Anaerobic treatment of sewage sludge containing selective serotonin reuptake inhibitors

Graphene oxide addition to anaerobic digestion of waste activated sludge: Impact on methane production and removal of emerging contaminants

The effect of graphene oxide on the anaerobic digestion of waste activated sludge was investigated at two graphene oxide concentrations (0.025 and 0.075 g graphene oxide per g volatile solids) using biochemical methane potential tests. The occurrence of 36 pharmaceuticals was monitored in the solid and liquid phases before and after the anaerobic treatment. The addition of graphene oxide improved the removal of most pharmaceuticals detected, even those that are considered persistent to biological degradation, such as azithromycin, carbamazepine, and diclofenac. No significant differences were observed in the final specific methane production without graphene oxide and with the lowest graphene oxide concentration, yet the highest graphene oxide concentration partially inhibited methane production. The relative abundance of antibiotic resistance genes was not affected by the graphene oxide addition. Finally, significant changes in the microbial community including bacteria and archaea were detected with graphene oxide addition.

Stability of 28 typical prescription drugs in sewer systems and interaction with the biofilm bacterial community

Identifying the attenuation characteristics of drugs in sewage and sewers is one of the important factors to improve the accuracy of wastewater-based epidemiology (WBE) application. In this study, 28 drugs including antidepressants, cardiovascular drugs, antihistamines, anticonvulsants and some of their human metabolites were chosen as the targets to study the hydrolysis, adsorption, and biodegradation at different temperatures in sewage and sewers. The interaction between drugs degradation and community structure of biofilm was also investigated. In the simulated sewers, the removal percentages of 12 parent or drug metabolites are 0-20%, such as demethylvenlafaxine, fluvoxamine, etc., which are highly stable chemicals and suitable to be chosen as biomarkers for WBE back-calculation under appropriate circumstances. Fourteen drugs including venlafaxine and citalopram have removal percentages of 20-60%. While paroxetine and sertraline, with removal percentage of 100%, are the most unstable and cannot be used as biomarkers. Among the 28 drugs, there are 25 drugs that have a higher loss rate in the aerobic sewer than that in the anaerobic sewer in this study. During drug exposure in anaerobic biofilms, species abundance first decreased and then increased. Species abundance and diversity in aerobic biofilm generally showed a decreasing trend. In addition, Proteobacteria and Spirochaetota were the dominant phyla in both sewers.

Transformation and fate of pharmaceuticals, personal care products, and per- and polyfluoroalkyl substances during aerobic digestion of anaerobically digested sludge

Post-anaerobic aerobic digestion (PAAD) is a promising strategy to further reduce the volume and improve the quality of anaerobically digested sludge (ADS). However, the effect of PAAD process on the fate of pharmaceuticals and personal care products (PPCPs) and per- and polyfluoroalkyl substances (PFAS) remains largely unknown. In this study, fourteen PPCPs and fifteen PFAS were detected in ADS and evaluated regarding their fate and transformation in a laboratory aerobic digester operated with a hydraulic retention time of 13 days under 22 ℃. Twelve PPCPs demonstrated significant (p < 0.05) decrease in their total concentrations (dissolved and adsorbed fractions combined) with six compounds presenting substantial transformation (> 80%) after aerobic digestion. On the contrary, PFAS were not removed and their concentrations were either increased (increasing ratio: 91 - 571%) or consistent in the sludge during PAAD process, suggesting their recalcitrance to post aerobic digestion. More than half of PPCPs and PFAS demonstrated medium to strong sorption onto solids with their solid fraction higher than 50% in the ADS. After PAAD process, sorption of four PPCPs and three PFAAs to solids was enhanced in sludge.

