Luc Malhautier
email: luc.malhautier@mines-ales.fr

Janick Rocher

Olivia Gouello

Luc Jobert

Claire Moura

Yann Gauthier

Aline Bertin

Jean-François Després

Jean-Louis Fanlo

Treatment of gaseous emissions from tire manufacturing industry using lab-scale biofiltration pilot units

Keywords:

Continuously seeking the improvement of environmental protection, the limitation of exhaust emissions is of significance for the tire manufacturing industry. The aim of this study is to assess the potential of biofiltration for the treatment of such gaseous emissions. This work highlights that biofiltration is able to remove both hydrophilic and hydrophobic compounds within a single pilot unit of biofiltration. Due to Ethanol/Alkanes ratios (95/ 5 and 80/20), high performance levels were observed for low EBRT (16 and 12 s). After twenty days of stable running, the dynamic of stratification patterns could be explained as a result of species coexistence mechanisms. While its impact on performance has not been observed under stable operating conditions, the use of an adsorbent support such as granular activated carbon (GAC) could be relevant to promote system stability in the face of further perturbations, such as transient regimes, that are problematic in full-scale industrial applications.

Introduction

Sustainability is now part of engineering and manufacturing by taking into consideration key objectives such as competitiveness, profit and yield. Different authors [START_REF] Rosen | Sustainable manufacturing and design: concepts, practices and needs[END_REF] highlight that, among industrial societies, the link between manufacturing processes and natural surroundings is now considered as a crucial factor in the decision making.

Along with the worldwide increased need of tyres with an annual manufacturing of about 1.4 billion products [START_REF] Sienkiewicz | Progress in used tyres management in the European Union: a review[END_REF], ongoing modifications in the tyre production process resulted in a substantive improvement of both protection of workers and limitation of the environmental impacts. According to the European Union Concerted Action EXASRUB database [START_REF] De Vocht | Exposure to inhalable dust and its cyclohexane soluble fraction since the 1970s in the rubber manufacturing industry in the European Union[END_REF][START_REF] Boniol | Cancer mortality in cohorts of workers in the European rubber manufacturing industry first employed since 1975[END_REF] individual exposures to rubber gaseous emissions and inhalable dust has regularly decreased since the 1970s (around 4% per year). It has been suggested that this reduction is mainly due to technological improvement ways, modernisation of ventilation and extraction equipment and changes in working practices. As an example, the evaluation of the environmental impact of the gaseous emissions from the rubber manufacturing by the Swedish Environmental Protection Agency in 1991 revealed that the cessation of chemicals use or the replacement of chemicals that are harmful to human health and environment by safer ones are part of a global approach which aims for improvements in the production process [START_REF] Forrest | The composition and nature of vulcanisation fumes in the rubber industry -a technical review[END_REF]. However it is important that besides the efforts towards safer workplaces, technologies are also developed and implemented to control the emissions to the environment in particular stack exhaust emissions [START_REF] Rosen | Sustainable manufacturing and design: concepts, practices and needs[END_REF], where it is common to find mixtures of biodegradable (such as alcohols) and more recalcitrant (mixtures of alkanes) Volatile Organic Compounds (VOCs). The composition of theses exhaust gases can vary from site to site depending on the chemicals being used in the processes and from country to country depending on the regulations in place.

The reduction of the environmental impacts of gaseous emissions is still topical and different studies are currently being conducted into the development of ever more effective and more technologically advanced treatment processes. It has been highlighted that biological technologies including biofilters, biotrickling filters, and bioscrubbers have been increasingly used due to their robustness, sensible cost-effectiveness and low environmental impact [START_REF] Devinny | Biofiltration for Air Pollution Control[END_REF][START_REF] Datta | Biofilter Technology[END_REF][START_REF] Malhautier | Biofiltration of volatile organic compounds[END_REF]. In industrial applications, operating parameters of biofilters and biotrickling filters can be adapted to The aim of this work is then to assess the potential of biofiltration for the treatment of gaseous emissions in the tire industry. The impact of gas velocity on the removal of chemicals will be firstly examined by using two pilot units fed with a synthetic mixture of biodegradable and hydrophobic compounds which is representative of on-site gaseous emissions. Then, the use of an adsorbent material (GAC) to improve biodegradation of alkanes will be examined.

Material and methods

Experimental design

Two identical polyvinyl chloride biofiltration columns entitled BF1 (BioFilter 1) and BF2 (BioFilter 2) (0.3 m internal diameter, 3.80 m height) were packed with sawmill wood chips (Table 1) to a height of 2 m. The bed height was subdivided into four compartments of 45-50 cmheight of material (Fig. 1). At the bottom of each column, a 10-cm Hiflow® rings layer was designed to homogenize the gas velocities before entering the organic material bed.

Gas-sampling ports were distributed at 0, 50, 105, 155 and 200 cm from the gas inlet. Gas-sampling ports were located in the 5-cm Hiflow® rings layers at the inlet and outlet of each compartment. On day 90, for BF1, the packing of the section near the gas outlet was removed and replaced by granular activated carbon (Table 1). For BF2, the packing of the section near the gas outlet was removed and replaced by a nonadsorbent synthetic packing material (confidential data) which was supplied by "" Manufacture Française des Pneumatiques Michelin ". This controlled package is comparable to GAC in terms of size.

Before both columns were filled with the material support, sawmill wood chips were seeded by dipping in activated sludge collected at a municipal wastewater treatment plant for one day. Granular Activated Carbon (GAC) and the non-adsorbent synthetic packing material have not been inoculated.

The packing material was regularly sprayed (four times a day) by a nutrient solution (Table 2) (agricultural fertilizer Optiplan, Duclos International, Lunel, France) according to a ratio carbon to total nitrogen 100/10 and corresponding to an average water supply of 15 L m -2 area day -1 , to maintain constant high moisture content and to provide essential nutrients for microbial growth [START_REF] Khammar | Link between spatial structure of bacterial communities and degradation of a complex mixture of volatile organic compounds in peat biofilters[END_REF]. The liquid medium did not provide any carbon as the only available carbon source was provided by the gas phase. pH of percolate waters was daily checked.

Inlet gas stream

BF1 and BF2 columns were run for more than 5 months, at ambient temperature, in an upward flow mode. Both biofilters were continuously fed by a synthetic gaseous effluent composed of a mixture of ethanol (VWR International France, Fontenay-sous-Bois, France) and solvent F (Essence F Onyx, Ardéa, Saint-Denis, France) mainly containing octane and methyl cyclohexane. Solvent F was designed as Alkanes along the entire manuscript. This gaseous effluent was representative of tire manufacturing emissions. This synthetic gaseous effluent was firstly saturated with moisture by using a downstream water scrubber before hydrophilic or lipophilic characteristics of the waste gas compounds [START_REF] Pérez | Abatement of styrene waste gas emission by biofilter and biotrickling filter: comparison of packing materials and inoculation procedures[END_REF][START_REF] San-Valero | Biotrickling filter modeling for styrene abatement. Part 1: Model development, calibration and validation on an industrial scale[END_REF]. Gas velocity within a biotrickling filter column could be 3-6 higher than for biofilter column, thus resulting in relatively small footprint. Even if a few works focus on evaluating clogging preventing methods [START_REF] Nukunya | Application of a pore network model to a biofilter treating ethanol vapor[END_REF][START_REF] Dobslaw | Prevention of clogging in a polyurethane foam packed biotrickling filter treating emissions of 2butoxyethanol[END_REF], this more compact design generally leads to higher specific loads, which may induce biofilm overgrowth and clogging [START_REF] Revah | Methods of Odor and VOC Control[END_REF][START_REF] Dobslaw | Biological waste air and waste gas treatment: overview, challenges, operational efficiency, and current trends[END_REF]. Hence, in this work, biofiltration has been used as both high surface and low water content of biofilters make them more appropriate for the treatment of the less hydrophilic pollutants in the VOCs mixture to be treated. In a biofiltration configuration, off-gas emissions pass through a packed bed of humidified porous material supporting microorganisms as a biofilm. Biofilters are designed to allow physicochemical mass transfer of pollutants from the gas to the biofilm (liquid phase) which is responsible for pollutant oxidation [START_REF] Malhautier | Biofiltration of volatile organic compounds[END_REF]. However, in some industrial applications, large footprint is needed for the treatment of less biodegradable VOCs for which the expected removal performance may not be achieved. Then, with increasing complexity of waste gas situations and tougher environmental regulatory constraints, multi-stage processes such as combinations of (non-)biological / biological processes are often required to yield performance expectations. Some applications may need physical/chemical pre-conditioning steps to achieve expected performance at short contact time such as around 10 s. Potential technologies such as UV oxidation (Kim et al., 2005;[START_REF] Zeng | Performance of a combined system of biotrickling filter and photocatalytic reactor in treating waste gases from a paintmanufacturing plant[END_REF], non-thermal plasma [START_REF] Dobslaw | VOC removal and odor abatement by a low-cost plasma enhanced biotrickling filter process[END_REF], electrostatic systems [START_REF] Quan | Effect of static magnetic field on trichloroethylene removal in a biotrickling filter[END_REF] could be used to achieve a partial oxidation of waste gas compounds (recalcitrant) to make the biodegradation easier. Technologies like adsorption could also be used to reduce the pollutants concentration variations at the biofilter inlet and different materials such as activated carbon [START_REF] Aizpuru | Biofiltration of a gaseous mixture of volatile organic compounds on granular activated carbon[END_REF], and more recently biochars from different agricultural residuals [START_REF] Hwang | Efficacy of different biochars in removing odorous volatile organic compounds (VOCs) emitted from swine manure[END_REF] and zeolite adsorber materials [START_REF] Dobslaw | VOC removal and odor abatement by a low-cost plasma enhanced biotrickling filter process[END_REF]) could be used. Moreover, these combinations.

