Performance of a pilot-scale submerged membrane bioreactor (MBR) in treating bathing wastewater

Bathing wastewater was treated by a pilot-scale submerged membrane bioreactor (MBR) for more than 60 days. The results showed that the removal rates of main pollutants of wastewater such as COD(Cr), LAS, NH(4)(+)-N and total nitrogen (TN) were above 93%, 99%, 99%, and 90%, respectively. The results of denaturing gel gradient electrophoresis (DGGE) and fluorescent in situ hybridization (FISH) indicated that the bacteria were stable. The abundant nitrobacteria intercepted by the membrane led to the high removal rate of ammonia and TN. FISH and 16S rDNA gene sequence analysis revealed that some specific phylogenetic group of bacteria, the Pseudomonas sp. Ochrobactrum anthropi sp. and Enterobacter sp. probably played a major role in the development of the mature biofilms, which led to the severe irreversible membrane biofouling.     

Removal of microbial indicators from municipal wastewater by a membrane bioreactor (MBR)

The impact of removable and irremovable fouling on the retention of viral and bacterial indicators by the submerged microfiltration membrane in an MBR pilot plant was evaluated. Escherichia coli, sulphite-reducing Clostridium spores, somatic coliphages and F-specific RNA bacteriophages were used as indicators. The membrane demonstrated almost complete removal of E. coli and sulphite-reducing Clostridium spores. However, there was no correlation with membrane fouling. The phage removal varied in accordance with the irremovable fouling, rising from 2.6 to 5.6 log₁₀ units as the irremovable fouling increased (measured by the change in the transmembrane pressure). In contrast, removable fouling did not have any effect on the retention of viruses by the membrane. These results indicate that irremovable membrane fouling may affect the removal efficiency of MBRs and, therefore, their capacity to ensure the required microbiological standards for the permeate achieved.     

Characteristics of simultaneous organic and nutrient removal in a pilot-scale vertical submerged membrane bioreactor (VSMBR) treating municipal wastewater at various temperatures

A pilot-scale vertical submerged membrane bioreactor (VSMBR) with anoxic and oxic zones in one reactor was operated in an attempt to reduce the problems concerning effective removal of organic matter and nutrients from municipal wastewater. Source water with total chemical oxygen demand (TCOD)/total nitrogen (TN) ratio of 5.5 was treated at various temperatures (13–25 °C) over an interval of about 1 year. As a result, total suspended solid (TSS) and TCOD were removed by 100% and higher than 98%, respectively. Moreover, the average removal efficiencies of TN and total phosphorus (TP) were found to be 74% and 78% at 8 h-hydraulic retention time (HRT) and 60-days sludge retention time (SRT). Under these conditions, the specific removal rates (SRR) of TN and TP were found to be 0.093 kg N m⁻³ day⁻¹ and 0.008 kg P m⁻³ day⁻¹, and the daily production of excess sludge (DPES), 0.058 kg TSS day⁻¹.     

Nitrogen removal from wastewater with a low COD/N ratio at a low oxygen concentration

The goal of the study was to determine the effectiveness of nitrification and denitrification and the kinetics of ammonia removal from a mixture of wastewater and anaerobic sludge digester supernatant in an SBR at limited oxygen concentration. In addition, the COD removal efficiency and sludge production were assessed.In the SBR cycle alternating aerobic and anaerobic phases occurred; in the aeration phase the dissolved oxygen (DO) concentration was below 0.7 mg O₂/L. The low DO concentration did not inhibit ammonia oxidation-nitrification and the efficiency was ca. 96-98%. However, a relatively high COD concentration in the effluent was detected. The values of K_m and V_max, calculated from the Michaelis-Menten equation, were 43 mg N-NH₄/L and 15.64 mg N-NH₄/L h, respectively. Activated sludge production was almost stable (0.62-0.66 g MLVSS/g COD). A high net biomass production resulted from a low specific biomass decay rate of 0.0015 d⁻¹.     

Effect of influent COD/N ratio on biological nitrogen removal (BNR) from high-strength ammonium industrial wastewater

The effect of influent COD/N ratio on biological nitrogen removal (BNR) from high-strength ammonium industrial wastewater was investigated. Experiments were conducted in a modified Ludzack–Ettinger pilot-plant configuration for 365 days. Total nitrification of an influent concentration of 1200 mg NH₄⁺–N l⁻¹ was obtained in this period. Influent COD/N ratios between 0.71 and 3.4 g COD g N⁻¹ were tested by varying the nitrogen loading rate (NLR) supplied to the pilot plant. An exponential decrease of nitrification rate was observed when the influent COD/N ratio increased.

