Extended anaerobic conditions in the biological wastewater treatment: Higher reduction of toxicity compared to target organic micropollutants

Individual and combined ecotoxic effects of water-soluble polymers

Water-soluble polymers (WSPs) are a class of high-molecular-weight compounds which are widely used in several applications, including water treatment, food processing, and pharmaceuticals. Therefore, they pose a potential threat for water resources and aquatic ecosystems. We assessed the ecotoxicity of four WSPs-non-ionic polyacrylamide (PAM) and polyethylene glycol (PEG-200), anionic homopolymer of acrylic acid (P-AA), and cationic polyquaternium-6 (PQ-6)-as single compounds and in mixture. For this purpose in vitro and in vivo assays were used to record baseline toxicity, mutagenic potential, endocrine effects, and growth inhibition in the freshwater alga Raphidocelis subcapitata. Furthermore, the mixture toxicity of the two polymers P-AA and PQ-6 which showed effects in the algae tests was evaluated with the concentration addition (CA), independent action (IA), and generalized concentration addition (GCA) model and compared with experimental data. No toxic effects were observed among the polymers and their mixtures in the in vitro assays. On the contrary, in the growth inhibition test with R. subcapitata the cationic PQ-6 caused high inhibition while the anionic P-AA and its mixture with the cationic polymer caused low inhibition. The non-ionic polymers PEG-200 and PAM showed no effect in R. subcapitata in the tested concentration range up to 100 mg/L. The IA model represented the mixture effect of the combination experiment better than the CA and GCA models. The results indicate (1) that the toxic effects of anionic and cationic polymers are most likely due to interactions of the polymers with the surfaces of organisms or with nutrients in the water and (2) that the polymers elicit their effects through different mechanisms of action that do not interact with each other.

Pesticide dynamics in three small agricultural creeks in Hesse, Germany

Background

Due to their high biodiversity, small water bodies play an important role for freshwater ecosystems. Nonetheless, systematic pesticide monitoring in small creeks with a catchment <30 km² is rarely conducted.

Methods

In this study, event-driven water samples were taken from May until November 2017 and March until July 2018 after 20 rain events at three sampling sites with catchment areas of <27 km² in the Wetterau, a region with intensive agriculture in Southern Hesse, Germany. Additionally, enriched extracts of the native water samples from the campaign in 2018 were used for the Microtox assay to determine baseline toxicity to invertebrates over time and sum of toxic units (STU) were calculated to compare the potential toxicity of the samples.

Results

Overall, 37 pesticides and 17 transformation products were found, whereby the herbicide metamitron (79 µg/L) showed the highest concentration. Regularly, pesticide concentrations peaked at the time of the highest water level within each sampling event. Within each sampling event maximum pesticide concentration was mostly reached in water samples taken during the first two hours. The sum of the time-weighted mean concentration values of all pesticides was between 2.0 µg/L and 7.2 µg/L, whereby the measured concentrations exceeded their regulatory acceptable concentration (RAC) at 55% of all sampling events for at least one pesticide. The mean EC₅₀ values varied between 28.6 ± 13.1 to 41.3 ± 12.1 REF (relative enrichment factor). The results indicated that several samples caused baseline toxicity, whereby the highest activity was measured at the time of highest water levels and pesticides concentrations, and then steadily decreased in parallel with the water level. Median STUs of invertebrates ranged from -2.10 to -3.91, of algae/aquatic plants from -0.79 to -1.84 and of fish from -2.47 to -4.24. For one of the three sampling sites, a significant linear correlation between baseline toxicity and STU_invertebratewas found (r² = 0.48).

Conclusion

The results of the present study suggest that (1) current pesticide monitoring programs underestimate risks posed by the exposure to pesticides for aquatic organisms and (2) pre-authorization regulatory risk assessment schemes are insufficient to protect aquatic environments.

Assessment of the aerobic and anaerobic biodegradation of contaminants of emerging concern in sludge using batch reactors

This work explores the degradation of xenobiotic compounds in aerobic and anaerobic batch reactors. Different inoculums were spiked with nine emerging contaminants at nominal concentrations ranging between 1 to 2 mg/L (ibuprofen, diclofenac, naproxen, acesulfame, sucralose, aspartame, cyclamate, linear alkylbenzene sulfonates, and secondary alkyl sulfonates). Ethanol was used as co-substrate in the anaerobic reactors. We found that the kinetic decay was faster in the aerobic reactors inoculated with a Spanish (S_pn) inoculum compared to a Brazilian (B_rz) inoculum, resulting in rection rates for LAS and SAS of 2.67 ± 3.6 h^-1 and 5.09 ± 6 h^-1 for the B_rz reactors, and 1.3 ± 0.1 h^-1 and 1.5 ± 0.2 h^-1 for the S_pn reactors, respectively. There was no evidence of LAS and SAS degradation under anaerobic conditions within 72 days; nonetheless, under aerobic conditions, these surfactants were removed by both the B_rz and S_pn inoculums (up to 86.2 ± 9.4% and 74.3 ± 0.7%, respectively) within 10 days. The artificial sweeteners were not removed under aerobic conditions, whereas we could observe a steady decrease in the anaerobic reactors containing the S_pn inoculum. Ethanol aided in the degradation of surfactants in anaerobic environments. Proteiniphilum, Paraclostridium, Arcobacter, Proteiniclasticum, Acinetobacter, Roseomonas, Aquamicrobium, Moheibacter, Leucobacter, Synergistes, Cyanobacteria, Serratia, and Desulfobulbus were the main microorganisms identified in this study.