The simultaneous elimination of VOC mixtures, representing different chemical groups by using biological ways has been thoroughly investigated by different authors for decades [START_REF] Aizpuru | Biofiltration of a gaseous mixture of volatile organic compounds on granular activated carbon[END_REF][START_REF] Cabrol | Bacterial dynamics in steady-state biofilters: beyond the functional stability[END_REF][START_REF] Yoshikawa | Biodegradation of volatile organic compounds and their effects on biodegradability under co-existing conditions[END_REF][START_REF] Dobslaw | Performance of different biological waste air purification processes in treatment of a waste gas mix containing tert-butyl alcohol and acetone: a comparative study[END_REF] as it is a challenging issue for industrial applications and special attention is required for hydrophobic VOCs removal [START_REF] Cheng | Challenges and solutions for biofiltration of hydrophobic volatile organic compounds[END_REF]. The performance in biological treatment of different VOCs mixture containing both hydrophilic and lipophilic compounds has been determined. A vertical gradient of biodegradation activities which may be referred to a diauxic behaviour has been observed with the elimination of hydrophilic compounds before lipophilic compounds are metabolized [START_REF] Khammar | Link between spatial structure of bacterial communities and degradation of a complex mixture of volatile organic compounds in peat biofilters[END_REF][START_REF] Zehraoui | Effect of methanol on the biofiltration of n-hexane[END_REF]. In this context, compound lipophilicity is a key parameter for microbial biodegradation as water solubility and, thus, substrate availability lowers with increasing lipophilicity [START_REF] Dobslaw | Biological waste air and waste gas treatment: overview, challenges, operational efficiency, and current trends[END_REF]. Another criterium is the molecular structure of compound. Even hydrophilic compounds might exhibit low elimination efficacy due to high steric hindrance towards enzymatic degradation [START_REF] Dobslaw | Performance of different biological waste air purification processes in treatment of a waste gas mix containing tert-butyl alcohol and acetone: a comparative study[END_REF]. Further systematic investigations will then be required to gain insight into substrate interaction mechanisms as knowledge concerning mutual effects on the metabolic process is still fragmented [START_REF] Yang | Simultaneous removal of multicomponent VOCs in biofilters[END_REF].

Finally, at industrial scale, a constantly operating biofiltration system is submitted to changing conditions (production shutdown periods, operational failures) that can impair their functional performance [START_REF] Cabrol | Integrating microbial ecology in bioprocess understanding: the case of gas biofiltration[END_REF]. It is then essential to identify these operating conditions (disturbance) that can reduce biofiltration performance, and to determine the capacity of the bioreactor to withstand a disturbance and to recover after disturbance. From these works, strategies to alleviate negative interactions among multiple VOCs will make it possible to promote full scale implementation of biofilters to multiple VOC removal [START_REF] Yang | Simultaneous removal of multicomponent VOCs in biofilters[END_REF]. being treated by biofiltration.

Operating conditions of both biofilters are given on Table 3. The ratio Ethanol/Alkanes was of 95/5 or 80/20. Different Empty Bed Retention Time (EBRT) was tested: 36, 16 and 12 s for BF1; 21 and 12 s for BF2. Due to the size of the reactors, the complexity of the experimental device and the operation costs, the impact of EBRT has been evaluated in this way. VOCs levels increased from 121 ± 10-336 ± 67 mg carbon m -3 air. The dynamic generation system allowed to maintain stable VOCs target concentrations ranging from 10% to 20% of the mean value. All the graphs in the section Results and discussion were obtained from operating data (Fig. 1 on Supplementary Materials) collected during each stable period (Table 3).

Sampling strategy and gas composition assessment

Gaseous effluent was sampled at the different biofilter bed heights by using 10 L Nalophan® bags and a KNFN86KN pump (Midisciences, Rousset, France).

Total hydrocarbons levels have been measured daily by using a VOC analyzer equipped with a flame ionization detector (CHROMATHC, Chromatotec® group, France) according to the specifications of the manufacturer. A calibration curve has been prepared with external standards of ethanol.

Gaseous concentrations of ethanol and alkanes were quantified by using a gas chromatograph (Trace, Thermo Electron, France). The chromatograph was equipped with a gas sampling valve (at a temperature of 160 • C) which was connected to an apolar capillary column (Equity-1 Supelco, 30 m, 0.32 mm internal diameter, 0.25 mm film thickness) with a carrier gas (helium 5.0) at a flow rate of 1 mL min -1 and a flame ionization detector. The temperature of the detector was 220 • C. The analytical method consisted of three steps: firstly 40 • C for 1 min; then 10 • C min -1 from 40 • to 100 • C; finally, 100 • C for 1 min. A calibration curve was prepared with external standards of ethanol for determining the gaseous concentrations.

Physico-chemical analysis

pH of percolate waters was measured by a digital pH meter (Symphony, VWR France, Illkirch, France). A digital differential manometer (vt100 model, Kimo® manufacturer, Canada) was used to determine pressure drop.

Results and discussion

Acclimatization

The acclimatization was defined as the required time to achieve high and stable removal efficiency level for a long period [START_REF] Muñoz | Biological technologies for the treatment of atmospheric pollutants[END_REF]. The efficiency profile during this period (121 ± 10 and 124 ± 7 mg carbon m -3 air for BF1 and BF2 respectively, Volume Ratio Ethanol/Alkanes (%) 95/5, from 1 to 53 days that is to say period I) was

Stratification patterns at steady state

The longitudinal pattern of biodegradation activity was determined for ethanol and alkanes chemical group at steady state (Fig. 2). The concentration ratio C/C0 against the height ratio h/h200 was represented. C is the concentration of chemicals (mg carbon m -3 air) which was measured at the sampled bed height h (m), C0 the concentration of chemicals to be treated (mg carbon m -3 air) and the total height of the packing material is called h200 (m).

Fig. 2 A and D revealed that, at steady state, ethanol was almost eliminated (C/C0 = 0.2) on the first 50 cm of the column for BF1 and on the first half of the column for BF2. Alkanes were eliminated on the last 150 and on the second half of the column for BF1 and BF2 respectively when ethanol was almost eliminated.

