Attached Growth Reactors Research Articles

Decolorization and toxicity evaluation of simulated textile effluent via natural microbial consortia in attached growth reactors

Textile wastewater is heterogeneous in nature with multiple types of dyes and other chemicals. Considering this point, attached growth bioreactors were constructed, using sludge (SD), alkalophilic (AK), and thermophilic (TH) bacterial consortia to develop an effective dye biodegradation system. Simulated dye wastewater, containing a 50 ppm mixture of three reactive azo dyes, viz. Reactive Blue (RB 221), Reactive Yellow (RY 145), and Reactive Red (RR 195) were treated under batch mode operation for up to 192 h. Overall, the color removal efficiency of the reactors varied from 85 to 94 % in 192 h. The thermophilic consortium achieved maximum decolorization (93.5 %), operated at 50 °C, while the alkalophilic consortium attained maximum COD reduction (93.0 %). Nitrites and nitrates were reduced to (14.7 – 79.3) – (84 – 239.4) mg/L, while sulfates ranged from 624.7 – 1003 mg/L. In addition, scanning electron microscopy (SEM) analysis revealed the biofilm community structure, indicating diverse bacterial interactions among each consortium. The biodegradation of dyes was further confirmed through Fourier-transform infrared spectroscopy (FTIR). Phytotoxicity and cytotoxicity analyses revealed that the dye mixture became non-toxic after treatment. This study outlines that natural microbial consortia are efficient dye decolorizers and confers the possibility of using microbial consortia for upscale biological treatment of dyeing effluents.

Simultaneous partial Nitrification, ANAMMOX and denitrification (SNAD) – A review of critical operating parameters and reactor configurations

• Critical operational parameters influencing the SNAD process are analyzed. • Performance of different reactor configurations for SNAD application is evaluated. • Research gaps for full scale applications of SNAD is discussed. Nitrogen removal is an important aspect of wastewater treatment. Conventional biological nitrogen removal process is widely adopted for its reliable and effective nitrogen removal. However, its high operational and capital costs have led to the development of more cost-effective solutions. The discovery of Anaerobic ammonium oxidation (ANAMMOX) bacteria and its integration with shortcut nitrogen removal processes has proved to be a sustainable solution. However, the requirement of carbon-free feed and discharge of high nitrate concentration in the effluent limit their practical applications. To overcome these challenges, an innovative nitrogen removal process, the simultaneous partial nitrification, anammox and denitrification (SNAD) process, has been studied. SNAD involves a synergistic relationship among Ammonia oxidizing bacteria (AOB), ANAMMOX and denitrifers for high nitrogen removal efficiency. This study provides a focused review of the recent developments in SNAD process, specifically covering the critical process parameters for efficient operation and different reactor configurations. A detailed assessment of the process parameters such as carbon/nitrogen ratio, substrate type, free ammonia, free nitrous acid and hydraulic retention time is provided to identify the factors affecting the SNAD efficiency and required control measures. A comparison of different suspended and attached growth reactor configurations is also provided to understand the process reliability and potential for full-scale operation. This review will provide guidance for future engineering applications for high efficiency and cost-effective nitrogen removal via SNAD process.

Enhanced Pb(II) removal from water using conductive carbonaceous nanomaterials as bacterial scaffolds: An experimental and modelling approach

This study investigated the abilities of electrochemically active bacteria (EAB) as bio-catalysts for Pb(II) bioreduction in an attached growth reactor. Electrically conductive carbon nanofibers (CNF) were used as bacterial scaffolds to facilitate electron transfer between EAB and Pb(II). Our results demonstrated that the CNF attached growth reactor can remove > 80% and > 90% of Pb(II) from solution at 0.5 mg/L and 5.0 mg/L concentrations, respectively, and maintained Pb(II) levels < 0.10 mg/L over repeated Pb(II) dosages dosed at all concentrations. Experimental measurements by SEM-EDX and ICP-OES provided evidence that Pb(II) was reduced to Pb0, suggesting that Pb(II) was adsorbed onto CNFs, and subsequently bioreduced. Numerical modelling was used to estimate Pb(II) concentrations along the CNFs via capturing Pb(II)’s diffusive transport, and the removal mechanisms governed by EAB and CNF adsorption. The model simulation results demonstrated that Pb(II) bioreduction was dominant in the reactor and the significance of Monod kinetics, biofilm thickness and Pb(II) dosage concentration on its removal. This study is the first to prove EAB’s ability to treat Pb(II) from contaminated waters in an attached growth configuration. The findings here demonstrate that CNFs can boost biological treatment efficacies in wastewater and/or water treatment to meet stringent water guidelines.