Removal of organic micropollutans by adsorptive membrane

Various emerging organic micropollutants, such as pharmaceuticals, have attracted the interest of the water industry during the last two decades due to their insufficient removal during conventional water and wastewater treatment methods and increasing demand for pharmaceuticals projected to climate change-related impacts and COVID-19, nanosorbents such as carbon nanotubes (CNTs), graphene oxides (GOs), and metallic organic frameworks (MOFs) have recently been extensively explored regarding their potential environmental applications. Due to their unique physicochemical features, the use of these nanoadsorbents for organic micropollutans in water and wastewater treatment processes has been a rapidly growing topic of research in recent literature. Adsorptive membranes, which include these nanosorbents, combine the benefits of adsorption with membrane separation, allowing for high flow rates and faster adsorption/desorption rates, and have received a lot of publicity in recent years. The most recent advances in the fabrication of adsorptive membranes (including homogeneous membranes, mixed matrix membranes, and composite membranes), as well as their basic principles and applications in water and wastewater treatment, are discussed in this review. This paper covers ten years, from 2011 to 2021, and examines over 100 published studies, highlighting that micropollutans can pose a serious threat to surface water environments and that adsorptive membranes are promising, particularly in the adsorption of trace substances with fast kinetics. Membrane fouling, on the other hand, should be given more attention in future studies due to the high costs and restricted reusability.

Occurrence and in vitro toxicity of organic compounds in urban background PM2.5

This study describes the chemical composition and in vitro toxicity of the organic fraction of fine particulate matter (PM_2.5) at an urban background site, which receives emissions either from Frankfurt international airport or the city centre, respectively. We analysed the chemical composition of filter extracts (PM_2.5) using ultrahigh-performance liquid chromatography coupled to a high-resolution mass spectrometer, followed by a non-target analysis. In parallel, we applied the bulk of the filter extracts to a Microtox and acetylcholinesterase-inhibition assay for in vitro toxicity testing. We find that both the chemical composition and toxicity depend on the prevailing wind directions, and the airport operating condition, respectively. The occurrence of the airport marker compounds tricresyl phosphate and pentaerythritol esters depends on the time of the day, reflecting the night flight ban as well as an airport strike event during November 2019. We compared the organic aerosol composition and toxicity from the airport wind-sector against the city centre wind-sector. We find that urban background aerosol shows a higher baseline toxicity and acetylcholinesterase inhibition compared to rural PM_2.5 that is advected over the airport. Our results indicate that the concentration and individual composition of PM_2.5 influence the toxicity. Suspected drivers of the acetylcholinesterase inhibition are i.e. organophosphorus esters like triphenyl phosphate and cresyldiphenyl phosphate, and the non-ionic surfactant 4-tert-octylphenol ethoxylate. However, further research is necessary to unambiguously identify harmful organic air pollutants and their sources and quantify concentration levels at which adverse effects in humans and the environment can occur.

Progress and prospects of applying carbon-based materials (and nanomaterials) to accelerate anaerobic bioprocesses for the removal of micropollutants

Carbon-based materials (CBM), including activated carbon (AC), activated fibres (ACF), biochar (BC), nanotubes (CNT), carbon xenogels (CX) and graphene nanosheets (GNS), possess unique properties such as high surface area, sorption and catalytic characteristics, making them very versatile for many applications in environmental remediation. They are powerful redox mediators (RM) in anaerobic processes, accelerating the rates and extending the level of the reduction of pollutants and, consequently, affecting positively the global efficiency of their partial or total removal. The extraordinary conductive properties of CBM, and the possibility of tailoring their surface to address specific pollutants, make them promising as catalysts in the treatment of effluents containing diverse pollutants. CBM can be combined with magnetic nanoparticles (MNM) assembling catalytic and magnetic properties in a single composite (C@MNM), allowing their recovery and reuse after the treatment process. Furthermore, these composites have demonstrated extraordinary catalytic properties. Evaluation of the toxicological and environmental impact of direct and indirect exposure to nanomaterials is an important issue that must be considered when nanomaterials are applied. Though the chemical composition, size and physical characteristics may contribute to toxicological effects, the potential toxic impact of using CBM is not completely clear and is not always assessed. This review gives an overview of the current research on the application of CBM and C@MNM in bioremediation and on the possible environmental impact and toxicity.