Stratification in terms of biodegradation with the firstly metabolism of biodegradable compounds and greater penetration of recalcitrant compounds within the filter bed has been reported into previous studies [START_REF] Aizpuru | Biofiltration of a mixture of volatile organic emissions[END_REF][START_REF] Álvarez-Hornos | Lab-scale evaluation of two biotechnologies to treat VOC air emissions: comparison with a biotrickling pilot unit installed in the plastic coating sector[END_REF][START_REF] Cabrol | Bacterial dynamics in steady-state biofilters: beyond the functional stability[END_REF][START_REF] Bruneel | Biofiltration of hexane, acetone and dimethyl sulphide using wood, compost and silicone foam[END_REF][START_REF] Flores-Barbosa | Evaluation of bioaerosols by flow cytometry and removal performance in a biofilter treating toluene/ethyl acetate vapors[END_REF]. This sequential removal may be explained by different assumptions. Short EBRT used in this work probably limit chemical mass transfer of poorly soluble alkanes compounds. Preferential hydrophilic substrate metabolism (ethanol) would be metabolized affecting the metabolism of hydrophobic compounds (alkanes) according to a competition between equivalent for BF1 and BF2. High functional efficiency was monitored after approximately twenty-five (25) days of functioning: 98.5 ± 1.1% and 99.4 ± 0.9% for BF1 and BF2 respectively. This start-up period has been currently reported by different authors [START_REF] Aizpuru | Biofiltration of a mixture of volatile organic emissions[END_REF]´Alvarez-Hornos et al., 2011;[START_REF] Cabrol | Bacterial dynamics in steady-state biofilters: beyond the functional stability[END_REF] for removing gaseous mixture of compounds by using biofiltration. Different parameters such as gas characteristics (nature and concentration of chemicals, physico-chemical properties of the chemicals (solubility, saturation vapor pressure, and biodegradability)), operating conditions and packing material characteristics such as changes in moisture content of the packing material, may influence the duration of this step. This delay can also be explained by the development of the microflora within the bioreactor and the selection of the most fitted species to operating conditions. When the biofilter has been inoculated by sludge from full-scale WWTP such as in this study, this delay could be due to changes in terms of growth conditions (attached versus planktonic microflora) and substrate accessibility (food to microorganism ratio) [START_REF] Cabrol | Integrating microbial ecology in bioprocess understanding: the case of gas biofiltration[END_REF].

At steady state (21 and 26 days for BF1 and BF2 respectively), removal efficiency remained at very high values: 98.7 ± 0.9% (BF1) and 99.4 ± 0.6% (BF2) for ethanol. The ability to remove alkanes was also high: 82.3 ± 7.0% and 93.2 ± 1.6% for BF1 and BF2 respectively. It should be stressed that the behavior of both biofilters was similar at the end of the acclimatization period. microbial populations degrading alkanes in the section near the gas inlet. Species interactions within microbial communities can be based on metabolic, physical, regulatory and/or signaling parameters. Moreover, these interactions can drive both temporal changes in microbial community composition and function, and spatial organization [START_REF] Widder | Challenges in microbial ecology: building predictive understanding of community function and dynamics[END_REF]. This potential shift of spatial organization could reveal positive metabolic interactions between functional populations. Among several possible mechanisms, it could be assumed that alkanes degrading populations benefits from the metabolite by-products of ethanol degrading populations, such as acetaldehyde and acetate, according to a cross-feeding of excreted metabolites phenomenon [START_REF] Widder | Challenges in microbial ecology: building predictive understanding of community function and dynamics[END_REF]. This exhibits the crucial role of the bacterial community. The imposed operating conditions (applied inlet load (g VOCs m -3 filter bed d -1 ), continuous air stream, microbial seeding, and attached microorganisms-mode development) shaped the biofilter microbiome which impacted the biofilter performance [START_REF] Cabrol | Management of microbial communities through transient disturbances enhances the functional resilience of nitrifying gas-biofilters to future disturbances[END_REF].

Impact of EBRT

Fig. 4 presents the global elimination capacity versus the applied inlet load. The observed steady state for each tested EBRT clearly highlights that the elimination capacity is quite equal to the applied inlet load. The VOCs mixture elimination is then nearly complete for all the tested applied loads. Both BF maintained a high and stable elimination capacity despite the decrease in EBRT.

Different authors [START_REF] Cabrol | Bacterial dynamics in steady-state biofilters: beyond the functional stability[END_REF][START_REF] Álvarez-Hornos | Lab-scale evaluation of two biotechnologies to treat VOC air emissions: comparison with a biotrickling pilot unit installed in the plastic coating sector[END_REF][START_REF] Aizpuru | Biofiltration of a gaseous mixture of volatile organic compounds on granular activated carbon[END_REF] stressed out the potential of biofiltration to clean industrial waste gases. In this study, such elimination capacity at low EBRT (16 and 12 s) could be explained by the prevalence of hydrophilic and biodegradable compound as both biofilters were fed with a gaseous effluent mainly composed of a biodegradable compound (ethanol/alkanes ratios of 95/5 or 80/20).

Different studies about the treatment of gaseous emissions containing ethanol by using biological processes have been reported by different authors. Some authors evaluated the potential of biological processes to remove ethanol [START_REF] Hodge | Modeling removal of air contaminants by biofiltration[END_REF][START_REF] Arulneyam | Biodegradation of ethanol vapour in a biofilter[END_REF][START_REF] Christen | Biofiltration of volatile ethanol using sugar cane bagasse inoculated with Candida utilis[END_REF][START_REF] Pérez | Effect of mineral salts addition on the behaviour of an ethanol biofilter[END_REF][START_REF] Lim | The treatment of waste-air containing mixed solvent using a biofilter: 1. Transient behavior of biofilter to treat waste-air containing ethanol[END_REF][START_REF] Nukunya | Application of a pore network model to a biofilter treating ethanol vapor[END_REF][START_REF] Vigueras | Hydrophobic response of the fungus Rhinocladiella similis in the biofiltration with volatile organic compounds with different polarity[END_REF][START_REF] Morotti | Analysis and comparison of biotreatment of air polluted with ethanol using biofiltration and biotrickling filtration[END_REF][START_REF] Lu | Development of a novel fungal fluidized-bed reactor for gaseous ethanol removal[END_REF] or a mixture of chemical compounds containing ethanol [START_REF] Kiared | Biological elimination of VOCs in biofilter[END_REF][START_REF] Baltzis | Modeling biofiltration of VOC mixtures under steady-state conditions[END_REF][START_REF] Leslous | Characterization and selection of materials for air biofiltration in fluidized beds[END_REF][START_REF] Jianping | Simultaneous removal of ethyl acetate and ethanol in air streams using a gas-liquid-solid three-phase flow airlift loop bioreactor[END_REF][START_REF] Lim | The treatment of waste-air containing mixed solvent using a biofilter 2. Treatment of waste-air containing ethanol and toluene in a biofilter[END_REF][START_REF] Lim | Treatment of mixed solvent vapors with hybrid system composed of biofilter and photo-catalytic reactor[END_REF][START_REF] Andres | Wood bark as packing material in a biofilter used for air treatment[END_REF][START_REF] Sempere | Performance evaluation of a biotrickling filter treating a mixture of oxygenated VOCs during intermittent loading[END_REF][START_REF] Rizzolo | Biofiltration of increasing concentration gasoline vapors with different ethanol proportions[END_REF][START_REF] Soares | Biofiltration of gasoline and ethanol-amended gasoline vapors[END_REF][START_REF] Ferdowsi | Steady state and dynamic behaviors of a methane biofilter under periodic addition of ethanol vapors[END_REF] or ethanol by-product (acetaldehyde) [START_REF] Duerschner | Biofiltration of acetaldehyde resulting from ethanol manufacturing facilities[END_REF]. Different VOCs mixtures, experimental design (filter beds whose volumes were Fig. 3. Alkanes concentration normalized by inlet alkanes concentration versus ethanol concentration normalized by inlet ethanol concentration according to pilot unit of biofiltration, EBRT and sampling day (between brackets). A:

