Wastewater treatment plants (WWTPs) rely on various chemicals for essential processes such as sludge treatment, odour control and disinfection. However, the handling and storage of these chemicals present significant safety challenges, as incompatible substances can react to form hazardous, toxic, flammable or explosive compounds. This study focuses on the Seine Aval wastewater treatment plant (Service public de l’assainissement francilien, SIAAP, France), where large-scale chemical storage increases the potential risks associated with accidental mixing. A systematic risk assessment was conducted using Safety Data Sheets (SDS) to identify the physico-chemical properties of stored chemicals and determine possible hazardous reactions, including exothermic events, toxic gas releases and combined thermal and chemical hazards. The study aims to enhance process safety and loss prevention by developing a hazard classification tool that categorizes risks based on reagent compatibility. This approach provides a structured framework for improving chemical risk management, optimizing storage and handling protocols, and ensuring safer operations in WWTPs.

The valorization of urine through the electro-oxidation of urea offers a promising alternative for industrial wastewater treatment plants. This operation, implemented at room temperature, allows, in addition to the depolluting action, the generation of hydrogen at the cathode. Using inexpensive electrodes and photo-assisting the process, this method has potential for industrial application. This review delves into the recent advancements in the electrochemical treatment of urea and ammonia from urine, understanding and optimizing the electrolysis process under various conditions. Notably, the electrolysis of urea and ammonia in alkaline medium over nickel oxyhydroxide (NiOOH) catalyst, has emerged as a promising avenue, offering enhanced selectivity and efficiency. The exploration extends to urine management, urea degradation, catalyst deactivation, reaction selectivity, and the detection of reaction products, as well as photoelectrochemical processes in a future reactor perspective, where the synergistic combination of photocatalysis and electrochemical oxidation opens new pathways for urine valorization.

Transition to turbulence in pipe has been extensively studied but is still not completely understood and even more for non-Newtonian fluids. We focus here on yield stress shear-thinning fluids and the mechanism leading to the transition in pipe, the so-called rheo-inertial transition to turbulence. An experimental setup has enabled us to identify flow regimes in a cylindrical pipe, using both flow visualizations and pressure drops measurements for a range of Reynolds numbers. We delimited the non-Newtonian specific regime in the laminar-turbulent transition triggered at a critical Reynolds number below the turbulent puffs onset. This pre-transition regime is associated with a velocity profile asymmetry in which its degree and position evolve as the Reynolds number increases. The origin for the stability of this rheo-inertial regime is discussed, as it could be due to a competition between the nonlinear contributions of rheological behavior and flow inertia. Beyond this regime, we quantified the intermittence of puff transit, revealing the delay to turbulence. We spotted for the first time a different rheo-inertial transitional behavior in the intermittency evolution vs Reynolds number, displaying a smoother transition on a broader range. Finally, the critical Reynolds numbers for different yield stresses are compared with previous works, and the novelty is the linear increase in the delay to turbulent puffs with the yield stress.

During wet weather events, combined sewer overflows (CSOs) transfer large amount of particulate matter and associated pollutants into surrounding water bodies, thereby deteriorating the recipients’ ecological health. Resuspension of sewer sediments during these events contributes significantly to pollution level of these discharges. However, how much this in-sewer process contributes to CSOs’ quality regarding microplastic (MP) pollution is little known. Therefore, an investigation on sewer deposits inside the Parisian combined sewer network was carried out. The study found high MP concentrations stored in this matrix, ranging from 5 × 10 3 to 178 × 10 3 particle/kg dry weight. Polymer composition is similar to what found in raw wastewater, containing a high proportion of polyethylene and polypropylene. Thus, the results indicated the persistence of MPs in sewer network during transport during dry weather periods to treatment facilities. Once resuspension of sewer deposits happens, MPs can be released into water flow and get discharged along with CSOs. This highlights another potential pathway of MPs into freshwater environment.

Regulations on wastewater treatment (UWWTD-1991; WFD 2000) have evolved considerably over the past 25 years with the development of increasingly efficient bioprocesses that limit environmental risks. High-performance bio-physico-chemical wastewater treatment technologies were implemented for the plants of the main urban areas i.e. biofiltration, membrane bioreactors. Thus, over the last ten years, new types of degradation of concrete structures were observed in wastewater treatment plants, mainly in nitrification basins treating nitrogen compounds (ammonium) in effluents. The exact origins of these degradations are not yet determined. In order to understand the degradation mechanisms of concrete in nitrogen compound treatment basins, mortar specimens based on CEM V and CAC cements were exposed (i) in situ of one nitrogen treatment basin and (ii) in reactor for biological lab test. The design and implementation of the biological test were developed to reproduce were developed to reproduce nitrogen biological treatment and evaluate the degradation of mortars in a more controlled environment than the full-scale process. This laboratory test allows the evaluation of the biotic aspect of nitrification and in particular, the influence of acid production during biotic reactions and the influence of carbonates on mortar specimens. These two approaches allow highlighting the significant impact of the biomass and the modification of the environmental conditions at the biofilm/material interface.

