Nitrifying Conditions Research Articles

High pH and chloramine suppress nontuberculous mycobacterial growth in a model water distribution system

This study reports the importance of maintaining a high pH and/or chloramine concentrations in water distribution system to supress the growth of nontuberculous mycobacteria (NTM) - a group containing some opportunistic pathogens. Four sets of reactor systems, each containing three reactors connected in series, were operated at three different feed water pH values (7.6, 8.4, and 9.0) and two different chloramine concentrations (2.6 and 3.8 mg/L). Altogether, 44 operational taxonomic units of NTM were identified. The NTM species Mycobacterium chelonae, M. europaeum, M. gordonae, M. stephanolepidis, M. llatzerense, M. lentiflavum, and M. kyorinense were detected in the majority of the samples. Among them, M. chelonae was highly dominant NTM species in majority of the tested samples. The NTM populations were in the range of 8.83E+ 01–6.30E+ 05 gene copies/mL. Higher relative abundances of NTM were noted in reactors containing higher chloramine residuals, but the number of NTM and total bacterial population increased with the decreasing chloramine concentration, under low pH (<8.4) and under nitrifying conditions. This study underscores the benefits of maintaining high pH in the feed as it not only increases the chloramine stability, but also suppresses the bacterial growth including NTM.

Unravelling the contribution of nitrifying and methanotrophic bacteria to micropollutant co-metabolism in rapid sand filters

The presence of organic micropollutant (OMP) in groundwater threatens drinking water quality and public health. Rapid sand filter (RSF) rely on biofilms with nitrifying and methanotrophic bacteria to remove ammonia and methane during drinking water production. Previous research observed the partial removal of OMPs with active nitrification and methane oxidation due to co-metabolic conversion of OMPs. However, the contribution of indigenous nitrifying and methanotrophic communities from RSF has yet to be fully explored. Accordingly, experiments were carried out with biofilm-covered sand collected from field-scale RSF, to assess the removal of nine OMPs by nitrifying and methanotrophic bacteria. Results indicated that stimulating nitrification resulted in significantly more removal of caffeine, 2,4-dichlorophenoxyacetic acid and bentazone. Stimulating methanotrophic conditions enhanced the removal of caffeine, benzotriazole, 2,4-dichlorophenoxyacetic acid and bentazone. Microbial community analysis based on 16 S rRNA gene sequencing revealed Nitrosomonas and Nitrospira are the dominant genus in the community under nitrifying conditions. The three genera Methylobacter, Methylomonas and Methylotenera were enriched under methanotrophic conditions. This study highlights that nitrifying and methanotrophic bacteria play important roles during OMP removal in field RSF. Furthermore, results suggest that bioaugmentation with an enriched nitrifying and methanotrophic culture is a promising approach to improve OMP removal in RSF.

Oxidation mechanism of chlortetracycline in a membrane aerated biofilm reactor

This study describes the oxidation of chlortetracycline (CTC) under nitrifying conditions in a membrane aerated biofilm reactor (MABR) in which microorganism uses O2 as the electron acceptor and NH4+-N and CTC as the electron donors. The MABR was operated at various hydraulic retention time (HRTs), O2 gas pressures and electron donors’ loadings. The results showed that decreasing O2 gas pressure and HRTs negatively influenced the removal of secondary electron donor (CTC) as it did not affect the removal of first electron donor (NH4+-N). The CTC flux reached particularly high values of up to 2.0 mg/m2.d at O2 pressures of 0.28 and 0.41 atm. Transformation products at very low concentrations and some low molecular weight fragmentation products with m/z ratio in the range of 64 and 408 were detected in the effluent. The carbon equivalents in the influent and effluent showed that a microbial oxidative degradation mechanism was responsible for the removal of CTC. Molecular community analysis revealed that the Betaproteobacteria bacterial group were dominant in the biofilm community for the oxidation of CTC.