Examination of single-stage anaerobic and anoxic/aerobic and dual-stage anaerobic-anoxic/aerobic digestion to remove pharmaceuticals from municipal biosolids

Many trace contaminants of emerging concern (CECs) including a number of pharmaceutically active compounds are not effectively removed during conventional wastewater treatment processes and instead accumulate in wastewater sludge. Unfortunately, many existing sludge stabilization treatments such as anaerobic digestion (AD) also have limited effectiveness against many of these CECs including the four pharmaceuticals ibuprofen, diclofenac, carbamazepine, and azithromycin which can then enter the environment through the disposal or land application of biosolids. Single-stage AD, single-stage cycling aerobic-anoxic (AERO/ANOX) and sequential digesters (AD followed by an AERO/ANOX digester) at sludge retention times (SRT) of 5 to 20-days were evaluated side-by-side to assess their effectiveness in removing pharmaceuticals and conventional organic matter. Single-stage ADs (35 °C) and AERO/ANOX (22 °C) digesters effectively removed total solids while sequential AD + AERO/ANOX digesters offered further improvements. Ibuprofen was not effectively removed during AD and resulted in up to a 23 ± 8% accumulation. However, ibuprofen was completely removed during AERO/ANOX digestion and in several sequential digestion scenarios. Each type of digestion was less effective against carbamazepine with slight (3 ± 2%) accumulations to low levels (14 ± 1%) of removals in each type of digestion studied. Diclofenac was more effectively removed with up 30 ± 3% to 39 ± 4% reductions in the single-stage digesters (AD and AERO/ANOX, respectively). While sequential digestion scenarios with the longest aerobic SRTs significantly increased diclofenac removals from their first-stage digesters, scenarios with the longest anaerobic SRTs actually decreased removals from first-stage digesters, possibly due to reversible biotransformation of diclofenac conjugates/metabolites. Up to 43 ± 6% of azithromycin was removed in AERO/ANOX digesters, while the best performing sequential-digester scenario removed up to 63 ± 7% of azithromycin. This study shows that different digester configurations can reduce the CEC burden in biosolids while also greatly reducing their volumes for disposal, although none can remove CECs completely.

Enhanced in vitro toxicity of plastic leachates after UV irradiation

Plastics can release numerous chemicals and thereby, contribute to the chemical pollution in aquatic systems. To which extent environmental degradation processes influence the release of plastic chemicals, is currently unknown and subject of research. We therefore evaluated aqueous leachates of 12 differently formulated plastics (e.g., pre-production, post-industrial and recycled pellets as well as final products) using in vitro bioassays and chemical analysis via LC-HRMS nontarget approach. We weathered these plastics by UV irradiation (UV-C and UV-A/B) under laboratory conditions in dryness and a subsequent leaching period in ultrapure water ('atmospheric' weathering) or directly in water ('aquatic' weathering, UV-A/B_aq). A dark control (DC) without UV light served as a reference treatment. Some plastics triggered several toxicological endpoints (low-density polyethylene recyclate (LDPE-R), starch blend (SB), bio-based polybutylene succinate (Bio-PBS) and polyvinyl chloride (PVC)), whereas others caused little to no effects (polyethylene terephthalate (PET), polystyrene (PS), polypropylene (PP) and LDPE). UV irradiation enhanced the plastics' toxicity, even for samples initially evaluated as toxicologically inconspicuous. The plastic samples caused oxidative stress (85%), baseline toxicity (42%), antiestrogenicity (40%) and antiandrogenicity (27%). Positive findings were measured after UV-C (63%) and UV-A/B_aq (50%) treatments, followed by UV-A/B (48%) and DC (33%). Overall, we detected between 42 (DC) and 2896 (UV-A/B_aq) chemical compounds. Our study demonstrates that differently formulated plastics leach toxic chemicals. UV exacerbates the plastics' toxicity by either generating active compounds and/or by facilitating their release. UV light even leads to the release of bioactive compounds from plastics of low chemical complexity. To prevent the exposure to plastic-associated chemicals, the application of chemicals could be reduced to a minimum, while on a regulatory level the evaluation of plastic eluates could be another focal point next to singular compounds.

