Operational factors affecting enhanced biological phosphorus removal at the waste water treatment plant in Helsingborg, Sweden

Enhanced biological phosphorus removal (EBPR) has since 1992 been run as a full-scale UCT-process in a part of the waste water treatment plant in Helsingborg. Between June 1993 and July 1994 an extended operational and microbiological investigation was conducted. It was shown that the major phosphorus removal mechanism was biological and that at the most 10% of the soluble phosphorus entering the biological reactor, was removed due to chemical reactions. The VFA-potential in pre-treated waste water has been found to be a key factor. At the waste water treatment plant in Helsingborg 1 mg phosphorus is removed for each 14 mg VFA-potential added. COD, soluble COD and BOD 1 are correlated to the VFA-potential, which means that these measurements can be used as operational parameters. If enough VFA-potential is present, the concentration of soluble phosphorus will be lower than 0.3 mg/l in the effluent even at temperatures below 10°C. The mean concentration of soluble phosphorus in the effluent has been 0.29 mg/l during the period October 1993-July 1994. Effluent nitrogen concentration was during the evaluation period between 8–10 mg/l and it was found that PHA was one of the major carbon sources for denitrification. Compared with a pre-denitrification process in combination with simultaneous precipitation, both the filament index and the DSVI were lower in the EBPR process. Other operational factors that affect the process are oxygen and nitrate concentrations in flows to the anaerobic reactor and the degree of internal recirculation from the aerobic to the anoxic reactor.