHz with D US = 50 W/L under sonication, [H 2 O 2 ] = 6.4 mM and [Fe 2+ ] = 0.134 mM).

  /L) < 2 COD (mg/L) < 30 TC (mg/L) 39.2 IC (mg/L) 29.4 TOC (mg/L) 9.8 (25 a ) Total Fe (mg/L) < 0.05 a After the addition of IBP.

Fig. 9 .

 9 Fig. 9. Effect of water matrix (DW: distillated water, WW: wastewater effluent) on sonolysis (US), Fenton (F) and sono-Fenton (US/F) oxidation of IBP: evolution of (A) pollutant and (B) TOC concentration ([IBP] 0 = 20 mg/L, pH 0 = 2.6 except for US in WW (pH 0 = 8.0), T = 25 °C, f US = 20 kHz with D US = 50 W/L under US, [H 2 O 2 ] 0 = 6.4 mM and [Fe 2+ ] = 0.134 mM for F and US/F).

  13 H 18 O 2 , purity 99.99%) was purchased from BASF Corporation and used as received. The physicochemical properties of IBP are listed in Table 1. Hydrogen peroxide (H 2 O 2 ) solution 30% w/w, monopotassium phosphate (KH 2 PO 4 ), sodium phosphate dibasic dehydrate (Na 2 HPO 4 •2H 2 O), potassium iodide (KI), titanium tetrachloride (TiCl 4 ), sodium sulfite (Na 2 SO 3 ) and iron sulfate heptahydrate (FeSO 4 •7H 2 O) were obtained from Sigma-Aldrich.

Table 1

 1 Physicochemical properties of ibuprofen.

	Properties
	Molecular weight	206.29 g/mol
	Molecular size	1.3 nm × 0.6 nm [24]
	Log Kow	3.97 [1]

pKa 4.9 (carboxylic group)

[START_REF] Thokchom | Ultrasonically enhanced electrochemical oxidation of ibuprofen[END_REF]

Solubility in water 21 mg/L at 25 °C [26] Henry's law constant 1.5 × 10 -7 atm.m 3 /mol [27] Vapor pressure 1.18 × 10 -8 atm at 25 °C

[START_REF] Ertel | Determination of ibuprofen vapor pressure at temperatures of pharmaceutical interest[END_REF]

Table 2

 2 Characteristics of sonication equipment.

	Properties	Equipment
		1	2	3
	Supplier	Sonics & Materials, Inc.	SinapTec	Meinhardt
				Ultraschalltechnik
	Model	VCX750	NexTgen	E/805/T/M
			Inside 500
	Frequency (kHz)	20	12	580-862
	Max nominal	180	200	250
	power (W) a
	Max calorimetric	131	156	32
	power (W) b
	Applied power	25, 50, 100	50	12.5
	(W) c
	Liquid volume	1000	1000	250
	(mL)
	L) d Applied D US (W/	25, 50, 100	50	50
	Probe diameter	51	35	40
	(mm)
	cm 2 ) e Applied I US (W/	1.2, 2.5, 4.9	5.2	1

a Nominal power displayed on generator. b Dissipated power measured by calorimetry

[START_REF] Goel | Sonochemical decomposition of volatile and non-volatile organic compounds-a comparative study[END_REF]

. c Power used in experiments. d Ultrasound density: applied power/liquid volume

[START_REF] Pilli | Ultrasonic pretreatment of sludge: a review[END_REF]

. e Ultrasound intensity: applied power/probe surface area

[START_REF] Pilli | Ultrasonic pretreatment of sludge: a review[END_REF]

.

Table 3

 3 Physicochemical properties of the WW.

Acknowledgements

The authors are grateful to ANR (French National Research Agency) for research funding through ANR project "SOFENcoMEM" (ANR-14-CE04-0006) and RISTEKDIKTI (Ministry of Research, Technology and Higher Education of Indonesia) for the scholarship of S. Adityosulindro (No. 2017/E4.4/K/2013). They also thank P. Calvet from Nailloux WWTP, G. Guittier (LGC), M.L. Pern (LGC) for their help on the analytical techniques and J.L. Labat (LGC) for the implementation of experimental setup.