The enzymology of sludge solubilisation utilising sulphate-reducing systems: the properties of lipases

• Published in: Water research (Oxford) Vol. 37; no. 2; pp. 289 - 296
• Main Authors: Whiteley, C.G., Burgess, J.E., Melamane, X., Pletschke, B., Rose, P.D.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 2003; Elsevier Science
• Subjects: Anaerobic digestion; Applied sciences; Biodegradation, Environmental; Enzymology; Exact sciences and technology; Hydrogen-Ion Concentration; Lipase - pharmacology; Lipases; Other industrial wastes. Sewage sludge; Pollution; Polymers - metabolism; Sewage - chemistry; Sewage - microbiology; Sludge solubilisation; Solubility; Sulfates - metabolism; Sulfur-Reducing Bacteria - physiology; Temperature; Waste Disposal, Fluid; Wastes; Water treatment and pollution; Enzymology; Lipases; Anaerobic digestion; Sludge solubilisation; Sonication; Organic matter; Enzyme; Waste treatment; Triacylglycerol lipase; Esterases; Sulfates; Sewage sludge; Optimization; Carboxylic ester hydrolases; Biological purification; Hydrolysis; Bioreactor; Hydrolases; Recycling; Biological treatment
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/S0043-1354(02)00281-6

The first stage in the degradation and recycling of particulate organic matter is the solubilisation and enhanced hydrolysis of complex polymeric organic carbon structures associated with the sulphidogenic environment. An investigation into the enzymology of these processes has shown that lipase enzyme activities were found predominantly associated with the organic particulate matter of the sewage sludge. Sonication of the sludge gave an increase in enzyme activity as the enzymes were released into the supernatant. pH and temperature optimisation studies showed optima between 6.5 and 8 and 50–60°C, respectively. All the lipase enzymes from the methanogenic bioreactors indicated extensive stability for at least an hour at their respective optimum temperatures and pH; sulphidogenic lipases reflected limited stability at these temperatures and pH during this time period. Though sulphate showed inhibitory properties towards lipases both sulphide and sulphite appeared to enhance the activity of the enzymes. It is argued that these sulphur species, liberated at different times during the sulphate reduction process, disrupt the integrity of the organic particulate floc by neutralising acidic components on the surface. The release of further entrapped enzymes from the organic particulate matter result in a subsequent enhancement of hydrolysis of polymeric material.