The experimental COD/N ratio for denitrification was 7.1±0.8 g COD g N⁻¹ while the stoichiometric ratio was 4.2 g COD g N⁻¹. This difference is attributable to the oxidation of organic matter in the anoxic reactor with the oxygen of the internal recycle. The influence of influent COD/N ratio on the treatment of high-strength ammonium industrial wastewater can be quantified with these results. The influence of COD/N ratio should be one of the main parameters in the design of biological nitrogen removal processes in industrial wastewater treatment.     

An innovative membrane bioreactor (MBR) system for simultaneous nitrogen and phosphorus removal

Membrane filtration was integrated with a post-denitrification process to form an innovative membrane bioreactor (MBR) system for effective organic degradation and nutrient (N and P) removal. The system comprised of an aerobic tank, an anoxic tank, an intermediate sedimentation tank, and a membrane filtration tank. The sedimentation tank functioned not only as a rough settler for sludge–water separation before membrane filtration but also as an anaerobic chamber for P release. While half of the influent flowed into the aerobic tank, the other half was fed into the anoxic tank to favor the proliferation of phosphorus accumulating organisms (PAOs). The experiment was conducted continuously for about 430 days. With a short overall treatment time of less than 10 h for municipal wastewater, the MBR-based process could achieve the total organic carbon, total nitrogen, and total phosphorus removals of around 94%, 85%, and 87%, respectively. The growth and activity of PAOs in the MBR system were evidenced by the significant P release in the anaerobic chamber followed by the luxury P uptake in the membrane tank. With the DAPI and PAO_mix probe staining, the increases of PAOs and polyhydroxybutyrate (PHB) in sludge during the experiment were well observed under the fluorescent microscope.     

Improving the performance of an aerobic membrane bioreactor (MBR) treating pharmaceutical wastewater with powdered activated carbon (PAC) addition

In this study, the effects of organic loading rate (OLR) and the addition of powdered activated carbon (PAC) on the performance and membrane fouling of MBR were conducted to treat real pharmaceutical process wastewater. Over 145 days of operation, the MBR system was operated at OLRs ranging from 1 to 2 kg COD m^?3 day^?1 without sludge wasting. The addition of PAC provided an improvement in the flux, despite an increase in the OLR:PAC ratio. The results demonstrated that the hybrid PAC-MBR system maintained a reduced amount of membrane fouling and steadily increased the removal performance of etodolac. PAC addition reduced the deposition of extracellular polymeric substance and organic matter on the membrane surface and resulted an increase in COD removal even at higher OLRs with low PAC addition. Membrane fouling mechanisms were investigated using combined adsorption fouling models. Modified fouling index values and normalized mass transfer coefficient values indicated that predominant fouling mechanism was cake adsorption.     

Performance of suspended and attached growth MBR systems in treating high strength synthetic wastewater

The performance of laboratory-scale attached growth (AG) and suspended growth (SG) membrane bioreactors (MBRs) was evaluated in treating synthetic wastewater simulating high strength domestic wastewater. This study investigated the influence of sponge suspended carriers in AG-MBR system, occupying 15% reactor volume, on the removal of chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP), and compared it to that of SG-MBR. Results showed that the removal efficiencies of COD, TN and TP in AG-MBR were 98%, 89% and 58%, respectively as compared to 98%, 74% and 38%, respectively in SG-MBR. Improved TN removal in AG-MBR systems was primarily based on simultaneous nitrification and denitrification (SND) process. These results infer that the presence of small bio-particles having higher microbial activity and the growth of complex biomass captured within the suspended sponge carriers resulted in improved TN and TP removal in AG-MBR.     

Enhanced COD and nitrogen removals for the treatment of swine wastewater by combining submerged membrane bioreactor (MBR) and anaerobic upflow bed filter (AUBF) reactor

In order to enhance performances of organics removal and nitrification for the treatment of swine wastewater containing high concentration of organic solids and nitrogen than conventional biological nitrogen removal process, a submerged membrane bioreactor (MBR) was followed by an anaerobic upflow bed filter (AUBF) reactor in this research (AUBF–MBR process). The AUBF reactor is a hybrid reactor, which is the combination of an anoxic filter for denitrification and upflow anaerobic sludge blanket (UASB) for acid fermentation. In the AUBF–MBR process, it showed a considerable enhancement of the effluent quality in terms of COD removal and nitrification. The submerged MBR could maintain more than 14,000 mg VSS/L of the biomass concentration. Total nitrogen (T-N) removal efficiency represented 60% when internal recycle ratio was three times of flow-rate (Q), although the nitrification occurred completely. Although the volatile fatty acids produced in AUBF reactor can enhance denitrification rate, but the AUBF–MBR process showed reduction of overall removal efficiency of the nitrogen due to the reduction of carbon source by methane production in the AUBF reactor compared to that of theoretical nitrogen removal efficiency.

