J Vanaret
email: isabelle.auquit@chu-rouen.fr

La couverture des pertes de substance de l'épaule Coverage of losses of substance in the shoulder I Auquit-Auckbur (1) , D

INTRODUCTION

Losses of substance in the shoulder area, at the root of the upper limb are less common than in other parts of the arm. The shoulder area is functionally pivotal insofar as it conditions the spatial orientation of the upper extremity. Articulation of the shoulder and the integrity of the musculoskeletal system are points of major importance, as are smoothness of the teguments and the integrity of the gliding planes. In reconstruction, the main objective consists in the restoration of these different elements. The shoulder area contains two zones, for which the aims of reconstruction will differ:

-The rounded curve of the shoulder The tegument is thin and pliable. The hypodermis is minimally thick. It overhangs the osteoarticular zone, where the gliding planes have an essential role on each side of the rotator cuffs. From a cosmetic standpoint, this zone is essential, as it ensures harmony between the base of the neck and the arm.

-The axillary area of the shoulder With the cutaneous reserve of the axillary crease, it provides the flexibility necessary to the elevation of the upper limb. In addition to protecting the vasculo-nervous elements that rise to its summit, thanks to the protein-rich sweat glands of the hypodermis, it fulfills the functions of homeostasis and thermoregulation.

As these two zones are distinct, this will be discussed in two different sub-chapters.

1-THE SHOULDER CURVE

Anatomy

The smooth flexible skin of the shoulder curve constitutes a surface extending from the base of the neck to the outer border of the arm from medial to lateral, and from the anterior pillar of the subclavicular axillary zone to the posterior pillar beneath the scapula spine, from anterior to posterior. The smooth glabrous skin follows the contours of the subjacent musculoskeletal structures, fulfilling a major cosmetic function. From a bone structure standpoint, the shoulder curve consists in the acromial area and the lateral extremity of the clavicle, providing protection for the rotator cuff and the scapulohumeral joint.

Etiologies of substance losses

Substance losses in this region occur more rarely than in other parts of the upper extremities. While burn injuries are predominant, other etiologies are tumoral (dermatofibrosarcoma, melanomas, epidermoid carcinomas) or subsequent to radiation therapy. In the event of failure or in young patients, and provided that the scapulothoracic articulation is intact, scapulohumeral arthrodesis may constitute an interesting alternative insofar as it permits stability and indolence. Even though mobility is lessened, the upper limb, particularly the hand, can regain spatial orientation.

-Skin reconstruction: Reconstructed skin must be both smooth and supple, with restoration of the form and the texture of the curve.

o While a thin skin graft may correspond to these criteria, to reduce retraction it is preferable to add an artificial dermis.

o While full-thickness graft yields less long-term cutaneous retraction and presents esthetic criteria superior to the thin-skin version, it is primarily used in cases of small-scale loss of substance.

o Flap-based reconstruction, particularly using a perforator flap, corresponds to exigencies of coverage and reconstruction of fine skin.

To cover the acromial region the flap needs to have fine, an exigency corresponding to fasciocutaneous, muscle, pedicled or free flaps.

Types de reconstruction

Grafts

The key characteristics of skin grafts have been recalled, and it is not necessary to return to the subject. That much said, given the objectives of reconstruction of the shoulder curve areas, a cosmetically optimal result is to be expected, which is why, when a thin skin graft is being positioned on a large-scale surface, addition of an artificial dermis is called for.

Our preferred product is Matriderm®, which permits one-step reconstruction, with a high probability of satisfactory engraftment (Fig 1 and2).

Local flaps

Local transposition or rotation flaps are less often used on the curve than at the level of the axillary crease. As elsewhere in the tegument, they are indicated mainly for limited losses of substance. Since the shoulder curve region is highly susceptible to hypertrophic and keloid scars or to large and unsightly scars, one must carefully avoid suturing under tension. To counteract these drawbacks, relative immobilization of the shoulder stump by Dujarier bandage is recommended.

Pedicled regional flaps

From the anterior aspect of the trunk -Supraclavicular artery island flap (SCAIF)

Based on the perforators of the supraclavicular artery emerging from the traverse cervical artery, this 20-centimeter-long flap [2] generally covers losses of substance on the lateral side of the cervical area. The pivotal point is located at the base of the cervical area, behind the clavicle, in close proximity to the outer edge of the sternocleidomastoid muscle. Thanks to its arc of rotation, it can be utilized to cover anterior or posterior shoulder lesions at the curve. The supraclavicular nerf can be harvested in or separated from the flap to preclude bothersome dysesthesias [3] The sequelae entailed by its harvesting seem minor [4].

Pectoralis major flap

The surgical technique is summarized not in this paper, but in a reference [5]. With a subclavicular pivot point and a sizable arc of rotation, the pectoralis major myocutaneous flap can be utilized to cover not only the anterior curve of the shoulder (Fig 3), but also the low cervical and sternal zone. Its main drawback consists in large-scale scarring of the anterior side of the trunk. In clinical practice, use of the pectoralis major myocutaneous flap is limited to male patients. As we shall see later, it can also be utilized as a pure muscle flap.

Pectoralis minor flap

It can be utilized to cover the anterior side of the shoulder curve, with fewer bothersome sequelae than the pectoralis major flap [START_REF] Palmer | Anterior shoulder reconstruction with pectoralis minor muscle flap[END_REF].

Deltopectoral flap

Based on the perforators of the 2 nd , 3 rd and 4 th intercostal spaces stemming from the medial thoracic artery, in its subclavicular location it extends to (and may even go beyond) the deltopectoral groove. Customarily utilized in ENT surgery (anterior cervical) prior to the advent of microsurgical reconstruction, its rotation arc enables it to reach the summit of the shoulder and to cover the clavicle (Fig 3). Its contours must be conserved when producing a pectoralis major flap in first-line intervention.

From the posterior aspect of the trunk

Occipito-cervico-thoracic flaps

These flaps are mainly utilized in treatment of the sequelae of lateral and anterior cervical burns. They are based on the perforators of the transverse cervical artery and its branches, including the superficial cervical artery. They feature a large arc of rotation and can ensure coverage of the summit of the shoulder (Fig 4). There exist several variants, one of them starting from the cervical perforators [START_REF] Ogawa | Clinical and basic research on occipito-cervico-dorsal flaps: including a study of the anatomical territories of dorsal trunk vessels[END_REF] and presenting a pedicled or "extra-fine" form.

Given their large arc of rotation, they can be utilized not only to cover the anterior cervical region [START_REF] Ghorbel | Interest of Thin Skin Flaps in the Treatment of Postburn Cervical Contractures: About Five Cases[END_REF] and the upper side of the shoulder, but also to cover the posterior side of the glenohumeral joint.

Distal trapezius pedicled flap

This harvesting technique is detailed on the "plast-e" you tube channel of M Revol [9]. Based on the dorsal scapular artery, the musculocutaneous flap is perfectly suited for treatment of limited losses of substance at the summit of the shoulder [START_REF] Rasheed | The extended lower trapezius flap for the reconstruction of shoulder tip defects[END_REF][START_REF] Motamed | Trapezius musculocutaneous flap in severe shoulder and neck burn[END_REF]. Musculocutaneous island harvesting based on the descending branch of the transverse cervical artery enlarges the arc of rotation and covers losses of occipital, acromial and acromioclavicular substances [START_REF] Bhathena | Caudal trapezius composite island flap for extensive shoulder defects[END_REF].

Scapular/parascapular flap

Based on a branch of the circumflex scapular artery that emerges from the triangular space of the posterior side of the shoulder, the scapular and parascapular flaps are fasciocutaneous flaps that can be harvested compositely with the teres minor muscle or the lateral edge of the scapula. Harvested face to the scapula spine, given its 90° rotation this pedicled flap can cover the anterior side of the shoulder joint [START_REF] Kim | Use of a pedicled parascapular flap for anterior shoulder and arm reconstruction[END_REF]. With its limited dimensions, it is self-closing.

Latissimus dorsi flap

Even if it is more generally utilized in cases of multitissue losses of substance in the shoulder, the pedicled latissimus dorsi flap is THE flap most essential to shoulder coverage. Given its unusually large arc of rotation, it can cover the anterior as well as the posterior side of the shoulder curve (Fig 3). As a result, it is utilized as coverage for complex shoulder traumas (Fig 5 -10). It can also be utilized in treatment of extended cutaneous losses of substance in cancer surgery (dermatofibrosarcoma exeresis following histological confirmation of a healthy deep anatomical barrier). As regards carcinologic outcome, the Saint Louis team has highlighted an improved cosmetic aspect [START_REF] Brabant | Dermatofibrosarcoma protuberans of the chest and the shoulder: wide and deep excisions with immediate reconstruction[END_REF]. The pedicled latissimus dorsal flap can likewise be useful in the context of a cosmetic shoulder curve objective following brachial plexus paralysis, for example [START_REF] Schoeller | Transfer of pedicled musculocutaneous latissimus dorsi flap for restoration of shoulder contour after neurogenic atrophy[END_REF]. If the latissimus dorsi is paralyzed, volume is provided by muscular trophicity alone. There is no attendant loss of shoulder function. Notwithstanding its unusually large coverage surface and sizable arch of rotation, latissimus dorsi harvest leaves few functional sequelae [START_REF] Legré | Analyse des séquelles du prélèvement du lambeau de grand dorsal. A propos de quarante-quatre cas revus et testés [Analysis of sequelae of the latissimus dorsi flap removal. Report of 44 cases reviewed and tested[END_REF]. Moreover, it is muscle-sparing, especially insofar as it skeletonizes vascular arborization. The latissimus can easily be harvested with a block in the dorsal decubitus position at the level of the spinous processes, all the while conserving its versatility and maintaining the possibility of multi-tissue harvesting [START_REF] Boa | Dorsal decubitus positioning: a novel method to harvest the latissimus dorsi flap for massive upper extremity defect reconstruction[END_REF].

