Abstract
The feasibility of applying direct, advanced treatment to municipal wastewater has been investigated. A two-stage scheme was implemented. The first stage was direct chemical coagulation of primary effluent using different coagulants to remove suspended solids and reduce the carbon-to-nitrogen ratio to a range suitable for nitrification. The second stage was the use of a biological sand-bed to oxidize ammonia to nitrate. The pilot plant was designed to treat 6 m 3 day −1. The results obtained show that chemical coagulation using ferric chloride gives high quality effluent suitable for agricultural purposes. Nitrification of the chemically treated effluent using a sand-bed at an overflow rate of 1.358 m 3 m −2 day −1 completely eliminated ammonia. Almost complete removal of suspended solids was achieved. Residual COD and BOD values were 45 and 15.5 mg l −1 respectively. Fish biotoxicity was completely eliminated after the nitrification process.
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