(BF1, 36 s, 22 day), ▴ (BF1, 36 s, 48 day); B: (BF2, 21 s, 27 day), ▴ (BF2, 21 s, 48 day).

substrates phenomenon. The development of different populations along the bed height involved in different compounds removal could explain the obtained result [START_REF] Cabrol | Integrating microbial ecology in bioprocess understanding: the case of gas biofiltration[END_REF][START_REF] Estrada | A comparative study of fungal and bacterial biofiltration treating a VOC mixture[END_REF][START_REF] Flores-Barbosa | Evaluation of bioaerosols by flow cytometry and removal performance in a biofilter treating toluene/ethyl acetate vapors[END_REF]. These populations could effectively be characterized by different growth rates and/or different substrate and oxygen consumption rates, which results in out competition of populations for oxygen consumption and spatial partition. Nevertheless, after twenty days of stable running, the dynamic of stratification patterns revealed that the more refractory compounds were removed (C/C0 ≤ 0.1) on the total height of the column for both BF1 and BF2 (Fig. 2B, C andE, F). Both elimination of ethanol and alkanes within the same compartments could be the result of an arrangement among populations resulting in species coexistence. This phenomenon could be due to functional complementarity through niche complementarity or positive interspecific interactions. These microbemicrobe interactions have been revealed for different microbial communities within natural and engineered ecosystems such as anoxic/ aerobic granular sludge in sequencing batch reactors, ammonia conversion in wastewater treatment plants [START_REF] Junier | Phylogenetic and functional marker genes to study ammoniaoxidizing microorganisms (AOM) in the environment[END_REF][START_REF] Daims | A new perspective on microbes formerly known as nitrite-oxidizing bacteria[END_REF][START_REF] Szabó | Microbial population dynamics and ecosystem functions of anoxic/aerobic granular sludge in sequencing batch reactors operated at different organic loading rates[END_REF]. It is more probable that a complex network of microbial interactions governs the microbial community activity in this study. These synergetic and competitive interactions within a microbial community were both observed in other engineered ecosystems such as bioreactors used for simultaneously removing nitrogen and phosphorus from wastewaters [START_REF] Zhang | Spatiotemporal heterogeneity of core functional bacteria and their synergetic and competitive interactions in denitrifying sulfur conversion-assisted enhanced biological phosphorus removal[END_REF]. Concerning VOC elimination, these interactions among co-existing chlorinated ethene, BTEX, and chlorinated methane have been observed by different authors: co-metabolism within aerobic conditions [START_REF] Leahy | Comparison of factors influencing trichloroethylene degradation by toluene-oxidizing bacteria[END_REF][START_REF] Chauhan | Oxidation of trichloroethylene, 1,1dichloroethylene, and chloroform by toluene/o-xylene monooxygenase from Pseudomonas stutzeri OX1[END_REF][START_REF] Yeager | Trichloroethylene degradation by toluene-oxidizing bacteria grown on non-aromatic substrates[END_REF][START_REF] Elango | Biodegradation of vinyl chloride and cis-dichloroethene by a Ralstonia sp. strain TRW-1[END_REF][START_REF] Nagarajan | Formulation of microbial cocktails for BTEX biodegradation[END_REF]; toxicity of VOC and their degradation products [START_REF] Hüsken | High-rate 3-methylcatechol production in Pseudomonas putida strains by means of a novel expression system[END_REF][START_REF] Furukawa | Biochemical and molecular characterization of a tetrachloroethene dechlorinating Desulfitobacterium sp. strain Y51: a review[END_REF][START_REF] Justicia-Leon | Dichloromethane fermentation by a Dehalobacter sp. in an enrichment culture derived from river sediment[END_REF]; enzymatic competition [START_REF] Alvarez | Substrate interactions of benzene, toluene, and paraxylene during microbial degradation by pure cultures and mixed culture aquifer slurries[END_REF][START_REF] Shim | Aerobic degradation of mixtures of chlorinated aliphatics by cloned toluene-o-xylene monooxygenase and toluene o-monooxygenase in resting cells[END_REF][START_REF] Im | Pollutant degradation by a Methylocystis strain SB2 grown on ethanol: bioremediation via facultative methanotrophy[END_REF]; catabolite repression [START_REF] Aranda-Olmedo | Role of the ptsN gene product in catabolite repression of the Pseudomonas putida TOL toluene degradation pathway in chemostat cultures[END_REF][START_REF] Moreno | The target for the Pseudomonas putida Crc global regulator in the benzoate degradation pathway is the BenR transcriptional regulator[END_REF].

Alkanes concentrations measured along the biofilter bed are plotted versus ethanol concentration (Fig. 3). Similar curves are obtained for both biofilters. After 20 days of operation, removal of alkanes occurred when ethanol RE (Removal Efficiency) values reached 80%. This plotting corroborates a longitudinal biodegradation of ethanol and alkanes. The profiles at t = 48 days of operation exhibits the simultaneous removal of alkanes and ethanol. It is probable that ethanol can act as a co-solvent by increasing alkanes partitioning into the biofilm. Mass transfer and bioavailability of alkanes are then favored [START_REF] Soares | Biofiltration of gasoline and ethanol-amended gasoline vapors[END_REF]. This phenomenon can be also explained by the development of mainly lower (from 165 mL to 41 L) than the volume used in this study (140 L)), operating conditions (gas velocities mainly lower (from 2 to 3-100 m h -1 ) than the velocity range (200-600 m h -1 ) used in this study), packing materials (such as sugar cane bagasse, compost, clay particles) and inocula (generalist inoculum such as compost extract or activated sludge versus specific inoculum such as fungal or bacterial strains) have been considered. Then, it is difficult to exhibit a comparative analysis of all these results although the experimental design carried out in this study seems to be more representative of industrial concerns. Nevertheless, the elimination capacity levels obtained in this work seem to be similar even higher than those observed in previous studies.

Stratification patters (Fig. 5) are similar to those observed at steadystate for an EBRT of 36 and 21 s (Fig. 2C andF). Ethanol and alkanes were mainly removed within the section near the gas inlet, that is to say, 85-100% and 50-70%, respectively, according to the gas velocity and the concentration of compounds. These results seem to confirm positive species interactions between functional populations.

The pressure drop values increased up from 10 to 70 and from 20 to 100 Pa/packing meter for BF1 and BF2 respectively within the study period. Both decrease of EBRT (from 36 to 12 s) and biofilm growth are factors which result in a reduction of the void degree. The pH values of the percolate waters are of 6.2 ± 0,8 and 6.4 ± 0,7 for BF1 and BF2, respectively. These results seem to indicate no buildup of organic acids, mainly acetic.

Improvement of alkanes biodegradation

In relation to a variable industrial activity, the performance of fullscale biofilters could be influenced by changes of operating conditions in terms of inlet load, residence time of compounds within the biofilter, flow rate. During the assay, the ratio has been modified from 95/5-80/ 20. These modifications of the gas stream concentration may impact the performance of the biofilter as the part of hydrophobic and recalcitrant compounds increased. Hence, to improve the removal efficiency of hydrophobic compounds and recover similar performance, activated carbon has been tested as packing material in the section near the gas outlet (last 50 cm of filter bed) for BF1. Sawmill wood ships were replaced by a synthetic material without adsorbent properties for BF2. The global concentration of VOCs is indicated on Table 1. The EBRT was 12 s for both biofilters (Table 2, GAC test).

The global performances slightly decreased to stabilize to 93.9 ± 2.2 and 96.7 ± 0.6% (volume ratio of Ethanol/Alkanes of 95/5) and 91.3 ± 2.2 and 94.2 ± 1.3% (volume ratio Ethanol/Alkanes of 80/20) for BF1 and BF2 respectively.

