Long-term performance and characterization of a membrane bioreactor in the treatment of wastewater containing high-molecular-weight compounds.

摘要

In the present study, a pilot-scale, ceramic membrane bioreactor (MBR) system was operated for over 4 years to assess its effectiveness in the treatment of a simulated municipal wastewater containing high molecular weight compounds. A bench-scale conventional activated sludge (AS) system was constructed and operated in parallel to the MBR, enabling a thorough evaluation of the advantages and limitations of the technology. A number of different studies were conducted to expand the state of the art of the MBR process.; The MBR system purified municipal wastewater containing primarily casein and starch to levels sufficient for indirect water reuse applications. The effluent was well within the esthetic limits of potable water in terms of turbidity, color, odor, pH and organic content. The produced water was free of microorganisms and viruses, satisfying potable water standards and significantly reducing the dose for final disinfection. The same inorganic membrane was used for about 4 years, verifying the durability, reliability, and economic feasibility of such units.; The bio-degradation mechanisms and pathways of the primary wastewater component were determined using aerobic respirometry under various initial substrate/biomass ratio conditions utilizing radioactively labeled casein. Respirometry studies also showed that, given sufficient contact time, the soluble fraction of the MBR mixed liquor was partially biodegradable, and that exocellular activity in the MBR was limited. The impact of various operational parameters and mixed liquor properties such as temperature, trans-membrane pressure, cross flow velocity, concentration of suspended solids, and concentration of soluble organic compounds on the permeate flux were determined.; Compared to the AS system, the MBR system retained all microorganisms, enzymes and difficult to degrade organic compounds, resulting in a highly active microbial culture capable of degrading a wider range of complex compounds. The bio-diversity of the microbial culture as well as physical parameters such as particle size distribution, filtrability, and settlebility of the mixed liquor were substantially different in the MBR than in the AS system.; Phosphorus was identified as an important compound in the operation of the MBR. The impact of excess and limited phosphorus conditions on the biological characteristics and filtration performance were evaluated. Shock loads of phosphorus resulted in temporary peaks in the concentration of organic compounds in the effluent. Excess free phosphorus lead to the formation of inorganic precipitants which caused abrasion of the active filtration layer of the ceramic membrane. These structural changes resulted in the deterioration of the produced water and, ultimately, in the failure of the system.; The effectiveness of the MBR system remained consistent at different solid retention times ranging from 30 days to 10 days. Biomass production rates and biomass viability increased steadily with decreasing SRT, whereas overall enzymatic activity did not vary significantly with SRT. A substantial reduction of specific enzymes was observed in the soluble mixed liquor of the MBR with decreasing SRT, verifying the retention of exo-cellular activity. Biomass population diversity in the MBR varied substantially, while the overall capacity of the biomass to degrade different carbon substrates did not change significantly at different SRTs. The concentration of metals in the MBR mixed liquor declined steadily with decreasing SRT. The effluent of the MBR contained negligible amounts of Fe, Zn, Mn, and Co at each condition, indicating the full retention of these metals regardless of SRT.