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A biological nutrient removal (BNR) activatedsludge (AS) scheme incorporating external nitrification in a fixed media system is evaluated. A laboratory scale investigation of the scheme indicates that it holds considerable potentialfor BNRAS system intensification through major reduction in sludge age and oxygen demand and significant improvement in sludge settleability. Because the BNRAS system is not required to nitrtfy, its anoxic mass fraction can be considerably enlarged at the expense of the aerobic mass fraction creating conditions that (i) allow it to achieve high N removals with domestic wastewaters with high TKN/COD ratios and (ii) promote anoxic P uptake polyphosphate accumulating organisms (PAO) to develop in the system. From this, andearlier investigations with conventional BNR systems, it appears that anoxic P uptake biological excess P removal (BEPR) is only about 2/3rds of aerobic P uptake BEPR. Inclusion of anoxic P uptake PAOs in, and exclusion of nitrtfiers from, the BNRAS system are not essentialfor the scheme. However, conditions that promote aerobic P uptake to maximize BEPR, are also conducive to nitrifier growth, which, if supported in the BNRAS system, would require virtual complete nitrification in the fixed media system to avoid nitrate interference with BEPR. Before the scheme can be implemented at large scale, an engineering and economic evaluation is required to quantify its potential benefits and savings.

Document Type: Research Article


Publication date: 2001-01-01

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