With respect to longitudinal patterns (Fig. 6), ethanol and alkanes are mainly eliminated on the section near the gas inlet: almost 85-90% and 65-70% for ethanol and alkanes respectively and for both BF. As for ,36,121,48;■ BF1,16,122,69;BF1,12,271,83;BF2,21,124,48;BF2,12,132,69;BF2,12,282,83 B: Alkanes;◆ BF1,36,121,48;BF1,16,122,69;BF1,12,271,83;BF2,21,124,48;BF2,12,132,69;BF2,12,282,83. the last section of both biofilters, it seems that the addition of GAC has no influence on biofilter performances. This surprising result could be due to the availability of the adsorption sites which is linked to the microbial colonization of the support and the moisture film covering activated carbon particles (hydrophilic properties of activated carbon) and then to the hydrophobic characteristic of alkanes. It has been reported that adsorption phenomena differ in the presence of a biofilm, and in this case, these phenomena seem to work against the adsorption of alkanes on granular activated carbon [START_REF] Aizpuru | Biofiltration of a gaseous mixture of volatile organic compounds on granular activated carbon[END_REF][START_REF] Dorado | Interaction between sorption and biodegradation in a biofilter packed with activated carbón[END_REF]. Within the upper section of BF1, low concentration of gaseous alkanes even for an Ethanol/Alkanes ratio of 80/20 (around 10 mg carbon m -3 ) combined with hydrophobic characteristics of alkanes could also explain this result.

Conclusion

This work highlights the potential of biofiltration to remove both hydrophilic and hydrophobic compounds within a single pilot unit of biofiltration. Due to the Ethanol/Alkanes ratios (95/5 and 80/20), high performance levels were observed even for low EBRT (16 and 12 s). After twenty days of stable running, the dynamics of stratification patterns can be explained by mechanisms of species coexistence with the setup of persistent trade-offs in the ability of species to exploit available resources (ethanol and alkanes) and to adapt to other operating conditions (moisture content, dissolved oxygen level, local pH value, packing material). These promising results seem to reveal the robustness of these biofilters with the studied operating conditions.

The improvement of alkanes performance by using GAC has not been observed in this study. Nevertheless, as industrial biofilters are usually operated under different ratio Ethanol/Alkanes and compounds concentration, it would be then appropriate to evaluate the system stability of these biofilters in the face of further perturbations, such as transient regimes (recurring shock loads) that are problematic in full-scale applications.

CRediT authorship contribution statement

Claire Moura, Jean-François Després, Jean-Louis Fanlo, Yann Gauthier, Luc Jobert and Luc Malhautier contributed to the formulation of overarching research goals and aims and designed the research. Olivia Gouello, Janick Rocher and Luc Malhautier performed the experiments and collected data. Luc Malhautier wrote the initial draft of the manuscript. Claire Moura, Jean-François Després, Jean-Louis Fanlo, Yann Gauthier, Luc Jobert and Luc Malhautier provided a critical review of the initial draft. The financial support for the project leading to this publication has been provided by Aline Bertin, Jean-François Després and Luc Jobert. All authors read the manuscript and approved it.

Declaration of Competing Interest

There are no conflicts to declare.

Fig. 1 .

 1 Fig. 1. Schematic representation of a pilot-scale biofiltration unit. Hiflow® rings, Sawmill wood chips.

Fig. 2 .

 2 Fig. 2. Temporal dynamics of longitudinal profiles of degradation activities along the bed height at steady state for both biofilters (from 22 to 48 operating days). A, B and C: BF1, EBRT: 36 s; D, E and F: BF2, EBRT: 21 s; A: 22 days; D: 27 days; B and E: 41 days; C and F: 48 days; ■ Ethanol;◆ Alkanes.

Fig. 4 .

 4 Fig. 4. VOCs elimination capacity for all tested EBRT.

Fig. 5 .

 5 Fig. 5. Longitudinal profiles of degradation activities of ethanol and alkanes at steady state according to pilot unit of biofiltration, EBRT (s), VOCs concentration (mgC m -3 ) and sampling day. A: Ethanol; ■ BF1, 36, 121, 48; ■ BF1, 16, 122, 69; BF1, 12, 271, 83; BF2, 21, 124, 48; BF2, 12, 132, 69; BF2, 12, 282, 83

Fig. 6 .

 6 Fig. 6. Spatial patterns of biodegradation activity of ethanol and alkanes according to Ethanol/Alkanes ratio (xx/xx) and sampling day (between brackets) for BF1 packed with sawmill chips and granular activated carbon and BF2 packed with sawmill wood chips and synthetic material. Operating parameters are indicated on

Table 1

 1 Main physico-chemical characteristics of used packing materials.

	Measured parameters	Sawmill wood	Granular activated
		chips	carbon
	Mean diameter (mm)	13.1 ± 0.1	2.8 ± 0.1
	Porosity of humid material (%) Bulk density(kg m -3 ) Specific surface area (m 2 m -3 ) Water-holding capacity (m 3 H 2 O m -3	60.4 ± 0.3 203 ± 25 269 ± 12 0.20 ± 0.03	40 ± 5 558 ± 30 2150 ± 57 0.30 ± 0.02
	material)
	pH	6.0 ± 0.0	7.8 ± 0.1

Table 2

 2 Composition

	Compound	Mass percent fraction (%)
	Nitrate	10
	Ammoniacal nitrogen	12.2
	Urea	1.8
	Phosphoric anhydride	20
	Potassium oxide	2
	Magnesium oxide	2
	Sulphur trioxide	4
	Boron	0.0125
	Copper	0.0025
	Manganese	0.0125
	Molybdenum	0.0012
	Zinc	0.010
	Iron	0.03

of the nutrient solution (agricultural fertilizer Optiplan, Duclos International, Lunel, France).

Table 3

 3 Operating conditions. GAC: Granular Activated Carbon. p: period.

			EBRT (s)	VOCs concentration (mg carbon m -3 air)	Volume Ratio Ethanol/Alkanes (%)	Applied inlet load (g VOC m -3 package material day -1 )	Duration (day)
	EBRT	BF1	36	121 ± 10	95/5	290 ± 25	1-53 (pI)
	test		16	122 ± 5	95/5	660 ± 26	54-75 (pII)
			12	271 ± 24	95/5	1951 ± 173	76-90 (pIII)
		BF2	21	124 ± 7	95/5	519 ± 29	1-53 (pI)
			12	132 ± 8	95/5	947 ± 55	54-75 (pII)
			12	282 ± 23	95/5	2008 ± 163	76-90 (pIII)
	GAC test	BF1	12	273 ± 33	95/5	1966 ± 238	91-136 (pIV)
			12	307 ± 50	80/20	2313 ± 402	137-159 (pV)
		BF2	12	279 ± 23	95/5	2008 ± 163	91-136 (pIV)
			12	336 ± 67	80/20	2419 ± 481	137-159 (pV)

Table 2

 2

	(GAC test). A: BF1 Ethanol; C: BF2 Ethanol; ■ 95/5 (2); 95/5 (43);	80/20 (2);	80/20 (16); B: BF1 Alkanes; D: BF2 Alkanes; ◆ 95/5 (2);	95/5 (43);
	80/20 (2);	80/20 (16).

Acknowledgments

This work was funded by Manufacture Française des Pneumatiques Michelin through a "Contrat de Coopeŕation dans le Cadre d ′ Etudes et de Recherches" established in 2018 between Manufacture Française des Pneumatiques Michelin, Olentica sas and IMT Mines Alès.

Appendix A. Supporting information

Supplementary data associated with this article can be found in the online version at doi:10.1016/j.jhazmat.2021.126614.


Mambaye Lo
email: mambaye.lo@mines-ales.fr

Pierre Couturier
email: pierre.couturier@mines-ales.fr

Evaluating Alternatives for Designing Mechatronic Systems in a Systems Engineering Context

The system analysis process (SEBoK 2012) allows « developers to objectively carry out quantitative assessments of systems in order to select and/or update the most efficient system architecture and to generate derived engineering data ». The goal is here to perform tradeoff studies. We focus here on the evaluation of costs, risks or effectiveness of Alternative System Design Solutions (ASDS) provided by the technical systems engineering processes (ISO/IEC 2008) considering two main constraints. First, iterative aspect of design approach induces a growing but uncertain maturity level of detail of the proposed solutions. Second, each decision resulting from evaluations must be argued considering stakeholder's requirements. It is particularly crucial to note here that these requirements can be more or less contradictory. They can be also relative to various domains and culture such as mechanics, electronics, or computer science. The proposed work aims at giving a methodological guide with embedded tools and innovative decision making methods to support the effectiveness evaluation of ASDS. It is here applied in the field of mechatronic systems analysis. This guide is the subject of methodological, conceptual and technical contributions summarized in the next sections.

