Assessment of the Nutritional Value of Single Cell Protein from Waste Activated Sludge: A Comprehensive Comparison with Fishmeal

Sludge from medium sized wastewater treatment plants [16-30 MLD (4.2-8.4 MGD)] was characterized for protein and amino acid content. An extraction procedure was developed to render the sludge free of toxic heavy metals and other recalcitrant organic pollutants. Recommendations are drawn on the type of animals utilized based on the amino acid distribution and nucleic acid content. Waste activated sludge from three wastewater treatment plants (Baviaanspoort, Zeekoeigat, Rooiwal) was studied. The sludge from Zeekoeigat had the highest crude protein content (38 %), and proteins were extracted from this sludge using thermal solubilisation. The protein concentration of the sludge that was digested at 120°C and 150°C was 0.82 mg/ml and 0.47 mg/ml, respectively. The heavy metal content (Zn; Cu; Cd; Mn; Pb) of the sludge was compared to that of maximum tolerable metal concentration in the feedstuffs of animals and were found to be higher. Thus, a heavy metals removal process was recommended using leaching by 1 M HCl or 1 M citric acid, which was shown to be effective.