A kinetic study on the nitrification process in the upflow submerged biofilter reactor

ABSTRACT In extent of this study, ammonium removal from wastewater through biological nitrification process was performed in upflow biofilm reactors. The effects of hydraulic retention time (HRT) and nitrogen loading rate (NLR) on the nitrification process were investigated. For the nitrification process, the optimum HRT and NLR were determined to be 80 hr and 0.044 kg/m3.day, respectively. It is observed that the efficiency increased from 53% to 96% along with the increase in HRT from 22 hr to 80 hr and the decrease in NLR from 0.165 kg/m3.day to 0.044 kg/m3.day.The substrate consumption kinetics were studied in the attached growth reactor, and the Monod kinetic model, first-order kinetic model, modified Stover-Kincannon and Grau second-order kinetic models were examined. For the substrate consumption kinetic study, experimental studies were performed at 125, 150, 175, 200, 225 mg NH4-N/L substrate concentrations and 62 hr at HRT during the nitrification process. As a result of the considering kinetic studies, it was determined that the kinetic study was suitable for the modified Stover-Kincannon kinetic model that had the highest coefficient of regression by 0.997 and when the effluent NH4-N concentrations and NH4-N removal efficiencies calculated using kinetic models were examined, it was observed that the results closest to the experimental results (4.5, 10.1, 19.7, 26.2 and 42.3 mg NH4-N/L) were obtained through the modified Stover-Kincannon model (4.16, 10.71, 18.92, 28.12 and 39.51 mg NH4-N/L).

Impacts of ammonia loading and biofilm age on the prevalence of nitrogen-cycling microorganisms in a full-scale submerged attached-growth reactor.

This study reports the impacts of seasonal ammonia load changes and biofilm age on the quantity of biomass and on the prevalence of ammonia- and nitrite-metabolizing organisms within a submerged attached-growth reactor (SAGR™) following lagoon treatment. Ammonia (NH3 ) loadings (0.12-3.17kg/d) in the primary SAGR were measured over 223days from May to December in 2017. Adjustment of the wastewater flow path on September 1 successfully increased NH3 loading to the primary SAGR, which subsequently caused reactor biomass to increase. The NH3 removal rate in October (0.5kg/d) was greater than rates in June and July (0.3 and 0.2kg/d) despite a water temperature decrease from >24 to 15.6°C. This elevated removal rate in October, and the sustained removal rate in December (0.4kg/d, 5.3°C) were associated with a measured increase in microbial biomass. The relative abundance of the anammox organism C.Brocadia was 5 times greater in the mature biofilm after 686days of growth, and the genus Pseudomonas increased sevenfold. The presence of Pseudomonas, which contains denitrifying species, and anammox suggests a high potential for removal of total nitrogen in SAGRs. PRACTITIONER POINTS: Pseudomonas prevalence and the presence of anammox suggest a high potential for total nitrogen removal in mature SAGR biofilms. The abundance of the anammox microorganism C.Brocadia was greater after 686days of biofilm growth compared with 33days. Simple operational changes can increase biomass in the SAGR to maintain, or even increase, NH3 transformation rates during cold weather.

Real municipal wastewater treatment using simultaneous pre and post-ozonation combined biological attached growth reactor: Energy consumption assessment

In this study, simultaneous pre and post-ozonation processes combined biological attached growth reactor were used in order to investigate the removal of COD, ammonium and total coliforms from real municipal wastewater. The biological process was carried out in a fixed bed aerobic bioreactor with an aeration rate of 6 L/min and hydraulic retention time of 5 h. The ozonation process was performed simultaneously in pre-ozonation and post-ozonation reactors, with 1 g/h ozone mass flow within 30 min every 8 h. The results showed that complete ammonium removal and 94 % COD removal were obtained. Also, total coliforms in the final effluent were measured to be about 0.51 MPN/mL. The analysis of energy consumption showed that the ozonation process was the dominant energy consumption source. The combination of fixed bed bioreactor and ozonation process showed a promising technology for the treatment of real municipal wastewater.