Methodological contribution: a generic set of evaluation activities

The proposed activities are here considered as generic and iterative activities for evaluation purpose in the System Analysis process. They are gathered into four main sets of activities for evaluation focusing respectively on:

• Defining the objectives of the evaluation and selecting the solutions to be evaluated.

• Preparing the job to be performed by defining decision model, selecting applicable multi-criteria analysis methods (Fülöp 2005) and tools and then selecting required data extracted from design models. • Performing the job including sensibility and traceability analyses.

• Delivering expected results, justifications, recommendations.

Conceptual contribution: a data model for evaluation

The goal is to provide a unified data model (Figure 1) that can be understood and shared by designers whatever may be their origin or business domain. This model formalizes concepts and relations between concepts representing classes of data required during evaluation. It integrates stakeholder, system designer and design evaluator points of view as promoted by (Blanchard and Wolter 2011;INCOSE 2011;Maier and Rechtin 2009). Stakeholders are interested by technical requirements, Measures Of Effectiveness (MOE) and Measures Of Performance (MOP). Designers are interested by ASDS, predictive models as described below, Design Considerations, and Design Dependant Parameters (DDP that can be splited up into input and output DDP namely iDDP and oDDP). Last, evaluators are interested by system architecture, evaluation criteria and associated Technical Indicators.

Conceptual and technical contribution: impact evaluation and evaluation traceability

The goal is to support evaluation activities and systematically trace design choices with a certain level of automation. Relying on the relationships, it is then possible to identify the possible influence of DDPs on the criteria. Then, a decision model is merged with a predictive model (Figure 2) in order to estimate the magnitude of such influences. applying multi-criteria analysis methods, for instance by using utility functions. However, the transformation from iDDPs to oDDPs may be unknown or marred by uncertainty. This mainly arises during the preliminary (or conceptual) design phase. So, an original approach based on qualitative influence analysis is proposed to deal with such an uncertainty issue. This approach consists in asking experts to advise on qualitative influence (improvement degradation) of iDDP choices on the value of utility function applied to each oDDP. It becomes then possible to highlight the most promising ASDS since the earliest stage of the design. For this, we adopt aggregation and propagation operators from (Imoussaten et al. 2011-1030-1037) and (Giorgini et al. 2002 -167-181).

Research and developments perspectives

It should be noticed the lack of interoperability between SE tools and multi-criteria analysis tools. The proposed contributions have been developed in order to be interoperable with classical SE tools. This is achieved by enriching system engineering meta model with the proposed evaluation data conceptual model. The approach has been tested particularly on the CORE V8 tool (Vitech 2011). A software platform supporting the entire guide is under development. The goal is now to enrich contributions by taking into account other -ilities evaluation as proposed by (De Weck et al. 2012).

Figure 1 :

 1 Figure 1: Evaluation data conceptual model (simplified)

  (SEBoK 2012) Pyster, A. and D.H. Olwell (eds). 2013. The Guide to the Systems Engineering Body of Knowledge (SEBoK), v. 1.1.2. Hoboken, NJ: The Trustees of the Stevens Institute of Technology. Accessed DATE. www.sebokwiki.org/ (ISO/IEC 15288) IEEE Standards 15288.2008, Systems engineering -System life cycle processes (2nd edition), 2008 (Fülop 2005) Fülöp, J., Introduction to Decision Making Methods, Laboratory of Operations Research and Decision Systems, Computer and Automation Institute, Hungarian Academy of Sciences, 2005 (Blanchard and Volter 2011) Blanchard, B.S., Wolter, J. F., Systems Engineering and Analysis, Fifth Edition, Prentice Hall Series, Industrial And Systems Engineering, , 2011 (INCOSE 2011) System Engineering Handbook, A Guide For System Life Cycle Processes And Activities, INCOSE Eds., 2011 (Maier and Rechitin 2009) Maier, M. W., Rechtin E., 2009, The Art of System Architecting, 3 rd ed., CRC Press, 2009 (Imoussaten 2011 -1030-1037) Imoussaten, A., Montmain J., Trousset F., Labreuche, C., Multi-criteria improvement of options, Proc. of 7 th conference of the European Society for Fuzzy Logic and Technology (EUSFLAT-2011) and LFA-2011, Advances in Intelligent Systems Research, Aix-les-Bains, France, Atlantis Press (Giorgini 2002 -167-181) Giorgini, P., Mylopoulos J., Nicchiarelli E., Sebastiani R., Reasoningwith Goal Models, 21st International Conference on ConceptualModeling (ER02), Tampere (Finland), 2002 (Vitech 2011) Vitech Corporation, A primer for Model Based Systems Engineering, 2011 (De Weck 2012) Olivier L. de Weck, Adam M.Ross, Donna H. Rhodes, Investigating Relationships and Semantic Sets amongst System Lifecycle Properties (Ilities), third International Engineering Systems Symposium CESUN 2012, Delft University of Technology


Bayd Hamza
email: hamza.bayd@mines-ales.fr

Guyot Patrice
email: patrice.guyot@mines-ales.fr

SLANGEN Bardy Benoit
email: benoit.bardy@umontpellier.fr

Automatic scoring of synchronization from fingers motion capture and music beats

Keywords: synchronization, motion capture, hand, finger, music beats, dynamic time warping

Thanks to various technological progresses such as musical rhythm estimation and motion capture systems, the evaluation of synchronization performances between motion and music beats is today possible. In this paper, we propose an innovative playful method to assess synchronization between hand motion and music. In this application, the hand gestures are tracked from live webcam motion capture based on MediaPipe open-source framework. Musical beats are estimated from the Librosa library. The synchronization between finger motion and beats is then computed from the dynamic time warping algorithm. A preliminary study was conducted with two different songs mixed with tempo beats at different intensities. The results are encouraging and show different levels of performance according to the tempo of the songs.

Introduction

Synchronization between music and human movements is typically based on the perception of a common rhythm. Humans respond to rhythmic parameters of music by synchronizing movement pattern to the beat, that explain the close connection between the perceptual and audio-motor system. In general, synchronization between individuals are based on predictive abilities that are fed by visual and auditory perception [START_REF] Bardy | Moving in unison after perceptual interruption[END_REF]. During the last few years, significant progress has been made in challenging computer vision problems, including human pose estimation, in particular for neural network and motion capture (MoCap) technology. The task of human pose estimation from video, nowadays applied in various domains such as sign language recognition, is usually based on body landmarks or keypoints from each video frame. Moreover high level semantics from motion such as joint collection distance and temporal displacement of the body (visual information) can also be computed [START_REF] Kadir | Can a simple approach identify complex nurse care activity?[END_REF][START_REF] Sun | Explicit spatiotemporal joint relation learning for tracking human pose[END_REF].

From the music side, beats are one of the most fundamental features linking to the accompanying movements. The ability to synchronize movements and music is primarily analyzed through the task of tapping. In more complex situations, such as walking, synchronization can be analyzed through the impact of the steps, and their correspondence with the strong beats of the music piece [START_REF] De Cock | Rhythmic abilities and musical training in Parkinson's disease: do they help?[END_REF]. However, the way in which sound and visual information interact in the perception and production of synchronization, intentional or spontaneous, is still poorly understood [START_REF] Ipser | Sight and sound persistently out of synch: stable individual differences in audiovisual synchronisation revealed by implicit measures of lip-voice integration[END_REF]. In the present study, we propose a webcam beat-tracking software that measure and quantify in real time a synchronization score between natural movements of hands and the musical beats.The rest of this paper is structured as follows. Section 2 presents a short review of related works for musical rhythm, human pose estimation and synchronization. Sections 3 provides an overview of the developed system. In Section 4, we describe a preliminary experiment and discuss the results.

