Rotating Biological Contactor System Research Articles

Remoción de materia orgánica presente en aguas residuales de una planta farmacéutica mediante un RBC (contactor biológico rotatorio)

A RBC (Rotating Biological Contactor) system is a technology using a biological process by which microorganisms present in wastewater arefixed to partially-submerged parallel rotating discs forming a biofilm through bioaugmentation processes. This technology allows for the removal of contaminating organic matter from the water improving treatment processes. In this research work, a laboratory-scale RBC composed of four discs submerged approximately 40 % in a volume of 1 l (0.001 m3) was used for the purpose of reducing high levels of COD and BOD contained in the wastewater of a pharmaceutical plant with the aid of two different microbial consortiums. An initial characterization of COD and BOD of the wastewater sample was carried out in order to compare with six samples obtained from the reactor in operation. A maximum COD removal of 2 560 mg O2/l was obtained which, although very high, is beyond of the permissible limits allowed by Colombian law ( ordinance 0631 of 2015) but is significant because it represents an efficient removal percentage of 99.67 % with respect to the values obtained at the initial characterization

Effect of Operating Parameters and Energy Expenditure on the Biological Performance of Rotating Biological Contactor for Wastewater Treatment

The rotating biological contactor (RBC) is resistant to toxic chemical and shock loadings, and this results in significant organic and nutrient removal efficiencies. The RBC system offers a low-energy footprint and saves up to 90% in energy costs. Due to the system’s low-energy demand, it is easily operable with renewable energy sources, either solar or wind power. An RBC was employed to degrade pollutants in domestic wastewater through biodegradation mechanisms in this study. The high microbial population in the RBC bioreactor produced excellent biological treatment capacity and higher effluent quality. The results showed that the RBC bioreactor achieved an average removal efficiency of 73.9% of chemical oxygen demand (COD), 38.3% of total nitrogen (TN), 95.6% of ammonium, and 78.9% of turbidity. Investigation of operational parameters, disk rotational speed, HRT, and SRT, showed the biological performance impact. Disk rotational speed showed uniform effluent quality at 30–40 rpm, while higher values of disk rotational speed (>40 rpm) resulted in lower effluent quality in COD, TN, and turbidity. The longer hydraulic retention time and sludge retention time (SRT) facilitated higher biological performance efficiency. The longer SRTs enabled the higher TN removal efficiency because of the higher quantity of microbial biomass retention. The longer SRT also resulted in efficient sludge-settling properties and reduced volume of sludge production. The energy evaluation of the RBC bioreactor showed that it consumed only 0.14 kWh/m3, which is significantly lower than the conventional treatment methods; therefore, it is easily operable with renewable energy sources. The RBC is promising substitute for traditional suspended growth processes as higher microbial activity, lower operational and maintenance costs, and lower carbon foot print enhanced the biological performance, which aligns with the stipulations of ecological evolution and environment-friendly treatment.

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.

A Review on Rotating Biological Contactors

Rotating biological contactors (RBC) is a wastewater treatment process that provides a both acceptable effluent quality and organic removal efficiency at a comparatively very low costs. It is highly attractive due to simplicity of operation, low sludge production, small foot-print, low maintenance, and low operational cost. Complete nitrification/denitrification can be achieved by varying the disk submergence level and operating the process under both anaerobic/anoxic conditions in a single unit. In this review, pros and cons of RBC are discussed in detail along with the factors affecting its performances. Organic and hydraulic loading and hydraulic retention time are the main parameters followed by additional parameters such as rotational speed, media, disk submergence, dissolved oxygen level, influent and effluent characteristics, and step-feeding in affecting the performance of an RBC system. RBC has shown promising results for the removal of biodegradable matter, nitrogen and phosphorous removal. The approaches for hybridization of biological processes to improve their overall performance are also review. Such success story is assess so explore possibility of developing RBC based hybrid processes. Hybrid RBC can be form from in-combination with other processes for minimizing energy requirements and maximizing the efficiency of the system.