An assessment of the persistence of putative pathogenic bacteria in chloraminated water distribution systems

This study investigated how a chloramine loss and nitrifying conditions influenced putative pathogenic bacterial diversity in bulk water and biofilm of a laboratory- and a full-scale chloraminated water distribution systems. Fifty-four reference databases containing full-length 16S rRNA gene sequences obtained from the National Centre for Biotechnology Information database were prepared to represent fifty-four pathogenic bacterial species listed in the World Health Organisation and Australian Drinking Water Quality Guidelines. When 16S rRNA gene sequences of all samples were screened against the fifty-four reference pathogenic databases, a total of thirty-one putative pathogenic bacteria were detected in both laboratory- and full-scale systems where total chlorine residuals ranged between 0.03 - 2.2 mg/L. Pathogenic bacterial species Mycolicibacterium fortuitum and Pseudomonas aeruginosa were noted in all laboratory (i.e. in bulk water and biofilm) and in bulk water of full-scale samples and Mycolicibacterium fortuitum dominated when chloramine residuals were high. Other different pathogenic bacterial species were observed dominant with decaying chloramine residuals. This study for the first time reports the diverse abundance of putative pathogenic bacteria resilient towards chloramine and highlights that metagenomics surveillance of drinking water can serve as a rapid assessment and an early warning of outbreaks of a large number of putative pathogenic bacteria.

Isotopic evidence for alteration of nitrous oxide emissions and producing pathways' contribution under nitrifying conditions

Abstract. Nitrous oxide (N2O) emissions from a nitrifying biofilm reactor were investigated with N2O isotopocules. The nitrogen isotopomer site preference of N2O (15N-SP) indicated the contribution of producing and consuming pathways in response to changes in oxygenation level (from 0 % to 21 % O2 in the gas mix), temperature (from 13.5 to 22.3 ∘C) and ammonium concentrations (from 6.2 to 62.1 mg N L−1). Nitrite reduction, either nitrifier denitrification or heterotrophic denitrification, was the main N2O-producing pathway under the tested conditions. Difference between oxidative and reductive rates of nitrite consumption was discussed in relation to NO2- concentrations and N2O emissions. Hence, nitrite oxidation rates seem to decrease as compared to ammonium oxidation rates at temperatures above 20 ∘C and under oxygen-depleted atmosphere, increasing N2O production by the nitrite reduction pathway. Below 20 ∘C, a difference in temperature sensitivity between hydroxylamine and ammonium oxidation rates is most likely responsible for an increase in N2O production via the hydroxylamine oxidation pathway (nitrification). A negative correlation between the reaction kinetics and the apparent isotope fractionation was additionally shown from the variations of δ15N and δ18O values of N2O produced from ammonium. The approach and results obtained here, for a nitrifying biofilm reactor under variable environmental conditions, should allow for application and extrapolation of N2O emissions from other systems such as lakes, soils and sediments.

Fate of triclosan, triclocarban, and their transformation products in wastewater under nitrifying conditions

The nitrification process was simulated using benchtop bioreactors to gain insight into the fate of the antimicrobials triclosan (TCS) and triclocarban (TCC), as well their transformation products, during wastewater treatment. Currently, little information exists on the impact of nitrification treatment on concentrations of TCC, TCC degradation products, and TCS degradation products. Reactors were run using samples collected from a large municipal wastewater treatment plant at two pH ranges (6.5–7.5 and 8.5–9.5) for 171 h to simulate an extended hydraulic retention time (HRT). TCS was degraded under both pH conditions, with a 28.5% overall reduction in solids samples when the pH range was 6.5–7.5 and an overall reduction of 83.2% in solids samples when the pH ranged 8.5–9.5. Methyltriclosan (MeTCS) was formed in solids samples during both treatment conditions. MeTCS formed the most rapidly during the first 25 h of treatment at pH 8.5–9.5. Levels of 2,4-dichlorophenol, a TCS photolysis product, and TCC did not change over the 171 h treatment period, indicating that nitrification is not an effective treatment for reduction of these compounds. Three TCC dechlorination products and triclosan-O-sulfate were not observed at or above the limit of quantitation in any bioreactor samples.

Effects of feed water NOM variation on chloramine demand from chloramine-decaying soluble microbial products during rechloramination