Biotreatment of Poultry Waste Coupled with Biodiesel Production Using Suspended and Attached Growth Microalgal-Based Systems

Poultry litter extract (PLE) was treated using a microbial consortium dominated by the filamentous cyanobacterium Leptolyngbya sp. in synergy with heterotrophic microorganisms of the poultry waste. Laboratory- and pilot-scale experiments were conducted under aerobic conditions using suspended and attached growth photobioreactors. Different dilutions of the extract were performed, leading to different initial pollutant (nitrogen, phosphorus, dissolved chemical oxygen demand (d-COD), total sugars) concentrations. Significant nutrient removal rates, biomass productivity, and maximum lipid production were determined for all the systems examined. Higher d-COD, nitrogen, phosphorus, and total sugars removal were recorded in the attached growth reactors in both laboratory- (up to 94.0%, 88.2%, 97.4%, and 79.3%, respectively) and pilot-scale experiments (up to 82.0%, 69.4%, 81.0%, and 83.8%, respectively). High total biomass productivities were also recorded in the pilot-scale attached growth experiments (up to 335.3 mg L−1d−1). The produced biomass contained up to 19.6% lipids (w/w) on a dry weight basis, while the saturated and monounsaturated fatty acids accounted for more than 70% of the total fatty acids, indicating a potential biodiesel production system. We conclude that the processing systems developed in this work can efficiently treat PLE and simultaneously produce lipids suitable as feedstock in the biodiesel manufacture.

Evaluation of cold-weather wastewater nitrification technology for removal of polar chemicals of emerging concern from rural Manitoba wastewaters

Aerated lagoons, typically used by small communities, often provide limited removal of wastewater nutrients. Given increasingly stringent wastewater standards, it is imperative that effective, but economical and easy-to-operate, treatment technologies be developed. The Submerged Attached Growth Reactor (SAGR®) is a treatment process developed to perform nitrification near freezing temperatures. Previous tests on full-scale installations have shown that SAGR could consistently remove ammonia to below current Canadian standards and provide additional total suspended solids and biochemical oxygen demand removal. In this study, we evaluated removal of polar chemicals of emerging concern (CECs), including pharmaceuticals, personal care products, and pesticides, at SAGR installations in two Manitoba First Nations communities (MCN and LPFN) under cold winter conditions. Both showed some removal of diclofenac, naproxen, clarithromycin, metoprolol, and trimethoprim, likely by biotransformation. Average naproxen removal was 21% (2.53 × 103 ng L−1) in MCN and 64% (1.58 × 103 ng L−1) in LPFN. Atenolol was well-removed by SAGR, by 80% on average (range of 64%–94%). Clarithromycin, metoprolol, and trimethoprim removal was similar within and between systems, ranging from 54% to 76% (30.8–3.07 × 102 ng L−1 removed). Carbamazepine was detected in nearly all samples, but was not well-removed, consistent with other treatment studies. Overall, results showed that SAGR technology could moderately remove CECs, while providing the designed treatment performance for other parameters. This work will help to improve our understanding of wastewater treatment in small and/or remote communities with limited infrastructure and challenging cold-weather conditions.

Ammonia, thiocyanate, and cyanate removal in an aerobic up-flow submerged attached growth reactor treating gold mine wastewater.

The objective of the study was to investigate the nitrification process, as well as the bio-chemical removal of cyanate and thiocyanate, while treating gold mining wastewater using an aerobic up-flow SAGR. A total of six SAGRs, each packed with locally sourced pea gravel (estimated specific surface area of 297m-2m-3), were operated at various HRTs and tested on both low- and high-strength gold mining wastewaters. The two sets of three SAGRs were operated at HRTs of 0.45 days, 1.20 days, and 2.40 days. Nitrification was successfully achieved in all six SAGRs regardless of the wastewater strength or HRT examined. The steady-state, 20°C surface area loading rate was determined to be 1.2g-TAN m-2 d-1 in order to comply with an effluent discharge limit at 10mg-TAN L-1 (i.e., with the wastewater sources examined). At all ammonia loading rates, thiocyanate was successfully removed, and residual concentrations were below 2mg-SCN-N L-1. Cyanate appeared to be hydrolyzed and subsequently nitrified. Acute toxicity tests conducted on both daphnia and trout revealed the effluent to be safe for direct discharge.

Effects of backwashing strategy and dissolved oxygen on arsenic removal to meet drinking water standards in a sulfidogenic attached growth reactor.

