Membrane Bioreactor Membrane Research Articles

Water reclamation using membranes: Permeate water quality comparison of MBR and tertiary membrane filtration

The purpose of this work is to compare two low pressure membrane filtration technologies commonly used to provide polished wastewater effluent. A pilot-scale membrane bioreactor (MBR) was operated in parallel with a full-scale conventional activated sludge (CAS) process. A portion of the secondary effluent from the full-scale plant was further treated by a pilot-scale tertiary membrane filtration (TMF) system. The MBR was operated at solids retention time (SRT) and mixed liquor suspended solids concentration (MLSS) values that were double and triple that of the CAS process, respectively. The permeate quality from these two pilot plants was monitored to detect differences in their performance. Analytes included COD, TOC, polysaccharides, proteins, color and specific UV 254 absorbance (SUVA). The MBR permeate COD and TOC concentrations were consistently significantly lower than those for the CAS–TMF permeate. The average polysaccharide concentration was also found to be significantly lower in the MBR permeate; however the average color and SUVA were significantly higher in the MBR permeate. It is suggested that the differences in permeate quality are attributed to the higher SRT in the MBR and increased retention of colloidal organics in the bioreactor.

Applied Research of Nanocomposite Membrane on Fouling Mitigation in Membrane Bioreactor

The nanocomposite membranes were prepared by mixing 2.5 wt% of TiO2 nanoparticles in casting solution. In order to determine the nanocomposite membrane property, a long-term operation of membrane bioreactor (MBR) was carried out and membrane flux were measured though the filtration tests. Results showed that TiO2 addition significantly improved the permeability of membrane and decreased the cake resistance compared with the sulfonated polyethersulfone (SPES) membrane in MBR.

Effect of biopolymer clusters on the fouling property of sludge from a membrane bioreactor (MBR) and its control by ozonation

Organic substances in the liquid phase of the sludge in a membrane bioreactor (MBR) have a profound impact on membrane fouling. In this study, a single-fibre microfiltration apparatus was developed to investigate the fouling propensity of MBR sludge and the effectiveness of ozonation in membrane fouling mitigation. The results show that biopolymer clusters (BPC) in the MBR suspension had a significant influence on the fouling potential of the sludge. An increase in BPC concentration by 20% and 60% from around 3.5 mg/l in the mixed sludge liquor drastically increased the fouling rate by 120% and 300%, respectively. Ozonation of the BPC solution greatly reduced the detrimental role of BPC in membrane fouling. An ozone dose of 0.03 mg/mg TOC of BPC could reduce the mean BPC size from 38 to 27 μm, which was further reduced to 12 μm at 0.3 mg O 3/mg TOC of BPC. In addition to BPC destruction, ozonation apparently also modified the surface properties of BPC, resulting in an increase in the filterable fraction and a decrease in the liquid viscosity. Based on the experimental findings, an approach for MBR membrane fouling control is proposed that applies ozonation to the supernatant containing BPC in a side-stream application.

Operation of MBR membrane modules used in a decentralised wastewater treatment plant: Field study and comparison of different cleaning strategies

Due to their compact design and their high quality and reliable treatment, package or containerised membrane bioreactor (MBR) units are used for decentralised and semi-decentralised wastewater treatment plants. The operational availability, performance and economical viability of these MBR systems depend on the filtration performance of the membrane modules. Current chemical cleaning strategies of MBR modules, based on regular (weekly) maintenance cleanings and/or occasional (quarterly to biannual) intensive cleanings proved not to be adapted to semi-central MBR applications (100 up to 1000 p.e.): regular maintenance cleanings require automation and lead to too much care and personnel requirement. Occasional intensive cleanings increase the operational risk of membrane fouling and low cleaning recovery. In addition, semi-central MBR applications are often designed with at least two redundant filtration lines. An alternative chemical cleaning strategy was therefore proposed, implemented and assessed in a containerised MBR unit serving a population of about 250 p.e.: at a given time, only one filtration line is in operation while the other one soaks in a low-grade chemical solution. The modules are switched alternately on a monthly basis. To identify a cleaning strategy and an agent showing a good recovery, one of the modules was cleaned with H 2 O 2 , while the other was cleaned with NaOCl. A cleaning step with citric acid is added when necessary. These cleanings were tested over 16 months with the goal to minimise maintenance effort and chemicals used.

