Assessment of nutritional value of single cell protein from waste activated sludge

Abstract

In recent years there has been pressure exerted on the feed industry in Southern Africa to produce enough animal feed to meet the region’s nutritional requirements. The increase in the cost of animal feed eventually affects the affordability and availability of high quality food to low income communities. However, the overall national production of protein feed can easily be surpassed by the amount of protein that could be extracted from sludge. For example, the amount of protein wasted through sludge in one province alone (Gauteng, South Africa) amounts to 106,763 metric tonnes/yr, and slightly lower than the national protein requirement of approximately 145,000 tonnes/yr. Waste Activated Sludge (WAS) from wastewater treatment plants treating domestic wastewater is shown to contain protein in a ratio of 2:1 against fishmeal. However, some of this protein content could be lost during processing. In this study, the protein content in sludge and fishmeal was evaluated in laboratory analyses conducted as a preliminary step towards designing a protein supplement substitute. A pilot test was conducted with 5 batches (10 chicken per batch), with fishmeal to sludge substitutions of 0%, 25%, 50%, 75%, and 100%. Metal content in the sludge was lowered by a rudimentary leaching process and its impact on the protein content was also evaluated. The initial mass gain rate, mortality rate, initial and operational costs analyses showed that protein from Waste Activated Sludge (WAS) could successfully replace the commercial feed supplements with a significant cost saving without adversely affecting the health of the animals. Copyright