Development of a Citric-Acid-Modified Cellulose Adsorbent Derived from Moringa peregrina Leaf for Adsorptive Removal of Citalopram HBr in Aqueous Solutions

A citric-acid-modified Moringa peregrina leaf substrate was prepared and studied as an effective adsorbent for the adsorptive removal of citalopram HBr (CTM). FTIR spectra were utilized to characterize the prepared solid. The effects of experimental variables on the percentage removal of citalopram HBr were investigated using response surface methodology. The optimum conditions selected for removal of CTM were 7 and 4 min, 0.17 g per 50 mL and 35 mg·L⁻¹ for pH, contact time, adsorbent dose and initial concentration of CTM, respectively. Under the optimized experimental conditions, 82.59% CTM (35 mg·L⁻¹) was removed. The Langmuir isotherm, Freundlich isotherm, pseudo second-order kinetic model and diffusion-chemisorption model explained the adsorption data successfully. The maximum adsorption capacity at 298 K was 8.58 mg·g⁻¹. A thermodynamic study illustrated that CTM adsorption was spontaneous and endothermic in nature.

Evaluating the stability of prescription drugs in municipal wastewater and sewers based on wastewater-based epidemiology

Wastewater-based epidemiology (WBE) is considered as an effective tool for monitoring drug consumption, which is often obtained by back-calculation using the influent concentration and other parameters of wastewater treatment plants. Lack of information on the transformation of drugs in municipal wastewater and sewers may lead to inaccurate consumption estimation. Fourteen prescription drugs in four major categories of diseases (cardiovascular, diabetes, depression, and asthma) were selected to study their adsorption and biodegradation in wastewater and biofilm sewers under different temperatures, pH and biofilms conditions. The result demonstrated that the decay percentage of drugs in wastewater is increased with temperature. Within 72 h, eleven of these 14 drugs, such as metformin, metoprolol, bezafibrate, etc., have decay percentages below 20% in wastewater, which are considered as stable drugs; and the decay percentages of the other three, monluster, paroxetine, and sertraline, are greater than 20%, which are the most unstable drugs. In lab-scale aerobic and anaerobic sewers, the decay percentages of metformin, glipizide, metoprolol, gemfibrozil, and atorvastatin are less than 20% within 24 h. The decay percentages of venlafaxine, citalopram, fluoxetine, salmeterol, and salbutamol within 24 h are 20%-60% and paroxetine and sertraline are close to or even exceed 80% within 6 h. Biodegradation of drugs in sewers with aerobic or anaerobic biofilms is higher than that in wastewater systems without biofilms. The results showed that when the per capita consumption of drugs is estimated by using the WBE method, the stability of drugs in wastewater and different types of sewers will significantly affect their residual concentrations.

Molecularly Imprinted Polymers for the Removal of Antidepressants from Contaminated Wastewater

Selective serotonin reuptake inhibitors (SSRIs) are a class of antidepressants regularly detected in the environment. This indicates that the existing wastewater treatment techniques are not successfully removing them beforehand. This study investigated the potential of molecularly imprinted polymers (MIPs) to serve as sorbents for removal of SSRIs in water treatment. Sertraline was chosen as the template for imprinting. We optimized the composition of MIPs in order to obtain materials with highest capacity, affinity, and selectivity for sertraline. We report the maximum capacity of MIP for sertraline in water at 72.6 mg g⁻¹, and the maximum imprinting factor at 3.7. The MIPs were cross-reactive towards other SSRIs and the metabolite norsertraline. They showed a stable performance in wastewater-relevant pH range between 6 and 8, and were reusable after a short washing cycle. Despite having a smaller surface area between 27.4 and 193.8 m²·g⁻¹, as compared to that of the activated carbon at 1400 m²·g⁻¹, their sorption capabilities in wastewaters were generally superior. The MIPs with higher surface area and pore volume that formed more non-specific interactions with the targets considerably contributed to the overall removal efficiency, which made them better suited for use in wastewater treatment.

