Throughout the industrialized world regulators are pushing towards more stringent discharge standards for municipal, industrial, and agricultural wastewater treatment facilities. Meeting these standards requires more and more facilities to apply methods of nutrient removal. Amongst
these methods, biological phosphorus removal is gaining popularity due to the potential for savings in chemical costs. Today, the mechanism of enhanced biological phosphorus removal (EBPR) is fairly well understood. Yet for many treatment plants that operate EBPR and anaerobic digestion, a
number of significant interrelations exist, some of which may hold the key to success and level of phosphorus removal. The main interrelations include the uptake and release of phosphate, magnesium, potassium, and ammonia; corresponding crystallization reactions, calcium phosphate precipitations;
solids processing recycle phosphate load; and the required load of readily biodegradable COD. This paper discusses some of the EBPR process optimization results and two years of operation experience at Durham Facility, Portland Tigard OR. While the facility has been delivering exceptional
biological phosphorus removal results (<0.2 mg/L secondary effluent PO4-P), questions regarding sustainability of the performance and the various trends and relationships that have been observed triggered a more detailed investigation into the fait in biological phosphorus removal.
The data collected at Durham suggest that other (chemical) processes play a major role in the overall phosphorus removal. During the investigation, a combination of biological and chemical process modeling was used to simulate the observed EBPR performance. The simulation results confirmed
our assumptions and are consistent with the finding of others. The metal phosphate precipitation can make as much as 60% of the digested solids phosphorus, which underlines the importance of the relationships between metals and EBPR. This paper points out some of the interrelations
between metal ions, EBPR, and phosphate crystallization.
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