Comparing Implementation of MBBR versus BAF on a Space Constrained Site

The City of San Diego has been evaluating high-rate technologies for the possible use at the Point Loma Wastewater Treatment Plant should an upgrade from chemically enhanced primary treatment be needed. The results of a biological aerated filters (BAF) pilot test conducted earlier by Brown and Caldwell shows that the BAF process should be considered. In addition, a concept involving high rate plate settler followed by moving bed bioreactor (MBBR) and dissolved air flotation clarification was investigated and compared with the BAF. Although the proposed MBBR process train seems viable, the proposed loading rates for each process unit were at the upper end of the typical operating range. The total project capital cost was about 116 million lower for the MBBR alternative as compared to BAF alternative. However, the net present value for the MBBR alternative was 40 million higher, mainly because of increased chemical and power demands.