Aerobic and Anaerobic Biodegradability of Organophosphates in Activated Sludge Derived From Kitchen Garbage Biomass and Agricultural Residues

Organophosphates (also known as organophosphate esters, OPEs) have in recent years been found to be significant pollutants in both aerobic and anaerobic activated sludge. Food waste, such as kitchen garbage and agricultural residues, can be used as co-substrates to treat the active sludge in sewage treatment plants (STPs). We investigated the biodegradability of nine OPEs derived from kitchen garbage biomass and agricultural residues under different conditions. Under anaerobic conditions, the rate of removal of triphenyl ester OPEs was significantly higher than that of chloride and alkyl OPEs. The addition of FeCl₃ and Fe powder increased the rate of degradation of triphenyl ester OPEs, with a DT₅₀ for triphenyl ester OPEs of 1.7–3.8 d for FeCl₃ and 1.3–4.7 d for Fe powder, compared to a DT₅₀ of 4.3–6.9 d for the blank control. Addition of an electron donor and a rhamnolipid increased the rate of removal of chlorinated OPEs, with DT₅₀ values for tris(2-carboxyethyl)phosphine) (TCEP) and tris(1,3-dichloroisopropyl)phosphate (TDCPP) of 18.4 and 10.0 d, respectively, following addition of the electron donor, and 13.7 and 3.0 d, respectively, following addition of the rhamnolipid. However, addition of an electron donor, electron acceptor, surfactant, and Fe powder did not always increase the degradation of different kinds of OPEs, which was closely related to the structure of the OPEs. No treatment increased the removal of alkyl OPEs due to their low anaerobic degradability. Tween 80, a non-ionic surfactant, inhibited anaerobic degradation to some degree for all OPEs. Under aerobic conditions, alkyl OPEs were more easily degraded, chlorinated OPEs needed a long adaptation period to degrade and finally attain a 90% removal rate, while the rates of degradation of triphenyl ester OPEs were significantly affected by the concentration of sludge. Higher sludge concentrations help microorganisms to adapt and remove OPEs. This study provides new insights into methods for eliminating emerging pollutants using activated sludge cultured with kitchen garbage biomass and agricultural residues.

Wastewater treatment efficacy evaluated with in vitro bioassays

Bioassays show promise as a complementary approach to chemical analysis to assess the efficacy of wastewater treatment processes as they can detect the mixture effects of all bioactive chemicals in a sample. We investigated the treatment efficacy of ten Australian wastewater treatment plants (WWTPs) covering 42% of the national population over seven consecutive days. Solid-phase extracts of influent and effluent were subjected to an in vitro test battery with six bioassays covering nine endpoints that captured the major modes of action detected in receiving surface waters. WWTP influents and effluents were compared on the basis of population- and flow-normalised effect loads, which provided insights into the biological effects exhibited by the mixture of chemicals before and after treatment. Effect removal efficacy varied between effect endpoints and depended on the treatment process. An ozonation treatment step had the best treatment efficacy, while WWTPs with only primary treatment resulted in poor removal of effects. Effect removal was generally better for estrogenic effects and the peroxisome proliferator-activated receptor than for inhibition of photosynthesis, which is consistent with the persistence of herbicides causing this effect. Cytotoxicity and oxidative stress response provided a sum parameter of all bioactive chemicals including transformation products and removal was poorer than for specific endpoints except for photosynthesis inhibition. Although more than 500 chemicals were analysed, the detected chemicals explained typically less than 10% of the measured biological effect, apart from algal toxicity, where the majority of the effect could be explained by one dominant herbicide, diuron. Overall, the current study demonstrated the utility of applying bioassays alongside chemical analysis to evaluate loads of chemical pollution reaching WWTPs and treatment efficacy.

Effects of biostimulation by sugarcane bagasse and coffee grounds on sewage sludges, focusing agricultural use: Microbial characterization, respirometric assessment and toxicity reduction

Sewage sludge (SS) exhibits a relevant agronomic potential due to the high content of organic matter and nutrients. However, the presence of several toxic substances can prevent its agricultural application. This study evaluated if the incorporation of stimulating agents (coffee grounds and sugarcane bagasse) could contribute to an effective increase of the SS biodegradability in order to decrease its toxicity. The samples were prepared mixing aerobic or anaerobic sludge with soil, soil and bagasse, and soil and coffee grounds. Respirometric tests showed that stimulating agents enhanced the CO₂ production. However, in terms of biodegradation efficiency, more satisfactory results were verified for the anaerobic SS, especially when mixed with coffee grounds. The biodegradation also favored the SS sanitization, eliminating the Enterobacteria. For baseline toxicity (Microtox with Aliivibrio fischeri) and phytotoxicity (Lactuca sativa), all the initial samples showed higher effects. Nevertheless, after the biodegradation, this toxicity was significantly decreased and the best results were obtained for the mixtures containing only soil and sludge. For the AREc32 assay (NRF₂ mediated oxidative stress response), although a very weak response was observed, this effect was attenuated for the aerobic SS or completely eliminated for the anaerobic SS after the biodegradation. Thus, even though the use of biostimulation agents during the biodegradation led to an enhancement of microbial respiration, their incorporation to the samples do not seem to interfere in the decrease of the toxic potential of the studied SSs. However, the SS biodegradation in aerobiosis was crucial for toxicity reduction and to accelerate its maturity.

