Experimental and modeling study on removal of pharmaceutically active compounds in rotating biological contactors

Optimization of operational parameters using RSM, ANN, and SVM in membrane integrated with rotating biological contactor

Membrane fouling is a critical bottleneck to the widespread adoption of membrane separation processes. It diminishes the membrane permeability and results in high operational energy costs. The current study presents optimizing the operating parameters of a novel rotating biological contactor (RBC) integrated with an external membrane (RBC + ME) that combines membrane technology with an RBC. In the RBC + ME, the membrane panel is placed external to the bioreactor. Response surface methodology (RSM) is applied to optimize the membrane permeability through three operating parameters (hydraulic retention time (HRT), rotational disk speed, and sludge retention time (SRT)). The artificial neural networks (ANN) and support vector machine (SVM) are implemented to depict the statistical modelling approach using experimental data sets. The results showed that all three operating parameters contribute significantly to the performance of the bioreactor. RSM revealed an optimum value of 40.7 rpm disk rotational speed, 18 h HRT and 12.4 d SRT, respectively. An ANN model with ten hidden layers provides the highest R2 value, while the SVM model with the Bayesian optimizer provides the highest R2. RSM, ANN, and SVM models reveal the highest R-square values of 0.97, 0.99, and 0.99, respectively. Machine learning techniques help predict the model based on the experimental results and training data sets.

Elimination of recalcitrant micropollutants by medium pressure UV-catalyzed bioelectrochemical advanced oxidation process: Influencing factors, transformation pathway and toxicity assessment

Bio-electro-Fenton (BEF) processes have been widely studied in recent years to remove recalcitrant micropollutants from wastewater. Though promising, it still faces the critical challenge of residual iron and iron sludge in the treated effluent. Thus, an innovative medium-pressure ultraviolet-catalyzed bio-electrochemical system (MUBEC), in which medium-pressure ultraviolet was employed as an alternative to iron for in-situ H₂O₂ activation, was developed for the removal of recalcitrant micropollutants. The influence of operating parameters, including initial catholyte pH, cathodic aeration rate, and input voltage, on the system performance, was explored. Results indicated that complete reduction of 10 mg L^-1 of model micro-pollutants ibuprofen (IBU) and carbamazepine (CBZ) was achieved at pH 3, with an aeration rate of 1 mL min^-1 and a voltage of 0.3 V, following pseudo-first-order kinetics. Moreover, potential transformation pathways and the associated intermediates during the degradation were deduced and detected, respectively. Thus, the MUBEC system shows the potential for the efficient and cost-effective degradation of recalcitrant micropollutants from wastewater.

Microalgal-based removal of contaminants of emerging concern

The presence of contaminants of emerging concern (CECs) in the environment has been recognized as a worldwide concern. In particular, water pollution by CECs is becoming a major global problem, which requires ongoing evaluation of water resources policies at all levels and the use of effective and innovative wastewaters treatment processes for their removal. Microalgae have been increasingly recognized as relevant for wastewater polishing, including CECs removal. These microorganisms are commonly cultivated in suspension. However, the use of planktonic microalgae for wastewater treatment has limitations in terms of microbiological contamination, process effectiveness and sustainability. The use of consortia of microalgae and bacteria represents a significant advance for sustainable wastewater polishing, particularly when the microorganisms are associated as biofilms. These immobilized mixed cultures can overcome the limitations of suspended-microalgae systems and improve the performance of the involved species for CECs removal. In addition, microalgae-bacteria based systems can offer a relevant combined effect for CECs removal and biomass production enhancement. This study reviews the advantages and advances on the use of microalgae for wastewater treatment, highlighting the potential on the use of microalgae-bacteria biofilms for CECs removal and the further biomass valorisation for third-generation biofuel production.

Treatment of mustard tuber wastewater (MTWW) using a pilot-scale packed cage rotating biological contactor system: process modeling and optimization

The water quality range for wastewater treatment projects in the food processing industry changes constantly. To fully understand the threshold for pollutant removal with the lowest possible energy consumption, the relationship between pollutant removal and wastewater treatment conditions was established using response surface methodology (RSM). The optimum conditions for total COD, TN, and NH₃-N removal from saline mustard tuber wastewater (MTWW) with a packed cage rotating biological contactor (RBC) system were investigated by experiments based on a Box-Behnken design (BBD). The independent variables were organic load (ORL), rotational disk velocity (RDV), and immersion rate (IR). Parameters of COD, TN, and NH₃-N removal efficiency were selected as responses. The optimal conditions for the best COD, TN, and NH₃-N removal efficiency with the lowest energy consumption were found to be at an ORL of 26.71 kg/day, a RDV of 1.62 rpm (7.62 m/s), and an IR of 46%. After the optimization, the energy cost was evaluated by coupling energy performance indicators with organic pollution efficiencies to be the highest class of performance. This research demonstrates that the suggested models have a good predicting and fitting ability in interrelations between the pollutant removal and process parameters of the packed cage RBC system treating saline MTWW.