PENGOLAHAN AIR LIMBAH DENGAN SISTEM REAKTOR BIOLOGIS PUTAR (ROTATING BIOLOGICAL CONTACTOR) DAN PARAMETER DISAIN

A rotating biological contactor (or RBC) is a type of fixed media filter which removes both organic matter and ammonia from water. It can be added to a packaged plant for more efficient ammonia removal, replacing the aerator in both location and function.The RBC consists of a series of rotating discs. These discs are coated with a biological slime like the slime on rocks in a healthy stream. This slime is rotated through the air and and then through the wastewater so that it picks up oxygen in the air and breaks down B.O.D. in the wastewater. Since the discs rotate through the air, there is no need to pump air into the wastewater. And since the slime stays on the discs, there is no need to recycle sludge. The present study describes basic consideration of rotating biological contactor (RBC) system for wastewater treatment. The design of an RBC system must include the following consideration sach as organics and surface loading criteria, staging of RBC units, peripheral velocity, temperature, effluent characteritics and secondary clarifier. The RBC system have some advantages : smaller basin, less upset, high loading rate, nitrification/de-nitrification, high tolerance, low OM Cost, durable constructions, odorless, no noise, and stable sludge characteristics. Kata Kunci : Reaktor bioloigis putar, air limbah, parameter disain.

Removal of pharmaceutical compounds from urban wastewater by an advanced bio-oxidation process based on fungi Trametes versicolor immobilized in a continuous RBC system.

Conventional wastewater treatment plants (WWTPs) are not able to remove completely some emerging contaminants, such as residual pharmaceutical compounds (PCs) with potential ecotoxicity to water bodies. An advanced bio-oxidation process (ABOP) using white-rot fungi (WRF) has been proposed as alternative biological treatment for degradation of non-biodegradable compounds. A synthetic and real wastewater spiked with 12 PCs at 50μgL-1 was treated by means of ABOP based on WRF in a rotating biological contactor (RBC) at 1day of hydraulic retention time (HRT). The ABOP achieved a remarkable biological performance in terms of TOC removal and reduction of N-NH4 + and P-PO4 3- nutrients. Likewise, 5 of the 12 PCs were eliminated with removal efficiencies ranging from 80 to 95%, whereas 6 of 12 PCs were eliminated with removal values ranging from 50 to 70%. The anaerobic digestion of the fungal sludge generated upon the treatment was also evaluated, obtaining a methane yield of 250mL CH4 gVS -1. These results evidenced that the proposed ABOP is a promising alternative for the sustainable wastewater treatment of urban effluents, combining advanced oxidation with biological operation for the removal of emerging PCs and energy recovery.

Performance of a modified RBC system in simulated municipal wastewater treatment

A new method based on rotating biological contactor (RBC) was employed for solving the problems of long hydraulic retention times (HRT) low specific surface area and organic loading rates (OLR) in conventional RBCs. The system showed its particular adsorption ability of microorganisms in the biofilm-attaching period. Microbes on the first cage were observed in comparison with the second one. Packing biodisc also had a good shock load tolerance. It was observed that the system performance improved at higher HRTs, while at the increased level of input OLR, the removal performance worsened slightly. The positive role of rotational speed in the treatment of municipal wastewater was more pronounced in the range of 10-12 rpm. Chemical oxygen demand (COD) removal rate achieved 94% under the optimal operating conditions, which were HRT of 1.5 h, rotational speed of 9.9 rpm. The modified RBC system is highly beneficial to engineering application for better system performance and lower energy consumption.

Low‐ammonia niche of ammonia‐oxidizing archaea in rotating biological contactors of a municipal wastewater treatment plant

The first step of nitrification is catalysed by both ammonia-oxidizing bacteria (AOB) and archaea (AOA), but physicochemical controls on the relative abundance and function of these two groups are not yet fully understood, especially in freshwater environments. This study investigated ammonia-oxidizing populations in nitrifying rotating biological contactors (RBCs) from a municipal wastewater treatment plant. Individual RBC stages are arranged in series, with nitrification at each stage creating an ammonia gradient along the flowpath. This RBC system provides a valuable experimental system for testing the hypothesis that ammonia concentration determines the relative abundance of AOA and AOB. The results demonstrate that AOA increased as ammonium decreased across the RBC flowpath, as indicated by qPCR for thaumarchaeal amoA and 16S rRNA genes, and core lipid (CL) and intact polar lipid (IPL) crenarchaeol abundances. Overall, there was a negative logarithmic relationship (R2 = 0.51) between ammonium concentration and the relative abundance of AOA amoA genes. A single AOA population was detected in the RBC biofilms; this phylotype shared low amoA and 16S rRNA gene homology with existing AOA cultures and enrichments. These results provide evidence that ammonia availability influences the relative abundances of AOA and AOB, and that AOA are abundant in some municipal wastewater treatment systems.