Process type is the key driver of the fate of organic micropollutants during industrial scale treatment of organic wastes

Organic micropollutants (OMPs) such as polycyclic aromatic hydrocarbons, nonylphenols and pharmaceutical products are ubiquitous in organic wastes generated by most human activities. Those wastes are mainly recycled by land spreading, most often after treatments, such as liming, dewatering, composting or anaerobic digestion. It has been shown essentially at lab scales that biological treatments have an effect on the removal of some OMPs. However, less is known on the role of each step of industrial treatment lines combining physico-chemical and biological treatments on the OMP fate and removal. The present study focuses on the impact of waste treatment on the fate of 53 OMPs along 10 industrial treatment lines treating urban, agricultural wastes or mixtures. The combination of studying a diversity of organic wastes and of OMPs with different characteristics (solubility, ionic charges, hydrophobicity etc.), sampling in situ industrial sites, quantifying native OMP concentrations and looking at each step of complete treatment lines allows for a global and representative view of the OMP fate in the French organic waste treatment sector. Less studied wastes, i.e. territorial mixtures, revealed intermediate OMP contents and compositions, between urban and agricultural wastes. Dewatering and liming, usually dismissed, had a noticeable effect on concentrations. Anaerobic digestion and composting had significant effects on the removal of all pollutant families. Combination of processes enhanced most OMP dissipation. Here we showed for the first time that the process type rather than the waste origin affects dissipation of organic micropollutants. Such data could be used to build and validate dynamic models for the fate of OMPs on solid waste treatment plants.

Assessment of the fate of organic micropollutants in novel wastewater treatment plant configurations through an empirical mechanistic model

Novel wastewater treatment plants (WWTPs) are expected to be less energetically demanding than conventional ones. However, scarce information is available about the fate of organic micropollutants (OMPs) in these novel configurations. Therefore, the objective of this work is to assess the fate of OMPs in three novel WWTP configurations by using a plant-wide simulation that integrates multiple units. The difference among the three configurations is the organic carbon preconcentration technology: chemically enhanced primary treatment (CEPT), high-rate activated sludge (HRAS) combined or not with a rotating belt filter (RBF); followed by a partial-nitritation (PN-AMX) unit. The simulation results show that the three selected novel configurations lead mainly to comparable OMPs removal efficiencies from wastewater, which were similar or lower, depending on the OMP, than those obtained in conventional WWTPs. However, the presence of hydrophobic OMPs in the digested sludge noticeably differs among the three configurations. Whereas the configuration based on sole HRAS to recover organic carbon leads to a lower presence of OMPs in digested sludge than the conventional WWTP, in the other two novel configurations this presence is noticeable higher. In conclusion, novel WWTP configurations do not improve the OMPs elimination from wastewater achieved in conventional ones, but the HRAS-based WWTP configuration leads to the lowest presence in digested sludge so it becomes the most efficient alternative.

Pharmaceuticals in source separated sanitation systems: Fecal sludge and blackwater treatment

This study investigated, for the first time, the occurrence and fate of 29 multiple-class pharmaceuticals (PhACs) in two source separated sanitation systems based on: (i) batch experiments for the anaerobic digestion (AD) of fecal sludge under mesophilic (37 °C) and thermophilic (52 °C) conditions, and (ii) a full-scale blackwater treatment plant using wet composting and sanitation with urea addition. Results revealed high concentrations of PhACs in raw fecal sludge and blackwater samples, with concentrations up to hundreds of μg L^-1 and μg kg^-1 dry weight (dw) in liquid and solid fractions, respectively. For mesophilic and thermophilic treatments in the batch experiments, average PhACs removal rates of 31% and 45%, respectively, were observed. The average removal efficiency was slightly better for the full-scale blackwater treatment, with 49% average removal, and few compounds, such as atenolol, valsartan and hydrochlorothiazide, showed almost complete degradation. In the AD treatments, no significant differences were observed between mesophilic and thermophilic conditions. For the full-scale blackwater treatment, the aerobic wet composting step proved to be the most efficient in PhACs reduction, while urea addition had an almost negligible effect for most PhACs, except for citalopram, venlafaxine, oxazepam, valsartan and atorvastatin, for which minor reductions (on average 25%) were observed. Even though both treatment systems reduced initial PhACs loads considerably, significant PhAC concentrations remained in the treated effluents, indicating that fecal sludge and blackwater fertilizations could be a relevant vector for dissemination of PhACs into agricultural fields and thus the environment.