From the arm

Proximal pedicled external brachial flap

The anterior and external regions of the shoulder curve can be covered by the external brachial flap (Fig 3). This septocutaneous flap is based on the perforators of the posterior branch of the collateral radial artery located in the external intermuscular septum of the arm. It is proximally pedicled, and can cover losses of substance exceeding 10cm in diameter without major scarring. The donor site can be reduced in size by concentric peripheral suture before being grafted [START_REF] Jordan | The pedicled lateral arm flap for oncologic reconstruction near the shoulder[END_REF].

Perforator flaps

Almost all of the previously described perforator flaps stemming from the arteries can, in principle, be utilized as propeller flaps to cover losses of substance in the shoulder region.

Using pen-tip Doppler or color Doppler ultrasound, it is easy to detect emergence of a perforator by means of the aponeurosis close to the loss of substance. Once plastic surgeons are sufficiently familiarized with Doppler ultrasound, they may carry out "free style" flap elevation, without being limited by anatomic variations. Over recent years numerous perforator flaps have been characterized and described in painstaking detail, even for profound losses of substance. One example is a perforator flap arising from the acromiothoracic artery and covering exposure of the glenohumeral joint after an electrical burn [START_REF] Rout | Reconstruction of high voltage electric burn wound with exposed shoulder joint by thoracoacromial artery perforator propeller flap[END_REF]. Different flaps are presently being studied and shall be considered in clinical cases. Another example is the perforator flap arising from the acromial branch of the acromiothoracic axis [START_REF] Portenard | Anatomical study of the perforator flap based on the acromial branch of the thoraco-acromial artery (abTAA flap): a cadaveric study[END_REF] (Fig 3). Occasionally harvested from "ultra-fine" structures, these flaps thoroughgoingly correspond to specifications for cutaneous reconstruction of the shoulder curve.

Tissue expansion

In the etiologies of burning or in cases of congenital nevus, tissue expansion is a preferred means of increasing the surface to be covered, and is part and parcel of the regional therapeutic arsenal [START_REF] Aubert | Forum: l'expansion tissulaire. L'expansion cutanée au membre supérieur [Forum on tissue expansion. Expansion of the upper limb[END_REF]. That much said, it necessitates special attention to a number of details pertaining to surgery and treatment. For example, the thin, axial suprascapular flap can be expanded in cases involving post-burn resurfacing [START_REF] Almeida | Expanded shoulder flap in burn sequela[END_REF]. Expansion of the flaps around the shoulder curve has also been described as a means of treating congenital nevus at the summit of the shoulder [START_REF] Margulis | Large and giant congenital pigmented nevi of the upper extremity: an algorithm to surgical management[END_REF].

Distant flaps

"Nourishing" flaps have yet to be described. However, free flaps branched on the thoracodorsal artery can allow access to large-scale reconstructions when the latissimus dorsi is unusable or insufficient.

The shoulder region as donor site / harvesting sequelae

The shoulder curve region is a preferred site for the harvesting of flaps contributing to reconstruction of the face and the neck (deltopectoral flap, supraclavicular flap…). The harvesting zones are themselves under reconstruction, restoration obligatorily corresponding to the esthetic exigencies of the anterior side of the trunk and the summit of the shoulder. In the majority of cases, reconstruction is achieved by the grafting of nonexpanded thin skin on an artificial dermis. More often than not, functional consequences of flap harvesting in this area of the shoulder are minimal or limited. As with the supraclavicular flap, abduction may in some cases be reduced after harvesting of the fasciocutaneous flaps [START_REF] Herr | Shoulder function following reconstruction with the supraclavicular artery island flap[END_REF]. However, another recent study showed that utilization of the supraclavicular flap entailed few functional, esthetic or nervous complications [START_REF] Spiegel | Shoulder Morbidity in Patients after Head and Neck Reconstruction with the Pedicled Supraclavicular Island Flap[END_REF]. As concerns the muscle flaps (latissimus dorsi…) utilized in reconstruction of the neck, with skin graft at the donor site, it appears that shoulder mobility is altered, even without any deep lesion [START_REF] Refos | Shoulder morbidity after pectoralis major flap reconstruction[END_REF].

THE AXILLARY REGION

Anatomy

The axillary region can be considered as a pyramid of which the relatively concave base flattens out in accordance with upward upper limb movement. It binds together the upper extremity and the trunk and serves as the of vasculo-nervous and lymphatic elements passageway toward that extremity. It is composed of:

-the cutaneous base: the axillary skin -a summit, or apex, atop or within, corresponding to an osteofibrous canal serving as a passageway for subclavian vessels and branches of the brachial plexus; -four sides: a/ an anterior side limited by the deep side of the pectoral muscles and the subclavius muscle, b/ a posterior side limited by the subscapularis, teres major and latissimus dorsi muscles covering the anterior side of the scapula, c/ a medial side, with the serratus anterior muscle covering the rib cage, d/ a lateral side, with the short brachial biceps and the coracobrachialis muscle.

In upward upper limb movements, the axillary pyramid flattens out and the anterior and posterior edges stretch out; the latter are known as axillary pillars.

From the base to the summit of the pyramid or from the surface to the depth of the axillary skin, the axillary crease is composed of: a/ fine skin of which the central hairy part contains pilosebaceous annexes and apocrine sweat glands, b/ subcutaneous adipose tissues, c/ a fascia, parallel to the cutaneous plane, prolonging the clavi-deltopectoral aponeurosis, d/ cellulo-adipose tissue, containing lymph nodes and vessels as well as sensitive nerve branches leading to the medial side of the arm, the "perforators". At the summit of the pyramid, the axillary vein(s), the overlying artery and the branches of the brachial plexus wend their way. Along the side or the walls of the axillary crease, the following vasculonervous elements appear: a) inside: the long thoracic nerve and the vascular pedicle of the serratus; b) in back: the vasculo-nervous pedicle of the latissimus dorsi; and c) in front: the nerve branches of the pectoral muscles or inlet of the pectoral nerves. The axillary crease fulfills two main functions: a/ to protect the vasculo-nervous elements leading to the upper extremity; b/ to enhance the mobility of the glenohumeral joint by being deformed, particularly by lengthening the anterior and posterior pillars.

Etiologies of substance losses

The main etiologies for losses of substance on the axillary crease differ from those of the shoulder curve:

-traumatic: burns or burn sequelae, which more often affect the axillary pillars, especially the anterior pillars, rather than the base. There are similarities to the sequelae of radiation therapy. Trauma is more rarely due to knife or gunshot wounds..

-infectious: subcutaneous abscesses, particularly in Verneuil's disease, suppurative adenitis. b-Controlled wound healing may be envisioned when the loss of substance is not overly extended and does not reach the axillary pillars. Cutaneous retraction is achieved at the expense of thoracic and brachial skin. Associated with a temporary abduction apparatus and kinesitherapy, it occasions little if any limitation of arm elevation, and is of particular interest in treatment of axillary injury ascribable to Verneuil's disease. On the other hand, it is not recommended for loss of substance in the axillary pillars.

c-Skin grafts

Skin grafts can accelerate would healing in the armpit and/or limit retractile sequelae in the pillars. As a matter of course, they necessitate solid anatomical substructures. They can be successfully associated with dermal substrates.

d-Local flaps

Multilayered or trident Z-plasties, IC flaps and multiple trapezoidal flaps [START_REF] Grishkevich | Postburn edge shoulder adduction contracture: anatomy and elimination with trapeze-flap plasty--a new approach[END_REF] are all of use, especially in treatment of burn sequelae in the axillary pillars. They increase maximum length of the pillars, thereby conserving shoulder mobility [START_REF] Seroussi | Lambeaux -IC : Application aux brides axillaires Chaouat[END_REF][START_REF] Karki | Role of Square Flap in Post Burn Axillary Contractures[END_REF].

Regional flaps -perforator flaps

The medial brachial flap: This cutaneous flap can be used as a propeller perforator or as a V-Y advancement flap compensating for loss of axillary substance. It is vascularized by one to three perforators of the brachial artery or the superior ulnar collateral [START_REF] Alharbi | Application of the inner arm perforator flap in the management of axillary hidradenitis suppurativa[END_REF] (Fig 4,[START_REF] Motamed | Trapezius musculocutaneous flap in severe shoulder and neck burn[END_REF][START_REF] Bhathena | Caudal trapezius composite island flap for extensive shoulder defects[END_REF].

The thoraco-dorsal perforator flap: Vascularization is usually provided by the perforator branch of the descending branch of the thoracodorsal artery, located 8 to 10 cm distal to the posterior axillary line and 2 cm behind the lateral edge of the latissimus dorsi muscle. It contributes a relatively large cutaneous zone without sacrificing the muscle itself [START_REF] Wormald | Surgical treatment of severe hidradenitis suppurativa of the axilla: thoracodorsal artery perforator (TDAP) flap versus split skin graft[END_REF][START_REF] Er | Reconstruction of axillary contractures with thoracodorsal perforator island flap[END_REF].(Fig

4, 13ab, 14ab).