Studying the efficiency of grey water treatment by using rotating biological contactors system

The need for water is growing with increasing population and the adverse impacts of climate change especially in the Mediterranean basin. Innovative concepts and technologies are urgently needed to close the loop for water. Among the options for innovative water resources, segregation of grey water and reuse is receiving crucial attention for decentralized areas as a sustainable approach. Grey water represents substantial portion of household water consumption in volume. Treated grey water to a level complying reuse rules and regulations can be reused for several purposes including agriculture, landscaping and toilet flush. The mathematical model was used to investigate the performance and treatment capability of Rotating Biological Contactors (RBC) to treat the grey water. The GPS-X (version 5.0) simulation program was used in this study to simulate the proposed RBC plant. The proposed Rotating Biological Contactors (RBC) plant is composed of three parts, first is the RBC tank unit, second is the settling tank unit and third is the disinfection tank unit. After the model optimization, three different concentrations of the grey water were used to run the proposed mathematical model. Low, medium and high concentrations of the grey water were used to run the model. The proposed model was verified by using data from RBC experimental pilot plant. The results of this study showed that, the treatment efficiency of the RBC system based on BOD removal was ranged between about 93.0% and 96.0%, and based on TSS removal was ranged between about 84.0% and 95.0 % for all concentrations of influent grey water. Also, the proposed model results indicated that grey water can be properly treated by RBC system and can be reused for many purposes after disinfection and sand filtration.

Experimental Study on Color Removal from Textile Industry Wastewater Using the Rotating Biological Contactor

Textile industry wastewater treatment is a cause for concern due to its intense color and high COD, which makes it difficult to treat it by conventional treatment options. Also, many of the dyes used in the industry fall under the category of hazardous wastes and are known to be toxic to microorganisms and aquatic life forms. An experimental study was conducted to observe the performance of Rotating Biological Contactor (RBC) system for color and COD removal from textile industry wastewaters. The RBC system could achieve up to 90±5% removal of color and 95±3% removal of COD in all four stages of RBC under optimum operating conditions. The first two stages of the RBC showed up to 75±2% of color and 85±2% of COD removal. The biofilm study concluded that a mixed culture of microorganisms (both bacteria as well as fungi) was responsible for the treatment of textile industry wastewater and the recovery of the RBC system could be very fast in case of any shock-loading occurred.

Biodegradation of an aldehyde biocide in rotating biological contactors

Biodegradation of an aldehyde biocide, glutaraldehyde (GA), in a single-stage laboratory-scale rotating biological contactor (RBC) was studied under biocide or organic loadings (OL) of 12–66 g COD m−2 day−1 and hydraulic retention times (HRT) of 0.6–3.0 h. Biofilms on the RBC were acclimated in 180 ppm GA at a hydraulic loading (HL) of 0.18 m3 m−2 day−1 and the HRT of 0.60 h. The results showed that under a constant initial chemical oxygen demand (COD) concentration and sufficient mineral salts available, the degree of GA removal in the RBC system was increased with either decreasing OL or increasing HRT. After a period of acclimation, treatment efficiency in terms of GA removal by the RBC receiving GA as a sole carbon source was 89%. The biofilms played an important role in biodegradation of biocide in the RBCs, whereas bio-oxidation of their planktonic counterparts was totally inhibited in the presence of 50 ppm GA. The biochemical oxygen demand (BOD) test could be used as an appropriate analytical procedure for investigating the efficiency of wastewater treatment units when seed was acclimated and had adequate amount.

