Utilization of sewage sludge as a resource for protein extraction and recovery

Abstract

The utilization of sewage sludge as a source of protein for recovery has been investigated. Three sewage works were chosen having various types of inlet, ranging from sewage of mainly domestic origin to that containing a considerable proportion of trade effluents. Protein concentration profiles were traced throughout the various stages of the sewage work operations. The results indicate that a certain amount of the protein material settles out during the primary sedimentation process but most is removed from the sewage effluent and incorporated into the secondary sludge through the biological oxidation and the coagulation processes at the secondary treatment stage. The protein contents of the primary sludge samples ranged between 12 and 29% (dry wt.) and those of the secondary sludge samples between 25 and 50% (dry wt.). Various means were examined for the extraction of protein from primary and secondary sludge samples. An extraction process, consisting of mechanical homogenization, acidification and thermal treatment, followed by pre-concentration and precipitation was proved practicable. The protein extracted from the secondary sludge samples was of better quality than that from the primary sludge samples, in terms of higher crude protein content and lower contamination levels. The recovered protein was considered to be of high nutritional value; chemical analysis indicated that it was rich in essential amino acids, particularly methionine, cysteine and lysine.