Ten years of full-scale experience with enhanced biological phosphorus removal (EBPR) has been evaluated. During the start-up period lack of carbon source was the main operational problem and a higher level of volatile fatty acids was secured by introducing a primary sludge hydrolysis. Acidic thermal sludge hydrolysis was used as the sludge treatment method at the plant during about three years. One effluent stream, rich in carbon and precipitant, was brought back to the process leading to an improvement of the phosphorus removal both by an improved biological process and chemical precipitation. A quite stable process of EBPR was developed with low levels of effluent phosphorus concentration. Stringent effluent discharge limits during short evaluation periods necessitated a continued work for improvement of the short-term stability. During periods with lack of carbon, such as industrial holiday or rainy periods, both simultaneous precipitation and reduced aeration have been successfully tested as strategies for securing low levels of effluent phosphorus.

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