A six‐stage membrane bioreactor (MBR) pilot plant was operated to determine and demonstrate the capability of this process to produce a low‐nutrient effluent, consistent with the nutrient reduction goals for the Chesapeake Bay. Biological nitrogen removal was accomplished using a multistage configuration with an initial anoxic zone (using the carbon in the influent wastewater), an aerobic zone (where nitrification occurred), a downstream anoxic zone (where methanol was added as a carbon source), and the aerated submerged membrane zone. The capability to reliably reduce effluent total nitrogen to less than 3 mg/L as nitrogen (N) was demonstrated. A combination of biological (using an initial anaerobic zone) and chemical (using alum) phosphorus removal was used to achieve effluent total phosphate concentrations reliably less than 0.1 mg/L as phosphorus (P) and as low as 0.03 mg/L as P. Alum addition also appeared to enhance the filtration characteristics of the MBR sludge and to reduce membrane fouling. Aeration of the submerged membranes results in thickened sludge with a high dissolved oxygen concentration (approaching saturation), which can be recycled to the main aeration zone rather than to an anoxic or anaerobic zone to optimize biological nutrient removal. Biological nutrient removal was characterized using the International Water Association Activated Sludge Model No. 2d. The stoichiometry of chemical phosphorus removal was also consistent with conventional theory and experience. The characteristics of the solids produced in the MBR were compared with those of a parallel full‐scale conventional biological nitrogen removal process and were generally found to be similar. These results provide valuable insight to the design and operating characteristics of MBRs intended to produce effluents with very low nutrient concentrations.
The effect of aluminum sulfate (alum) addition on membrane performance was investigated, with a particular focus on membrane fouling. During initial operation, alum was added and the performance monitored. After terminating alum addition, the transmembrane pressure (TMP), which is indicative of membrane resistance to flow or fouling, increased. Accompanying the increase in TMP was an increase in the organic nonsettleable fraction (colloidal + dissolved) content of the mixed liquor and deterioration of permeate quality and floc strength. Permeate polysaccharide concentrations increased significantly, suggesting a preferential binding of solution polysaccharides by alum. Upon reinitiating alum addition, the TMP only partially recovered, indicating some irreversible fouling, while mixed liquor nonsettleable organic material, permeate quality, and floc strength returned to initial levels. These results suggest that direct alum addition to membrane bioreactors can improve membrane performance by reducing the organic fouling material and improving floc structure and strength. It appears that bulk liquid polysaccharides may contribute to irreversible membrane fouling, and this fraction can be efficiently controlled through the alum addition.
The paper describes a pilot study that confirmed that membrane bioreactor (MBR) technology can cost-effectively meet level-of-technology limits for nutrients, organics, and removal of pathogens. The study was conducted for the Loudoun County Sanitation Authority (LCSA) and was operated from
The proper evaluation of advanced waste treatment (AWT) process alternatives for water reclamation (WR) is particularly important for those planning new or expanded facilities. Recent advances in technology, particularly with regard to the successful use of membranes in wastewater treatment applications, have provided the industry with many possible process combinations that did not exist just a few years ago.The focus of the paper will be on an evaluation that compared conventional and membrane AWT processes for the reclamation of municipal wastewater. The evaluation led to the determination that membrane bioreactor (MBR) processes are suitable for large-scale WR applications. The evaluation also led to the development of a unique process configuration using two immersed membrane reactors in series. The first reactor is a multi-zone MBR for biological treatment configured for nutrient removal and the second reactor is an immersed membrane reactor with powdered-activated carbon (PAC) addition for the removal of residual organic materials. The results of the study and the innovative solutions described in the paper may set the tone for WR in the twenty-first century.
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