Are bioplastics and plant-based materials safer than conventional plastics? In vitro toxicity and chemical composition

Plastics contain a complex mixture of known and unknown chemicals; some of which can be toxic. Bioplastics and plant-based materials are marketed as sustainable alternative to conventional plastics. However, little is known with regard to the chemicals they contain and the safety of these compounds. Thus, we extracted 43 everyday bio-based and/or biodegradable products as well as their precursors, covering mostly food contact materials made of nine material types, and characterized these extracts using in vitro bioassays and non-target high-resolution mass spectrometry. Two-third (67%) of the samples induced baseline toxicity, 42% oxidative stress, 23% antiandrogenicity and one sample estrogenicity. In total, we detected 41,395 chemical features with 186-20,965 features present in the individual samples. 80% of the extracts contained >1000 features, most of them unique to one sample. We tentatively identified 343 priority compounds including monomers, oligomers, plastic additives, lubricants and non-intentionally added substances. Extracts from cellulose- and starch-based materials generally triggered a strong in vitro toxicity and contained most chemical features. The toxicological and chemical signatures of polyethylene (Bio-PE), polyethylene terephthalate (Bio-PET), polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polylactic acid (PLA), polyhydroxyalkanoates (PHA) and bamboo-based materials varied with the respective product rather than the material. Toxicity was less prevalent and potent in raw materials than in final products. A comparison with conventional plastics indicates that bioplastics and plant-based materials are similarly toxic. This highlights the need to focus more on aspects of chemical safety when designing truly "better" plastic alternatives.

Tandem anaerobic-aerobic degradation of ranitidine, diclofenac, and simvastatin in domestic sewage

There is a consensus among scientists that domestic sewage treatment plants are the main sources of drugs entry into the aquatic environment. Therefore, this work studies the biodegradation of the drugs ranitidine (RNT), diclofenac (DCF), and simvastatin (SVT) (50 μg L^-1, each), in real domestic sewage, using a continuous anaerobic-aerobic reactor with immobilized biomass and an anaerobic batch reactor. The continuous anaerobic-aerobic reactor was operated for 6 months with hydraulic retention time (HRT) of 8 h. The initial degradation rates and the maximum oxidation capacities (MOC) of the system were estimated, achieving 90, 72, and 62% removals and 100, 93, and 72% of MOC for RNT, DCF and SVT, respectively, as well as 71% removal of soluble chemical oxygen demand (COD). RNT was degraded throughout the reactor, while DCF was degraded mainly in the two anaerobic chambers and SVT in the first anaerobic chamber. Anaerobic batches were used for the identification of biodegradation by-products (2,6-dichloro-N-(2-methylphenyl) aniline and simvastatin acid), the evaluation of the specific methanogenic activity (SMA) inhibition, and the estimation of acute and chronic ecotoxicities using the ECOSAR 1.11 software. The present study showed that, even at environmental concentrations, RNT, DCF, and SVT were capable of inhibiting the SMA. Lipophilicities dictated the behavior of those three drugs. The greater their lipophilicities, the greater the SMA inhibition and their ecotoxicity.

Benchmarking the in Vitro Toxicity and Chemical Composition of Plastic Consumer Products

Plastics are known sources of chemical exposure and few, prominent plastic-associated chemicals, such as bisphenol A and phthalates, have been thoroughly studied. However, a comprehensive characterization of the complex chemical mixtures present in plastics is missing. In this study, we benchmark plastic consumer products, covering eight major polymer types, according to their toxicological and chemical signatures using in vitro bioassays and nontarget high-resolution mass spectrometry. Most (74%) of the 34 plastic extracts contained chemicals triggering at least one end point, including baseline toxicity (62%), oxidative stress (41%), cytotoxicity (32%), estrogenicity (12%), and antiandrogenicity (27%). In total, we detected 1411 features, tentatively identified 260, including monomers, additives, and nonintentionally added substances, and prioritized 27 chemicals. Extracts of polyvinyl chloride (PVC) and polyurethane (PUR) induced the highest toxicity, whereas polyethylene terephthalate (PET) and high-density polyethylene (HDPE) caused no or low toxicity. High baseline toxicity was detected in all "bioplastics" made of polylactic acid (PLA). The toxicities of low-density polyethylene (LDPE), polystyrene (PS), and polypropylene (PP) varied. Our study demonstrates that consumer plastics contain compounds that are toxic in vitro but remain largely unidentified. Since the risk of unknown compounds cannot be assessed, this poses a challenge to manufacturers, public health authorities, and researchers alike. However, we also demonstrate that products not inducing toxicity are already on the market.