The inframammary extending lateral intercostal artery perforator (LICAP) flap: Harvested in the inframammary zone, this flap is vascularized by one or more intercostal lateral perforator muscles located at the junction of the anterior edge of the latissimus dorsi and the inferior edge of the third rib. It provides coverage of axillary defects when the posterior region of the shoulder is not useable [START_REF] Stillaert | The inframammary extending lateral intercostal artery perforator flap for reconstruction of axillary contractures: a case report[END_REF].

-fasciocutaneous flaps

The posterior brachial flap is a vascularized skin flap originally developed by Masquelet and Rinaldi in 1982 on the basis of anatomical studies. It is vascularized by a direct cutaneous posteriorly positioned perforator of the brachial artery. It can be harvested with the posterior cutaneous nerve of the arm, a maneuver allowing transfer of a sensitive pedicled flap, which can be utilized for coverage of losses of substance in the axillary region [START_REF] Masquelet | Anatomical basis of the posterior brachial skin flap[END_REF][START_REF] Hodgins | The posterior arm flap in reconstruction of axillary defects: A lifeboat when soft tissue cover is limited[END_REF].

Scapular and parascapular flaps

Vascularization of these flaps is provided by the circumflex scapular artery, which itself stems from the subscapular artery. The circumflex scapular artery transits between the teres major and the teres minor muscles at the axillary edge of the scapula and extends its terminal branches with a horizontal branch for the scapular flap and a descending vertical branch for the parascapular flap. These flaps can be used in a pedicled form for armpit reconstruction, particularly in the context of burn sequelae treatment [START_REF] Nişanci | Treatment modalities for post-burn axillary contractures and the versatility of the scapular flap[END_REF][START_REF] Chen | Surgical treatment of severe or moderate axillary burn scar contracture with transverse island scapular flap and expanded transverse island scapular flap in adult and pediatric patients-A clinical experience of 15 cases[END_REF].

-musculocutaneous flaps

The latissimus dorsi flap Vascularization is provided by the pectoral branch of the thoraco-acromial artery. It can be utilized in axillary reconstruction as a muscle flap, a more or less extended musculocutaneous flap [START_REF] Iblher | The extended pectoralis major flap for reconstruction of the upper posterior chest wall and axilla[END_REF] or a cutaneous perforator flap [START_REF] Kosutic | Use of pectoralis major perforators for local "free-style" perforator flap in axillary reconstruction: a case report[END_REF]. Its main drawback consists in esthetic sequelae at the level of the donor site, especially in women. The pectoralis minor muscle can be indicated in some instances of axillary reconstruction [START_REF] Shah | Reconstruction in the axilla with a pedicled pectoralis minor muscle flap[END_REF] Fig3.

The serratus anterior flap

Vascularized by a branch of the thoracodorsal artery, this pedicled muscle flap provides coverage for some losses of axillary substance. To minimize the functional sequelae of harvesting, it is recommended to transpose only the lower portion of the muscle (outlying bundle) [START_REF] Vu | Anatomic basis of serratus anterior muscle flap transposition[END_REF] [START_REF] Ogawa | Reconstruction of axillary scar contractures--retrospective study of 124 cases over 25 years[END_REF][START_REF] Jandali | Thoracodorsal artery perforator flaps and muscle-sparing latissimus dorsi myocutaneous flaps for the treatment of axillary hidradenitis[END_REF]. When the zone to be covered is sizable, it can be associated with other flaps stemming from the subscapular artery (serratus anterior, scapular or parascapular...) Fig 3 and4.

Distant flaps

Given the multiplicity of loci-regional solutions, they are hardly ever indicated at the axillary level. That said, possibilities include free groin flaps, anterolateral thigh flaps and superficial temporal fascia flaps [START_REF] Chen | Anterolateral Thigh Flap for Reconstruction in Postburn Axillary Contractures[END_REF].

Massive shoulder reconstruction

Major losses of substance in the shoulder are primarily caused by carcinological exeresis (sarcoma…). Given the exposure of noble elements and the need for pluritissular reconstruction, the flaps to be preferred are based on the thoracodorsal artery and the subscapular arterial tree. In coverage of the anterior side of the shoulder with exposure of the subclavian vessels and the plexus, combination of a pedicled latissimus dorsi flap and a serratus anterior flap is a composite solution providing a highly reliable, large-scale coverage surface [START_REF] Haddad | Exérèse large d'un sarcome de l'épaule et reconstruction en un temps par double lambeau de grand dorsal et de grand dentelé pédiculé. Discussion à propos d'un cas[END_REF]. Either in its "pure muscle" or its musculocutaneous version, the pedicled latissimus dorsi flap features a sizable arc of rotation over a considerable surface. In a reported series of shoulder sarcomas it offered appreciable vascular safety while minimizing risks of infection when synthetic materials were implanted [START_REF] Behnam | The pedicled latissimus dorsi flap for shoulder reconstruction after sarcoma resection[END_REF].

A combination of pedicled flaps (latissimus dorsi, grand pectoral…) corresponds to the exigencies proper to some cases of major shoulder substance loss. When pedicled or "pure" muscle flap grafts are utilized, the esthetic sequelae are lessened [START_REF] Al-Qattan | Coverage of complex defects of the shoulder girdle and posterior neck triangle following tumor resection[END_REF] .

The reconstruction of motricity

When the joints and muscles of the shoulder are being reconstructed, it is with the objective of restoring movement. Flaps expressly aimed at motricity reconstruction have been described, albeit in exceptional indications. In the context of deltoid restoration, a bipolar latissimus dorsi flap has been reported [START_REF] Smet | Bipolar latissimus dorsi flap transfer for reconstruction of the deltoid[END_REF]. In a recent anatomical study on the restoration of deltoid function, the feasibility of bipolar pedicled latissimus dorsi transfer was demonstrated, particularly for the middle and posterior portions. As regards bipolar transfer of the pectoralis major, it has been shown to successfully restore the anterior portion of the deltoid muscle [START_REF] Hanneur | Options of bipolar muscle transfers to restore deltoid function: an anatomical study[END_REF]. In unusual cases, free transfers with vascular and nervous anastomosis have likewise proven conducive to restoration of the deltoid function (the tensor fascia flap…) [START_REF] Ihara | Tensor fasciae latae flap: alternative donor as a functioning muscle transplantation[END_REF].

Amputations Proximal arm amputations

To lengthen an insufficiently long humeral amputation stump, a composite scapular pedicled stump (bone only or fasciocutaneous + bone) has been developed. It represents a regional solution (pedicled flap) for a problem of pluritissular local reconstruction. Using the spine of scapular, an short humeral stump can be effectively lengthened, thereby enhancing the autonomy of a patient amputated in the proximal portion of the upper extremity, who is subsequently to be fitted out for an apparatus. With a series of 8 cases, V Pinsolle put forward this solution in 2007 [START_REF] Pinsolle | The pedicled vascularised scapular bone flap for proximal humerus reconstruction and short humeral stump lengthening[END_REF].

Interscapular-thoracic amputations

Inter-scapular thoracic amputations are major interventions possibly requiring reconstruction of the zone exposed in major exeresis of the upper extremity root. For these highly exceptional cases, a number of authors have proposed free composite elbow tissue transfer [START_REF] Koulaxouzidis | Shoulder silhouette and axilla reconstruction with free composite elbow tissue transfer following interscapulothoracic amputation[END_REF]. The concept of free or pedicled composite flap taken from an amputated or unreimplantable limb and used as coverage for an extended loss of substance or as means of lengthening a stump is an "ultimate" solution that a reconstructive surgeon should feel compelled to take into consideration. While the concept can prove useful at any and every level, it is of particular interest in shoulder reconstruction [START_REF] Küntscher | The concept of fillet flaps: classification, indications, and analysis of their clinical value[END_REF] .

CONCLUSION

In shoulder skin reconstruction, restoration of tegument flexibility is of paramount importance when endeavoring to ensure as much as feasible the effective functioning of the glenohumeral joint and the integrity of the gliding planes. For the axillary crease and the shoulder curve, numerous regional solutions are possible (pedicled or perforator flaps…), including in cases necessitating extended reconstructions. While the anterior side of the trunk is a donor zone, the sequalae may be highly unsightly. Scar visibility can be minimized by prioritizing the edges of the lateral thorax or the medial arm.

  Traumatic or infectious causes are less frequent. Cancerology of the osteoarticular system can in certain cases necessitate the intervention of a plastic surgeon for reconstruction following tumor exeresis (especially for shoulder sarcomas). Reconstruction objectives Reconstruction of the rounded curve of the shoulder corresponds to several objectives: -Osteoarticular reconstruction This is not the main subject of the present paper. That said, it seems important to recall the main objectives of shoulder reconstruction: mobility and spatial orientation of the upper limb. Multidisciplinary work involving our colleagues in orthopedics is conducive to choice of the most suitable option when a patient's osteoarticular system is altered. The plastic surgeon has elements of interest to propose: vascularized fibula flap for reconstruction of the clavicle, composite osteo-musculocutaneous composite flap... While humeral reconstruction prostheses exist, their mobilization presupposes restoration of the rotator cuff and the deltoid muscles [1].

-

  tumoral: skin cancers or lymph localizations. The objectives of reconstruction When reconstructing the axillary crease, there are two objectives: a) in cases involving deep loss of substance, to ensure coverage of vasculo-nervous elements; b) more frequently, to provide the pillars with more supple and pliable skin, thereby facilitating upward movement of the upper extremity. Reconstruction must utilize tissue thick enough to pad the summit of the axillary crease, ensuring protection for the vasculo-nervous elements when the loss of substance is deep, and flexible enough to be extended at the level of the pillars to avoid shoulder girdle movement restriction. The types of reconstruction Local a-Direct suture is suited to when there is little skin loss in the center of the axillary crease. It often necessitates production of local tissue plasty at the pillars to avoid extension.