Thermal hydrolysis of sewage sludge partially removes organic micropollutants but does not enhance their anaerobic biotransformation

Pretreatment technologies prior to anaerobic digestion (AD) have been developed with the aim of enhancing biogas productivity and reducing the presence of pathogens in digested sludge. Among them, thermal hydrolysis (TH) appears as the most promising one. In wastewater treatment plants (WWTPs) sludge is the end point of many organic micropollutants (OMPs), which was proved to lead to important environmental and human risks since sludge is commonly used in agriculture. The objective of this work is to determine the fate OMPs in TH and subsequent AD. Sewage sludge was pretreated in a TH pilot plant at 170 °C for 20 min. Afterwards, two anaerobic digesters with a working volume of 14 L fed with fresh and pretreated sludge were operated in parallel in mesophilic conditions. TH proved to be an effective technology to partially or totally remove the dissolved fraction of OMPs as well as the fraction sorbed into those suspended solids that are solubilised after this pretreatment. However, it did not affect the OMPs sorbed concentration into solids that are not solubilised. Globally, the OMPs removal efficiency during TH appears to be linked to the solids solubilisation during this process. Afterwards, the OMPs biotransformation efficiency in AD of fresh and pretreated sludge was determined. Noticeable differences between the microbiome of both reactors was determined, but the anaerobic biotransformation was not substantially different for most of the OMPs. However, it affected musk fragrances, which presented considerably lower biotransformation efficiency in the reactor fed with pretreated sludge. Therefore, TH was proved effective in partially removing OMPs but not in enhancing their bioavailability and subsequent anaerobic biotransformation.

Role of methanogenesis on the biotransformation of organic micropollutants during anaerobic digestion

Several studies showed that some organic micropollutants (OMPs) are biotransformed during anaerobic digestion (AD). Yet, most of them aim at reporting removal efficiencies instead of understanding the biotransformation process. Indeed, how each of the main AD stages (i.e., hydrolysis, acidogenesis, and methanogenesis) contribute to OMP biotransformation remains unknown. This study focuses on investigating the role of methanogenesis, the most characteristic step of AD, to OMP removal. More specifically, the sorption and the biotransformation of 20 OMPs by methanogenic biomass were analyzed determining their concentrations in both liquid and solid phases. Sorption onto methanogenic biomass displayed a similar behavior as reported for digested sludge. Most of the OMPs were biotransformed to a medium extent (35-70%) and only sulfamethoxazole was completely removed. Comparing these results with those reported for the complete AD process, methanogenesis was proven to play a key role, accounting for more than 50% of the OMP biotransformation (except for roxithromycin) during AD. An increase in the organic loading rate from 1 to 2gCOD/Ld, typical loads employed in sewage sludge anaerobic digesters, did not exert a clear cometabolic effect on the OMPs biotransformation. It is hypothesized that biotransformation occurs in both liquid and solid phases because no link between the partition coefficient (Kd) and the overall biotransformation efficiency was found. These findings allow a better understanding of the OMPs fate under anaerobic conditions, which is necessary to design efficient biological mitigation strategies.

Applicability evaluation of advanced processes for elimination of neurophysiological activity of antidepressant fluoxetine

Presence of the antidepressant fluoxetine in different water bodies has raised significant concerns due to its detrimental effects on non-targeted organisms, especially on fish. When seeking for an appropriate technology able to remove fluoxetine residue from a complex water matrix, special attention needs to be paid to the elimination of the neurophysiological activity that eventually lies behind the noxious effects of the parent compound. Our aim was to probe the applicability of advanced oxidation techniques for this purpose using in situ generated free radical system based on OH-initiated peroxyl radical-mediated processes. By performing product analysis experiments along with quantum chemical calculations, the most probable reaction paths were analyzed including aromatic hydroxylation, defluorination, O-dealkylation and C-dealkylation. The candidates for neurophysiological activity were further investigated by molecular docking. The hydroxylated derivatives are well accommodated in the binding pocket of the corresponding protein, suggesting that these compounds may retain the activity of the parent compound. From a worst-case perspective, we suggest that prolonged treatment needs to be applied to further transform hydroxylated derivatives.

