Werf: Application of Membrane Bioreactor (Mbr) Technology for Wastewater Treatment

Abstract

One of the most promising and innovative technologies in water reclamation today is the membrane bioreactor (MBR) process. (Adham et al., 1998) However, the limits of the MBR process for wastewater treatment are not very well understood to date. With funding provided by WERF and in-kind contributions provided by the City of San Diego, the project team investigated the MBR process for wastewater treatment. Two MBR pilot units were operated in parallel to effectively evaluate each test condition on domestic wastewater in San Diego, California. The project was designed to evaluate the limitations and the advantages associated with the MBR process. The first part of the study evaluated the MBR process under high organic loading rates while sustaining nitrification at relatively long sludge ages. The second part of the study evaluated the MBR process under non-nitrifying conditions and reduced suspended solids concentrations. Through out the entire period of testing, regardless of extreme operating conditions, the MBRs consistently produced water that resulted in non-detect BOD 5 values and an average COD removal of greater than 90%. The effluent turbidities averaged 0.1 NTU through out the testing period. In addition, the MBR effluents consistently exceeded the water quality of the full-scale tertiary plant that was treating the same wastewater.

The Effect of Organic Loading on Membrane Fouling in a Submerged Membrane Bioreactor Treating Municipal Wastewater

“…Cicek et al (2001), working with an EMBR treating synthetic wastewater, found that the specific flux decreased when the F/M reached 1.05 gCOD/gVSS . d. Trussell et al (2000) found that the membrane fouling rate in an SMBR treating municipal wastewater increased at an F/M of 1.10 gBOD/gVSS . d. Because Trussell et al (2000) and Cicek et al (2001) did not operate at constant MLSS, it is possible that the low MLSS values they obtained at high F/Ms were responsible in part for membrane fouling .…”

“…In previous SMBR experiments on municipal wastewater Trussell et al (2000) obtained a median effluent COD value of 22 mg/L and a 90 th percentile value of 28 mg/L over the range of MCRT values from 1.5 d to 35 d. At an MCRT below 2 d, Trussell et al (2000) found that the effluent COD increased to a median value of 30 mg/L and a 90 th percentile value of 32 mg/L. At an MCRT of 2 d, Cicek et al (2001) found that the median effluent COD increased to 23 mg/L from 3.5 mg/L at a 5-d MCRT.…”

“…When an SMBR process fails, the effluent quality is not severely affected, but the effluent flow rate decreases. Regardless of operating conditions, SMBR effluents contain undetectable concentrations of total suspended solids (TSS) (< 2 mg/L) and have low chemical oxygen demand (COD) (20-30 mg/L) because of the filtration provided by the membrane (Adham et al, 2001, Trussell et al, 2000. At frequent intervals in a vacuum-driven SMBR operating cycle (min), the vacuum is released and most of the materials accumulated on the membrane surface are removed by coarse bubble aeration.…”

“…To maintain membrane permeability, the SMBR process is limited to maximum mixed liquor suspended solids (MLSS) concentrations of 10 -20 g/L (Cote et al, 1998, Mourato et al, 1999, Shimizu et al, 1996, Trussell et al, 2000, Ueda et al, 1997. Current practice is to operate the SMBR process at MLSS levels of approximately 10 g/L (ZENON Environmental Services, Inc.; Mitsubishi Rayon, Inc.; Kubota Inc.).…”

“…Biological foaming caused by nocardioform bacteria was controlled by mechanical means ( Figure 5) rather than with an NaOCl surface spray (Trussell et al, 2000). When the membrane tank intermittent aeration was on, its liquid level was higher than that in the ML recycle line; when the membrane tank intermittent aeration was off, its liquid level was lower than that in the ML recycle line.…”