Performance and fouling characteristics of different pore-sized submerged ceramic membrane bioreactors (SCMBR)

The membrane bioreactor (MBR), a combination of activated sludge process and the membrane separation system, has been widely used in wastewater treatment. However, 90% of MBR reported were employing polymeric membranes. The usage of ceramic membranes in MBR is quite rare. Four submerged ceramic membrane bioreactors (SCMBRs) with different membrane pore size were used in this study to treat sewage. The results showed that the desirable carbonaceous removal of 95% and ammonia nitrogen removal of 98% were obtained for all the SCMBRs. It was also showed that the ceramic membranes were able to reject some portions of the protein and carbohydrate, whereby the carbohydrate rejection rate was much higher than that of protein. Membrane pore size did not significantly affect the COD and TOC removal efficiencies, the composition of EPS and SMP or the membrane rejection rate, although slight differences were observed. The SCMBR with the biggest membrane pore size fouled fastest, and membrane pore size was a main contributor for the different fouling potential observed.

Desalination of domestic wastewater effluents: phosphate removal as pretreatment

Water shortage has become a global issue and not only a problem relevant to arid zones. In the past decade desalination of sea and brackish water has been found to be a technically and economically acceptable solution for water shortage. More recently, desalination of wastewater effluents has also begun to be considered for sustainable water reclamation and reuse. Performance of membrane desalination processes, such as reverse osmosis (RO), is restricted by different fouling and clogging constraints, including inorganic scaling as well as organic fouling and biofouling. Utilization of effluents for desalination introduced to the membrane systems new feed water characteristics with reduced salinity but higher concentration of dissolved organic matter and predominant inorganic ions that are less common in sea water. Phosphate scaling is found to be a main obstacle for effluents desalination, mainly due to the lack of appropriate antiscalants to cope with its precipitation, especially at high recovery rates. This work was aimed to study the chemical coagulation of phosphate from wastewater effluents as a pretreatment for RO desalination. Based on preliminary jar test experiments, sodium aluminate (SAL) at concentrations of 20–30 mg/L, was found as an efficient coagulant for phosphate and turbidity reduction. SAL coagulation was tested either as simultaneous phosphate removal during membrane bioreactor (MBR) treatment or as postremoval of phosphate from secondary effluents from activated sludge process, followed by microfiltration. Both alternative treatments resulted in almost complete phosphate removal (≥99%). Batch desalination of both kinds of pretreated effluents showed also that calcium carbonate was a second scaling agent upon phosphate removal. The simultaneous MBR-coagulation, which in addition to complete phosphate removal displayed a significant reduction of alkalinity (75%), produced higher quality effluents and reduced the effect of calcium carbonate scaling, as compared to the post-coagulation of secondary effluents. Furthermore, the simultaneous MBR-coagulation process showed no detrimental effects on the MBR membrane performance or on the biological activity and avoided the need of an additional sedimentation or filtration step prior to RO. In conclusion, the MBR-chemical coagulation process seems to be a technically feasible pretreatment of domestic effluents for further desalination.

The status of membrane bioreactor technology

In this article, the current status of membrane bioreactor (MBR) technology for wastewater treatment is reviewed. Fundamental facets of the MBR process and membrane and process configurations are outlined and the advantages and disadvantages over conventional suspended growth-based biotreatment are briefly identified. Key process design and operating parameters are defined and their significance explained. The inter-relationships between these parameters are identified and their implications discussed, with particular reference to impacts on membrane surface fouling and channel clogging. In addition, current understanding of membrane surface fouling and identification of candidate foulants is appraised. Although much interest in this technology exists and its penetration of the market will probably increase significantly, there remains a lack of understanding of key process constraints such as membrane channel clogging, and of the science of membrane cleaning.

Domestic wastewater treatment by a submerged MBR (membrane bio-reactor) with enhanced air sparging

The air sparging technique has been recognised as an effective way to control membrane fouling. However, its application to a submerged MBR (Membrane Bio-Reactor) has not yet been reported. This paper deals with the performances of air sparging on a submerged MBR for wastewater treatment. Two kinds of air sparging techniques were used respectively. First, air is injected into the membrane tube channels so that mixed liquor can circulate in the bioreactor (air-lift mode). Second, a periodic air-jet into the membrane tube is introduced (air-jet mode). Their applicability was evaluated with a series of lab-scale experiments using domestic wastewater. The flux increased from 23 to 33 l m(-2) h(-1) (43% enhancement) when air was injected for the air-lift module. But further increase of flux was not observed as the gas flow increased. The Rc/(Rc+Rf), ratio of cake resistance (Rc) to sum of Rc and Rf (internal fouling resistance), was 23%, indicating that the Rc is not the predominant resistance unlike other MBR studies. It showed that the cake layer was removed sufficiently due to the air injection. Thus, an increase of airflow could not affect the flux performance. The air-jet module suffered from a clogging problem with accumulated sludge inside the lumen. Because the air-jet module has characteristics of dead end filtration, a periodic air-jet was not enough to blast all the accumulated sludge out. But flux was greater than in the air-lift module if the clogging was prevented by an appropriate cleaning regime such as periodical backwashing.