Developmental exposure to the SSRI citalopram causes long-lasting behavioural effects in the three-spined stickleback (Gasterosteus aculeatus)

Selective Serotonin re-uptake inhibitors (SSRIs) are a class of psychotropic drugs used to treat depression in both adolescents and pregnant or breast-feeding mothers as well as in the general population. Recent research on rodents points to long-lasting behavioural effects of pre- and perinatal exposure to SSRIs which last into adulthood. In fish however, studies on effects of developmental exposure to SSRIs appears to be non-existent. In order to study effects of developmental SSRI exposure in fish, three-spine sticklebacks were exposed to 1.5 µg/l of the SSRI citalopram in the ambient water for 30 days, starting two days post-fertilisation. After approximately 100 days of remediation in clean water the fish were put through an extensive battery of behavioural tests. Feeding behaviour was tested as the number of bites against a piece of food and found to be increased in the exposed fish. Aggression levels were measured as the number of bites against a mirror image during 10 min and was also found to be significantly increased in the exposed fish. Novel tank behaviour and locomotor activity was tested in an aquarium that had a horizontal line drawn half-way between the bottom and the surface. Neither the latency to the first transition to the upper half, nor the number of transitions or the total time spent in the upper half was affected by treatment. Locomotor activity was significantly reduced in the exposed fish. The light/dark preference was tested in an aquarium where the bottom and walls were black on one side and white on the other. The number of transitions to the white side was significantly reduced in the exposed fish but there was no effect on the latency to the first transition or the total time spent in the white half. The results in the current study indicate that developmental SSRI exposure causes long-lasting behavioural effects in fish and contribute to the existing knowledge about SSRIs as environmental pollutants.

Cometabolic Enzymatic Transformation of Organic Micropollutants under Methanogenic Conditions

Anaerobic digestion (AD) has been shown to have the biological potential to decrease concentrations of several organic micropollutants (OMPs) in sewage sludge. However, the mechanisms and factors behind these biotransformations, which are essential for elucidating the possible transformation products and to foster the complete removal of OMPs via operational strategies, remain unclear. Therefore, this study investigated the transformation mechanisms of 20 OMPs during the methanogenic step of AD with a focus on the role of acetate kinase (AK), which is a key enzyme in methane production. The results from lab-scale methanogenic reactors showed that this step accounts for much of the reported OMP biotransformation in AD. Furthermore, enzymatic assays confirmed that AK transforms galaxolide, naproxen, nonylphenol, octylphenol, ibuprofen, diclofenac, bisphenol A, and triclosan. Except for galaxolide, for which further studies are required to refine conclusions, the OMP's chemical structure was a determinant for AK action because only compounds that contain a carboxyl or hydroxyl group and have moderate steric hindrance were enzymatically transformed, likely by phosphorylation. For these seven compounds, this enzymatic mechanism accounts for 10-90% of the measured methanogenic biotransformation, suggesting that other active enzymes of the AD process are also involved in OMP biotransformation.

Determination and characterization of pharmaceuticals in sludge from municipal and livestock wastewater treatment plants