Efficiency and feasibility of two backwashing methods (water-nitrogen and water-air assisted) on arsenic and its co-pollutants removal were assessed through running a sulfidogenic attached growth reactor (AGR) treating arsenic spiked simulated groundwater for about 600 days. Replacing water with nitrogen assisted backwashing (WNAB) by water with air assisted backwashing (WAAB) introduced dissolved oxygen (DO) as an additional electron acceptor, which required an increased empty bed contact time (EBCT) to retain the entire terminal electron accepting zones (DO, nitrate, arsenate and sulfate) within the reactor. Removal of arsenic to below 10 μg/L required a longer EBCT at higher influent DO in backwash water. Notably, MiSeq sequencing analysis confirmed the presence of diverse bacterial community on biofilm which can utilize multiple terminal electron acceptors present in the bioreactor.

Concurrent removal of nitrate, arsenic and iron from simulated and real-life groundwater to meet drinking water standards: Effects of operational and environmental parameters

The aim of this work was to study concurrent removal of nitrate, arsenic and iron in an attached growth reactor (AGR) based on bio-sulphidogenesis treating simulated and real-life ground water. A lab-scale bioreactor system was monitored for a period of 511 days under conditions identical to those prevailing at full-scale to assess the relative influence of empty bed contact time (EBCT) (20–90 min), backwash strategies (water-nitrogen and water-air), temperature (20–50 °C), pH (6.6–8.4) and shut down on reactor performance and recovery. Complete removal of nitrate (50 mg/L) and over 95% removal of iron (3 mg/L) occurred. Arsenic removal efficiency was around 99% (500 μg/L) and treated water arsenic concentration was in compliance with the World Health Organization and Indian Standard of 10 μg/L. Port sampling along the depth of bioreactor shows shifting of terminal electron accepting process zones at lower EBCT of 20 min and after air assisted backwashing. The temperature range of 20–50 °C and pH range of 6.6–8.4 were applicable for arsenic removal in natural conditions. Precipitated biosolids were analysed using electron microscopy. Biogenic sulphides resulted in the precipitation of arsenosulphides and iron sulphides, which concurrently removed arsenic and iron. This study suggests that a sulphidogenic bioreactor may help to set the basis for concurrent removal of nitrate, arsenic and iron from real-life groundwater using mixed biofilm bacterial community.

Stability against arsenic leaching from biogenic arsenosulphides generated under reduced environment

This paper examines the stability of biogenic arsenosulphides formed in the absence of iron and other metal sulphides, in a sulphidogenic attached growth reactor (AGR) through long term column leaching, aging and Toxicity Characteristics Leaching Procedure (TCLP). Around half of the reactor was packed with waste activated carbon (WAC) to promote biofilm growth and applied for treatment of arsenic spiked water. The FESEM/EDX and XRD analyses confirmed that the biosolids largely consists of orpiment and realgar. While aging and TCLP experiments were performed in anoxic and oxic environment with the goal to assess the stability of bio-sludge carrying arsenosulphides, the long term leaching experiments were performed through passing aerated distilled water to assess the stability of the exhausted WAC. With the prolonged aging period, leached arsenic was at the maximum of 167 and 306 μg/L during anoxic and oxic aging periods, respectively. In conformity with the results of the tests conducted, it can be concluded that the biogenic arsenosulphides formed under reduced environment is stable and do not falls under the category of hazardous waste.

Submerged attached-growth reactors as lagoon retrofits for cold-weather ammonia removal: performance and sizing.

Small towns that operate wastewater treatment lagoons struggle to meet ammonia limits in cold weather. Here we report the performance of a lagoon, retrofitted with submerged attached growth reactors (SAGRsTM), to provide insight on ammonia effluent compliance and optimal SAGR sizing as functions of water temperature. The lagoon-SAGR water resource recovery facility (WRRF) removed 95% of incoming ammonia with 94% attributed to the SAGRs. The high treatment capacity of the two primary SAGRs, evidenced by nearly continuous dissolved oxygen saturation and exceedingly high ammonia removals, suggested the two secondary SAGRs were essentially unnecessary and that all four SAGRs should be reduced in size. Furthermore, without the secondary SAGRs, the primary SAGR effluent would have exceeded the permitted ammonia discharge limit only four times in the 2.5-year study. At its current size, the lagoon-SAGR WRRF never exceeded permitted ammonia limits, but size reductions should be used for future retrofits.