An innovative microbial electrochemical ultraviolet photolysis cell (MEUC) for efficient degradation of carbamazepine

Discharge of recalcitrant pharmaceuticals into aquatic environments can lead to serious negative environmental effects. While traditional wastewater treatment plants (WWTPs) are efficient for a wide range of non-toxic pollutants (i.e. ammonia), some wastewater streams contain recalcitrant toxic trace micropollutants such as pharmaceuticals that cannot be removed by the treatment processes that are typically employed in common WWTPs. Herein, an innovative 20 L microbial electrochemical ultraviolet photolysis cell (MEUC) was developed for the first time by the integration of a UV irradiation and a bioelectrochemical system, which exhibited efficient treatment of carbamazepine-a model pharmaceutical compound. Notably, neither the UV irradiation nor the bioelectrochemical system alone could effectively eliminate carbamazepine. The effect of operational parameters including applied voltage, cathodic aeration rate, UV intensity, and hydraulic retention time were evaluated. The obtained results elucidated that the degradation of carbamazepine was consistent with pseudo-first-order reaction kinetics, and required a lower energy input than traditional advanced oxidation processes. Five main transformation products were identified, and probable transformation pathways were established. Furthermore, the eco-toxicity as tested by Vibrio fischeri showed no significant bioluminescence inhibition by the treated carbamazepine effluent. Finally, the MEUC system was further tested with a real wastewater matrix, which again exhibited effective removal of carbamazepine. This paper provides a proof-of-concept verification of the novel MEUC system, which contributes insight for the subsequent vigorous development of the application of such efficient and cost-effective technologies for the treatment of trace pharmaceuticals wastewater.

Un-steady state modeling for free cyanide removal and biofilm growth in a RBC batch process

Biofilm growth and free cyanide biological removal from gold mine wastewater were modeled and simulated using a bench-scale rotating biological contactor (RBC). Eight batch cultures were run in three independent compartments (1.7 L, each) of the RBC. The system worked under the following conditions: [CN_i^-] = 0.3 g/L, pH = 10.5 ± 0.5, T = 20 ± 5 °C, ω =5 rpm, and 40.5 % of disc submersion. During each culture, biofilm thickness, biomass, and free cyanide concentration in the liquid were quantified. Subsequently, μ_max, [Formula: see text] , [Formula: see text] were determined using experimental data to later model and simulate the biofilm thickness and free cyanide biological removal with Wolfram Mathematica software. After the experiments, free cyanide biological removal was 96.33 % after three days, and maximum biofilm thickness was 0.0292 cm in the 16th day. Moreover, biofilm growth and free cyanide consumption models were adjusted to the experimental data with r² = 0.90 and r² = 0.99. Also, there was an equivalent error of 7.89 and 7.38 and a standard deviation of 10.89 % and 10.17 %, between the models and their experimental data, respectively. Finally, the proposed models will allow improvement of reactor operation and its design.

Are pharmaceuticals removal and membrane fouling in electromembrane bioreactor affected by current density?

Pharmaceutical active compounds (PhACs) have been detected at significant concentrations in various natural and artificial aquatic environments. In this study, electro membrane bioreactor (eMBR) technology was used to treat simulated municipal wastewater containing widely-used pharmaceuticals namely amoxicillin (AMX), diclofenac (DCF) and carbamazepine (CBZ). The effects of varying current density on the removal of PhACs (AMX, DCF and CBZ) and conventional pollutants (chemical oxygen demand (COD), dissolved organic carbon (DOC), humic substances, ammonia nitrogen (NH₄-N), nitrate nitrogen (NO₃-N) and orthophosphate (PO₄-P) species) were examined. High COD and DOC removal efficiencies (~100%) were obtained in all the experimental runs regardless of applied current density. In contrast, enhanced removal efficiencies for AMX, DCF and CBZ were achieved at high current densities. Membrane fouling rate in eMBR with respect to conventional MBR was reduced by 24, 44 and 45% at current densities of 0.3, 0.5 and 1.15 mA/cm², respectively. The mechanism for pharmaceutical removal in this study proceeded by: (1) charge neutralization between negatively-charged pharmaceutical compounds and positive electro-generated aluminium coagulants to form larger particles and (2) size exclusion by membrane filtration.