  Fig 3. The muscle or musculocutaneous latissimus dorsi flap This flap is distinguished by a large-scale coverage surface. It is vascularized by the thoracodorsal artery. It can be harvested as a pure muscle, musculocutaneous or musclesparing latissimus dorsi flap

BIBLIOGRAPHY1

  Gouin F, Creen V. Reconstruction après résection pour tumeur osseuse de l'épaule [Reconstruction following shoulder resection for bone tumor]. Bull Cancer. 2014;101(10):951-7.

Fig 1 :

 1 Fig 1 : Darier-Ferrand dermatofibrosarcoma of the right shoulder, preoperative view

Hemin Sheriff, Carmen Vega Garcia, Suzan Jaber, Débora Bernárdez Ojea, Shokha Shahab Kareem, Manuel Fernandez Garrido, et al. Supraclavicular Artery Island Flap: Relation Between Length and Distal End Necrosis. International Microsurgery Journal 2018;2(1):5

Sands TT, Martin JB, Simms E, Henderson MM, Friedlander PL, Chiu ES. Supraclavicular artery island flap innervation: anatomical studies and clinical implications. J Plast Reconstr Aesthet Surg. 2012;65(1):68-71.

Spiegel JL, Pilavakis Y, Canis M, Welz C. Shoulder Morbidity in Patients after Head and Neck Reconstruction with the Pedicled Supraclavicular Island flap. Plast Reconstr Surg Glob Open. 2018;6(4):e1711.

Acknowledgments:

We wish to cordially thank Professo D Le Nen (CHU Brest) and Doctor R Carloni (Hopital Privé de l'Estuaire-Le Havre) for illustration of this manuscript taking into full account a number of their clinical cases.

Conflicts of interest:

The authors have no conflicts of interest to declare with regard to this publication.


Taibi Abdelkader
email: abdelkader.taibi@hotmail.

Keywords: cystic lymphangioma, omentum, cystic lesion

A 50-year-old man, with no remarkable antecedent history or comorbidity, was admitted through the emergency department for abdominal pain with epigastric discomfort of one week's duration.

Physical examination identified a palpable epigastric and peri-umbilical mass associated with abdominal tenderness but without true guarding. Abdomino-pelvic computerized tomography (CT) showed a supra-vesical mass measuring 10 x 8.6 x 14.2 cm overlying the proximal portion of the mesenteric vessels (Fig 1 resectability. However, laparotomy represents the treatment of choice to achieve complete surgical resection [START_REF] Mabrut | IMesenteric and mesocolic cystic lymphangiomas. Diagnostic and therapeutic management[END_REF][START_REF] Hureibi | Mesenteric cystic lymphangioma mimicking malignancy[END_REF]. Recurrence occurs in 40% of patients in case of incomplete resection.

Conflicts of interest: none

Figure 1 :

 1 Figure 1: Sagittal slice of abdominopelvic CT: well defined hypodense mass (A), homogenous contents, located behind the bladder (B). This 10 cm x 8.6 cm x 14.2 cm mass compresses the rectum (C) posteriorly.

Figure 2 :

 2 Figure 2: Sagittal slice of MRI: cystic mass (A) providing a homogeneous multilocular (*) liquid T2 hypersignal, with enhanced walls after injection of gadolinium.

Figure 3 :

 3 Figure 3: Intra-operative view of the stomach (A) and the cystic mass (C) appended to the greater omentum (B).

Figure 4 :

 4 Figure 4: Intra-operative view of the cystic mass (A) appended to the omentum (B). (C) and (D) represent the mesentery and jejunum.

Surgical image

Cystic mass appended to the greater curvature of the stomach? cystic lymphangioma of the greater omentum A Taibi 1,2* ; S Derbal 1 ; M Mathonnet 1 ; S Durand Fontanier 1,2


Doris Brockmann
email: doris.brockmann@inrae.fr

Yves Gérand

Chul Park

Kim Milferstedt

Arnaud Hélias

Jérôme Hamelin

Wastewater treatment using oxygenic photogranule-based process has lower environmental impact than conventional activated sludge process

Keywords: oxygenic photogranules, life cycle assessment, cyanobacteria, anaerobic digestion, granular biomass

The Life Cycle Assessment (LCA) methodology was applied to assess the environmental feasibility of a novel wastewater treatment technology based on oxygenic photogranules (OPG) biomass in comparison to a conventional activated sludge (CAS) system. LCA using laboratory scale experimental data allowed for eco-design of the process during the early stage of process development at laboratory scale. Electricity consumption related to artificial lighting, the fate of the generated biomass (renewable energy and replacement of mineral fertilizer), and the nitrogen flows in the OPG system

Introduction

Recently, the development of oxygenic photogranules (OPG) from activated sludge has been reported (e.g. Milferstedt et al., 2017b;[START_REF] Quijano | Microalgal-bacterial aggregates: Applications and perspectives for wastewater treatment[END_REF]. OPG are roughly spherical biological aggregates with a diameter of up to 5 mm [START_REF] Abouhend | The oxygenic photogranule process for aeration-free wastewater treatment[END_REF].

In OPG, the phototrophic biomass produces oxygen through photosynthesis and uses carbon dioxide for growth. Conversely, the heterotrophic biomass produces carbon dioxide and consumes the produced oxygen. The close vicinity of phototrophs and heterotrophs engaged in this syntrophy makes mass transfer more efficient than between dispersed cells found in high rate algal pond [START_REF] Judd | Algal remediation of CO2 and nutrient discharges: A review[END_REF]. It has been shown that OPG can perform simultaneous oxidation of organic carbon and nitrogen removal [START_REF] Abouhend | The oxygenic photogranule process for aeration-free wastewater treatment[END_REF]Arcila & Buitrón, 2017;[START_REF] Arcila | Microalgae-bacteria aggregates: effect of the hydraulic retention time on the municipal wastewater treatment, biomass settleability and methane potential[END_REF]. A novel OPG-based wastewater treatment technology was proposed, considering carbon and nitrogen removal by OPG coupled to anaerobic digestion of harvested biomass for the production of renewable energy (Milferstedt et al., 2017b;[START_REF] Park | Algal-sludge granule for wastewater treatment and bioenergy feedstock generation[END_REF].

Internally produced oxygen by OPG entirely replaces the energy intensive external supply of oxygen for wastewater treatment. External aeration in conventional wastewater treatment accounts for 45-75% of the overall electric energy consumption of the wastewater treatment plant (WWTP; or water resource recovery facility) [START_REF] Longo | Monitoring and diagnosis of energy consumption in wastewater treatment plants. A state of the art and proposals for improvement[END_REF]. The overall biomass yield (per gram of removed organic carbon) of OPG treating wastewater is up to three times higher than for activated sludge [START_REF] Abouhend | The oxygenic photogranule process for aeration-free wastewater treatment[END_REF]). The biological methane potential (BMP) of the produced OPG is about 15-20% higher compared to activated sludge (Park et al., 2015), which is in line with other works on digestion of an algal-sludge biomass [START_REF] Shoener | Energy positive domestic wastewater treatment: the roles of anaerobic and phototrophic technologies[END_REF][START_REF] Ward | Anaerobic digestion of algae biomass: A review[END_REF].

The differences in aeration requirements, sludge production and BMP, compared to activated sludge systems, may result in significant net energy savings when using the OPG process. However, a closer look at environmental performances of this innovative process combining OPG production and anaerobic digestion has not yet been done and therefore is required.

The aim of the present study was to evaluate the environmental performance of a putative OPG process compared to conventional technology. For this, Life Cycle Assessment (LCA) will be used, a standardized methodology (ISO 14040, 2006;ISO 14044, 2006) to assess potential environmental impacts considering the entire life cycle of products, processes or services based on the function they fulfill, in this case the treatment of municipal wastewater. A product, process or service is modeled along its life cycle (from raw material extraction to its end of life). Its impact is assessed with regard to different impact categories (e.g., global warming, ozone depletion, eutrophication, and acidification). LCA has been applied in the field of wastewater treatment to assess the environmental impact of both conventional activated sludge (CAS) wastewater treatment systems (e.g. [START_REF] Foley | Comprehensive life cycle inventories of alternative wastewater treatment systems[END_REF][START_REF] Hospido | A comparison of municipal wastewater treatment plants for big centres of population in Galicia (Spain)[END_REF], and advanced wastewater treatment technologies (e.g. advanced oxidation [START_REF] Muñoz | Environmental assessment of different advanced oxidation processes applied to a bleaching Kraft mill effluent[END_REF] and high rate algal ponds (Colzi [START_REF] Lopes | Energy balance and life cycle assessment of a microalgae-based wastewater treatment plant: A focus on alternative biogas uses[END_REF]). While the use of LCA for assessing the environmental impact of existing wastewater treatment technologies increases, its use for the eco-design of emerging treatment processes under development is rare.

The present study aimed at evaluating the environmental performances of the novel OPG treatment system using LCA in order to determine whether the OPG system is a feasible technology from an environmental perspective in comparison to a CAS system.

