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Assessment of Nutritional Value of Single‐Cell Protein from Waste‐Activated Sludge as a Protein Supplement in Poultry Feed

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 fishmeal. 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 fishmeal) 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%.