Long-term operation of the submerged MBR showed that the throughputs of the submerged MBR were respectively 74, 63, and 31 days at 10, 15, and 30 L/m² h (LMH) of permeate flux. Resistance to filtration by rejected solid is the primary cause of fouling, however the priority of cake resistance (R_c) and fouling resistance (R_f) with respect to filtration phenomenon was different according to the amount of permeate flux. The submerged MBR, here, achieved a steady-state flux of 15 LMH at 0.4 atm. of trans-membrane pressure (TMP) but the flux can be enhanced in the future because shear force by tangential flow will be greater when multi-layer sheets of membrane were used.     

Effect of the N/P ratio on biomass productivity and nutrient removal from municipal wastewater

The aim of this study is to investigate the effect of the N/P ratio on biomass growth with the simultaneous removal of nutrients from municipal wastewaters. An optical panel photobioreactor is employed for this investigation because it provides a uniform light distribution within the reactor, which enhances the efficiency of the reactor in the cultivation of microalgae. The N/P ratio is varied over a wide range, i.e., from 5 to 30, for the assessment of its effect on biomass productivity. There is not a strong correlation between biomass productivity and TN removal, and these factors do not seem to be proportional in the wastewater using the microalgae we employed. In contrast, the TP removal depends greatly on both the N/P ratio and biomass productivity. The optimum value of the N/P ratio for biomass productivity in and nutrient removal from municipal wastewater treatment using microalgae varies from 5 to 30, depending on the ecological conditions in the wastewater.     

Use of cloth-media filter for membrane bioreactor treating municipal wastewater

This study evaluated three different textile materials (Acrylate, Polyester, and Nylon) as filter media for MBR treating municipal wastewater. Chemical oxygen demand (COD) loading rates were 1.71, 1.65 and 1.84 g/l d while feed/microorganisms (F/M) ratios were 0.32, 0.31 and 0.33 in Reactor 1, Reactor 2 and Reactor 3, respectively. The actual hydraulic retention times were 8.6, 8.9 and 8.0 h in R1, R2 and R3. At 5.3-5.5 g/l mixed liquor suspended (MLSS) and 26.3 days solid retention time (SRT) the membrane bioreactors were effective in removing 93-95% of COD, 99% of total suspended solids (TSS) and turbidity, 89-94% of total kjeldahl nitrogen (TKN) and 90-96% of total ammonia nitrogen. Phosphorous removal was limited to 51-55% while faecal coliform was reduced by four logs. Quality of the treated effluents met both Saudi and Egyptian reuse standards for restricted irrigation and could be easily disinfected to meet the unrestricted irrigation standards.     

Anaerobic submerged membrane bioreactor (AnSMBR) treating low-strength wastewater under psychrophilic temperature conditions

An anaerobic submerged membrane bioreactor (AnSMBR) treating low-strength wastewater was operated for 90 days under psychrophilic temperature conditions (20 °C). Besides biogas sparging, additional shear was created by circulating sludge to control membrane fouling. The critical flux concept was used to evaluate the effectiveness of this configuration. Biogas sparging with a gas velocity (U_G) of 62 m/h together with sludge circulation (94 m/h) led to a critical flux of 7 L/(m² h). Nevertheless, a further increase in the U_G only minimally enhanced the critical flux. A low fouling rate was observed under critical flux conditions. The cake layer represented the main fouling resistance after 85 days of operation. Distinctly different volatile fatty acid (VFA) concentrations in the reactor and in the permeate were always observed. This fact suggests that a biologically active part of the cake layer contributes to degrade a part of the daily organic load. Hence, chemical oxygen demand (COD) removal efficiencies of up to 94% were observed. Nevertheless, the biogas balance indicates that even considering the dissolved methane, the methane yield were always lower than the theoretical value, which indicates that the organic compounds were not completely degraded but physically retained by the membrane in the reactor.     

Process efficiency and microbial monitoring in MBR (membrane bioreactor) and CASP (conventional activated sludge process) treatment of tannery wastewater

In this study a pilot-scale membrane bioreactor (MBR) and a conventional activated sludge plant (CASP), treating the same tannery wastewaters and in the same operating conditions, have been compared in order to evaluate the overall treatment efficiency, the presence and distribution of Gram negative bacteria and the kinetics of nitrifying bacteria. Process efficiency was evaluated in terms of organic and nitrogen compounds: the MBR showed a higher COD removal (+4%) and a more stable and complete nitrification. The Gram negative bacteria were detected by fluorescent in situ hybridization (FISH) with phylogenetic probes monitoring of alpha-, beta- and gamma-Proteobacteria, of the main ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria of the Nitrobacter and Nitrospira genera. The results showed that the main differences between the two sludges were: the higher abundance of alpha- and gamma-Proteobacteria in the MBR bioreactor and the presence of AOB aggregates only on the surfaces of MBR flocs. Finally, the titrimetric (pH-stat, DO-stat) tests showed similar values of the kinetic parameters of the nitrifiers both in MBR and CASP sludge.     