The study was based on a hypothetical model of an average, midsize treatment plant and data derived from laboratory scale process operation, having in mind that many technological problems are still unsolved before considering industrialization. The goal of the assessment at this early stage was to identify potential bottlenecks and critical parameters with high environmental impact. Future research can then target these areas to improve within an eco-design approach the process design prior to detailed process engineering studies. In particular, it was considered how far artificial lighting can be used for the OPG system without substantially deteriorating the environmental performance.

Materials and methods

LCA -Goal and scope

The goal of the LCA was to evaluate the environmental feasibility of the OPG system with regard to a reference CAS system and to assess the impact of different operating scenarios of the OPG system during early process development allowing the identification of design considerations with highest environmental impact. Those will then be targeted in future research to eco-design an up-scaled system. The system under study included in addition to the operation phase, the construction of the infrastructure and nutrient recycling from the sludge by agricultural use. Sludge utilization is considered an integral part of wastewater treatment and the basis of a water resource recovery facility.

The functional unit, based on which the processes are compared, is "the treatment of 1 m 3 of urban wastewater in an average, midsize WWTP". Environmental impacts were computed in SimaPro (version 9.0.0.35, PRé Consultants) using the Ecoinvent database version 3.5 (Wernet et al., 2016) and the Environmental Footprint life cycle impact assessment method [START_REF] Fazio | Supporting information to the characterisation factors of recommended EF Life Cycle Impact Assessment methods[END_REF].

A challenge when assessing the impact of a novel process is the availability of process operation data. Here, the evaluation of the OPG system was based on experimental data from the authors' laboratory scale OPG experiments [START_REF] Abouhend | The oxygenic photogranule process for aeration-free wastewater treatment[END_REF]Milferstedt et al., 2017b). These first experimental studies were mostly conducted to demonstrate a proof of concept and were not dedicated towards optimization and intensification of the process. A large margin of progress is to be expected in the future. Data from the authors' own experimental studies were complemented with laboratory scale data from another research group working on municipal wastewater treatment using microalgaebacteria aggregates (Arcila & Buitrón, 2017;[START_REF] Arcila | Microalgae-bacteria aggregates: effect of the hydraulic retention time on the municipal wastewater treatment, biomass settleability and methane potential[END_REF]) that resemble the OPGs used in the authors' works. Nonetheless, several assumptions were made, that are laid out in detail later, regarding reactor configuration, operating conditions, and treatment performance in a full-scale implementation as the process currently exists only at the laboratory scale. Given the low technical readiness level of the innovative OPG process, some variables remain unknown and need to be estimated from sparse data. The present work, therefore, displays LCA results depending on the estimated value of these variables, such as energy balance and nitrogen flow through the process.

Life Cycle Inventory

The life cycle inventories for both OPG and CAS systems were estimated for an hypothetical average midsize WWTP (10,000 to 50,000 people equivalent), which is equivalent to a WWTP of the Swiss capacity class 3, inventoried in the Ecoinvent 3.5 database [START_REF] Doka | Life cycle inventories of waste treatment services -ecoinvent report[END_REF]. A low loaded wastewater was considered here based on 6 experiments carried out using primary effluent from a US WWTP [START_REF] Abouhend | The oxygenic photogranule process for aeration-free wastewater treatment[END_REF]. Its raw wastewater characteristics are presented in Table 1.

Table 1 Figure 1 Reference system: Conventional activated sludge system

The reference scenario for this comparative LCA is a conventional midsize wastewater treatment plant as described in Ecoinvent [START_REF] Doka | Life cycle inventories of waste treatment services -ecoinvent report[END_REF] and presented in Figure 1 a. Grit removal is followed by primary settlers (not shown in the figure). Organic carbon and nitrogen are removed in an activated sludge process. Phosphorus is removed by precipitation using Fe(III)Cl3. The sludge is separated from the treated water in secondary settlers. Primary and secondary sludge are treated together by anaerobic digestion. The digester supernatant is returned to the influent of the WWTP. Digested and dewatered sludge is assumed to be spread on land as organic fertilizer.

The Ecoinvent datasets for WWTPs of different sizes are based on average treatment efficiencies of Swiss WWTPs dating from 1993-2002 [START_REF] Doka | Life cycle inventories of waste treatment services -ecoinvent report[END_REF] and do not reflect current treatment efficiencies. Consequently, only infrastructure data for the sewer grid and the WWTP were used from the dataset for the midsize treatment plant. Mass balances for chemical oxygen demand (COD), nitrogen, phosphorus, total suspended solids (TSS), and volatile suspended solids (VSS) for the CAS plant were calculated following textbook mass balance equations for biological wastewater treatment (Henze et al. 2008). A sludge retention time (SRT) of 15 days, a mixed liquor suspended solids (MLSS) concentration of 4 g/L, and a design wastewater temperature of 10°C were considered. N2O emissions from wastewater treatment were estimated using an emission factor of 0.03 g N2O-N/g Ndenitrified [START_REF] Foley | Comprehensive life cycle inventories of alternative wastewater treatment systems[END_REF][START_REF] Kampschreur | Nitrous oxide emission during wastewater treatment[END_REF]. Treatment efficiencies for aerobic carbon oxidation, nitrification, and nitrogen removal calculated from mass balance equations were 90%, 84% and 70%, respectively. Phosphorus (P) not incorporated into biomass is precipitated, assuming that 2.5 g Fe(III)Cl3/g Premoved are needed and that 4.9 g FePO4/g Premoved are produced [START_REF] Rittmann | Environmental Biotechnology: Principles and Applications[END_REF].

Mass balances for COD, nitrogen, TSS, VSS, biogas and flow rates for the anaerobic digester were calculated using the steady state model for anaerobic digestion developed by [START_REF] Sötemann | Modelling material mass balances over wastewater treatment plants[END_REF], considering a hydraulic retention time of 10 days based on Ekama (2009). Kinetic parameters for anaerobic digestion of primary and secondary sludge were taken from [START_REF] Ekama | Using bioprocess stoichiometry to build a plant-wide mass balance based steady-state WWTP model[END_REF] and [START_REF] Sötemann | Modelling material mass balances over wastewater treatment plants[END_REF]. BMPs of primary and secondary sludge vary widely (e.g. [START_REF] Mottet | Estimating anaerobic biodegradability indicators for waste activated sludge[END_REF]. For primary sludge, a methane production of 230 mL CH4/g VSS was assumed based on a hydrolysis rate of 2 g COD/L/d [START_REF] Sötemann | Modelling material mass balances over wastewater treatment plants[END_REF]. This is in the range of methane productions of primary sludge reported by [START_REF] Elbeshbishy | Biochemical methane potential (BMP) of food waste and primary sludge: Influence of inoculum pre-incubation and inoculum source[END_REF]. For secondary sludge, a methane production of 195 mL CH4/g VSS was assumed (Park et al., 2015). A lower methane production of secondary sludge compared to primary sludge is in accordance with literature (e.g. [START_REF] Mahdy | Algaculture integration in conventional wastewater treatment plants: Anaerobic digestion comparison of primary and secondary sludge with microalgae biomass[END_REF]. A biogas composition of 65% CH4 and 35% CO2 was considered.

All CH4 was assumed to be oxidized to CO2 during biogas combustion, producing 3 kWh electricity per m 3 CH4 [START_REF] Nowak | Benchmarks for the energy demand of nutrient removal plants[END_REF]. The solids concentration the digested and dewatered sludge was assumed to be 200 kg TSS/m 3 .

A mean electricity consumption of the WWTP of 0.4 kWh/m 3 was considered based on average data for European WWTPs [START_REF] Jonasson | Energy benchmark for wastewater treatment processes -a comparison between Sweden and Austria[END_REF]. Half of the overall electricity consumption was assumed to be spent for aeration [START_REF] Longo | Monitoring and diagnosis of energy consumption in wastewater treatment plants. A state of the art and proposals for improvement[END_REF]. It was considered that electricity produced from biogas combustion is used onsite, covering a part of the needed electricity. For the remainder of needed electricity, an average European electricity mix was considered produced from fossil fuels (50%), nuclear power (27%), hydropower (17%), renewable sources and others (6%) [START_REF] Itten | Life cycle inventories of electricity mixes and grid[END_REF].

Digested and dewatered sludge was assumed to be applied to farmland as organic fertilizer, replacing ammonium nitrate and triple superphosphate application at equivalent nutrient rates. The long-term nitrogen mineral fertilizer equivalent (MFE) of the sludge, nitrogen field emissions from sludge spreading, and avoided field emissions from mineral fertilizers were calculated following Brockmann et al. ( 2018), considering a nitrogen content of 9.7 kg N per m 3 sludge (6.4% total ammonia nitrogen (TAN) and 93.6% organic nitrogen (Norg)) as calculated from the mass balance equations. For phosphorus, a MFE value of 0.95 was assumed. Phosphorus field emissions were estimated following [START_REF] Brockmann | Environmental assessment of nutrient recycling from biological pig slurry treatment -impact of fertilizer substitution and field emissions[END_REF]. Sludge application by broadcaster without incorporation and mean French soil and climate conditions were assumed. Tables 2 and3

Differences in the oxygenic photogranule (OPG) system

The only difference between the considered reference CAS and the OPG plant layouts is the basin for secondary treatment and the absence of secondary settlers (Figure 1 b). In the OPG system, secondary treatment took place in sequencing batch reactors (SBR).