Study of rotating biological contactor performance in wastewater treatment using multi-culture biofilm model

The rotating biological contactor (RBC) process offers the specific advantages of a biofilm system in treatment of wastewater for removal of soluble organic substances and stabilisation of nitrogen compounds. Being a unique adaptation of the moving-medium biofilm system, it facilitates easy and effective oxygen transfer. However, process optimisation and adaptability under different conditions remain challenging tasks for the efficient use of this technology. Although modelling helps to study system performance under various external conditions, satisfactory mathematical representation is lacking due to the dynamic nature of the RBC system. In this work, it has been attempted to frame a mathematical model for a three-stage RBC process in simple and realistic ways. The model is based on the well-known principles of one-dimensional mass transfer and transport of substances. The biochemical conversion process is adopted from the Activated Sludge Model No. 3 which represents a mixed-culture biomass environment. Owing to the dynamic nature of oxygen transfer, which is the typical limiting substrate in municipal wastewaters, the boundary layer is assumed to be completely mixed and concentrations averaged over the entire volume. A part of the boundary layer is assumed to be exposed to air and the rest submerged in bulk liquid at all times. The model results are compared with laboratory-scale experimental data available at 25 'C. Sensitivity analysis is performed with the model to study the significance of variation of different system parameters or the surrounding environment. In essence, the model helps to explore the flexibilities within a RBC system and optimise the process design accordingly.

Physico-Chemical and Biological Treatment of Olive Mill Wastewater by Rotating Biological Contactor (RBC) Reactors

The removal performance of total poly phenols and orthodiphenols (o-diphenols) content in olive mill waste (OMW) was investigated with a three stages cross flow laboratory scale rotating biological contactor (RBC) in the present study. Due to high COD and other pollutant in the original OMW, physico-chemical treatment was effected for COD and other pollutant reduction prior to biological treatment of OMW by the RBC system. Inoculation of RBC was effected by sludge from olive oil factory. In biological treatment, effect of operating parameters such as hydraulic loading (HL) and influent COD were examined. The study of the physico-chemical treatment before biological treatment of OMW showed, that about 9.1% of total poly phenols, 3.2% of o-diphenols and 12% of COD were removed by physical treatment. The effect of chemical treatment by different coagulants, alum, bentonite and zeolite at different pH and concentrations showed that bentonite at pH 6.5 and 15g/l resulted in the best removal efficiency of 20% for poly phenols and o-diphenols. The experimental results in RBC system show that at low HL, significant removal efficiency was observed for poly phenols and o-diphenols, at the first stage, but with increasing HL, other stages took part in removal efficiency. Also, decreasing COD from 5000 to 2500 at different HL caused an increase in poly phenols and o-diphenols removal efficiency.

Effect of glutaraldehyde biocide on laboratory-scale rotating biological contactors and biocide efficacy

The effect of glutaraldehyde, a commercial biocide widely used in paper and pulp industry, on the performance of laboratory-scale rotating biological contactors (RBCs) as well as biocide efficacy was studied. Biofilms were established on the RBCs and then exposed to 0 - 180 ppm glutaraldehyde at a dilution rate of 1.60 h -1 . The results showed that the biofilms became acclimated to glutaraldehyde and eventually could degrade it. Acclimation to the biocide took longer at the higher biocide concentrations. The degree of biocide degradation and chemical oxygen demand (COD) removal depended on acclimation period, the presence of other organic matters and the amount of mineral salts available. Glutaraldehyde at up to 80 ppm had no effect on treatment efficiency and populations of biofilms and planktonic phase of the system whereas glutaraldehyde at 180 ppm caused a progressive decline in all measured values. However, no glutaraldehyde concentration used in the study was sufficiently high to kill microorganisms in the RBC system. The presence of biofilm provided additional resistance to glutaraldehyde to bacteria because the biocide had to penetrate through biofilm to reach bacteria. The increased resistance of bacteria to glutaraldehyde due to acclimation should be considered in biocide applications.

