The Mass Balances of Nitrogen and Carbon in a Compact Nitrogen and Phosphorus WWTP

Abstract

This paper presents the overall mass balances for water, total nitrogen and organic carbon in a WWTP in Vestfjorden Avløpsselskap (VEAS), Norway in 1997.

The treatment process consists of chemical pre-precipitation followed by upstream biofilm nitrification and denitrification filters and side stream removal of ammonia by air stripping from sludge filtrate water after digestion of sludge. This new process is very compact, with a total water retention time of less than 4 hours, achieving 74 % nitrogen and 96 % phosphorus removal in 1997.

Controls indicate that the water and total nitrogen mass balances are very reliable. The carbon mass balances are also good, but there seem to be some methodological problems concerning determination of carbon in the sludge streams. A way of avoiding the problems is described.

The chemical pre-precipitation step is very efficient as it removes 31 % of the nitrogen and 82 % of the carbon from the water before biological treatment. The ammonia stripping removed 12% of nitrogen with a potential of 19%.