The amount of protein wasted through sludge in Gauteng, South Africa, amounts to 95 000 metric tonne/yr, with the order of magnitude of the national protein requirement of approximately 145 000 metric tonne/yr. Waste-activated sludge (WAS) from wastewater treatment plants (WWTPs) that treat domestic wastewater contains protein in a ratio of 2:1 against fishmeai. This protein source has not been utilized because of the high content of toxic heavy metals and other potential carcinogenic pollutants in the sludge, in this study, a pretreatment method of modified aqua regia dilute acid wash was used to lower the metal content by approximately 60%. However, this resulted in a 33% loss of amino acids in the acid-washed WAS. A feed substitution test in poultry with different fishmeal-sludge ratios (0%, 25%, 50%, 75%, and 100% WAS as percent substitution of fishmeai) showed no impact of sludge single-cell protein (SCP) on mortality rate. However, sludge substitution in the feed yielded weight gains and cost savings up to 46%. Water Environ. Res., 84, 2106Res., 84, (2012.

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