This study investigated 24 pharmaceuticals compounds belonging to the classes of analgesics, stimulants, anti-seizures, non-steroidal anti-inflammatory drugs (NSAIDs), and antibiotics in the sludge of 12 municipal sewage treatment plants (S-sludge) and 4 livestock wastewater treatment plants (L-sludge) located across Korea. Over 70% of the target compounds were detected in at least one sample of S-sludge and L-sludge. The total concentration of the target pharmaceutical compounds detected in S-sludge was 2.622-422.8 mg kg^-1and the most dominant compound was acetylsalicylic acid (ASA: 0.374-367.0 mg kg^-1) whereas in L-sludge, the total concentration was 43.87-156.8 mg kg^-1and the most abundant compound was oxytetracycline (OTC: 34.54-86.39 mg kg^-1). Cluster analysis revealed two distinct groups: group A, which were S-sludge samples including ASA, carbamazepine (CBM), and others, and group B were L-sludge samples, dominated by antibiotics (CTC, OTC, LIN). The total daily load amount of the target pharmaceuticals in S-sludge was 0.010-268.9 kg day^-1 while the L-sludge was 0.021-0.529 kg day^-1. The estimated amounts of the target pharmaceutical discharged from S-sludge and L-sludge into the Korean environment were 150.2 ± 47.94 ton yr^-1 and 15.05 ± 5.671 ton yr^-1 respectively, but the discharged amount of antibiotics from S-sludge (6.945 ton yr^-1) was lower than that from L-sludge (9.234 ton yr^-1).

Application of nanoscale zero valent iron and iron powder during sludge anaerobic digestion: Impact on methane yield and pharmaceutical and personal care products degradation

Lab scale and single stage high solid anaerobic digestion of sewage sludge spiked with freshly synthesized nanoscale zero valent iron (nZVI) and commercial iron powder (IP) under mesophilic condition (37±1°C) was performed. The effects of both additives on methane yield, and pharmaceutical and personal care product (PPCP) removal were investigated. Results showed that methane yield was increased by 25.2% and 40.8% in the presence of nZVI (0.1%) and IP (1.6%), respectively. Removal efficiencies of chemical oxygen demand were 54.4% and 66.2% in the presence of nZVI and IP, respectively, which were higher compared to the control group (44.6%). In addition, most PPCPs could be partly or completely removed during the anaerobic digestion process. The application of nZVI and IP showed positive impact on the removal of chlorinated PPCPs (p<0.05), but did not show significant impact on other PPCPs (p>0.05). Our finding suggests that the application of nZVI and IP in anaerobic digestion could be a promising way to enhance methane yield but had less improvement on PPCP degradation.

Is anaerobic digestion effective for the removal of organic micropollutants and biological activities from sewage sludge?

The occurrence of emerging organic micropollutants (OMPs) in sewage sludge has been widely reported; nevertheless, their fate during sludge treatment remains unclear. The objective of this work was to study the fate of OMPs during mesophilic and thermophilic anaerobic digestion (AD), the most common processes used for sludge stabilization, by using raw sewage sludge without spiking OMPs. Moreover, the results of analytical chemistry were complemented with biological assays in order to verify the possible adverse effects (estrogenic and genotoxic) on the environment and human health in view of an agricultural (re)use of digested sludge. Musk fragrances (AHTN, HHCB), ibuprofen (IBP) and triclosan (TCS) were the most abundant compounds detected in sewage sludge. In general, the efficiency of the AD process was not dependent on operational parameters but compound-specific: some OMPs were highly biotransformed (e.g. sulfamethoxazole and naproxen), while others were only slightly affected (e.g. IBP and TCS) or even unaltered (e.g. AHTN and HHCB). The MCF-7 assay evidenced that estrogenicity removal was driven by temperature. The Ames test did not show point mutation in Salmonella typhimurium while the Comet test exhibited a genotoxic effect on human leukocytes attenuated by AD. This study highlights the importance of combining chemical analysis and biological activities in order to establish appropriate operational strategies for a safer disposal of sewage sludge. Actually, it was demonstrated that temperature has an insignificant effect on the disappearance of the parent compounds while it is crucial to decrease estrogenicity.