Elimination of Micropollutants in Activated Sludge Reactors with a Special Focus on the Effect of Biomass Concentration

This study aimed to investigate the effects of sludge retention time (SRT), hydraulic retention time (HRT), and biomass concentration (CTSS) in activated sludge systems on removal of various micropollutants (MPs), covering a wide spectrum of biodegradability. The influence of biomass concentration on the classical pseudo-first-order rate constant was verified. Results showed that the removal rate constants were affected by both the HRT and SRT. The enhancement of the SRT increased the removal of all the MPs except for two macrolide antibiotics. Application of a higher HRT also improved MP removal, as was expected from the measured removal rate constants. More interesting, our results indicated that, logically, the increase of biomass concentration (expressed as total suspended solids CTSS) from 3 to 5 gTSS L−1 significantly enhanced the removal rate of the highly and moderately degradable compounds. Conversely, a further increase to 8 gTSS L−1 produced only an unexpected moderate effect, showing that the rate was not proportional to biomass concentration, contrary to what is generally postulated. Therefore, the use of classical kinetic models is questionable, since they do not cover the entire range of boundary conditions in activated sludge systems. This work opens new research paths and suggests potential improvements to processes.

A Review on Biological Processes for Pharmaceuticals Wastes Abatement-A Growing Threat to Modern Society

Over the last decades, the production and consumption of pharmaceuticals and health care products grew manifold, allowing an increase in life expectancy and a better life quality for humans and animals, in general. However, the growth in pharmaceuticals production and consumption comes with an increase in waste production, which creates a number of challenges as well as opportunities for the waste management industries. The conventional current technologies used to treat effluents have shown to be inefficient to remove or just to reduce the concentrations of these types of pollutants to the legal limits. The present review provides a thorough state-of-the-art overview on the use of biological processes in the rehabilitation of ecosystems contaminated with the pharmaceutical compounds most commonly detected in the environment and eventually more studied by the scientific community. Among the different biological processes, special attention is given to biosorption and biodegradation.

A microbial electro-fenton cell for removing carbamazepine in wastewater with electricity output

High electrical energy is required for the electro-Fenton process to remove pharmaceuticals and personal care products (PPCPs) in wastewater. The aim of this study was to develop a novel and more cost-effective process, specifically a microbial electro-Fenton cell (MeFC), for treating PPCPs in wastewater. Acetylene black was selected as the catalyst for H₂O₂ electrogeneration and Fe-Mn binary oxide for hydroxyl radical production. In addition to lowering energy needs, the MeFC produced a maximum power density of 112 ± 11 mW/m² with 1 g/L acetate as a representative substrate and 10 mg/L carbamazepine (CBZ) as a typical PPCP. Comparing with electro-Fenton process, the CBZ removal in the MeFC was 38% higher within 24 h operation (90% vs. 62%). Furthermore, the CBZ removal rate in the MeFC was 10-100 times faster than that in other biological treatment processes. Such enhanced degradation of CBZ in the MeFC was attributed to the synergistic reactions between radical oxidation of CBZ and biodegradation of degradative intermediates. The MeFC provides a promising method to remove PPCPs from wastewater coupling with efficient removal of other biodegradable organics.

Toxicity assessment of pharmaceutical compounds on mixed culture from activated sludge using respirometric technique: The role of microbial community structure