A new enzymatic method assessing the impact of wastewater treatment plant effluents on the assimilative capacity of small rivers

Microorganisms play an important role in maintaining a good water quality in rivers by degrading organic material, including toxic substances. In the present study, we analyzed the potential impact of municipal wastewater treatment plant (WWTP) effluents as a major stress factor on the assimilative capacity of small rivers. It was the aim to develop a new bioassay for assessing such impacts in the receiving rivers by measuring the activity of extracellular enzymes (exoenzymes) in bacteria. Therefore, we established a specific in-vitro assay to detect inhibitory effects of solid phase-enriched water samples on β-glucosidase (BGL) activity of the actinobacterium Cellulomonas uda as a proxy for the microbial decomposition of organic substances and thus for the assimilative capacity of surface waters. We found significant reductions of BGL activity in the WWTP effluents and in the receiving waters directly downstream as well as a relative quick recovery over the further course of the water bodies. The new bioassay offers a promising tool for the assessment of the assimilative capacity in surface waters and a potential impact of WWTP effluents on this key ecosystem function. Abbreviations WWTP wastewater treatment plant BGL β-glucosidase EU-WFD European Water Framework Directive FAU Formazin Attenuation Units PE population equivalents REF relative enrichment factor; SPE solid phase extraction MTBE methyl-tert-buthyl-ether DMSO dimethyl-sulfoxide NPG 4-nitrophenol-β-d-glucopyranoside DOC dissolved organic carbon.

Systematic Review of Toxicity Removal by Advanced Wastewater Treatment Technologies via Ozonation and Activated Carbon

Upgrading wastewater treatment plants (WWTPs) with advanced technologies is one key strategy to reduce micropollutant emissions. Given the complex chemical composition of wastewater, toxicity removal is an integral parameter to assess the performance of WWTPs. Thus, the goal of this systematic review is to evaluate how effectively ozonation and activated carbon remove in vitro and in vivo toxicity. Out of 2464 publications, we extracted 46 relevant studies conducted at 22 pilot or full-scale WWTPs. We performed a quantitative and qualitative evaluation of in vitro (100 assays) and in vivo data (20 species), respectively. Data is more abundant on ozonation (573 data points) than on an activated carbon treatment (162 data points), and certain in vitro end points (especially estrogenicity) and in vivo models (e.g., daphnids) dominate. The literature shows that while a conventional treatment effectively reduces toxicity, residual effects in the effluents may represent a risk to the receiving ecosystem on the basis of effect-based trigger values. In general, an upgrade to ozonation or activated carbon treatment will significantly increase toxicity removal with similar performance. Nevertheless, ozonation generates toxic transformation products that can be removed by a post-treatment. By assessing the growing body of effect-based studies, we identify sensitive and underrepresented end points and species and provide guidance for future research.

Biotransformation of organic micropollutants by anaerobic sludge enzymes

Biotransformation of organic micropollutants (OMPs) in wastewater treatment plants ultimately depends on the enzymatic activities developed in each biological process. However, few research efforts have been made to clarify and identify the role of enzymes on the removal of OMPs, which is an essential knowledge to determine the biotransformation potential of treatment technologies. Therefore, the purpose of the present study was to investigate the enzymatic transformation of 35 OMPs under anaerobic conditions, which have been even less studied than aerobic systems. Initially, 13 OMPs were identified to be significantly biotransformed (>20%) by anaerobic sludge obtained from a full-scale anaerobic digester, predestining them as potential targets of anaerobic enzymes. Native enzymes were extracted from this anaerobic sludge to perform transformation assays with the OMPs. In addition, the effect of detergents to recover membrane enzymes, as well as the effects of cofactors and inhibitors to promote and suppress specific enzymatic activities were evaluated. In total, it was possible to recover enzymatic activities towards 10 out of these 13 target OMPs (acetyl-sulfamethoxazole and its transformation product sulfamethoxazole, acetaminophen, atenolol, clarithromycin, citalopram, climbazole, erythromycin, and terbutryn, venlafaxine) as well as towards 8 non-target OMPs (diclofenac, iopamidol, acyclovir, acesulfame, and 4 different hydroxylated metabolites of carbamazepine). Some enzymatic activities likely involved in the anaerobic biotransformation of these OMPs were identified. Thereby, this study is a starting point to unravel the still enigmatic biotransformation of OMPs in wastewater treatment systems.

