Abstract
Membrane bioreactors (MBRs) are an exciting and evolving technology that replaces gravity sedimentation with micro- or ultra-filtration. MBRs are typically operated at low mean cell residence times (MCRTs), but there are cases when operating at very low MCRT may be more beneficial. In this study, a laboratory-scale MBR and SBR were operated in parallel and at very low MCRTs (3 d, 2 d, 1 d and 0.5 d) to assess the relative bioreactor performance, biomass characteristics, and microbial yield. This study confirmed that the MBR maintains higher solids levels and better overall effluent quality than conventional bioreactors at all MCRTs tested. The MBR biomass particles were approximately 10 μm, which was significantly smaller than those of the SBR under all operating conditions tested. The MBR sludge typically did not dewater as well as that of the SBR. As the MCRT was decreased, the SBR particle size became smaller and the dewaterability improved, which supports the notion that smaller particles dewater better because there is less bound water present. The MBR sludge was more hydrophobic, which should result in more sorption of organic micro-pollutants like pharmaceutical compounds. These experiments also showed that the MBR biomass true yield was higher than that of the SBR. This study expands the MBR dataset available for very low MCRT operation. Water SA Vol.32 (2) 2006: pp.193-198
Highlights
Membrane bioreactors (MBRs) are an evolving wastewater treatment technology that uses a suspended growth bioreactor, like in conventional activated sludge, but replaces gravity sedimentation with micro- or ultra-filtration
The MBR volatile suspended solids (VSS) levels were higher than those for the SBR, and the VSS levels for both bioreactors decreased as the mean cell residence times (MCRTs) was lowered
The SBR capillary suction time (CST) values were from 6 to 23 s, and the average value was 14 s. These results show that the MBR sludge typically dewatered more poorly and may require more polymer addition for effective average CST (s)
Summary
Membrane bioreactors (MBRs) are an evolving wastewater treatment technology that uses a suspended growth bioreactor, like in conventional activated sludge, but replaces gravity sedimentation with micro- or ultra-filtration. MBRs tend to operate at long mean cell residence times (MCRTs) in order to maintain high MLSS concentrations and to support nitrification, but under these operating conditions the aeration requirements pose a serious process limitation because of the high oxygen demand and the need to scour the membrane to slow the rate of fouling. Another concern at long MCRT is the production of soluble microbial products which can cause membrane fouling and produce too much colour (Rittmann and McCarty, 2001). MBR operation at low MCRT may be a prudent option for facilities that wish to avoid these disadvantages, reduce energy requirements, or reuse waste biosolids for the production of renewable resources like methane gas or biodegradable biopolymers (i.e. polyhydroxyalkanoates)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