As settling of the OPG was carried out in the SBRs during a settling phase, secondary settlers were not needed. The model of the full-scale OPG system was based on data from the authors' laboratory scale OPG studies [START_REF] Abouhend | The oxygenic photogranule process for aeration-free wastewater treatment[END_REF]Milferstedt et al., 2017b) complemented with data from laboratory scale experiments with microalgaebacteria aggregates treating municipal wastewater (Arcila & Buitrón, 2017;[START_REF] Arcila | Microalgae-bacteria aggregates: effect of the hydraulic retention time on the municipal wastewater treatment, biomass settleability and methane potential[END_REF]. Based on the authors' laboratory scale OPG experiments, operation in SBRs at a hydraulic retention time (HRT) of 0.5 days and a MLSS concentration of 4 g/L was assumed. For these operating conditions, the overall SBR reactor volume needed is similar to that of the activated sludge reactor plus the secondary settlers. Therefore, the same environmental impact for the required infrastructure was assumed for both systems.

Sludge production was estimated based on a biomass yield of 0.7 g VSS/g CODconsumed (1.26 g COD/g CODconsumed) and a COD/VSS ratio of the OPG of 1.8 g COD/g VSS [START_REF] Abouhend | The oxygenic photogranule process for aeration-free wastewater treatment[END_REF]). An average organic carbon removal efficiency of 85% was considered [START_REF] Abouhend | The oxygenic photogranule process for aeration-free wastewater treatment[END_REF][START_REF] Arcila | Microalgae-bacteria aggregates: effect of the hydraulic retention time on the municipal wastewater treatment, biomass settleability and methane potential[END_REF], assuming that 50% of the removed organic carbon was incorporated into the heterotrophic part of OPG biomass.

The remaining 50% of the removed organic carbon were assumed to be oxidized and then available for phototrophic uptake. An average ammonia transformation efficiency of 90% was considered [START_REF] Abouhend | The oxygenic photogranule process for aeration-free wastewater treatment[END_REF], including nitrogen incorporation into biomass and nitrification. Nitrogen incorporation into biomass was estimated using a nitrogen content of the OPG of 10% (as for CAS), resulting in 54% of the organic and ammonia nitrogen being incorporated into OPG (vs. 22% calculated for CAS). The remaining unaccounted transformed ammonia was assumed to be nitrified. Based on this assumption, 33% of the NH4-N transformed was converted to NO3-N, which was below an observed NO3-N production rate of 50% (Abouhend et al., 2018; Arcila & Buitrón, 2016), but of the same order of magnitude as reported by [START_REF] Arcila | Influence of solar irradiance levels on the formation of microalgae-bacteria aggregates for municipal wastewater treatment[END_REF]. Denitrification by OPG has, so far, not been reported, but the presence of genes (Stauch-White et al., 2017) and of 16S rRNA bacterial sequences (Milferstedt et al., 2017b) associated with denitrification was revealed. It was assumed that the OPG system includes a denitrification step with a denitrification efficiency similar to the reference system (80%). Overall, a total nitrogen removal efficiency of 71% was obtained based on mass balances, which was equivalent to the CAS system. A methane production of 290 mL CH4/g VSS for OPG [START_REF] Arcila | Microalgae-bacteria aggregates: effect of the hydraulic retention time on the municipal wastewater treatment, biomass settleability and methane potential[END_REF]) and a biogas composition of 65% CH4 and 35% CO2 were considered.

In contrast to the CAS system, the OPG system does not require aeration since OPG produces oxygen under light. Based on laboratory scale experiments with 3. For land application of the OPG, a long-term MFE of 0.562 was calculated, based on a nitrogen content of 13.4 kg N/m 3 OPG (15.4% TAN and 84.6% Norg), as calculated from mass balance equations. Table 2 Table 3 Operating scenarios OPG is exposed to sunlight during the day, enabling oxygen production by photosynthesis. For providing oxygen during night-time, when OPG is not exposed to sunlight and thus not photosynthetically active, different operating scenarios were considered:

• Scenario 1: Artificial lighting is provided during the night. Considering overall 14 h/day of illumination and assuming that natural light covers on average 7 h/day, the same duration of artificial lighting is needed.

• Scenario 2: Aeration replaces the 7 h/day of artificial lighting. Thus, aeration is needed for 7 h/day and mixing for 15 h/day.

• Scenario 3: OPG is not exposed to sunlight at all and artificial lighting is provided 14 h/day.

• Scenario 4: As scenario 1 but with a 50% reduction in light energy provided. Scenario 1 was used as the default scenario for the OPG system. The impact of the other operating scenarios was assessed in a sensitivity analysis.

Results and discussion

Comparison of the two treatment systems

The environmental impact of treating 1 m 3 municipal wastewater and applying the resulting sludge on farm land was compared using a CAS system and the OPG system (scenario 1). A graphical representation of this comparison is shown as radar plot in Figure 2 for all evaluated impact categories. The black line signifies the CAS system as reference, and the blue line the OPG system. For most impact categories, the OPG system's environmental impact is inferior of the CAS impact ranging from a 4% difference for freshwater eutrophication to 61% for ionizing radiation. The two notable exceptions are for the impact categories terrestrial eutrophication and acidification being 2 and 3 times higher, respectively, compared to the CAS system. Figure 2 In Figure 3, the environmental impacts in the various impact categories are related to where they are generated, i.e., treatment infrastructure, emissions from treatment, electricity consumption, Fe(III)Cl3 use for precipitation, sludge spreading and the substitution of mineral fertilizer. Contributions that are identical for both systems are not displayed even though considered in the overall calculations (e.g., sewer grid infrastructure, emissions from overload discharge, grit removal, and treatment plant infrastructure). It should be noted that sewer grid and treatment plant infrastructure are major contributors to the environmental impact. But in this comparison, this impact is not considered relevant as it is assumed to be independent of the biological configuration of the treatment plant. Figure 3 reveals that the significantly higher impacts of the OPG system in the impact categories acidification, terrestrial eutrophication, and respiratory inorganics can be considered a mass effect, as significantly larger quantities of digested sludge are land-applied. The impact is not specific to OPG. In particular, most of the increased impact on terrestrial eutrophication, acidification, and respiratory inorganics from sludge spreading is caused by higher ammonia emissions from land application. Ammonia emissions from sludge spreading contributed 114%, 107%, and 64%, respectively, to the mentioned impact categories.

Twice as much nitrogen was recovered in the digested OPG and spread on land than for the CAS system (203 kg N/d vs. 110 kg N/d). The amount of nitrogen emissions from land application does not only depend on the amount of nitrogen applied, but also on the method of sludge application. Surface application of sludge without subsequent incorporation into the soil is the worst case with respect to ammonia emissions. The significantly lower impact of the OPG system on ionizing radiation is due to a much lower electricity consumption from the grid compared to the CAS system. The OPG system has an overall electricity consumption of 359 Wh/m 3 , of which 269 Wh/m 3 are covered by combustion of the produced biogas and 90 Wh/m 3 by electricity from the grid. In contrast, to cover the overall electricity consumption of the CAS system of 400 Wh/m 3 , 263 Wh/m 3 are needed from the grid as only 137 Wh/m 3 are produced from biogas combustion. Lower impacts on ozone depletion, photochemical ozone formation, human health effects, freshwater ecotoxicity, and resource use are due to lower electricity consumption and higher amounts of mineral fertilizers replaced by landapplied digested biomass. The reduced impact on climate change, compared to the CAS system, result from lower N2O emissions from wastewater treatment and lower electricity consumption of the OPG system. As for the CAS system, N2O emissions from wastewater treatment with OPG were estimated based on the amount of nitrogen denitrified and may change using real data. Nonetheless, climate change impacts of the OPG system remain inferior to the ones of the CAS system even when the contribution of N2O emissions is excluded.

Effects of alternative illumination scenarios on the environmental impact of an OPG treatment plant

The default OPG system (scenario 1) operated with 7 h/day artificial lighting, even in its immature design state, outperforms the CAS system. In the following, the sensitivity of the LCA results is assessed using three envisioned operating scenarios, which affect the electricity consumption of the OPG treatment plant: 7 h/day aeration (scenario 2), 14 h/day artificial lighting (scenario 3) and a modified scenario 1 with a 50% cut-off in light energy provided to the system (scenario 4). It is acknowledged that scenarios 2 and 4 could affect the stability and the performance of the OPG system. Despite these potentially important unknowns, the suggested scenarios allow to assess whether these or similar approaches are environmentally feasible, before even starting the appropriate experiments. The LCA methodology should be considered here a modeling approach that evaluates the environmental impact of putative potential alternatives. For this evaluation, it was assumed that operating conditions for scenarios 3 and 4 impact only electricity consumption, while biochemical conversion rates and overall treatment plant performance remained unchanged. For scenario 2 (7 h/day aeration), the phototrophic biomass yield was reduced, assuming that with only half of the light, half of the phototrophic growth will occur. The reduced phototrophic biomass yield entails lower biomass and, thus, biogas and electricity production. Replacing artificial lighting during night by aeration reduced electricity consumption by about 25% and electricity production by about 15%, requiring only 48 Wh/m 3 from the grid. It may be surprising that the partially aerated system is less energy consuming than the fully photosynthetic system. This is possibly because of the substantial increase of energy recovered from the digested phototrophic sludge. A lower biomass production also implicates lower ammonia emissions from field application of the digested biomass, and lower amounts of mineral fertilizers replaced. Figure 4 shows that the reduced electricity consumption from the grid decreased environmental impacts of the OPG system on ionizing radiation by 35% and on resource use of energy carriers by 11%, compared to scenario 1.