Micropollutants of emerging concern such as pharmaceuticals can significantly affect the performance of secondary biological processes in wastewater treatment plants. The present study is aimed to evaluate the toxicity and inhibition of three pharmaceutical compounds (caffeine, sulfamethoxazole and carbamazepine) on two cultures of microbial consortia enriched from wastewater aerobic activated sludge. One of them was acclimated to pharmaceuticals and the other was non-acclimated as control bioassay. The toxic and inhibitory effects on these cultures were assessed by respirometric tests through the oxygen uptake rate as an indicator of their capacity to degrade a readily available carbon source. Higher values of toxicity and inhibition of pharmaceutical compounds were observed for the control culture as compared to the acclimated one. Sulfamethoxazole and carbamazepine exhibited higher toxicity and inhibition effects than caffeine in both acclimated and control cultures. The microbial diversity of the two cultures was also studied. The composition of microbial community of acclimated and control cultures, was determined by targeting the 16S ribosomal RNA gene. It was observed that Proteobacteria was the most abundant phylum, with Gammaproteobacteria dominating both cultures. Control culture was dominated by Gammaproteobacteria and mostly by the genera Pseudomonas and Sodalis, which belong to common families present in wastewater. Results suggested that the acclimated culture to the three pharmaceuticals was mostly comprised of the extremely multiresistant genera Escherichia-Shigella (38%) of Gammaproteobacteria, resulting to higher resistance as compared to the control culture (Escherichia-Shigella, 7%). Finally, the microbial structure of the microorganisms present in a real bioreactor, which was initially seeded with the acclimated culture and fed in a continuous mode with the selected pharmaceuticals, was also analyzed. The continuous loading of pharmaceuticals in the bioreactor affected its microbial diversity, leading to the dominance of Betaproteobacteria and to the resistant genus Rhizobium of Alphaproteobacteria.

Treating organic cyanide-containing groundwater by immobilization of a nitrile-degrading bacterium with a biofilm-forming bacterium using fluidized bed reactors

Organic cyanide are widely used as an ingredient in the production of plastics, synthetic rubbers, polymers, pharmaceuticals and pesticides or used in laboratories and industries as solvents. Although nitrile-containing wastewater is subjected to primary and secondary treatments, residual nitriles may slowly seep and further migrate through groundwater, resulting in the micropollution of groundwater by organic pollutants. In this study, water samples were collected from different study areas in North China during a period of 3y (from 2013 to 2015) and analyzed to evaluate organic cyanide (CN^-) contamination in groundwater. Three parallel lab-scale fluidized bed reactors (FBRs) were tested for their ability to remove organic cyanide from groundwater. The organic cyanide concentration in groundwater increased significantly (P < 0.05) from 2013 to 2015. With an optimal hydraulic residence time (HRT) of 54 min, reactor R3 (inoculated with a nitrile-degrading bacterium, BX2, and a biofilm-forming bacterium, M1) effectively removed 99.8% of CN^- under steady operation, which was better than that of other reactors. Short-term shutdowns of FBRs had no serious effects on the efficiency of treating organic cyanide. This work demonstrated that the biofilm-forming bacterium could facilitate the fixation of nitrile-degrading bacterium and enhance the efficiency of removing organic cyanide from groundwater.

17α-Ethinylestradiol and 17β-estradiol removal from a secondary urban wastewater using an RBC treatment system

The presence of micropollutants that include endocrine-disrupting compounds (EDC) in aquatic environments is currently one of the most relevant aspects of water quality due to their adverse effects on aquatic organisms and human health. From the several categories of EDC, 17β-estradiol (E2) is a natural hormone, which is prevalent in vertebrates, associated with the female reproductive system and maintenance of the sexual characters. 17α-Ethinylestradiol (EE2) is a synthetic hormone produced from the natural hormone E2 and is an essential component of oral contraceptives. These compounds are susceptible to bioconcentration and have high potential to bioaccumulation. Wastewater treatment plants are the main point source of E2 and EE2 into aquatic environments, but conventional wastewater treatment systems are not specifically designed for steroid removal. To overcome this problem, biological tertiary treatment may be a solution for the removal of emergent pollutants such as E2 and EE2. The main purpose of the present study is to provide a solution based on the optimization of a rotating biological contactor system to remove estrogens, specifically E2 and EE2, and to quantify their removal efficiency on different matrices, namely real wastewater and different synthetic wastewaters. All assays presented viable removal efficiencies for compound E2 with values always above 50%; real wastewater yielded the highest removal efficiencies. EE2 removal had better removal efficiencies with synthetic wastewater as feed solution, with removals above 15%, whereas the removal efficiency with real wastewater was inexistent.

