Pilot Study on Treatment of Wastewater from an Ethylene Plant with Membrane Bioreactor Technology
Pilot studies were conducted with an anoxic/aerobic concept membrane bioreactor (MBR) technology and a hollow fiber Petro ® MBR system with capacity of 12 m 3 /d was operated continuously (24-hour) during the study. Trials on different membrane fluxes were conducted to obtain the sustainable flux while mixed liquor suspended solid (MLSS) was maintained at 9-11 g/L. The results of the MBR pilot trials showed that no obvious fouling of the membrane was found when the plant was operated at the flux of 12 L /m 2 /h (LMH) over 3 months and 15 LMH over one month during the pilot study. Design guidelines such as hydraulic retention time (HRT), sludge retention time (SRT), anoxic and aera- tion volume ratio, re-circulation flow rate and air scouring were obtained for a full-scale plant. It was concluded that treatment of wastewater from an ethylene plant without addition of any chemicals using MBR technology is feasible. The product quality consistently met the requirement for discharge and was suitable for the feed of further reverse osmosis (RO) post-treatment.
New option of MBR-RO process for production of NEWater from domestic sewage
Abstract The membrane bioreactor (MBR), a combination of conventional activated sludge process (ASP) and membrane separation, can produce consistently high quality of effluent from municipal wastewater. Successful pilot studies have already demonstrated the advantages of MBR technology for reclaiming the domestic sewage in Singapore. The objective of this pilot study was to further investigate a new option of the MBR-RO process to produce high grade water directly from domestic sewage. The MBR-RO process was evaluated over 5 months for its ability to produce better quality effluent. Trial runs on various fluxes of the RO membrane were conducted. Comparison of the new MBR-RO process to the conventional ASP-MF-RO process was also made. The results showed that the new MBR-RO process demonstrated the capability of producing the same or more consistent product quality (in terms of TOC, NH4 and NO3) compared to the conventional ASP-MF-RO process in reclamation of domestic sewage. RO membranes in the MBR-RO process could be operated at 22 L m−2 h−1 without CIP during the whole study period of 5 months, which was 30% higher than that (17 L m−2 h−1) in the ASP-UF-RO process for NEWater production. RO permeate quality was improved with increasing the membrane flux. It was concluded that the MBR-RO process could be a new option for NEWater production.
AXIOMATISABILITY OF WEAKLY FLAT, FLAT, AND PROJECTIVE S-ACTS
ABSTRACT This paper gives necessary and sufficient conditions on a monoid S that the class of flat left S-acts be (first order) axiomatisable. It presents also a streamlined version of the result of Stepanova that the class of projective left S-acts is axiomatisable if and only if the strongly flat left S-acts are axiomatisable and S is left perfect.