Furthermore, the reduced amount of land-applied digested OPG reduced environmental impacts on acidification and terrestrial eutrophication by 24% and on respiratory inorganics by 13%, but increased the environmental impact on resource use of minerals and metals by 14%, compared to scenario 1. Impacts in other impact categories changed by less than 7%. For scenario 3, where artificial lighting needed to be provided 14 h/day, electricity consumption from the grid more than doubled compared to scenario 1, but remained below the electricity consumption from the grid of the CAS system. Due to increased electricity consumption from the grid, environmental impacts on ionizing radiation doubled and increased by 46% for resource use of energy carriers and land use, and by 31% ozone depletion (Figure 4, orange line). Impacts on other impact categories increased by 1 to 17%. The artificial lighting system considered here represents a largely non-optimized solution. The efficiency of LED lighting is drastically developing and will likely improve significantly over the next years (Zhang et al., 2018), reducing the energy requirements to yield a given photoactive radiation. This kind of development is not expected for the aeration in the CAS system, which is already a mature technology. In addition, the use of white light LEDs was assumed here of which a considerable bandwidth is not suitable for photosynthesis. The use of LEDs with adapted spectra for phototrophic light alone could yield significant energy savings at a similar biological activity [START_REF] Abomohra | Night illumination using monochromatic light-emitting diodes for enhanced microalgal growth and biodiesel production[END_REF]. In addition, the use of suspended, free-moving LED [START_REF] Murray | Wirelessly powered submerged-light illuminated photobioreactors for efficient microalgae cultivation[END_REF]) may further reduce energy consumption for artificial lighting.

Therefore, an optimized artificial lighting system with an assumed improved energy efficiency of LED lighting of 50% (scenario 4) was evaluated here and compared to scenario 1. All other parameters of scenario 1 were kept. With optimized artificial lighting, the electricity consumption of scenario 1 decreased to 293 Wh/m 3 , requiring only 23 Wh/m 3 from the grid. Thus, with an optimized artificial lighting system, an energy neutral treatment system may be within reach.

Operation of the OPG system at higher biomass concentrations

The presented impact assessment was computed for operating the OPG system at the same biomass concentration as the laboratory scale reactor (4 g/L). This is a typical biomass concentration for CAS systems and a relatively low MLSS concentration compared to other granular biomass systems (Milferstedt et al., 2017a). For example, aerobic granular sludge systems can be operated at biomass concentrations up to 10 g/L [START_REF] Keller | Advancements in aerobic granular biomass processes[END_REF]. It is worthwhile investigating the OPG treatment performance at higher biomass concentrations and lower HRT, while maintaining the SRT in the system, to reduce the overall reactor volume of the treatment system. This will decrease treatment plant infrastructure needs, which significantly contribute to environmental impacts on land use, human health effects, freshwater ecotoxicity, resource use, photochemical ozone formation, and respiratory inorganics. Assuming operation of the OPG system at a biomass concentration of 6 g/L and keeping the sludge retention time unchanged, reduces the HRT to 0.33 days and the required reactor volume by 30%.

Energy requirements for mixing need to be considered in a putative OPG system.

Several alternative modes of mixing could be envisioned, e.g., intermittent gas sparging or mixing by pulse-like waves (e.g., oloid.ch). Here, a traditional mixing approach using constantly turning impellers was considered. Energy needs for mixing will decrease with reduced reactor diameter, as the impeller diameter decreases, but energy requirements for artificial light supply may increase with a higher biomass concentration. It is assumed here that the potentially higher energy requirements for artificial light supply compensate the energy savings from reduced energy needs for mixing. This means that the reduction of the reactor volume does not significantly affect the overall electricity consumption of the OPG system. It is further considered that operation at higher biomass concentration and shorter HRT does not result in a considerable loss of treatment performance. Based on the aforementioned assumptions, the reduction of the required reactor volume decreases the environmental footprint with regard to resource use of minerals and metals by 50%, to land use by 37%, to ozone depletion and non-cancer human health effects by 17%, and to photochemical ozone formation by 16%. Reductions on other impact categories range from 0.7 to 13%. These results are based on assumptions that still need to be validated experimentally, but show the interest (from an environmental perspective) of a more compact treatment system.

Nitrogen flows in the OPG system

In the LCA model, nitrogen emissions in the forms of ammonia, nitrite/nitrate, and organic nitrogen from wastewater treatment with OPG were on the same order of magnitude as for the reference CAS system. N2O emissions from biological treatment, estimated based on the amount of nitrogen denitrified, were lower for the OPG system, because more nitrogen was incorporated into biomass, requiring less denitrification. The same emission factor for estimating N2O emissions from a wastewater treatment with OPG and CAS system was used. The factor is based on Foley et al. (2010) and [START_REF] Kampschreur | Nitrous oxide emission during wastewater treatment[END_REF] and remains to be estimated using experimental data from the OPG system. It was demonstrated that major nitrogen emissions occurred also downstream of the treatment plant, at the stage of land application of the digested biomass (Figure 3), affecting largely the impact categories terrestrial eutrophication, acidification, and respiratory inorganics. This was caused by significantly higher biomass produced by the OPG system, resulting in twice as much nitrogen spread on land with the digested OPG than with the activated sludge produced by the CAS system. Consequently, significantly higher nitrogen field emissions for the same volume of wastewater treated can be expected (23 kg NH3/d for OPG system vs. 5.1 kg NH3/d for CAS system). Optimization of the environmental impact of the assessed OPG system should, therefore, also consider the fate of the generated biomass in applications downstream of the treatment plant. The observed large contribution of land application of the digested biomass to the environmental burdens of the treatment systems is in line with other works considering land application of sludge and replacement of mineral fertilizers (e.g. [START_REF] Brockmann | Environmental assessment of nutrient recycling from biological pig slurry treatment -impact of fertilizer substitution and field emissions[END_REF][START_REF] Pasqualino | LCA as a decision support tool for the environmental improvement of the operation of a municipal wastewater treatment plant[END_REF].

In the default scenario, land application of digested sludge by a broadcaster, without incorporation into the soil was assumed. This is common agricultural practice [START_REF] Loyon | Overview of animal manure management for beef, pig, and poultry farms in France[END_REF]) and known to be the worst case scenario with regard to ammonia field emissions [START_REF] Bittman | Options for ammonia mitigation: Guidance from the UNECE task force on reactive nitrogen[END_REF]. Land application of digested biomass by deep injection, considered the best case scenario with regard to ammonia field emissions [START_REF] Bittman | Options for ammonia mitigation: Guidance from the UNECE task force on reactive nitrogen[END_REF], significantly reduced ammonia field emissions in the LCA model from 1504 g NH3/m 3 sludge to 301 g NH3/m 3 sludge for OPG, and from 452 g NH3/m 3 sludge to 91 g NH3/m 3 sludge for activated sludge. The decreased ammonia field emissions yielded in larger amounts of ammonia nitrogen available to the plants, increasing the nitrogen MFE values for OPG (0.64 vs. 0.56) and CAS (0.62 vs. 0.59). Consequently, more mineral fertilizers could be replaced by the digested biomass (10.2 kg N/m 3 sludge vs. 9 kg N/m 3 sludge from OPG, 7.2 kg N/m 3 sludge vs. 6.9 kg N/m 3 sludge from CAS).

The effect of agricultural practice is illustrated in Figure 5. Optimizing the land application of digested biomass from broadcaster application to deep injection significantly decreased the environmental impact in three categories: terrestrial eutrophication, acidification, and respiratory inorganics. The double effect of reducing ammonia emissions from land application of digested biomass and increasing the amount of replaced mineral fertilizers and associated emissions yields in a lower environmental footprint of the OPG system for all 16 impact categories. Thus, in addition to modifications at the treatment plant, the fate of the excess sludge is a determining factor for the environmental impact of the OPG process, and as well for CAS. Particularly, changes of the sludge disposal method can considerably drive the environmental impact and must be considered already in the process design.

Use of produced OPG biomass

For a water resource recovery facility, the produced biomass is a resource that can be transformed into bioenergy and other bioproducts. Even though the high yield in an OPG system and the high degree of uniform phototrophic biomass may make other transformations and valorization ways possible, a 'classical' transformation of the biomass into energy and organic fertilizer by anaerobic digestion was considered in this study. Considering the same biomass transformation for the OPG and the reference CAS system made it possible to show that wastewater treatment using the evaluated OPG system allows for higher energy and nitrogen recovery than the CAS system. The OPG system produced twice as much methane per m 3 of treated wastewater as the CAS system (0.090 vs. 0.046 Nm 3 CH4/m 3 wastewater) and replaced 75% more mineral nitrogen fertilizer (per m 3 wastewater treated) through agricultural use of the digested biomass. This 'base' case of agricultural use was considered because it is current common agricultural practice in France, Spain, and Ireland (European Commission, 2019a) and commonly used when assessing the environmental impact of wastewater treatment [START_REF] Foley | Comprehensive life cycle inventories of alternative wastewater treatment systems[END_REF][START_REF] Hospido | A comparison of municipal wastewater treatment plants for big centres of population in Galicia (Spain)[END_REF]. The land application of digested sludge is probably the worst case with regard to the environmental impact/benefit of the biomass use. In addition, land application of digested sewage sludge will be more restricted in the EU due to more stringent limits for contaminants following the new Fertilizing Products Regulation of the EU (European Commission, 2019b). Electricity generation from biogas is only one potential use of the biogas. Other uses such as upgrading to biomethane as a substitute for natural gas or as a raw material to produce platform chemicals [START_REF] Tsui | A critical review: emerging bioeconomy and waste-to-energy technologies for sustainable municipal solid waste management[END_REF]) should be considered as well in the future.