Applications of membrane bioreactors for water reclamation: Micropollutant removal, mechanisms and perspectives

Membrane bioreactors (MBRs) have attracted attention in water reclamation as a result of the recent technical advances and cost reduction in membranes. However, the increasing occurrence of micropollutants in wastewaters has posed new challenges. Therefore, we reviewed the current state of research to identify the outstanding needs in this field. In general, the fate of micropollutants in MBRs relates to sorption, biodegradation and membrane separation processes. Hydrophobic, nonionized micropollutants are favorable in sorption, and the biological degradation shows higher efficiency at relatively long SRTs (30-40 days) and HRTs (20-30 h), as a result of co-metabolism, metabolism and/or ion trapping. Although the membrane rejection rates for micropollutants are generally minor, final water quality can be improved via combination with other technologies. This review highlights the challenges and perspectives that should be addressed to facilitate the extended use of MBRs for the removal of micropollutants in water reclamation.

Insights into the variability of microbial community composition and micropollutant degradation in diverse biological wastewater treatment systems

The biological potential of conventional wastewater treatment plants to remove micropollutants mainly depends on process conditions and the predominant microbial community. To explore this dependence and to connect the occurrence of genera with operating conditions, five pilot-scale reactors with different process conditions were combined into two reactor cascades and fed with the effluent of the primary clarifier of a municipal WWTP. All reactors and the WWTP were analyzed for the removal of 33 micropollutants by LC-MS/MS and the presence of the microbial community using 16S rRNA gene sequencing. The overall removal of the micropollutants was slightly improved (ca. 20%) by the reactor cascades in comparison to the WWTP while certain compounds such as diatrizoate, venlafaxine or diclofenac showed an enhanced removal (ca. 70% in one or both cascades). To explore the diverse bacteria in more detail, the general community was divided into a core and a specialized community. Despite their profoundly different operating parameters (especially redox conditions), the different treatments share a core community consisted of 143 genera (9% of the overall community). Furthermore, the alpha- and beta-biodiversity as well as the occurrence of several genera belonging to the specialized microbial community could be linked to the prevalent process conditions of the individual treatments. Members of the specialized community also correlated with the removal of certain groups of micropollutants. Hence, the comparison of the specialized community with micropollutant removal and operating conditions via correlation analysis is a valuable tool for an extended evaluation of prevalent process conditions. Based on an extended data set this approach could also be used to identify organisms as indicators for operating conditions which are beneficial for an improved removal of specific micropollutants.

Why are organic micropollutants not fully biotransformed? A mechanistic modelling approach to anaerobic systems

Biotransformation of most organic micropollutants (OMPs) during wastewater treatment is not complete and an unexplained steady decrease of the biotransformation rate with time is reported for many OMPs in different biological processes. To minimize and accurately predict the emission of OMPs into the environment, the mechanisms and limitations behind their biotransformations should be clarified. Aiming to achieve this objective, the present study follows a mechanistic modelling approach, based on the formulation of four models according to different biotransformation hypotheses: Michaelis-Menten kinetics, chemical equilibrium between the parent compound and the transformation product (TP), enzymatic inhibition by the TP, and a limited compound bioavailability due to its sequestration in the solid phase. These models were calibrated and validated with kinetic experiments performed in two different anaerobic systems: continuous reactors enriched with methanogenic biomass and batch assays with anaerobic sludge. Model selection was conducted according to model suitability criteria (goodness of fitting the experimental data, confidence of the estimated parameters, and model parsimony) but also considering mechanistic evidences. The findings suggest that reversibility of the biological reactions and/or sequestration of compounds are likely the causes preventing the complete biotransformation of OMPs, and biotransformation is probably limited by thermodynamics rather than by kinetics. Taking into account its simplicity and broader applicability spectrum, the reversible biotransformation is the proposed model to explain the incomplete biotransformation of OMPs.

Anaerobic biodegradation of pharmaceutical compounds: New insights into the pharmaceutical-degrading bacteria

Antibiotics and hormones are among the most concerning trace contaminants in the environment. Therefore, the present work aimed to identify anaerobic microorganisms with the ability to remove pharmaceutical products (PhPs) belonging to these two classes (ciprofloxacin, 17β-estradiol and sulfamethoxazole) under different anaerobic conditions, and to elucidate the bio-removal mechanisms involved. Ciprofloxacin was efficiently biodegraded under both nitrate- and sulfate-reducing conditions reaching a PhP removal superior to 80%, whereas 17β-estradiol was only biodegraded under nitrate-reducing conditions reaching a removal of 84%. No biodegradation of sulfamethoxazole was observed. In nitrate-reducing conditions the ciprofloxacin-degrading community was composed of Comamonas, Arcobacter, Dysgonomonas, Macellibacteroides and Actinomyces, genera while Comamonas and Castellaniella were the main bacteria present in the 17β-estradiol-degrading community. In sulfate-reducing conditions the community was mainly composed by bacteria affiliated to Desulfovibrio, Enterococcus and Peptostreeptococcus. Interestingly, the PhP under study were biodegraded even in the absence of additional carbon source, with 85% of ciprofloxacin removed under sulfate-reducing conditions and 62% and 83% of ciprofloxacin and estradiol removed, respectively, under nitrate-reducing conditions. This work provides new insights into anaerobic bioremediation of PhP and novel PhP-degrading bacteria.