Related works

Musical rhythmic features extraction

Rhythm in music denotes the element of time. While a series of notes repeats in a regular cycle, they form a rhythmic pattern. Moreover to indicate the annotation timings for the respective notes, musical rhythm can also specify the duration and intensity. The best way to describe beat in real life is the moment when people taps feet or hand while listening to a song. The tempo in music is the number of beats per minute (bpm), and can change over the course of the music audio [START_REF] Sogorski | Correlated microtiming deviations in jazz and rock music[END_REF]. Some of the main characteristics that humans can understand and perceive when listening to music are tempo, rhythm, onset and tatum [START_REF] Fuentes | Multi-scale computational rhythm analysis : a framework for sections, downbeats, beats, and microtiming[END_REF], as shown in Table 1. The continuous repetition of a musical pattern with its variation as it moves over time Tempo

The speed at which the music is played and is measured in beats per minute Onsets

The time instant of the detectable start of a melodic note Beat

The fundamental feature to the perception of timing in music usually grouped in bars Downbeat

The first beat of a measure, the strongest in any meter Tatum Corresponds to the fastest perceived pulsation in the metrical structure

The music information retrieval is an interdisciplinary research field that enhances a wide range of applications such as beat tracking, structural analysis and music classification. It relies traditionally on features can be extracted in two domains, time domain or frequency domain, within different levels of abstraction. On one hand, low level features make sense for the machine as statistics features which are extracted directly from the audio such as amplitude envelope, energy, spectral centroid, spectrogram and MFCC (Mel Frequency Cepstral Coefficents) [START_REF] Ganesh | Tempo, Beat and Downbeat estimation for Electronic Dance Music[END_REF][START_REF] Jensenius | Developing Tools for Studying Musical Gestures within the Max/MSP/Jitter Environment[END_REF]. On the other hand, high-level features are related to the perception of rhythm.

Recent works on beat tracking are based on deep learning models to predict the beat position, using recurrent neural network and LSTM (Long Short Term Memory networks). These models directly process magnitude spectrograms at multiple levels and provide output feature recognizing beats and downbeats [START_REF] Böck | Joint Beat and Downbeat Tracking with Recurrent Neural Networks[END_REF]. Furthermore, other researches relies on a temporal convolution network framework [START_REF] Davies | Temporal convolutional networks for musical audio beat tracking[END_REF].

Human movement and MoCap

Human movement can be mathematically described in terms of distance, displacement, speed and articulations. Table 2 shows detailed motion features. Skeleton-based action is defined as the problem of localizing human joints also known as 2D and 3D keypoints (hands, elbows, wrists, etc) in images or videos. These features plays a critical role in various applications and has been widely used in multimedia applications such as human computer interaction [START_REF] Ren | Robust hand gesture recognition with kinect sensor[END_REF]. For example, they make up the backbone for yoga, dance, and fitness applications [START_REF] Zou | Intelligent fitness trainer system based on human pose estimation[END_REF]. A wide range of systems are available to collect continuous movement data. The most popular in the recent years is MoCap (motion capture), usually referring to motion representations in digital formats to allow quantitative analysis or realtime processing. Approaches can be split into two broad categories: marker-based approaches rely on infrared cameras and reflective markers (single or multiple instances), while marker-less approaches are only based on cameras (RGB-only images vs depth data RGB-D).

Table 2. Visual motion features

Feature Definition Body landmarks

The spatial location of human body articulation (keypoints) from visuals such as images and videos, each points described by three coordinates (x, y, z) Articulation angles and orientation

Rotation between two adjacent body articulation with different orientation Translation and rotation

translation and rotation related to the world coordinate axis (tx,ty,tz,rx,ry,rz) Temporal displacement and acceleration

Predict spatiotemporal features and velocity from the previous frame to the current frame Joint collection distances

Represent the changes over time of joint angles computed at each time frame and a fixed point of the skeleton Human hand motion is highly articulate, but also highly constrained, which makes it difficult to model [START_REF] Wu | For vision-based human computer interaction[END_REF]. Vision-based hand pose estimation analysis has been an important research topic as this can play an essential role in enhancing the experience on a variety of technology disciplines and platforms in order to control devices or to interact with computer interfaces. This analysis process can be resumed in two steps: detection and tracking. The first major block will detect hand position that contains palm from frames of video. This can be achieved via an oriented hand bounding box by means of depth based methods [START_REF] Gattupalli | Towards deep learning based hand keypoints detection for rapid sequential movements from rgb images[END_REF], or alternatively by RGB based methods [START_REF] Sridhar | Real-time joint tracking of a hand manipulating an object from rgb-d input[END_REF]. The second stage is the tracking pipeline that can track multiple hands in real-time by detecting the keypoints coordinates using regression model [START_REF] Zhang | Mediapipe hands: On-device real-time hand tracking[END_REF]. The hand can be also modelled in several aspects like shape, kinematical structure, dynamics, and semantics.

Audiomotor synchronization

The human audio-motor systems are practically connected during musical performance. Moreover listening to music can easily encourage the motor system to act in the form of head nodding, foot tapping, and even dancing [START_REF] Schalles | Musical Sequence Learning and EEG Correlates of Audiomotor Processing[END_REF]. Further research on audio-motor systems is trying to test the ways in which audio-motor coordination is influenced by visual cues from a conductor's gestures [START_REF] Colley | The influence of visual cues on temporal anticipation and movement synchronization with musical sequences[END_REF]. Another popular tool for the systematic assessment of audio-motor system is the BAASTA (Battery for the Assessment of Auditory Sensorimotor and Timing Abilities) [START_REF] Bella | BAASTA: Battery for the assessment of auditory sensorimotor and timing abilities[END_REF], that uses finger tapping with music and adaptive tapping to a sequence with a tempo change in order to evaluate the synchronization performance of the participants.

Musical cognition refers to the study of musical thinking field, that focuses to understand the mental processes and the way of human brain perception such as cortical activity during listening to the auditory rhythms through the methods of cognitive science, and neurological methods based on auditory motor synchronization [START_REF] Damm | Why do we move to the beat? A multi-scale approach, from physical principles to brain dynamics[END_REF]. Following this notion, recent research suggests that the processes of action-perception between neural and mechanical activities synchronize in different forms during musical activities, linking body movement and high level musical features [31].

Methodology

This section will present our approach to measure and quantify in real time the "synchronization score" between natural movements of hand (fingers) and the musical beats. Its workflow is presented in Figure 1. Inspired by the success attained in hand tracking and music beat tracking methods, we propose to exploit these methods in order to evaluate the synchronization with temporal alignment using dynamic time warping (DTW) algorithms. This will be applied to measure similarity between two temporal sequences of motion and music beat while the participant is listening to the music using human computer interaction based on computer vision.

Motion parameters

The presented process relies on MediaPipe [START_REF]MediaPipe: Cross-platform ML solutions made simple[END_REF], an open source framework to detect in real time the hand keypoints (x,y) captured by the camera [START_REF] Zhang | Mediapipe hands: On-device real-time hand tracking[END_REF]. The MediaPipe module predicts 21 hand landmarks based on three axes: x (horizontal), y (vertical) and z that represents the depth of landmark. Then the hand score, indicating the accuracy of hand presence in the input image is generated. Finally a simple classification occurs between left and right hand. In this study, the landmarks of index fingers are firstly determined. Figure 2 presents hand landmark in MediaPipe [START_REF]MediaPipe: Cross-platform ML solutions made simple[END_REF]. The left hand index finger is shown by coordinates [START_REF] De Cock | Rhythmic abilities and musical training in Parkinson's disease: do they help?[END_REF][START_REF] Ipser | Sight and sound persistently out of synch: stable individual differences in audiovisual synchronisation revealed by implicit measures of lip-voice integration[END_REF][START_REF] Ganesh | Tempo, Beat and Downbeat estimation for Electronic Dance Music[END_REF][START_REF] Fuentes | Multi-scale computational rhythm analysis : a framework for sections, downbeats, beats, and microtiming[END_REF] for example. These landmarks are then used to make condition of tapping based on position and the angle of articulation corresponding to image width and height.