Sewage Treatment in a Rotating Biological Contactor (RBC) System

The treatment of domestic wastewater at a temperature of 12–24°C was investigated in an RBC system. The RBC consists of a two stage system connected in series. The system was operated at different organic loading rates (OLR's) and hydraulic retntion times (HRT's) in order to optimize the RBC performance. The overall removal efficiencies for chemical oxygen demand (CODtotal, CODsuspended and CODcolloidal) significantly decreased when decreasing the total HRT from 10 to 2.5 h and increasing the OLR from 11 to 47 g COD/m2.d. However, the effluent quality of CODsoluble remained unaffected. Most of the COD was removed in the 1st stage and nitrification took place in the 2nd stage of the two stage system.The overall nitrification efficiency was 49% at total OLR of 11 gCOD/m2.d. At total HRT's of 10, 5 and 2.5 h, the Escherchia coli (E. coli) concentration was reduced by a value of 1.6, 1.5 and 0.8 log10 respectively. The sludge volume index (SVI) decreased as the OLR increased. However, the SVI of the excess sludge produced in the RBC under different OLR's was always <74 ml/gTS, which indicates vadjust a good settleability. The performance of the single versus two stage RBC operated at the same total OLR of 22 g COD/m2.d and the same HRT of 5.0 h was examined. The results obtained showed that the COD concentration and the E. coli content in the final effluent of a two stage were lower than in the effluent of the single stage RBC. Moreover, the nitrification efficiency in the two stage system was higher comapred to one stage system.

Effect of Organic Loading on Rotating Biological Contactor Efficiency

Organic loading (weight per unit time per volume) is useful for the design of rotating biological contactors (RBC) and for comparison with the other processes such as activated sludge or oxidation ponds. The present study puts emphasis on the significance of this control or design parameter because it allows direct comparison of the RBC system's performance when operated under various circumstances and with different kinds of wastewater. The results of the paper proved that, the COD removal in rotating biological contactor systems is a function of the organic loading rate. However, each of the wastewater concentration and flow rate are also influence on the system efficiency but theirs impact can be combined by the effect of organic loading. The majority of COD removal (40-85 % of the total removal depending on the organic loading applied) occurs in the first stages of the system. There is a strong correlation between the organic loading and the concentration of the suspended solids in the rotating biological contactor basin. At higher loadings higher concentrations noted. At a loading of about, (24 g/m(2).d) suspended solids were 225, 125, 35, and 25 mg/L in the first, second, third and, the fourth stage respectively. To achieve an effluent quality of (BOD <or= 25 mg/L, COD <or= 60 mg/L), the system must be operated on organic loadings of about (22 gBOD/m(2).d and 65 gCOD/m(2).d) respectively. For nitrification process, the system must be designed to operate at organic loading of about (10 g/m(2).d) or less and, the reactor or basin volume should be designed to achieve a hydraulic loading of about (40 L/m(2).d) or less.

Performance and operation of a rotating biological contactor in a tilapia recirculating aquaculture system

This paper describes the performance characteristics of an industrial-scale air-driven rotating biological contactor (RBC) installed in a recirculating aquaculture system (RAS) rearing tilapia at 28°C. This three-staged RBC system was configured with stages 1 and 2 possessing approximately the same total surface area and stage 3 having approximately 25% smaller. The total surface area provided by the RBC equaled 13,380m2. Ammonia removal efficiency averaged 31.5% per pass for all systems examined, which equated to an average (± standard deviation) total ammonia nitrogen (TAN) areal removal rate of 0.43±0.16g/m2/day. First-order ammonia removal rate (K1) constants for stages 1–3 were 2.4, 1.5, and 3.0h−1, respectively. The nitrite first-order rate constants (K2) were higher, averaging 16.2h−1 for stage 1, 7.7h−1 for stage 2, and 9.0h−1 stage 3. Dissolved organic carbon (DOC) levels decreased an averaged 6.6% per pass across the RBC. Concurrently, increasing influent DOC concentrations decreased ammonia removal efficiency. With respect to dissolved gas conditioning, the RBC system reduced carbon dioxide concentrations approximately 39% as the water flowed through the vessel. The cumulative feed burden – describes the mass of food delivered to the system per unit volume of freshwater added to the system daily – ranged between 5.5 and 7.3kg feed/m3 of freshwater; however, there was no detectable relationship between the feed loading rate and ammonia oxidation performance.

