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Study of the adaptation of an MBR system to double the wastewater purification capacity of the Barranco Seco II treatment plant

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The relative efficiencies of three membrane materials for use in a submerged membrane bioreactor treating domestic wastewater were evaluated. A glass-filled hydrophobic polypropylene membrane allowed no flow through the membrane. A polysulphone membrane (PS, 0.4 mm pore size) did not achieve a steady-state flux although a flux of 7l m-2 h-1 occurred on the last day of the steady-state run. A melt-blown polypropylene membrane (NWPP, 5 μm pore size) gave a steady-state flux of 5l m-2 h-1. Membrane productivity was low due to irreversible fouling in the NWPP membrane and reversible fouling in the PS membrane. It was found that the PP membrane gave a 5-log reduction in total coliforms whereas the PS membrane gave a 9-log reduction. CBOD5, COD, SS, NH3-N and turbidity removal was similar with both the PS and the NWPP membranes. It was concluded that although the NWPP membrane was relatively inexpensive and achieved a high degree of organic matter removal, due to its inability to remove bacteria from the effluent it would be inappropriate to apply it to domestic wastewater in a submerged MBR.
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Membrane bioreactor (MBR) technology for wastewater treatment has been developed for over three decades. Our latest survey shows that MBR applications for wastewater treatment are still in rapid growth today. This review summarizes the pros, cons and progress in full-scale MBR applications. Critical statistics on the capital cost, operating cost, footprint, energy consumption and chemical consumption of full-scale MBRs are provided, and are compared to those of conventional activated sludge (CAS) processes with/without tertiary treatment. The efficiencies in full-scale treatment of ordinary pollutants (C, N and P), pathogens (bacteria and viruses) and emerging pollutants (e.g., trace organic pollutants) are reviewed. The long-term operation stability of full-scale MBRs is also discussed with several examples provided, with special attention placed on the seasonal variation of membrane fouling. Finally, the future challenges of MBR application are outlined from the perspectives of fouling control, pollutant removal, cost-effectiveness and competitiveness in specific fields of application.
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A ceramic micro-filtration cross-flow membrane coupled to an aerobic bioreactor has been successfully operated as alternatively the system aerator or as a filter of treated waste in the biological remediation of a food industry waste-stream. Membranes with nominal pore sizes ranging from 1.2 to 0.2 μm with the same air supply provide 20 to 70% higher aeration rates than a traditional ring-sparger. In addition, by acting as a physical barrier, the membrane allowed an indigenous waste-specific microflora to develop (109 cfu/ml) which under conditions of nitrogen deficiency, provided a high level of remediation coupled to very low sludge production. At 25°C (typical waste-stream temperature), with COD inputs of up to 9600 mg/l and BOD5 up to 5300 mg/l, reductions in excess of 95% in membrane permeate levels were obtained. Suspended solids in the permeate were also kept low at less than 25 mg/l.
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This study investigated changes in the structure and metabolic capabilities of the bacterial community in a full-scale membrane bioreactor (MBR) treating municipal wastewater. Microbial monitoring was also conducted for a parallel-running conventional activated sludge (CAS) process treating the same influent. The mixed-liquor suspended solid concentration in the MBR reached a steady-state on day 73 after the start-up. Then the MBR maintained higher rates of removal of organic compounds and nitrogen than the CAS process did. Terminal restriction fragment length polymorphism analysis revealed that the bacterial community structure in the MBR was similar to that in the CAS process at the start-up, but it became very different from that in the CAS process in the steady state. The bacterial community structure of the MBR continued to change dynamically even after 20 months of the steady-state operation, while that of the CAS process was maintained in a stable condition. By contrast, Biolog assay revealed that the carbon source utilization potential of the MBR resembled that of the CAS process as a whole, although it declined transiently. Overall, the results indicate that the bacterial community of the MBR has flexibility in terms of its phylogenetic structure and metabolic activity to maintain the high wastewater treatment capability.
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Nitrification of the MBR process for sewage treatment was investigated with a pilot scale plant in this study. Complete nitrifcation occurred where the sludge retention time (SRT) was over 5 days. The maximum nitrification rate (Rmax) of the biomass was determined with batch tests and was found to be around 1.71 - 2.0 mgNO3-N/gVSS-h. Nitrification was affected more by the influent C/N ratio than SRT.
