The ecotoxicological safety of the water bodies relies on the reduction of micropollutant emissions from wastewater treatment plants (WWTP). The ecotoxicological safety of the water bodies relies on the reduction of micropollutant emissions from wastewater treatment plants (WWTP). Quantification of micropollutant removal at full-scale WWTP is scarce. To our knowledge, the anaerobic conversion rates determined at conventional activated sludge processes are, so far, scarcely available in the literature for most of the micropollutants. In this research, we quantified the biotransformation rate constants and the removal efficiencies of 16 micropollutants (4,5-methylbenzotriazole, azithromycin, benzotriazole, candesartan, carbamazepine, clarithromycin, diclofenac, gabapentin, hydrochlorothiazide, irbesartan, metoprolol, propranolol, sotalol, sulfamethoxazole, trimethoprim, and venlafaxine), under aerobic, anoxic, and anaerobic redox conditions; using as inoculum wastewater and biomass from a full-scale conventional activated sludge (CAS) system in the Netherlands. Clarithromycin was the compound that exhibited the highest aerobic (76%) and anaerobic (78%) removal efficiencies, while gabapentin showed the highest removal under anoxic conditions (91%). A preference for cometabolic biotransformation of the targeted micropollutants was observed. The highest biotransformation rate constants obtained were: at aerobic conditions clarithromycin with 1.46 L.g_SS⁻¹.d⁻¹; at anoxic conditions, gabapentin with 2.36 L.g_SS⁻¹.d⁻¹; and at anaerobic redox conditions clarithromycin with 1.87 L.g_SS⁻¹.d⁻¹. The obtained results of biotransformation rates will allow further modelling of micropollutant removal in CAS systems, under various redox conditions. These biotransformation rates can be added to extended ASM models to predict effluent concentration and optimize targeted advanced oxidation processes allowing savings in the operational costs and increasing the process viability.

Fouling is a major challenge for the economic feasibility and applicability of membrane bioreactors. Several strategies have been proposed for fouling control, and among them, addition of flux enhancers (FE) have shown promising results. Previous research revealed a high variability of the required optimal dosage of FE for different types of sludge; however, studies analysing the causes for such variability are lacking. Therefore, this research examines the effect of sludge characteristics on the optimal FE dosage required for sludge filterability improvement (D_opt). We applied the cationic polymer Adifloc KD451 as FE, and determined D_opt with short-term cross-flow filtration tests. Sludge samples were obtained from five different pilot and full-scale anaerobic membrane bioreactors (AnMBRs) treating municipal or industrial wastewater. Results showed that D_opt was significantly correlated with colloidal organic matter concentration, sludge filterability, capillary suction time, and concentration of soluble polysaccharides. Furthermore, we derived empirical models to predict D_opt based on the significantly correlated sludge characteristics as input variables. This research identifies the factors affecting the required dosage of FE for different sludges and provides guidelines for safe continuous dosing of FE in AnMBR for fouling control.

Cationic polymers have proven to be suitable flux enhancers (FEs) in large‐scale aerobic membrane bioreactors (MBRs), whereas in anaerobic membrane bioreactors (AnMBRs) research is scarce, and so far, only done at lab‐scale. Results from MBRs cannot be directly translated to AnMBRs because the extent and nature of membrane fouling under anaerobic and aerobic conditions are different. Our research focused on the long‐term effect of dosing the cationic polymer Adifloc KD451 to a pilot AnMBR, fed with source‐separated domestic blackwater. A single dosage of Adifloc KD451 at 50 mg L⁻¹ significantly enhanced the filtration performance in the AnMBR, revealed by a decrease in both fouling rate and total filtration resistance. Nevertheless, FE addition had an immediate negative effect on the specific methanogenic activity (SMA), but this was a reversible process that had no adverse effect on permeate quality or chemical oxygen demand (COD) removal in the AnMBR. Moreover, the FE had a long‐term positive effect on AnMBR filtration performance and sludge filterability. These findings indicate that dosing Adifloc KD451 is a suitable strategy for fouling mitigation in AnMBRs because it led to a long‐term improvement in filtration performance, while having no significant adverse effects on permeate quality or COD removal.

The application of cationic polymers to enhance membrane fluxes in anaerobic membrane bioreactors has been proposed by several authors. However, literature shows contradictory results on the influence of those chemicals on the biological activity. In this research, we studied the effect of a cationic polymer on the production of methane from acetate by acetoclastic methanogens. We assessed the effect of polymer concentration on the accumulated methane production (AMP) and the specific methanogenic activity (SMA) in batch tests. Batch tests results showed lower SMA values at higher concentrations of polymer and no effect on the final AMP. Different inhibition models were calibrated and compared to find the best fit and to hypothesize the prevailing inhibition mechanisms. The assessed inhibition models were: competitive (M1a), non-competitive (M2a), un-competitive (M3a), biocide-linear (M4a), and biocide-exponential (M5a). The parameters in the model related to the polymer characteristics were adjusted to fit the experimental data. M2a and M3a were the only models that fitted both experimental SMA and AMP. Although M1a and M4a adequately fitted the experimental SMA, M1a simulations slightly deviated from the experimental AMP, and M4a considerably underpredicted the AMP at concentrations of polymer above 0.23 gCOD L^-1. M5a did not adequately fit either experimental SMA and AMP results. We compared models a (M1a to M5a), which consider the inhibition by the concentration of polymer in the bulk liquid, with models b (M1b to M5b) considering the inhibition being caused by the total concentration of polymer in the reactor. Results showed that the difference between a and b models' simulations were negligible for all kinetic models considered (M1, M2, M3, M4, and M5). Therefore, the models that better predicted the experimental data were the non-competitive (M2a and M2b) and un-competitive (M3a and M3b) inhibition models, which are biostatic inhibition models. Consequently, the decreased methanogenic activity caused by polymer additions is presumably a reversible process.