Earlier, we reported on soluble microbial products-mediated chloramine decay in nitrifying waters. However, we neither separated the agent(s) nor identified the factors that enhanced the production of chloramine-decaying soluble microbial products (cSMPs). Experiments were conducted by feeding reactor sets (each consisting of five reactors connected in series) with treated water (3–8 mg-DOC.L−1) obtained from a water treatment plant. The reactors simulated various nitrifying conditions that are experienced in a chloraminated system. In unfiltered samples obtained from nitrified reactors, about 89–93% of the dosed chloramine decayed within 40 h. The cSMP-mediated decay accounted for 21–39% of all chloramine decay in the samples from 0 to 5 mg-C.L−1 fed reactors and 15% in the samples from 7 to 8 mg-C.L−1 fed reactors. Microbial processes (mediated by nitrifiers and/or heterotrophs) and biomass-associated microbial products (BMPs) in insoluble form accounted for 13–21% for the reactors fed with 0–5 mg-C.L−1 and 34% for those fed with 7–8 mg-C.L−1. The cSMPs were separable with a 30 kDa cut-off membrane but not with 50 or 100 kDa membranes, i.e., they were above 30 kDa but below 50 kDa in size, and were confirmed to be a protein(s). The protein(s) accelerated chloramine decay by accelerating chloramine auto-decomposition and nitrite oxidation. As opposed to the traditional belief, unknown factors accounted for approximately 34–53% in commonly encountered re-chloraminated nitrifying waters (2–5 mg-DOC.L−1). Understanding the identity and role of these factors – such as cSMPs, BMPs, heterotrophs - will lead to a better control of chloramine.

Degradation of oxytetracycline under autotrophic nitrifying conditions in a membrane aerated biofilm reactor and community fingerprinting

Pharmaceuticals in waterbodies are a growing concern due to their extensive uses and adverse effects on aquatic life. Oxytetracycline (OTC) is one of tetracycline antibiotic group used for treatment of animals and humans. This study evaluates the simultaneous oxidation of OTC and ammonium under autotrophic nitrifying conditions by using a membrane aerated biofilm reactor (MABR) as it provides an appropriate environment for the antibiotic-degrading bacteria. The results showed that MABR achieved fluxes of 1.62 mg OTC/m2.d and 1117 mg N/m2.d while the fluxes of O2 (JOTC-O2) utilized for OTC and NH4-N (JNH4-N-O2) oxidation were calculated to be 2.94 and 5105 mg O2/m2.d, respectively. Three transformation products, 4-Epi-OTC, α-Apo-OTC and β-Apo-OTC, were identified and measured at ppb levels. The biofilm community comprised of Bacteria environmental samples, b-proteobacteria, CFB group bacteria, g-proteobacteria, d-proteobacteria and a-proteobacteria.

Protists as bioindicators in activated sludge: Identification, ecology and future needs

When the activated sludge process was developed, operators and scientists soon recognized protists as valuable indicators. However, only when Curds et al. (1968) showed with a few photographs the need of ciliates for a clear plant effluent, sewage protistology began to bloom but was limited by the need of species identification. Still, this is a major problem although several good guides are available. Thus, molecular kits should be developed for identification. Protists are indicators in two stages of wastewater treatment, viz., in the activated sludge and in the environmental water receiving the plant effluent. Continuous control of the protist and bacterial communities can prevent biological sludge foaming and bulking and may greatly save money for sludge oxygenation because several protist species are excellent indicators for the amount of oxygen present. The investigation of the effluent-receiving rivers gives a solid indication about the long term function of sewage works.The literature on protist bioindication in activated sludge is widely distributed. Thus, I compiled the data in a simple Table, showing which communities and species indicate good, mediocre, or poor plant performance. Further, many details on indication are provided, such as sludge loading and nitrifying conditions. Such specific features should be improved by appropriate statistics and more reliable identification of species. Then, protistologists have a fair chance to become important in wastewater works.Activated sludge is a unique habitat for particular species, often poorly or even undescribed. As an example, I present two new species. The first is a minute (∼30μm) Metacystis that makes an up to 300μm-sized mucous envelope mimicking a sludge floc. The second is a Phialina that is unique in having the contractile vacuole slightly posterior to mid-body. Finally, I provide a list of species which have the type locality in sewage plants.

Biotransformation of pharmaceuticals under nitrification, nitratation and heterotrophic conditions

The effect of nitrification, nitratation and heterotrophic conditions on the biotransformation of several pharmaceuticals in a highly enriched nitrifying activated sludge was evaluated in this study by selective activation of ammonia oxidizing bacteria (AOB), nitrite oxidizing bacteria (NOB) and heterotrophic bacteria. Nitrifiers displayed a noticeable capacity to process ibuprofen due to hydroxylation by ammonia monooxygenase (AMO) to produce 2-hydroxy-ibuprofen. Naproxen was also biotransformed under nitrifying conditions. On the other hand, heterotrophic bacteria present in the nitrifying activated sludge (NAS) biotransformed sulfamethoxazole. In contrast, both nitrifying and heterotrophic activities were ineffective against diclofenac, diazepam, carbamazepine and trimethoprim. Similar biotransformation rates of erythromycin, roxithromycin and fluoxetine were observed under all conditions tested. Overall, results from this study give more evidence on the role of the different microbial communities present in activated sludge reactors on the biological removal of pharmaceuticals.

