Membrane Bioreactors for Water Reclamation - Phase II

City of San Diego; San Diego CA.
November 2000

Report #60 - Executive Summary -

The City of San Diego and its program manager, Montgomery Watson, performed a parallel comparison of MBRs from two leading manufacturers - Zenon Environmental Systems, Inc., and Mitsubishi Rayon Corp. Both systems were operated on a pilot-scale for over 6,500 hours (270 d). Each system was operated in a nitrification/denitrification and a nitrification only mode. The effluent from each MBR system was further treated by two RO pilot units operated in a single-stage mode.

The MBR was evaluated both for its ability to produce high quality effluent as well as its ability to produce water suitable for use by an RO system. Both membranes demonstrated little fouling thoughout the testing period. Both systems were capable of producing water with BOD₅ values of less than 3 mg/L, and up to 6-log removal of total coliforms. The effluent water had consistent turbidity values less htan 0.1 NTU and SDI values of less than 3 leading to little fouling by the subsequent RO membranes.

The cost competitiveness of the MBR technology with current water reclamation technologies was also evaluated. A cost comparison was performed analyzing several technologies capable of producing conventional secondary effluent, Title 22 reclaimed water, and water suitable for use by an RO system. The cost analysis evaluated capital and O&M costs to assess the feasibility of future MBR application on an economic basis. The analysis revealed that the MBR is a cost competitive alternative to producing water suitable for use by an RO system at a 1 and 5-MGD capacity. However, existing techologies remain more cost competitive for producing Title 22 reclaimed water.