Diffusion and sorption of organic micropollutants in biofilms with varying thicknesses

Solid-liquid partitioning is one of the main fate processes determining the removal of micropollutants in wastewater. Little is known on the sorption of micropollutants in biofilms, where molecular diffusion may significantly influence partitioning kinetics. In this study, the diffusion and the sorption of 23 micropollutants were investigated in novel moving bed biofilm reactor (MBBR) carriers with controlled biofilm thickness (50, 200 and 500 μm) using targeted batch experiments (initial concentration = 1 μg L^-1, for X-ray contrast media 15 μg L^-1) and mathematical modelling. We assessed the influence of biofilm thickness and density on the dimensionless effective diffusivity coefficient f (equal to the biofilm-to-aqueous diffusivity ratio) and the distribution coefficient K_d,eq (L g^-1). Sorption was significant only for eight positively charged micropollutants (atenolol, metoprolol, propranolol, citalopram, venlafaxine, erythromycin, clarithromycin and roxithromycin), revealing the importance of electrostatic interactions with solids. Sorption equilibria were likely not reached within the duration of batch experiments (4 h), particularly for the thickest biofilm, requiring the calculation of the distribution coefficient K_d,eq based on the approximation of the asymptotic equilibrium concentration (t > 4 h). K_d,eq values increased with increasing biofilm thickness for all sorptive micropollutants (except atenolol), possibly due to higher porosity and accessible surface area in the thickest biofilm. Positive correlations between K_d,eq and micropollutant properties (polarity and molecular size descriptors) were identified but not for all biofilm thicknesses, thus confirming the challenge of improving predictive sorption models for positively charged compounds. A diffusion-sorption model was developed and calibrated against experimental data, and estimated f values also increased with increasing biofilm thickness. This indicates that diffusion in thin biofilms may be strongly limited (f ≪ 0.1) by the high biomass density (reduced porosity).

Fate and mass balance of contaminants of emerging concern during wastewater treatment determined using the fractionated approach

Contaminants of emerging concern (CECs) are often poorly removed from wastewater using conventional treatment technologies and there is limited understanding of their fate during treatment. Inappropriate sampling strategies lead to inaccuracies in estimating removals of CECs. In this study, we used the "fractionated approach" that accounts for the residence time distribution (RTD) in treatment units to investigate the fate of 26 target CECs in a municipal wastewater treatment plant (WWTP) that includes primary, secondary and tertiary treatment steps. Prior hydraulic calibration of each treatment unit was performed. Wastewater and sludge samples were collected at different locations along the treatment train and the concentrations of target CECs were measured by liquid chromatography mass spectrometry. The most substantial aqueous removal occurred during activated sludge treatment (up to 99%). Removals were <50% in the primary clarifier and tertiary rotating biological contactors (RBCs) and up to 70% by sand filtration. Mass balance calculations demonstrated that (bio)degradation accounted for up to 50% of the removal in the primary clarifier and 100% in activated sludge. Removal by sorption to primary and secondary sludge was minimal for most CECs. Analysis of the selected metabolites demonstrated that negative removals obtained could be explained by transformations between the parent compound and their metabolites. This study contributes to the growing literature by applying the fractionated approach to calculate removal of different types of CECs across each wastewater treatment step. An additional level of understanding of the fate of CECs was provided by mass balance calculations in primary and secondary treatments.

Biological removal of pharmaceutical compounds using white-rot fungi with concomitant FAME production of the residual biomass

The efficiency of two white-rot fungi (WRF), Trametes versicolor and Ganoderma lucidum, to eliminate thirteen pharmaceutical pollutants with concomitant biodiesel production from the accumulating lipid content after treatment, was examined. The removal efficiency was studied using both individual and combined strains. The results of individual and combined strains showed a total removal (100%) of diclofenac (DCF), gemfibrozil (GFZ), ibuprofen (IBP), progesterone (PGT) and ranitidine (RNT). Lower removals were achieved for 4-acetamidoantipyrin (AAA), clofibric acid (ACF), atenolol (ATN), caffeine (CFN), carbamazepine (CZP), hydrochlorothiazide (HCT), sulfamethoxazole (SMX) and sulpiride (SPD), although the combination of both strains enhanced the system's efficiency, with removals ranging from 15 to 41%. This increase of the removal efficiency when combining both strains was attributed to the interactions developed between them (i.e., competition). Results from enzymatic and cytochrome P450 examination suggested that both extracellular (laccase, MnP, LiP) and intracellular oxidation mechanisms participate in the biological removal of pharmaceuticals. On the other hand, the "green" potential of the fungal sludge generated during the biological removal process was assessed for biodiesel production by means of one-step direct (in-situ) transformation. This process consists of the simultaneous extraction and conversion of lipids contained in the sludge by catalytic esterification/transesterification using a robust acid heterogeneous Zr-SBA-15 catalyst. This catalytic system provided conversions close to 80% of the saponifiable fraction (including free fatty acids and glycerides) in the presence of high amount of impurities. The overall weight FAME yield, based on the initial dried mass, was close to 30% for both strains.