Removal of hydrocarbons in a rotating biological contactor with biodrum

A novel rotating biological contactor (RBC) with biodrum was designed to remove hydrocarbons in wastewater from industrial discharges, and its performance was investigated. The biodrum, a cylindrical mesh drum, filled with random packing of polyurethane foam cubes retaining petroleum-degrading achlorophyllous micro-alga Prototheca zopfii cells, was approximately 40% submergence in the culture. The amount of algal cells, immobilized in the 10-mm-cube pieces, was greater than in pieces of smaller pore size under the experimental conditions studied. A mixture of n-alkanes (C 14, C 15 and C 16) was used as a model oil, and the influent hydrocarbons were removed by immobilized cells in the biodrum. The single-stage RBC system was operated at 25 °C and at pH 7.0 in a batch mode. The removal rate for n-alkanes in the RBC with biodrum system was significantly increased as compared to those in the RBC system with polycarbonate biodisk.

Potentials of using a rotating biological contactor (RBC) for post-treatment of anaerobically pre-treated domestic wastewater

This study has been carried out in order to assess the impact of COD biod. in an UASB effluent applied to a single stage, a two stage RBC system and an anoxic up-flow submerged bio-filter followed by a segmental two stage aerobic RBC on the removal efficiency of different COD fractions, Escherichia coli, ammonia and partially nitrate removal. The two (single stage) RBC's were operated at a constant HRT of 2.5 h and temperature of 21 °C but at different OLR's, viz. of 10 and 14 g COD biod./m 2 day due to the highly different UASB effluent qualities. The results clearly show that the residual values of COD total, ammonia and E. coli in the final effluent are significantly lower at the lower imposed OLR of 10 g COD biod./m 2 day. In view of the results obtained we recommend to use a single stage RBC system at OLR of 10 g COD biod./m 2 day and at HRT of 2.5 h for post-treatment of the effluent of UASB reactor operated at high temperature of 30 °C as generally prevails in tropical countries. The performance of a single stage versus two stage RBC system for post-treatment of the effluent of an UASB reactor operated at a low temperature of 12 °C has been evaluated. The single stage and a two stage RBC system were operated at the same OLR of 18 g COD biod./m 2 day and at HRT of 2.5 h. The results show that the COD fractions, ammonia and E. coli content in the final effluent of a two stage RBC system were significantly lower than the effluent of the single stage RBC system. Accordingly, we recommend a two stage RBC system at an HRT of 2.5 h and OLR of 18 g COD biod./m 2 day for post-treatment of the effluent of a conventional UASB reactor operating at a low temperature of 12 °C. The nitrogen removal from the nitrified effluent was investigated using a biofilm system consisting of three stages, viz. an anoxic up-flow submerged bio-filter followed by a segmental two stage aerobic RBC. The nitrified effluent of the second stage RBC was recycled to the anoxic up-flow submerged bio-filter reactor. The results obtained reveal that the introduction of an anoxic reactor as a first stage combined with recirculation of the nitrified effluent of the second stage RBC is accompanied with a conversion of nitrate into ammonia, at least in case the content of COD biod. in the UASB effluent is low. In such a situation the ammonia needs to be nitrified two times, which obviously should be avoided. Therefore in such situations of a too high quality anaerobic effluent in terms of biodegradable COD content, the introduction of a separate anoxic reactor for denitrification as final post-treatment step can not be recommended.

Physico-chemical factors affecting the [formula omitted] removal in a rotating biological contactor (RBC) treating UASB effluent

The removal mechanism of E. coli from UASB effluent using a Rotating Biological Contractor (RBC) has been investigated. Preliminary batch experiments in a RBC indicate a first-order removal kinetics. Variation in the dissolved oxygen concentration and E. coli counts over the depth of the RBC has been recorded and indicates that the RBC is not a completely mixed reactor. Therefore batch experiments were carried out in a beaker where the different operating conditions can be controlled. Factors affecting the removal of E. coli via a biofilm system as stirring, dissolved oxygen concentration, pH, and addition of cationic polymer were investigated. The results obtained indicated that the most important removal mechanism of E. coli in the biofilm is the adsorption process, followed by sedimentation. Die-off is a relatively minor removal mechanism in an RBC system. Higher removal rate of E. coli was observed in an aerobic compared to an anaerobic biofilm system. Variation of dissolved oxygen concentration (3.3–8.7 mg l −1) and pH-values between 6.5 and 9.3 did not exert any significant effect on the removal rate of the E. coli by the heterotrophic biofilm. A rapid adsorption of E. coli to the biofilm occurred during the first days after adding the cationic polymer, after which the adsorption slowed down.