Identification of toxic substances in phenol-acetone wastewater on activated sludge and selective toxicity removal performance with ferrous pretreatment

We investigated the effects of toxic wastewater generated during the production of phenol-acetone on activated sludge and tested pretreatment methods to selectively remove the toxicity. We found that the microbial activity in the activated sludge was inhibited by the wastewater, in which cumene hydroperoxide (CHP) with a medium effective concentration (EC₅₀) of 225 mg L^-1 was the main toxic substance. We tested one pretreatment method with ferrous iron to selectively remove the CHP. The CHP decomposition process, which mainly produced acetophenone, was very quick. The CHP was selectively transformed into low-toxicity organics, and a maximum of 92% was removed when 1.08 mmol L^-1 of ferrous iron was added, for a reaction time of 10 min, a pH of 5, and a temperature of 25 °C, and the resulting wastewater only slightly inhibited the oxygen uptake rate of activated sludge. The acclimation of activated sludge was accelerated, and a COD removal rate of more than 85% was achieved within a week. Our results confirm that ferrous iron provides a cost-effective method to selectively remove toxins from wastewater.

Ecotoxicological impacts of surface water and wastewater from conventional and advanced treatment technologies on brood size, larval length, and cytochrome P450 (35A3) expression in Caenorhabditis elegans

Anthropogenic micropollutants and transformation products (TPs) negatively affect aquatic ecosystems and water resources. Wastewater treatment plants (WWTP) represent major point sources for (micro)pollutants and TPs in urban water cycles. The aim of the current study was to assess the removal of micropollutants and toxicity during conventional and advanced wastewater treatment. Using wild-type and transgenic Caenorhabditis elegans, the endpoint reproduction, growth, and cytochrome P450 (CYP) 35A3 induction (via cyp-35A3::GFP) were assessed. Samples were collected at four WWTPs and a receiving surface water. One WWTP included the advanced treatments: ozonation followed by granular activated carbon (GAC) or biological filtration (BF), respectively. Relevant micropollutants and WWTP parameters (n = 111) were included. Significant reproductive toxicity was detected for one WWTP effluent (31-83% reduced brood size). Three of four effluents significantly promoted the growth of C. elegans larvae (49-55% increased lengths). This effect was also observed for the GAC (34-41%) and BF (30%) post-treatments. Markedly, significant cyp-35A3::GFP induction was detected for one effluent before and after ozonation, being more pronounced for the ozonated samples (5- and 7.4-fold above controls). While the advanced treatments decreased the concentrations of most micropollutants, the observed effects may be attributed to effects of residual target compounds and/or compounds not included in the target chemical analysis. This highlights the need for an integrated assessment of (advanced) wastewater treatment covering both biological and chemical parameters.

Small but with big impact? Ecotoxicological effects of a municipal wastewater effluent on a small creek

Municipal wastewater treatment plants (WWTPs) discharge micropollutants like pharmaceuticals, pesticides, personal care products or endocrine disrupting chemicals but also nutrients. Both can adversely influence the freshwater ecosystem and may finally affect the ecological conditions. Many studies focus on the potential impact of large WWTPs even if smaller ones are more common, often less efficient and discharge into small creeks or the upper reaches of rivers. As a result, the receiving waters are characterized by relatively high shares of treated wastewater. Thus, the primary objective of this study was to investigate the ecotoxicological effects of a small WWTP on freshwater amphipods and mollusks in a small creek using an active and passive monitoring approach, accompanied by laboratory experiments (LE). In vitro assays with recombinant yeasts and the microtox assay with Aliivibrio fischeri were performed in parallel to determine the endocrine potential and the baseline toxicity. The evaluation of the effects of the analysed WWTP was possible due to its shutdown during our study and the application of the same in vivo and in vitro assays before and after the shutdown. During the operation of the WWTP the discharge of treated wastewater caused significantly higher mortalities and lower reproduction of the anaylsed invertebrates in the active and passive montoring as well as in the LEs. Furthermore, the amphipod species assemblage in the creek was affected downstream of the WWTP effluent. Besides, the endocrine activity and baseline toxicity were significantly higher downstream of the effluent. After the shutdown of the WWTP, the in vitro activity levels and adverse in vivo effects in the receiving water recovered quickly with no significant differences downstream of the former WWTP effluent compared to the upstream station. Furthermore, the previously disturbed amphipod species assemblage recovered significantly with a shift in favor of Gammarus fossarum downstream of the effluent. These biological results are consistent with a marked decline by 81.5% for the detected micropollutants in the receiving creek after the shutdown which points to a prominent role of micropollutants for the observed effects.