Based on overall mass balances for water, total nitrogen and organic carbon in the VEAS WWTP in 1997, alternative strategies for nitrogen removal are discussed based on cost optimisation. Marginal costs for biological removal are compared with total costs for side stream treatment by ammonia stripping. If the plant has sufficient capacity to meet the effluent requirements with biological removal alone, this study demonstrates that the price of methanol determines whether or not invetment in ammonia stripping still is a cost efficient solution.
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© IWA Publishing 2000