Growth of Daphnia magna on urban wastewaters tertiarily treated with Scenedesmus sp.

Abstract

The productivity and composition of Daphnia magna were measured for high density populations grown in 5-litre flow-through tanks supplied with a tertiary effluent. This effluent was urban secondary wastewaters biologically treated with intensive cultures of a microalga Scenedesmus sp. Three daily feeding rates (575, 1150, 1750 mg dry weight algae day −1 tank −1), obtained by adjusting the flow of a tertiary effluent containing 115 mg dry weight of algae litre −1, allowed average productions of 0·9, 1·6 and 2·6 g of Daphnia (wet basis) litre −1 week −1 which were proportional to the rations. When the flow of tertiary effluent was increased to 40 litres day −1 tank −1 ( ad libitum), the average yield rose to 3·6 g of daphnids (wet basis) litre −1 week −1. The maximum population reached 48 000 individuals litre −1. The daphnid/algae evergy conversion ratio was 0·4. Algae were removed by Daphnia at a maximum efficiency of 95%. The composition of Daphnia biomasses was 59·5% protein, 9·5% fat and 5·6% carbohydrate on a dry weight basis. No deficiencies in methionine and linolenic acid were noted. Results indicated the remarkable potential of urban wastewaters for the production of protein and the high productivity of Daphnia magna.