Domestic sewage and some types of agroindustrial waste, although highly polluting wastes, could become important energy and protein sources because they are wastes which contain significant amounts of organic matter and nutrients used by human beings.

Based on this concept, experiments at different scales (laboratory, semi-pilot and pilot) have been carried out to verify the viability of a system composed of an anaerobic pond, an algae pond and a Zooplankton pond for the treatment of domestic sewage and, at the same time, to reuse the Zooplankton as animal feed. Scenedesmus sp and Daphnia sp were introduced into the algae and zoo-plankton ponds, respectively, to be maintained as the predominant biological element.

The best operational performance was obtained when the Zooplankton pond was operated with a semicontinuous flow system, with 50% of the Zooplankton pond water being renewed with effluent from the algae pond every 2 or 3 days.

The productivity of Daphnia sp under these operational conditions reached around 35 mg/l (dry weight). This corresponds to a production of 700 kg of microcrustaceans per day for a city with 100,000 inhabitants.

The BOD removal efficiency obtained during the experiment was 95-97%, and total ? and total ? removals were 42-59% and 37-48%, respectively. The final effluent had high transparency. In the Zooplankton pond, the algae concentration was reduced from 106cells/ml to 102 cells/ml, which corresponds to a removal efficiency of 99.99%.

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