Co-digestion of primary sewage sludge and industrial wastewater under anaerobic sulphate reducing conditions: enzymatic profiles in a recycling sludge bed reactor

The first stage in the degradation and recycling of primary sewage sludge and particulate organic matter is the solubilisation and enhanced hydrolysis of complex polymeric organic carbon structures associated with the anaerobic sulphidogenic environment. Solubilization of complex carbon substrates provides the primary reaction in the BioSURE Process, and is effected in the recycling sludge bed reactor (RSBR). During the process of anaerobic digestion, macromolecules are broken down into simpler low molecular weight compounds in the presence of extracellular enzymes. Though hydrolysis of the complex carbon sources was enhanced under biosulphidogenic conditions, no studies have examined the role of enzymes and the enzymatic profiles in the RSBR. To investigate the overall enzymology in the RSBR variations in COD, pH, sulphate, sulphite and sulphide concentrations, carbohydrates, protein and activities of glucosidases, proteases and lipases were studied over 50 days in the reactor at three different depths: 0-16 cm; 16-32 cm; 32-50 cm. While the pH profile remained fairly constant between 6.9 and 7.3 the sulphate and sulphide levels, as expected, changed dramatically as sulphate reduction took place. Proteases, lipases and glucosidases all showed enhanced activity with depth in the bioreactor. It is suggested that the increased sulphide concentration generated during the sulphate reduction process stimulates the enzymes, leading to enhanced solubilisation of primary sewage sludge.