Music Parameters

Instead of using low level acoustic features, the high level music features rhythm is adopted. Therefore tempo, onset and beat are used to represent musical rhythm. Beat in music theory is the most used feature in audio conditioned motion [START_REF] Huang | Dance revolution: Long-term dance generation with music via curriculum learning[END_REF], that tracks the periodic element in music. Moreover detecting beat and tempo are closely related to onset detection. First the music audio signal is converted into spectrogram, then the coefficients of spectrogram are analyzed through neural network in order to classify each frame as onset or not onset. Finally, the beat location are founded by processing periodic patterns in the onset location. The public Librosa [START_REF] Mcfee | librosa: Audio and music signal analysis in python[END_REF] is leveraged to extract the beats from the audio-based music. The beats features is a 1D vector, representing the annotation timings for the respective beats in which we consider it as rhythm information. Intuitively, the motion rhythm has to match the musical rhythm.

Similarity and score of synchronization

The aim of this paper is to develop more sophisticated methods for automated synchronization scoring between the hands movement and musical beat. As shown in the previous section we take temporal features with aggregation in real time from motion and music. Dynamic Time Warping is an algorithm that produces a better similarity measurement compared to others methods such as Hamming, Euclidean and Manhattan distance. The greatest advantage of DTW is to cope with signals of different length and in synchronization signals which move exactly at the same speed and time. Finally DTW can be used as a score component for synchronization between hand movement and musical beat [START_REF] Cheong | Four ways to quantify synchrony between time series data[END_REF].

The distance between two time series data n-dimensional space can be computed via the Euclidean distance x = [x 1 , x 2 , ..., x n ] and y = [y 1 , y 2 , ..., y n ]

dist(x, y) = ∥x -y∥ = (x 1 -y 1 ) 2 + (x 2 -y 2 ) 2 + • • • + (x n -y n ) 2 (1)
However, if the length of x is different from y, then the euclidean formula cannot be used to compute the similarity distance. Instead, a more flexible method must be developed to find the best mapping with the minimum distance from elements in x to those in y in order to compute the similarity synchronous.

Let x and y two vectors of lengths m and n :

D(i, j) = |x(i) -y(j)| + min    D(i -1, j) D(i -1, j -1) D(i, j -1)    (2)
DTW is used to align the signals and computes the euclidean distance at each frame across every other frames to reach the minimum path that will match the two signals.

Experiments

Set-up

The objective of this demo showcase is to present a real application based on our innovative and robust hand-music synchronisation system. The main objective is to study a playful configuration coupled with an innovative method using the webcam sensor, in order to improve the automatically generated synchronisation score between the music rhythm and the hand movements (see Figure 4). To test the synchronization, participants were asked to tap as regularly as possible with their two index fingers (Right and Left) in both directions and on the specific red button, in order to be synchronized to a rhythmic input music. We propose to the participants to test our demo in four difficulty levels to study the perception rhythm ability of each participant. The music was delivered over headphones at a comfortable sound volume level. The first "easy" level contains a clear beats pulse that were added in the background of the music, that can help the participants to match the beats rhythm easily. For the second level "moderate", the same musical audio is used but with low volume of the short pulses annotation... until level 4 "insane" that contains the audio music without beat pulses added to the original music. For this experiment two music clips of 35 seconds were selected, with different tempo and different style of music i.e. Ruby Baby Act One with 80 beats/minute including 39 beats, then Daft Punk One More Time but with 125 beats/minute and 65 of the placement beats.

Our algorithm was implemented in Python. All experiments are running on DELL with a Intel Core i5-8400H CPU 2.50GHz × 8 processor and 16 GB of RAM, and the Ubuntu 20.04.2 operating system. The lived processed images video is refreshed at 25 frames per second, with 1280×720 resolution. Fig. 4. The screen contains four black boxes to choose the music. 4 options can be selected with audio music that has annotated timings for the respective beats annotations with lower pitched pulses in order to help the participant to match the beats rhythm on four difficulty levels. Then there are two red buttons in the center of the screen to follow the beats with the fingers, and it can be done by moving the index finger in both directions on the specific red button, in order to synchronize with the rhythms of the audio music in the background.

Results

The present study was carried out on 3 non-musicians students (2 males and 1 female, average age 21). This experiment was designed to investigate the level of synchronization at different intensity of beats annotation and to examine the impact of the tempo on the performance (slow-rhythm and fast-rhythm ). Figure 5 shows one of the 35s music clip with aligned musical beats and motion beats for participant #2. Then the global synchronization score for every frame in the audio-video, the music beats marked by the green dashed line and the motion with the black dash-dotted line. It can be observed that the motion fingers tapping occur in very similar ways where the musical beats occur. The consecutive matched beats correspond to tapping index finger on left and right alternatively. For beat matching, the motion beats extracted from each frame and their corresponding input music beats are compared using euclidean distance and dynamic time warping. Then the score of synchronization is computed and displayed. Results show fairly good performances of the participants. The best synchronization score (97.8%) is achieved for the song Act One at 80 bpm with an easy level of difficulty, and the smallest score (70.4%) for One ore time at 123 bpm with an insane level of difficulty. The average synchronization score is decreasing proportionally to the difficulty level. The overall average of synchronization score is higher (88.48%) for the first song at 80 bpm than for second one the (83.87%) at 123 bpm. This shows that the tempo impacts the ability of synchronization, in line with previous studies [START_REF] Repp | Sensorimotor synchronization: A review of the tapping literature[END_REF]. The overall best performance is achieved by participant #2 with 97.8% synchronization score. However the best performance with fast tempo is performed by participant #1 with 95.1% synchronization score.

Interviews were conducted with each participants after the experiments. The main feedback is that participants really appreciated the synchronization experience through this playful developed tools, and founded the application very easy to use. In addition, Participant 1's comments reveal that he is a fan of the One more time song. This could explain why he scores better on this song than on the first, unlike the other participants.

Conclusion

In this paper, we propose an efficient and accurate playful method for the automatic notation of the synchronization of hand movements and musical rhythms, using the real-time webcam display and musical audio as input.

This also enables to test the level of synchronization for a musical piece by tapping fingers with the beat times position. Moreover, an experiment was conducted trough four difficulty, with beat pulses added to the music and different mixing levels. The results show that the synchronization score decreases proportionally as the level of difficulty increase.

Future work will consider increasing the number of participants in the experiment to achieve statistical processing of the data. We will also integrate novel multi-scale music features contribution, such as downbeat and tatum. In order to increase the robustness of our synchronization score method we will extract the peaks and calculate the phase difference between the musical beat and finger movements at each cycle.

Finally, motion capture will be generalized to the whole body using different features such as articulation, joint collection distance and temporal displacement of the body landmarks. This will produce accurate body movement descriptors leading to fine analysis of synchronization between the human body and fullydescribed music features of the listened song.

Fig. 1 .

 1 Fig. 1. Workflow Method Research

Fig. 2 .

 2 Fig. 2. The labeled keypoints generated by MediaPipe

Fig. 3 .

 3 Fig. 3. Audio-based music waveform and the estimated beat positions

Fig. 5 .

 5 Fig. 5. Beat tracking for music waveform and motion beat, participant #2, lev moderate.

Table 1 .

 1 Characteristics of Rhythm

	Feature	Definition
	Rhythm

Table 3 .

 3 Performance synchronization score (in percent)

		Ruby Baby -Act One (80 bpm, 39 beats)
	Difficulty levels	Participant #1	Participant #2	Participant #3
	Easy	93.2	97.8	95.4
	Moderate	88.5	94.7	89.6
	Hard	83.2	90.5	82.3
	Insane	76.1	88.7	78.9
	Daft Punk -One more time (123 bpm, 65 beats)
	Difficulty levels	Participant #1	Participant #2	Participant #3
	Easy	95.1	86.8	88.7
	Moderate	91.3	85.4	86.6
	Hard	86.5	79.1	83.9
	Insane	80.02	72.5	70.4