Pharmaceutical residues in sewage sludge: effect of sanitization and anaerobic digestion

The fate of pharmaceutical residues in treatment of WWTP sludge was evaluated during mesophilic anaerobic digestion (AD) and six sanitization technologies (pasteurization, thermal hydrolysis, advanced oxidation processes using Fenton's reaction, ammonia treatment, thermophilic dry digestion, and thermophilic anaerobic digestion). Sludge spiked with a selection of 13 substances was used and in total 23 substances were detected. A correlation between substance lipophilicity and sludge partitioning was found after sample centrifugation, with e.g., SSRI drugs (90-99%) and estrogens (96-98%) mainly found in the solid phase. A correlation between lipophilicity and persistence of pharmaceutical residues during AD was also detected, indicating that hydrophobic substances are less available to degrading microorganisms. Overall, AD was found to be the most effective technology in reducing a wide spectrum of organic substances (in average ca 30% reduction). Similar effects were obtained for both AD treatments, suggesting that temperature (mesophilic or thermophilic) is less important for micropollutant reduction. Advanced oxidation processes using Fenton's reaction also affected several compounds, including substances showing general stability over the range of treatments such as carbamazepine, propranolol, and sertraline. Pasteurization, ammonia treatment, and thermophilic dry digestion exhibited relatively modest reductions. Interestingly, only thermal hydrolysis efficiently removed the ecotoxicologically potent estrogenic compounds from the sludge.

Effects of a gradually increased load of fish waste silage in co-digestion with cow manure on methane production

This study examined the effects of an increased load of nitrogen-rich organic material on anaerobic digestion and methane production. Co-digestion of fish waste silage (FWS) and cow manure (CM) was studied in two parallel laboratory-scale (8L effective volume) semi-continuous stirred tank reactors (designated R1 and R2). A reactor fed with CM only (R0) was used as control. The reactors were operated in the mesophilic range (37°C) with a hydraulic retention time of 30 days, and the entire experiment lasted for 450 days. The rate of organic loading was raised by increasing the content of FWS in the feed stock. During the experiment, the amount (volume%) of FWS was increased stepwise in the following order: 3% - 6% - 13% - 16%, and 19%. Measurements of methane production, and analysis of volatile fatty acids, ammonium and pH in the effluents were carried out. The highest methane production from co-digestion of FWS and CM was 0.400 L CH4 gVS(-1), obtained during the period with loading of 16% FWS in R2. Compared to anaerobic digestion of CM only, the methane production was increased by 100% at most, when FWS was added to the feed stock. The biogas processes failed in R1 and R2 during the periods, with loadings of 16% and 19% FWS, respectively. In both reactors, the biogas processes failed due to overloading and accumulation of ammonia and volatile fatty acids.

Distribution of antidepressant residues in wastewater and biosolids following different treatment processes by municipal wastewater treatment plants in Canada

The fate of 14 antidepressants along with their respective N-desmethyl metabolites and the anticonvulsive drug carbamazepine (CBZ) was studied in 5 different sewage treatment plants (STPs) across Canada. Using two validated LC-MS/MS analytical methods, the concentrations of the different compounds were determined in raw influent, final effluent and treated biosolids samples. Out of the 15 compounds investigated, 13 were positively detected in most 24-h composite raw influent samples. Analysis showed that venlafaxine (VEN), its metabolite O-desmethylvenlafaxine (DVEN), citalopram (CIT), and CBZ were detected at the highest concentrations in raw influent (up to 4.3 μg L(-1) for DVEN). Cumulated results showed strong evidence that primary treatment and trickling filter/solids contact has limited capacity to remove antidepressants from sewage, while activated sludge, biological aerated filter, and biological nutrient removal processes yielded moderate results (mean removal rates: 30%). The more recalcitrant compounds to be eliminated from secondary STPs were VEN, DVEN and CBZ with mean removal rates close to 12%. Parent compounds were removed to a greater degree than their metabolites. The highest mean concentrations in treated biosolids samples were found for CIT (1033 ng g(-1)), amitriptyline (768 ng g(-1)), and VEN (833 ng g(-1)). Experimental sorption coefficients (K(d)) were also determined. The lowest K(d) values were obtained with VEN, DVEN, and CBZ (67-490 L kg(-1)). Sorption of these compounds on solids was assumed negligible (log K(d) ≤ 2). However, important sorption on solids was observed for sertraline, desmethylsertraline, paroxetine and fluoxetine (log K(d) > 4).