Role of biotransformation, sorption and mineralization of 14C-labelled sulfamethoxazole under different redox conditions

14C-sulfamethoxazole biotransformation, sorption and mineralization was studied with heterotrophic and autotrophic biomass under aerobic and anoxic conditions, as well as with anaerobic biomass. The 14C-radiolabelled residues distribution in the solid, liquid and gas phases was closely monitored along a total incubation time of 190h. Biotransformation was the main removal mechanism, mineralization and sorption remaining below 5% in all the cases, although the presence of a carbon source exerted a positive effect on the mineralization rate by the aerobic heterotrophic bacteria. In fact, an influence of the type of primary substrate and the redox potential was observed in all cases on the biotransformation and mineralization rates, since an enhancement of the removal rate was observed when an external carbon source was used as a primary substrate under aerobic conditions, while a negligible effect was observed under nitrifying conditions. In the liquid phases collected from all assays, up to three additional peaks corresponding to 14C-radiolabelled residues were detected. The highest concentration was observed under anaerobic conditions, where two radioactive metabolites were detected representing each around 15% of the total applied radioactivity after 180h incubation. One of the metabolites detected under anoxic and anaerobic conditions, is probably resulting from ring cleavage of the isoxazole ring.

Removal of p-nonylphenol isomers using nitrifying sludge in a membrane sequencing batch reactor

The aim of this study was to assess p-nonylphenol removal mechanisms under nitrifying conditions in a bioreactor system. The removal of a technical mixture of p-nonylphenol isomers was evaluated in a membrane sequencing batch reactor without the addition of an organic carbon source in enriched nitrifying sludge. The p-nonylphenol concentration was quantified in the liquid and solid phases to accurately differentiate between biodegradation and sorption mechanisms. The predominant removal mechanism was p-nonylphenol biodegradation (62%), followed by sorption, which resulted in a total removal of 96%. In addition, ammonium-oxidizing microorganisms controlled the biodegradation of p-nonylphenol, and 1,2-benzenedicarboxylic acid, mono(2-ethylhexyl)ester was identified as the main intermediary metabolite. These results suggested that co-metabolic biodegradation by heterotrophic microorganisms is necessary to completely mineralize p-NP isomers under nitrifying conditions. This study provides an important contribution to existing knowledge of nonylphenol biodegradation.

The synergistic effects of dissolved oxygen and pH on N2O production in biological domestic wastewater treatment under nitrifying conditions

Nitrous oxide (N2O) is a potent greenhouse gas, which is produced during nitrifying and denitrifying processes. Some factors and mechanisms affecting N2O emission have been reported in previous literature, but wastewater biological nitrification is accompanied by a dynamic process of dissolved oxygen (DO) consumption and pH reduction, it is more meaningful to study the synergistic effects between DO and pH on N2O production. In this study, the synergistic effects between DO and pH on N2O production were investigated with real domestic wastewater. The results showed that high DO levels and a high pH could improve the oxidation ratio of and the production ratio of while effectively reducing the accumulation ratio of N2O. The was a prerequisite for nitrifier denitrification; when was oxidized completely, there would be no N2O production and an even higher concentration of The pH factor is shown to directly affect N2O emission, although free ammonia and free nitrous acid which changed with pH had no correlation with N2O emission. There were two reasons: (1) pH can influence the flow direction of electrons afforded by NH2OH oxidation; at high pH, electrons were mainly used for combining H+ and O2 (O2 + 4H+ + 4e− = 2H2O), the accumulation of cannot be a result of denitrification, and a higher DO can get more electrons to prefer and (2) was the prerequisite for NH2OH oxidation, since NH2OH oxidation process was the way to provide electrons for nitrifier denitrification.