The effects of co-digesting sewage sludge (SS) and horse waste (HW), the composition of HW, and the ratio of HW:SS were studied using two semi-continuous digesters of 9.5 L of working volume. These digesters were operated in parallel with the mono-digestion of SS in digester 1 (D1) and the co-digestion of SS and HW in digester 2 (D2). In digester 2, there were two phases of digestion (durations of 40 and 43 weeks, respectively). The composition of HW in the first phase was 85% wheat straw (WS), 14% wood chips (WC), and 1% horse manure (HM), with 99% wheat straw (WS) and 1% horse manure (HM) in the second phase. Variable ratios of HW:SS were studied in the digesters. The co-digestion of sewage sludge (SS) and horse waste (HW) produced more biogas than the mono-digestion of SS alone, with a maximum of 15.8 L·d−1, compared to 9 L·d−1 at the end of the experiment. When comparing the results obtained in both phases, the production of methane in phase 2 was 18 NmL·gVS−1 higher than in phase 1. This slight increase in methane yield could be linked to the absence of wood chips (WC), which is considered to have a diluting effect on methane production. Therefore, this study shows that an organic loading rate (OLR) of 4.8 kgVS·m−3·d−1, a ratio of HW:SS of 3, and a composition of HW (99% WS, 1% HM) should be respected in the actual experimental conditions for a well-functioning anaerobic digestion.

La baignade est une activité récréative phare de la saison estivale. Ses aspects sanitaires, essentiellement d’origine microbiologique, sont cadrés par une réglementation qui s’est renforcée depuis 2006. En conséquence, la baignade en milieu urbain est un défi à l’approche des jeux Olympiques de Paris en 2024, alors que le fleuve emblématique de la capitale, longtemps considéré comme impropre à la baignade, fait l’objet d’un programme d’actions pour rétablir une qualité compatible avec cette activité. Le Syndicat interdépartemental pour l’assainissement de l’agglomération parisienne (Siaap) a lancé des travaux d’assainissement et a été mandaté pour étudier et vérifier la compatibilité de la qualité des eaux avec la baignade dans la Seine à cette échéance. Ce travail, réalisé en collaboration avec la Saur, aborde le facteur de risque lié aux incertitudes de mesure des contaminants microbiologiques réglementés, Escherichia coli (EC) et entérocoques intestinaux (EI), présenté par diverses méthodes disponibles sur le marché. Cinq méthodes ont été étudiées, incluant approches culturales et biologie moléculaire. L’objectif de ces mesures comparatives est de fournir aux responsables de baignades des outils opérationnels d’aide à la décision dans leur gestion active et prédictive. Ainsi, les présents travaux investiguent les risques de dépassements des seuils d’interdiction de baignade inhérents à chaque méthode : des abaques modélisant les facteurs de risque pour les seuils spécifiques à EC et EI sont présentés, en fonction de la charge bactérienne dans les eaux et le nombre de tests. La méthodologie présentée s’adresse aux gestionnaires de sites de baignade pour leur permettre d’établir leurs propres analyses. Une attention particulière est portée sur le cas de l’eau de Seine à l’aval de Paris, de la station de Colombes et des principaux déversoirs d’orage du syndicat, en préparation des épreuves aquatiques qui se situeront au cœur de la ville de Paris et seront le centre d’intérêt des yeux de la planète.

Phosphorus recovery is a vital element for the circular economy. Wastewater, especially sewage sludge, shows great potential for recovering phosphate in the form of vivianite. This work focuses on studying the iron, phosphorus, and sulfur interactions at full-scale wastewater treatment plants (Viikinmäki, Finland and Seine Aval, France) with the goal of identifying unit processes with a potential for vivianite formation. Concentrations of iron(III) and iron(II), phosphorus, and sulfur were used to evaluate the reduction of iron and the formation potential of vivianite. Mössbauer spectroscopy and X-ray diffraction (XRD) analysis were used to confirm the presence of vivianite in various locations on sludge lines. The results show that the vivianite formation potential increases as the molar Fe:P ratio increases, the anaerobic sludge retention time increases, and the sulfate concentration decreases. The digester is a prominent location for vivianite recovery, but not the only one. This work gives valuable insights into the dynamic interrelations of iron, phosphorus, and sulfur in full-scale conditions. These results will support the understanding of vivianite formation and pave the way for an alternative solution for vivianite recovery for example in plants that do not have an anaerobic digester.