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Membrane bioreactor (MBR) package systems are providing affordable and simple-to-use decentralized waste-water treatment solutions for small to medium sized communities that face the challenge of balancing environmental and regulatory responsibilities with budgetary limitations. With a greater confidence and under-standing of MBR technology, there is an increasing incentive in using MBR technology for these types of applications. Furthermore, valued qualities such as compact footprint, quick installation and start-up, process reliability, ease of operation, and superior effluent quality suitable for direct surface discharge and water reclamation have made MBR package system a preferred solution for decentralized wastewater treatment applications. This paper presents a retrofit solution for the Whitehouse Terrace Wastewater Treatment Plant. The existing extended aeration activated sludge package plant was retrofitted with a pre-engineered newterra MicroClear™ MBR package system for a small community along St Lawrence River in Brockville, Ontario. Five years full scale operation data of the MBR package system is presented and it is evident that the MBR package system consistently delivered high quality effluent that is far better than the required limit for direct surface water discharge to the St. Lawrence's river, with average effluent quality of 2.4, 2.6, 0.5, 0.05 mg/L, 1.7 counts/100 mL and 7.4 for biochemical oxygen demand, TSS, TP, TAN, Escherichia coli and pH, respectively.
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Membrane fouling remains a significant drawback for membrane bioreactors (MBRs). The solids retention time (SRT) has been widely acknowledged to be an important factor influencing membrane fouling. In general, lower membrane fouling rates are observed at elevated SRTs, however, the direct mechanisms through which a high SRT alleviates fouling are unclear. Since it has also been reported that activated sludge bioflocculation is an important factor in membrane fouling, this paper studies the impact of SRT on bioflocculation with respect to membrane fouling. A pilot-scale MBR was operated for more than two years at three different SRTs during which bioflocculation was closely monitored by means of an automated image analysis procedure while the fouling rate was recorded on-line for different fluxes and different filtration/relaxation cycles. In addition, the Delft filtration characterization method (DFCm) was employed to assess the activated sludge fouling propensity. Based on these data, it is shown that stable operation of a membrane bioreactor requires a good activated sludge condition and that bioflocculation is a crucial factor within that context. In the tested SRT range (10–30–50 days), a higher SRT contributes to better activated sludge bioflocculation and as a consequence, to lower fouling rates.
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With new EEC regulations, alternative treatment and disposal techniques of the excess sludge produced by Activated Sludge (AS) wastewater treatment plants have to be performed. In order to reduce the excess sludge produced, experiments have been carried out with a Membrane BioReactor (MBR) to study the maintenance and cryptic growth phenomena of Pseudomonas fluorescens culture taken as a model when grown on a limiting substrate complex medium similar to a synthetic urban wastewater. Experiments with various imposed wasting rates showed that viability and sludge production yield decreased when sludge age increased. Same variations were observed on the cell content ratio protein/polysaccharide by analysis of the cell lysis products released after discontinuous thermal treatment. Biomass growth on these cell lysis products was achieved to characterize cryptic growth and its impact on sludge production yield. Finally, a continuous sludge thermal treatment system was operating with MBR to amplify sludge breakage and consequently biomass growth on the lysis products. With the promising results obtained, this work gives a new outlook on the AS process and leads to the development of processes with control and reduction of sludge production.
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A different approach of wastewater treatment has been investigated in this study by operating bioreactor at low mixed liquor suspended solids (MLSS) concentrations, thereby maintaining high F/M ratio to target higher nutrient removal through higher biomass yield. A 10-L capacity laboratory-scale bioreactor followed by settling-cum-membrane separation employing hollow fiber membrane module (pore size: 0.1 μm) was set up and operated under batch mode at a hydraulic retention time (HRT) of 24 h using simulated domestic wastewater as feed. Average removal efficiencies of bioreactor were approximately 84% soluble chemical oxygen demand (SCOD), 95.5% total COD (TCOD), 90% NH4+–N, and 87% total Kjeldahl nitrogen (TKN). True yield coefficient (YT) and decay coefficient (Kd) for bioreactor were estimated at 0.397 kg VSS/kg SCOD and 0.0549 day− 1, respectively. Significant proliferation of non-flocculating microorganisms was observed in the system with decreasing solids retention time (SRT) and thereby deteriorating biomass settling property indicated by enhanced sludge volume index (SVI). Significant proliferation of non-flocculating microorganisms with better ability to access substrate from bulk solution through smaller mass transfer resistance most probably contributed to better organics removal. The modified approach of wastewater treatment can be a good basis to develop high-growth membrane bioreactor (MBR) as opposed to conventional MBR operation.Research Highlights► Reactor at high F/M ratio with membrane separation for better wastewater treatment. ► Higher true yield coefficient (YT) at high F/M ratio ensured high-growth condition. ► High-growth reactor system showed 84% SCOD, 95.5% TCOD, 90% NH4+–N, 87% TKN removal. ► Excellent organics removal due to significant proliferation of dispersed biomass. ► Modified approach of wastewater treatment is a good basis to develop high-growth MBR.