Nutrient removal via nitrite from reject water and polyhydroxyalkanoate (PHA) storage during nitrifying conditions

AbstractBACKGROUNDNutrient removal via nitrite was investigated in a sequencing batch reactor (SBR) treating reject water produced from the anaerobic digestion of sewage sludge and the subsequent dewatering process. The polyhydroxyalkanoate (PHA) storage capacity of the biomass obtained under nitrifying (nitritation) and non‐nitrifying aerobic conditions was investigated in batch reactors for biomass taken from the SBR.RESULTSIn situ activity tests showed that the nitritation rate was not affected by the type of external organic carbon source that was added (i.e. propionic acid ‐ HPr and sludge fermentation liquid ‐ SFL). In contrast, the specific nitrite uptake rate (sNUR) and the specific phosphate uptake rate (sPUR) via nitrite were much higher when SFL was applied compared with HPr (22.39 ± 1.08 mgN g−1VSS h−1 and 3.41 ± 1.71mgP g−1VSS h−1 when SFL was added compared with 7.80 ± 1.23mgN g−1VSS h−1 and 1.09 ± 0.12mgP g−1VSS h−1 when HPr was added). The majority of phosphorus removal was attributed to the normal growth of biomass rather than the activity of phosphorus accumulating organisms (PAOs). The PHA yield was 0.65–0.67 C‐mmol PHA/C‐mmol short chain fatty acid (SCFA) when nitrification was inhibited, and 0.60–0.63 C‐mmol PHA/C‐mmol SCFA when nitritation also occurred.CONCLUSIONThe PHA yield was not adversely affected under nitrifying conditions, demonstrating that nitritation can be integrated with the production of PHA. © 2014 Society of Chemical Industry

Performance of permeable media rotating reactors used for pretreatment of wastewaters.

The impact of organic loading rate (OLR) on carbonaceous materials and ammonia removal was assessed in bench scale rotating media biofilm reactors treating real wastewater. Media composition influences biofilm structure and therefore performance. Here, plastic mesh, reticulated coarse foam and fine foam media were operated concurrently at OLRs of 15, 35 and 60 g sCOD m(-2)d(-1) in three bench scale shaft mounted advanced reactor technology (SMART) reactors. The sCOD removal rate increased with loading from 6 to 25 g sCOD m(-2)d(-1) (P < 0.001). At 35 g BOD5m(-2)d(-1), more than double the arbitrary OLR limit of normal nitrifying conditions (15 g BOD5m(-2)d(-1)); the removal efficiency of NH(4)-N was 82 ± 5, 27 ± 19 and 39 ± 8% for the mesh, coarse foam and fine foam media, respectively. Increasing the OLR to 35 gm(-2)d(-1) decreased NH(4)-N removal efficiency to 38 ± 6, 21 ± 4 and 21 ± 6%, respectively. The mesh media achieved the highest stable NH(4)(+)-N removal rate of 6.5 ± 1.6 gm(-2)d(-1) at a sCOD loading of 35 g sCOD m(-2)d(-1). Viable bacterial numbers decreased with increasing OLR from 2 × 10(10)-4 × 10(9) cells per ml of biofilm from the low to high loading, suggesting an accumulation of inert non-viable biomass with higher OLR. Increasing the OLR in permeable media is of practical benefit for high rate carbonaceous materials and ammonia removal in the pretreatment of wastewater.

Behavior of nanoscale titanium dioxide in laboratory wastewater treatment plants according to OECD 303 A

The fate assessment of nanomaterials in municipal sewage treatment plants (STP) is a crucial step for their environmental risk assessment and may be assessed by monitoring full scale STP, dosage to medium scale pilot STP or by laboratory testing. For regulatory purposes preferably standardised test protocols such as the OECD guidelines for testing of chemicals should be used. However, these test protocols have not yet been specifically designed for nanoparticles. Therefore, the fate and behavior of a TiO2 nanomaterial (P25, average hydrodynamic diameter <250nm) was investigated in laboratory sewage treatment plants according to the OECD Guideline for the Testing of Chemicals 303 A. It is concluded that this guideline is applicable for the testing of nanomaterials if modifications regarding the dosage, nitrifying conditions, and a characterisation of the nanoparticles in the effluent are applied. A compilation of the cumulative mass balance by comparison of the total dosage added with the amount in the outflow and in the activated sludge is recommended. In this study, the majority of the TiO2 nanomaterial (>95%) was retained in the sewage sludge and only 3–4% was found in the effluent. No effect of the TiO2 nanomaterials on the biodegradation or nitrification was observed.