Bioreactors for efficient treatment of phenol and nitrogen from wastewater

Bioreactors are operated in aerobic, anaerobic and anoxic environment either as single unit or in series of sequence for treatment of various types of wastewater for desirable outcome. The working force microbes grow in suspension in suspended growth reactor configuration or may be grown in attachment of some support media (mostly referred as bed) in attached growth reactor configuration. Therefore, in suspended system, microbes are kept suspended in the liquor whereas in attached growth system, some carrier material is provided in the reactors for use as a bed for microbial growth. Both suspended growth and attached growth bioreactors are used for removal of complex wastewater containing inorganics, organics and various metals. The review article possesses an insight of comparison of various reactors used for treatment of complex wastewater with phenol and ammonia component.

Investigation on stability and leaching characteristics of mixtures of biogenic arsenosulphides and iron sulphides formed under reduced conditions

Arsenic is removed from aqueous phase through precipitation as arsenosulphides and/or co-precipitation and adsorption on iron sulphides. Studies were carried out to ascertain the stability of reduced biogenic arsenic and iron sulphide precipitates formed in an attached growth reactor (AGR) through a series of experiments based on Toxicity Characteristic Leaching Procedure (TCLP), aging and long term leaching tests. About half of the AGR was initially added with waste activated carbon (WAC) to support the growth of mixed microbial consortia and used for treatment of arsenic and iron contaminated simulated groundwater. The X-ray diffraction (XRD), X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy results indicated that the biosolids were mainly composed of arsenosulphides and iron sulphides. While TCLP and aging tests were conducted in anoxic as well as oxic conditions with the aim to evaluate stability of biomass containing biogenic sulphides, long term leaching test was conducted through supply of aerated distilled water to evaluate the stability of spent WAC as well. Results generated from the research indicate that the concentration of leached arsenic never exceeded 123 μg/L under all conditions tested, thus biosolids not imposing an environmental hazard.

Simultaneous removal of arsenic, iron and nitrate in an attached growth bioreactor to meet drinking water standards: Importance of sulphate and empty bed contact time

Abstract There are several reports on simultaneous occurrence of arsenic, iron and nitrate in drinking water sources especially in groundwater at wide range of concentrations. However, there is no report available, so far, on simultaneous successful removal of arsenic, iron and nitrate from contaminated groundwater, and effects of one contaminant on the overall performance of a biological reactor. The present study investigates the roles of sulphate and empty bed contact time on simultaneous removal of arsenic, iron and nitrate to meet the drinking water standards in an attached growth bioreactor. An attached growth reactor was fabricated using Perspex cylinder, inoculated with mixed microbial culture and operated in downflow mode in absence of oxygen at 30 °C for more than 500 days under varying influent arsenate (500–1500 μg/L as arsenic), iron (2.0–10 mg/L) and nitrate concentrations (50–200 mg/L) in simulated groundwater, and empty bed contact time of 45–120 min. Acetate was used as external carbon source and electron donor in this project. Iron and arsenic removal met the drinking water standards, while complete nitrate removal was observed at all tested concentrations. Roles of sulphate concentration and empty bed contact time were found to be very important to improve efficiency of the reactor. The reactor was also fed with real groundwater containing arsenic and iron of up to 295 μg/L and 13.2 mg/L respectively. The reactor could remove both the contaminants to meet drinking water standards after supply of sufficient amount of sulphate and adjustment of empty bed contact time. Results of field emission scanning electron microscopy and X-ray diffraction analyses suggested that precipitation in the form of arsenosulphides (orpiment and realgar) and iron sulphides (pyrite and pyrrohite) were the removal mechanisms for arsenic and iron. Hence, this study demonstrates an excellent potential of application of biological process on simultaneous removal of arsenic, iron and nitrate to meet drinking water standards.

Simultaneous removal of arsenic and nitrate in absence of iron in an attached growth bioreactor to meet drinking water standards: Importance of sulphate and empty bed contact time

Abstract There are several reports on simultaneous occurrence of arsenic and nitrate in drinking water sources especially in groundwater at wide range of concentrations. However, there is no report available, so far, on simultaneous successful removal of arsenic and nitrate from contaminated groundwater in absence of iron, and effects of one contaminant on the overall performance of a biological reactor. The present study investigates the roles of sulphate and empty bed contact time (EBCT) on simultaneous removal of nitrate and arsenic to meet the drinking water standards in an attached growth bioreactor in absence of iron. An attached growth reactor (AGR) was fabricated using Perspex cylinder, inoculated with mixed bacterial culture and operated in downflow mode in absence of oxygen at 30 °C for more than 400 days under varying influent arsenate (200–750 μg/L) and nitrate concentrations (50–200 mg/L), and EBCT of 45–60 min. Acetate was used as external carbon source and electron donor in this study. Complete nitrate removal was observed at all tested concentrations. Arsenic removal was high (up to 99.8%) and was well below drinking water standards from initial concentrations of up to 750 μg/L. The arsenic removal efficiency was found to depend on sulphate reduction and EBCT of the reactor. Results of X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) analyses suggested that arsenic precipitation in the form of arsenosulphides (orpiment and realgar) was the removal mechanism.