Membrane fouling in a membrane bioreactor (MBR): sludge cake formation and fouling characteristics

A submerged membrane bioreactor (MBR) with a working volume of 1.4 L and a hollow fiber microfiltration membrane was used to treat a contaminated raw water supply at a short hydraulic retention time (HRT) of approximately 1 h. Filtration flux tests were conducted regularly on the membrane to determine various fouling resistances, and confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) were employed to characterize the biofouling development and sludge cake formation on the membrane. The experimental results demonstrate that the MBR is highly effective in drinking water treatment for the removal of organic pollutants, ammonia, and UV absorbance. During the MBR operation, the fouling materials were not uniformly distributed on the entire surface of all of the membrane fibers. The membrane was covered partially by a static sludge cake that could not be removed by the shear force of aeration, and partially by a thin sludge film that was frequently washed away by aeration turbulence. The filtration resistance coefficients were 308.4 x 10(11) m(-1) on average for the sludge cake, 32.5 x 10(11) m(-1) on average for the dynamic sludge film, and increased from 10.5 x 10(11) to 59.7 x 10(11) m(-1) for the membrane pore fouling after 10 weeks of MBR operation at a filtration flux of 0.5 m3/m2 x d. Polysaccharides and other biopolymers were found to accumulate on the membrane, and hence decreased membrane permeability. More important, the adsorption of biopolymers on the membrane modified its surface property and led to easier biomass attachment and tighter sludge cake deposition, which resulted in a progressive sludge cake growth and serious membrane fouling. The sludge cake coverage on the membrane can be minimized by the separation, with adequate space, of the membrane filters, to which sufficient aeration turbulence can then be applied.     

Factors affecting the removal of organic micropollutants from wastewater in conventional treatment plants (CTP) and membrane bioreactors (MBR)

As a consequence of insufficient removal during treatment of wastewater released from industry and households, different classes of organic micropollutants are nowadays detected in surface and drinking water. Among these micropollutants, bioactive substances, e.g., endocrine disrupting compounds and pharmaceuticals, have been incriminated in negative effects on living organisms in aquatic biotope. Much research was done in the last years on the fate and removal of those compounds from wastewater. An important point it is to understand the role of applied treatment conditions (sludge retention time (SRT), biomass concentration, temperature, pH value, dominant class of micropollutants, etc.) for the efficiency of conventional treatment plants (CTP) and membrane bioreactors (MBR) concerning the removal of micropollutants such as pharmaceuticals, steroid- and xeno-estrogens. Nevertheless, the removal rates differ even from one compound to the other and are related to the physico-chemical characteristics of the xenobiotics.     

Microbial community structures in conventional activated sludge system and membrane bioreactor (MBR)

The microbial community structures of a conventional activated sludge and MBR systems treating the municipal wastewater were studied using Fluorescent in-situ Hybridization (FISH) analysis to identify differences in both systems. The oligonucleotide probes specific for overall bacteria, including α-, β-, and γ-subclasses of Proteobacteria, ammonia-oxidizing bacteria (Nitrosomonas), and nitrite-oxidizing bacteria (Nitrobacter) were used to compare the microbial community structure of both systems. A trend of less hybridization with bacteria-specific probe EUB338 was observed in MBR systems operated under aerobic condition, compared to conventional activated sludge system. The less hybridization trend with the probes could be associated with low ribosomal RNA (rRNA) content in the biomass, which suggests that the biomass in the MBR system was not in a physiological state characteristic for growth due to low substrate per unit biomass     

Application of zinc oxide and sodium alginate for biofouling mitigation in a membrane bioreactor treating urban wastewater

Abstract

This research aimed to mitigate fouling in membrane bioreactors (MBR) through concurrent usage of zinc oxide as an antibacterial agent (A) and sodium alginate as a hydrophilic agent (H) within a polyacrylonitrile membrane (PM) structure. The antibacterial polymeric membranes (APM) and antibacterial hydrophilic polymeric membranes (AHPM) synthesized showed a higher porosity, mechanical strength and bacterial inhibition zone, and a lower contact angle in comparison with PM membranes. EDS, SEM and AFM analyses were used to characterize the chemical, structural, and morphological properties of PM, APM, and AHPM. The flux of PM, APM, and AHPM in MBR was 37, 48, and 51?l m^?2 h^?1 and COD removal was 81, 93.5, and 96.7%, respectively. After MBR operation for 35?days in an urban wastewater treatment, only 50% of the flux of PM was recovered, while the antibacterial and hydrophilic agents yielded a flux recovery of 72.7 and 100% for APM and AHPM, respectively.