Wider presence of accelerated chemical chloramine decay in severely nitrifying conditions

Popularity of chloramine has been dampened by nitrification, which is believed to highly accelerate chloramine decay. This can seriously compromise the primary goal of using chloramine as a secondary disinfectant. Our previous laboratory-scale studies showed that highly accelerated chemical decay of chloramine was caused by soluble microbial products (SMPs) released by microbes under severely nitrifying conditions. To understand whether a similar phenomenon exists in full-scale distribution systems, samples were collected from four full-scale systems supplied from different water sources and have been compared with results obtained from laboratory-scale systems. The results verified that the acceleration typical in severely nitrified water is common in full-scale chloraminated systems under severely nitrifying conditions.

Removal and degradation characteristics of quinolone antibiotics in laboratory-scale activated sludge reactors under aerobic, nitrifying and anoxic conditions

This work describes the removal of 6 quinolone antibiotics from wastewaters under different redox conditions (aerobic, nitrifying and anoxic) through batch experiments in laboratory scale activated sludge reactors using mixed liquor from a membrane bioreactor pilot plant (MBR). The main removal pathways for antibiotics from wastewaters involved in each treatment are described. Mass balances indicated that sorption on sludge played a dominating role in the elimination of antibiotics. Sorption potential depended on the redox conditions, being lower in nitrifying (Kd, 414–876 L kg−1) and anoxic (Kd, 471–930 L kg−1) sludge in comparison with aerobic sludge (Kd, 534–1137 L kg−1). Kd was higher for piperazinylic quinolones. Redox conditions also influenced biodegradation, a secondary pathway, which followed first-order kinetics with degradation rates constants ranging from 1.8·10−3 to 8.2·10−3 h−1. Biodegradation rates under anoxic conditions were negligible. The experimental results have also demonstrated much higher removal efficiency by biodegradation (36.2–60.0%) under nitrifying conditions in comparison with aerobic conditions (14.9–43.8%). The addition of allylthiourea, an ammonia monooxygenase inhibitor, inhibited nitrification completely and reduced significantly the biodegradation of target antibiotics (16.5–29.3%). The residual biodegradation in the presence of allylthiourea may be due to the activity of heterotrophs in the enriched nitrifier culture. The removal of the selected antibiotics under the studied redox conditions depended significantly on the bacteria composition of the sludge. These results suggest that despite the known persistence of this group of antibiotics it is possible to enhance their degradation using nitrifying conditions, which at adequate working conditions as high SRT, typical in MBR, become a promising alternative for improving quinolones removal from environment.

Major mechanism(s) of chloramine decay in rechloraminated laboratory scale system waters

abstract Traditionally it is believed that nitrification was solely responsible for the widely observed chloramine loss under nitrifying conditions. On the contrary, recent results have shown that an unidentified agent (soluble microbial products or modified natural organic matter) chemically accelerates chloramine decay in rechloraminated nitrifying samples which were filtered to eliminate microbes. However, how those agents accelerate chloramine decay is not known. Mildly and severely nitrified samples were collected from a laboratory scale system and microbes were separated through filtration and then rechloraminated. To understand the mechanism, simple stoichiometry was employed. In all samples, rechloramination induced ammonia loss possibly by auto-decomposition, especially in the initial stages. In severely nitrified samples, accelerated auto-decomposition and nitrite oxidation were found to be the major mechanisms chemically accelerating the chloramine loss indicating that the agent did not demand ...

Influence of nitrifying conditions on the biodegradation and sorption of emerging micropollutants

High biodegradation efficiencies of different emerging micropollutants were obtained with nitrifying activated sludge (NAS) working at high nitrogen loading rates (NLR), that boosted the development of biomass with high nitrifying activities (>1 g N-NH4+/g VSS d). Come-tabolic biodegradation seemed to be responsible for the removal of most compounds due to the action of the ammonium monooxygenase enzyme. NAS showed a different affinity for each compound, probably due to steric hindrance, activation energy limitations or the presence of specific functional groups. Increasing loading rates of micropollutants were removed at shorter hydraulic retention times, although the biodegradation efficiencies of compounds with slow/intermediate kinetics, such as fluoxetine, erythromycin, roxithromycin and trimethoprim, diminished due to kinetic and/or stoichiometric limitations. Solids retention time, always above the minimum to avoid the washout of nitrifiers, did not enhance the biodegradation of any of the selected compounds, with the exception of diclofenac. Regarding sorption, the solid–liquid distribution coefficients (Kd) obtained in NAS were very similar to those found in conventional activated sludge by other authors. No correlation between Kd values and any of the operational parameters was found for the selected substances.