Performance of nitrogen removal in attached growth reactors with different carriers

Abstract Two waste materials, concrete and sponge, were used as biomass carriers in the attached growth reactor in a nitrogen wastewater treatment system. The nitrogen removal performance was compared to a control reactor using commercial carrier material. The highest nitrogen removal efficiency, 87%, was found in the sponge reactor, with the concrete reactor showing 82% efficiency ahead of the commercial reactor of 76%. A thick biofilm developed on the fiber of the sponge carrier, with the biomass increasing from 270 g-VSS/m3-carrier to 1,000 g-VSS/m3-carrier. For the concrete carrier, biomass was observed on the concrete cracks and also as a biofilm on the surface. The maximal biomass was 630 g-VSS/m3-carrier. The content of the biomass agglomerated in the commercial carrier was 310 g-VSS/m3-carrier. Nitrification and denitrification simultaneously occurred to remove nitrogen in the sponge and the commercial carrier reactor. However, in the concrete reactor, nitrification mainly occurred during the aeration phase and denitrification occurred in the non-aeration phase. These results demonstrate that the sponge was the best carrier, with high nitrogen removal efficiency, dense biomass and tolerance to shock loading. The simplicity inherent in the system design together with good performance make it suitable for use in wastewater treatment systems.

Interactive effect of trivalent iron on activated sludge digestion and biofilm structure in attached growth reactor of waste tire rubber

ABSTRACTWaste tire rubber (WTR) has been introduced as an alternative, novel media for biofilm development in several experimental systems including attached growth bioreactors. In this context, four laboratory-scale static batch bioreactors containing WTR as a support material for biofilm development were run under anoxic condition for 90 days using waste activated sludge as an inoculum under the influence of different concentrations (2.5, 6.5, 8.5 mg/l) of trivalent ferric iron (Fe3+). The data revealed that activated sludge with a Fe3+ concentration of 8.5 mg/l supported the maximum bacterial biomass [4.73E + 10 CFU/ml cm2]; besides, it removed 38% more Chemical oxygen demand compared to Fe3+ free condition from the reactor. Biochemical testing and 16S rDNA phylogenetic analysis of WTR-derived biofilm communities further suggested the role of varying concentrations of Fe3+ on the density and diversity of members of Enterobacteria(ceae), ammonium (AOB) and nitrite oxidizing bacteria. Furthermore, Fluorescent in situ hybridization with phylogenetic oligonucleotide probes and confocal laser scanning microscopy of WTR biofilms indicated a significant increase in density of eubacteria (3.00E + 01 to.05E + 02 cells/cm2) and beta proteobacteria (8.10E + 01 to 1.42E + 02 cells/cm2), respectively, with an increase in Fe3+ concentration in the reactors, whereas, the cell density of gamma proteobacteria in biofilms decreased.

Removal of pharmaceuticals from municipal wastewater by aerated submerged attached growth reactors

The performance of four aerated submerged attached growth bioreactors was studied for the removal of three pharmaceutical micro-pollutants (fluoxetine, mefenamic acid and metoprolol) from municipal wastewater. Two packing materials (polyethylene tapes and polyurethane cubes) were compared and the effects of different organic loads (3.0, 6.0, 9.0 and 12 gCOD m−2 d−1) and of the effluent recirculation were investigated. The obtained solid retention times were in the range of 4–37 d. The reactors packed with polyurethane cubes allowed 11–26% higher biomass accumulation than the ones with polyethylene tapes and higher solid retention times. The low organic loads, high solid retention times and the implementation of effluent recirculation enhanced the removal of the three pharmaceutical compounds. The highest removals were achieved at organic load of 3 gCOD m−2 d−1 and 50% of effluent recirculation, with hydraulic residence times of 3.1–4.3 h and the solid retention times of 19–32 d. At this condition, the removals of the fluoxetine, mefenamic acid and metoprolol were up to 95, 82 and 73% respectively. The reactors with polyurethane cubes showed higher removals compared with the ones packed with polyethylene tapes.