The objective of this LCA was to guide research efforts to eco-design and improve the sustainability of the OPG process. It is therefore wise to envision alternative uses of the produced OPG, possibly even resulting in larger environmental benefits. One area of active research is the downstream use of extracellular polymeric substances from granular sludge [START_REF] Quijano | Microalgal-bacterial aggregates: Applications and perspectives for wastewater treatment[END_REF][START_REF] Van Loosdrecht | Anticipating the next century of wastewater treatment[END_REF]. OPG may be a suitable candidate for this approach, as these granules are composed of a mat-like outer layer densely populated by filamentous cyanobacteria (Milferstedt et al., 2017b). This layer contains large amounts of extractible extracellular polymeric substance (EPS) produced by cyanobacteria (e.g. [START_REF] Ansari | Effects of seeding density on photogranulation and the start-up of the oxygenic photogranule process for aeration-free wastewater treatment[END_REF]Milferstedt et al., 2017b). The extracted EPS may serve, depending on the physico-chemical properties (e.g., molecular weight, charge, hydrophobicity) as hydrogels, biosurfactants or bioflocculants, as demonstrated in part already for aerobic granules [START_REF] Lin | Sustainable polysaccharide-based biomaterial recovered from waste aerobic granular sludge as a surface coating material[END_REF]. It is of great advantage that through the syntrophy between heterotrophs and phototrophs, heterotrophically produced CO2 is apparently immediately fixed in OPG by the growing phototrophic biomass. Resource recovery and conservation of fixed nitrogen are intrinsic feature of this biomass and must be taken advantage of.

Research perspectives

Two major groups of bottlenecks in the development of a potential OPG-based bioprocess have been identified in the analysis: reducing the environmental costs of providing light to OPGs and increasing the environmental benefit of generating OPG biomass.

Light dependencies touch reactor configuration as much as they potentially affect the biological activity of the phototrophic biomass. Research on the activity of OPGs as a function of lighting, possibly even at the scale of individual photogranules, must be coupled to identifying actual lighting conditions in current or prospective bioreactor designs. This research must also consider effects of biomass density and mixing to successfully narrow down process engineering constraints.

While coupling of microbiological and engineering research has been successfully done for years, biomass valorization requires the establishment of new collaborations. Novel valorization approaches will be a compromise between constraints from wastewater treatment (e.g., treatment efficiency) and the target quality and quantity of potential bioproducts. Developing a value chain that meets these requirements can only be done through the commitment of public and private entities across sectoral borders and disciplines.

Conclusions

The environmental impact of a novel OPG-based treatment process was evaluated using LCA and compared with the well-established conventional activated sludge (CAS) process. The environmental impact of a non-optimized OPG scenario was generally lower than for the reference CAS system. Electricity consumption related to artificial lighting, the fate of the generated biomass (renewable energy and replacement of mineral fertilizer), and the nitrogen flows in the OPG system were identified as the major contributors to the potential environmental impact of the OPG treatment system.

With an optimized artificial lighting system, an energy neutral treatment system is within reach.

Acknowledgements

This work was financed through the French "Agence Nationale de la Recherche" grant ANR-16-CE04-0001-01. J. H. benefited from the Explore the international mobility wastewater by the OPG system (scenario 1) and the CAS system as reference. Black: CAS system, blue: OPG system. All calculated environmental impacts were normalized by the impact obtained for the reference CAS system. Distances between circles are log2 scaled. Scenario 1 (as reference): 7 h/day artificial light (solid blue line). Scenario 2: 7 h/day aeration instead of lighting (short yellow dashes). Scenario 3: 14 h/day artificial lighting (orange dots). Scenario 4 (light-optimized scenario 1): 7 h/day artificial lighting with twice more efficient lighting system (dash-dots).

Figure 5: Effects of agricultural practice on the environmental impact of the OPG (scenario 1) and the reference CAS systems. Black, solid: default CAS system, including surface spreading of sludge; blue, solid: OPG system (scenario 1), including surface spreading of sludge; Black, dashed: CAS system with deep injection of digested biomass; blue, dash-dots: OPG system with deep injection of digested biomass. For each impact category, calculated environmental impacts were normalized by the impact obtained for the reference CAS system.

The distance between circles is log2-scaled. 30

  summarize characteristics of the CAS system and calculated emissions from wastewater treatment and sludge spreading. Parameters and emission factors used for calculating field emissions were taken from Brockmann et al. (2014) and Brockmann et al. (2018).

  5 hours illumination per 6 hours cycle (Milferstedt et al., 2017b), illumination during 14 hours for the four daily cycles is considered. With an oxygen production rate of the OPG under light of 12.6 mg O2/(g VSS•h) (Abouhend et al., 2018), oxygen production by OPG with 14 h/day illumination exceeds the oxygen requirements for organic carbon oxidation and nitrification. To ensure adequate suspension of OPG, mechanical mixing is needed. Electricity consumption for mixing of OPG was estimated following Walas (1990) considering a turbulent regime and a reactor geometry similar to that of activated sludge reactors. Considering an anchor or gate paddle per reactor and a mixing time of 22 h/day, mixing of OPG consumes 26 Wh/m 3 electricity. Electricity consumption for lighting was estimated based on a photosynthetically active radiation (PAR) of 150 µmol/m 2 /s (Abouhend et al., 2018) and a PAR efficiency of 2 µmol/s/W (Blanken et al., 2013), yielding an electricity consumption of 75 W/m 2 . The enlightened surface area was assumed twice the footprint of the reactors without further detailed design of the artificial lighting system, resulting in an electricity consumption of 134 Wh/m 3 wastewater. This way of operation represents a generic, non-optimized solution. An electricity consumption for pumping, valves, sensors etc. of 200 Wh/m 3 was estimated based on the electricity consumption of the CAS system without aeration. Thus, the overall electricity consumption of the OPG system consists of 200 Wh/m 3 for pumping, valves etc., 26 Wh/m 3 for 22 hours of mixing, and 134 Wh/m 3 for lighting.

Figure 3

 3 Figure 3

Figure 4

 4 Figure 4

Figure 5

 5 Figure 5

  49. Wernet, G., Bauer, C., Steubing, B., Reinhard, J., Moreno-Ruiz, E., Weidema, B. 2016. The ecoinvent database version 3 (part I): overview and methodology. The International Journal of Life Cycle Assessment, 21(9), 1218-1230. 50. Zhang, X., Dong, H., Hu, W. 2018. Organic semiconductor single crystals for electronics and photonics. Advanced Materials, 30(44), 1801048.

Figure 1 :

 1 Figure 1: Process schemes of the two compared wastewater treatment systems. a)

Figure 2 :

 2 Figure 2: Comparison of environmental impacts of the treatment of 1 m 3 urban

Figure 3 :

 3 Figure 3: Environmental impacts by impact category and differentiated by their origin (colored stacks) for the treatment of 1 m 3 municipal wastewater in the OPG

Figure 4 :

 4 Figure 4: Environmental impact of different operating scenarios for the OPG system.

34

 34

Figure 2 :

 2 Figure 2:

Figure 3 : 36

 336 Figure 3:

Figure 4 :

 4 Figure 4:

Figure 5 :

 5 Figure 5:

Table 1 :

 1 Raw municipal wastewater characteristics (US)

	8 Tables
	Parameter	Symbol	Unit	Values
	Flow rate	Qin	m 3 /d	15000
	Total chemical oxygen demand Total COD	g COD/m 3	500
	Soluble chemical oxygen demand	Soluble COD	g COD/m 3	200
	Total Kjeldahl Nitrogen (Norg. + NH4-N)	TKN	g N/m 3	30
	Ammonia nitrogen	NH4-N	g N/m 3	20
	Nitrate nitrogen	NO3-N	g N/m 3	0
	Total phosphorus	Total P	g P/m 3	6
	Orthophosphate	Ortho-P	g P/m 3	4
	Total suspended solids	TSS	g TSS/m 3	250
	Volatile suspended solids	VSS	g TSS/m 3	-

Table 3 :

 3 Emissions from wastewater treatment and sludge spreading, and avoided emissions from mineral fertilizers as calculated from mass balances. Units are per m 3 wastewater for wastewater treatment and per m 3 sludge for sludge spreading.

		Unit	CAS	OPG
	Effluent characteristics
	COD	g COD/m 3	31.3	48.3
	TKN	g N/m 3	3.8	4.6
	NH4-N	g N/m 3	1.2	2.0
	NO3-N	g N/m 3	3.7	2.3
	Total P	g P/m 3	1.8	1.8
	Emissions from wastewater treatment
	N2O-N	g N/m 3	0.44	0.29
	Biogenic CO2 from carbon removal	g CO2/m 3	283	202
	Biogenic CO2 from AD	g CO2/m 3	45	89
	Biogenic CO2 from CH4 combustion	g CO2/m 3	84	165
	Emissions from sludge spreading
	NH3	g/m 3 sludge	452	1504
	N2O	g/m 3 sludge	173	250
	NOx	g/m 3 sludge	243	316
	NO3 -	g/m 3 sludge	4764	6581
	P	g/m 3 sludge	47	33
	Avoided emissions from mineral fertilizers
	NH3	g/m 3 sludge	255	333
	N2O	g/m 3 sludge	122	159
	NOx	g/m 3 sludge	174	227
	NO3 -	g/m 3 sludge	3383.6	4424.8
	P	g/m 3 sludge	11.6	8.2