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A membrane bioreactor was used to calculate the maintenance coefficients ms, mo2; g · g−1h−1) and theoretical maximum yields (Yx/s, Yx/o2; g · g−1) of Pseudomonas fluorescens cultures taken as a model when grown on a limiting substrate complex medium, similar to a synthetic wastewater. The total control of the aerobic process of wastewater treatment in this type of reactor, and the perspective of the reduction of sludge production were directly related to this purpose. The operating conditions were either a total cell recycle or various imposed breeding rates; similar values of growth constants were obtained. It was established that the substrate mass flow (fixed by the dilution rate, Ds, independent of the breeding rate Db), had no influence on the values of m and Y. No deviation of the slope of the linear regressions serving to calculate these parameters was observed, even at low biomass breeding rates Db (<5% μmax). The concept of the maintenance energy coefficient and the advantages of this technical tool are discussed.
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The recognition that microorganisms satisfy their maintenance energy requirements in preference to producing additional biomass has revealed possible methods to reducing the generation of excess biomass during wastewater treatment. A relationship describing substrate utilization for maintenance and biomass production in substrate-limited continuous microbial cultures is presented. In continuously-fed, substrate-limited, microbial populations, it is proposed that the biomass production decreases proportionally to biomass concentration. To evaluate the significance of biomass concentration on biomass production, a laboratory chemostat containing Pseudomonas putida grown aerobically was fitted with a second stage in which the biomass in the reactor effluent was concentrated and a portion was recycled to enhance the biomass concentration. Overall substrate removal efficiency remained constant at each of the various biomass concentrations investigated. Increasing biomass concentration from 3 to 6 g l−1 reduced biomass production by 12% and analysis of a similar system observed that increasing biomass concentration from 1.7 g l−1 to 10.3 g l−1 reduced biomass production by 44%. Maintenance energy coefficients and true growth yields for operation both as a chemostat and with biomass recycle were found to be similar; qm=0.027±0.004 g substrate g biomass−1 h−1 and YG=0.359±0.003 g biomass g substrate−1 and qm=0.021±0.008 g substrate g biomass−1 h−1 and YG=0.385±0.022 g biomass g substrate−1, respectively. The relevance of these findings for biomass production in wastewater processes are discussed.
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Membrane bioreactors (MBRs) have been increasingly employed for municipal and industrial wastewater treatment in the last decade. The efforts for modelling of such wastewater treatment systems have always targeted either the biological processes (treatment quality target) as well as the various aspects of engineering (cost effective design and operation). The development of Activated Sludge Models (ASM) was an important evolution in the modelling of Conventional Activated Sludge (CAS) processes and their use is now very well established. However, although they were initially developed to describe CAS processes, they have simply been transferred and applied to MBR processes. Recent studies on MBR biological processes have reported several crucial specificities: medium to very high sludge retention times, high mixed liquor concentration, accumulation of soluble microbial products (SMP) rejected by the membrane filtration step, and high aeration rates for scouring purposes. These aspects raise the question as to what extent the ASM framework is applicable to MBR processes. Several studies highlighting some of the aforementioned issues are scattered through the literature. Hence, through a concise and structured overview of the past developments and current state-of-the-art in biological modelling of MBR, this review explores ASM-based modelling applied to MBR processes. The work aims to synthesize previous studies and differentiates between unmodified and modified applications of ASM to MBR. Particular emphasis is placed on influent fractionation, biokinetics, and soluble microbial products (SMPs)/exo-polymeric substances (EPS) modelling, and suggestions are put forward as to good modelling practice with regard to MBR modelling both for end-users and academia. A last section highlights shortcomings and future needs for improved biological modelling of MBR processes.
Criterios técnico-económicos para la implantación de la tecnología de bioreactores de membrana, Tecnología del agua
  • J Lopetegui-Garnika
  • E Trouvé
J. Lopetegui-Garnika, E. Trouvé, Criterios técnico-económicos para la implantación de la tecnología de bioreactores de membrana, Tecnología del agua., 253 (2004) 62-69.
-10) Demonstration Unit, Installation and Operation Manual, Revision 4
  • Zenon
Zenon, Zeeweed-10 (ZW-10) Demonstration Unit, Installation and Operation Manual, Revision 4, 2003.