Experience with Biological Nutrient Removal at Low Temperatures
Abstract:Operating experience for the first enhanced biological phosphorus (EBPR) and biological nutrient removal (BNR) plant in Norway are summarized. The primary objective during the first years of operation was to remove phosphorus at low temperatures both in an EBPR mode and a BNR mode. Enhanced biological phosphorus removal was accomplished at 5 °C with 0.6 mg/L total phosphorus in the effluent, and BNR was achieved at 6 to 8 °C with an average of 0.25 mg/L phosphorus and 5.3 to 9.6 mg/L nitrogen in the effluent. Solids were separated by gravity settling only. Sufficient solids retention time resulted in biological phosphorus and nitrogen removal at low temperatures with two-thirds of the sludge production compared with chemical phosphorus removal. In the approximate plug-flow biological reactor, a completely stirred tank reactor with seven compartments, a mixed liquor suspended solids concentration of 6000 to 8000 mg/L was maintained because of the excellent settling characteristics of the sludge (diluted sludge volume index 5 60 to 80 mL/g). Plug-flow mixing characteristics result in a substrate gradient that promotes growth of rapid-settling bacteria and depresses growth of filamentous bacteria. Organic reduction in the anaerobic and anoxic zones results in a low organic loading rate to the aerobic zones with subsequent favorable conditions for nitrification.
Document Type: Research Article
Publication date: July 1, 2000
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