The implications for the UK of the forthcoming Urban WasteWater Directive 1991 will mean at many sites a tightening of existing discharge standards. At those sites classified as discharging to sensitive watercourses, limits for nutrient removal (N and P) will be imposed and for the largest works above 100,000 PE implementation is required by 1998.

Very little experience of N and P removal currently exists in the UK and water companies will need to develop the necessary investment strategies based for the most part on retrofitting well proven technologies to existing secondary treatment works.

A strategy has been developed for nutrient removal in Severn Trent Hater, a company which serves a sewered population of 8 million and controls 1043 waste water treatment plants.

The paper outlines the technologies that will be retrofitted to existing trickling filter installations and activated sludge plants to achieve the necessary standards for N and P removal.

A comparison of the various options for biological P removal is included and that the preferred UCT process configuration or sidestream Phostrip process have been selected as preferred options.

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