Assessment of the mechanisms involved in the removal of emerging contaminants by microalgae from wastewater: a laboratory scale study

Aerated batch reactors (2.5L) fed either with urban or synthetic wastewater were inoculated with microalgae (dominated by Chlorella sp. and Scenedesmus sp.) to remove caffeine, ibuprofen, galaxolide, tributyl phosphate, 4-octylphenol, tris(2-chloroethyl) phosphate and carbamazepine for 10 incubation days. Non-aerated and darkness reactors were used as controls. Microalgae grew at a rate of 0.25 d(-1) with the complete removal of N-NH4 during the course of the experiment. After 10 incubation days, up to 99% of the microcontaminants with a Henry's law constant higher than 3 10(-1) Pa m(3) mol(-1) (i.e., 4-octylphenol, galaxolide, and tributyl phosphate) were removed by volatilization due to the effect of air stripping. Whereas biodegradation was effective for removing ibuprofen and caffeine, carbamazepine and tris(2-chloroethyl) phosphate behaved as recalcitrant compounds. The use of microalgae was proved to be relevant for increasing the biodegradation removal efficiency of ibuprofen by 40% and reducing the lag phase of caffeine by 3 days. Moreover, the enantioselective biodegradation of S-ibuprofen suggested a biotic prevalent removal process, which was supported by the identification of carboxy-ibuprofen and hydroxy-ibuprofen. The results from microalgae reactors fed with synthetic wastewater showed no clear evidences of microalgae uptake of any of the studied microcontaminants.

A comparative assessment of intensive and extensive wastewater treatment technologies for removing emerging contaminants in small communities

Ecosystem pollution due to the lack of or inefficient wastewater treatment coverage in small communities is still a matter of great concern, even in developed countries. This study assesses the seasonal performance of 4 different full-scale wastewater technologies that have been used in small communities (<2000 population equivalent) for more than 10 years in terms of emerging contaminant (EC), chemical oxygen demand (COD), total suspended solids (TSS) and NH4-N removal efficiency. The studied technologies, which were selected due to their widespread use, included two intensive treatment systems (an extended aeration system (AS) and a rotating biological contactor (RBC)) and two extensive treatment systems (a constructed wetland (CW) and a waste stabilization pond (WSP)), all located in north-eastern Spain. The studied compounds belonged to the groups of pharmaceuticals, sunscreen compounds, fragrances, antiseptics, flame retardants, surfactants, pesticides and plasticizers. The 25 ECs occurred in wastewater at concentrations ranging from undetectable to 80 μg L(-1). The average removal efficiency was 42% for the CW, 62% for the AS, 63% for the RBC and 82% for the WSP. All the technologies except the WSP system showed seasonal variability in the removal of ECs. The ecotoxicological assessment study revealed that, whilst all the technologies were capable of decreasing the aquatic risk, only the WSP yielded no risk in both seasons.

Sorption and biodegradation of selected benzotriazoles and hydroxybenzothiazole in activated sludge and estimation of their fate during wastewater treatment

Biodegradation of benzotriazole (BTR), 5-chlorobenzotriazole (CBTR), xylytriazole (XTR), 4-methyl-1H-benzotriazole (4TTR), 5-methy-1H-lbenzotriazole (5TTR) and 2-hydroxybenzothiazole (OHBTH) was studied in activated sludge batch experiments under aerobic and anoxic conditions, presence of organic substrate and different sludge residence times (SRTs). Their sludge-water distribution coefficients were also calculated in sorption experiments and ranged between 87 and 220 L kg(-1). Significant biodegradation of BTR, CBTR, XTR and OHBTH was observed in all biotic experiments. Half-life values ranged between 23 and 45 h (BTR), 18 and 47 h (CBTR), 14 and 26 h (XTR), 6.5 and 24 h (OHBTH). The addition of substrate did not suppress biodegradation kinetics; whereas in some cases accelerated biodegradation of microcontaminants. Except for CBTR, no effect of SRT on biodegradation constants was observed. Prediction of micropollutants removal in Sewage Treatment Plants (STPs) indicated that they will be partially removed, mainly due to aerobic biodegradation. Higher removal is expected at STPs operating at higher SRT and higher suspended solids concentrations.