To reduce the energy cost and environmental impact of biological nitrogen removal in wastewater treatment plants, it would be advantageous to treat urea contained in urine at the source. In this perspective, FTO/Ti-Fe2O3 (nanorods) photoelectrodes decorated with Ni as catalyst are developed and tested for urea photoelectrocatalytic oxidation under solar illumination. Gains up to 0.50 V in oxidation onset potential vs. metallic Ni are obtained thanks to a Ni photoelectrodeposition method. In situ transmission measurements (based on NiOOH light absorption) during electrochemical cycling allowed to evaluate the state of active Ni sites and confirmed that urea oxidation mechanism is of EC type. Photoelectrolyses give faradaic efficiencies of 10-18% and 9-35% for N-2 and O-2 formation, respectively. A significant and unexpected NO2 production (similar to 65%) is detected indicating another or incomplete reaction pathway. The photoelectrocatalytic removal of nitrogen from urea solutions is demonstrated but requires catalysts with higher selectivity towards N-2.

This paper aimed to study the value of horse manure through anaerobic digestion. The study involved characterization of different components of horse waste and the evaluation of their biochemical composition, physicochemical characterization and the influence of the composition of horse waste on biochemical methane potential. More specifically, two bedding mixtures were studied: the first one was composed of wheat straw (WS), wood chips (WC) and horse manure (HM) with a volumetric composition of 85%, 14% and 1%, respectively; and the second one was a mixture of WS and HM with a volumetric composition of 99% and 1%, respectively. The analysis was carried out on the two bedding mixtures and on each substrate separately with 406 samples from May 2017 to October 2019. Biochemical methane potential tests conducted on these samples showed that the composition and structure of the substrate influenced the BMP. WS had the highest mono-digestion methane production with 176.1 NmL·gVS−1. The second bedding mixture (99% WS, 1% HM) showed a production of 189.4 NmL·gVS−1 compared to 127 NmL·gVS−1 by bedding mixture 1 (85% WS, 14% WC, 1% HM). The difference was due to a dilution effect on methane production caused by the presence of WC rich in lignin.

L’observatoire MeSeine est l’observatoire du milieu naturel développé et exploité par le Syndicat interdépartemental pour l’assainissement de l’agglomération parisienne (Siaap), via sa direction Innovation. Fondé sur la mesure de l’oxygène en Seine au début des années 1990, il a depuis intégré des modalités de surveillance en pointe, incluant depuis quelques années les méthodes basées sur les effets sur le vivant ou bioessais. Ces méthodes permettent d’investiguer les pollutions modernes de l’eau d’une manière novatrice et complémentaire aux méthodes analytiques historiques, qui montrent certaines limites dans ce contexte. Pour autant, ce sont des approches difficiles à appréhender et à interpréter pour les non-spécialistes. Le présent travail expose ainsi les stratégies de conceptualisation et d’appropriation des bioessais par le Siaap pour assurer leur intégration dans l’Observatoire. Les données générées entre 2017 et 2019 via l’implémentation de méthodes de mesure de toxicité générale multi-organismes et de perturbateurs endocriniens in vivo sont mises en lumière au travers des occurrences de détection, de l’intensité des réponses obtenues et des corrélations avec les marqueurs de pressions anthropiques, le long d’un linéaire de Seine et de Marne de plus de 100 kilomètres. Ces méthodes permettent de mettre en évidence les dynamiques d’établissement des impacts biologiques de l’amont vers l’aval, en matière de détections positives, intensités de réponse, mais aussi répartition spatiale ou temporelle selon les sites considérés.

L’objectif de cet article est de proposer des protocoles de caractérisation thermo-rhéologique des boues digérées pour réaliser un dimensionnement pertinent des installations de traitement en station de traitement des eaux usées (STEU). Pour cela, tous les aspects rhéologiques pouvant impacter l’écoulement des boues dans les composants hydrauliques sont abordés, notamment le seuil d’écoulement, le comportement rhéofluidifiant, la thixotropie, la viscoélasticité ou encore la dépendance thermique des caractéristiques rhéologiques. Un protocole de détermination de chacune de ces propriétés rhéologiques adapté aux boues digérées issues de STEU est détaillé. Les lignes directrices proposées ici se basent sur les retours d’expériences de campagnes de caractérisation menées en laboratoire sur des boues digérées prélevées en STEU. Les résultats des caractérisations menées grâce à l’application des protocoles décrits confirment la présence d’un seuil d’écoulement et d’un caractère rhéofluidifiant pour des boues digérées issues de STEU. Ils montrent également que dans le cas d’une boue digérée, la thermo-rhéologie peut être simplifiée, car la thixotropie, la viscoélasticité et la dépendance thermique ont un impact négligeable sur l’écoulement de la boue digérée dans les conditions typiques des procédés en STEU.