Biodegradation of soap in anaerobic digesters and on sludge amended soils

Water hardness plays an important role in waste water treatment processes. Calcium and/or magnesium salts of organic products are mostly precipitated due to their low solubility and they are less biodegradable than the equiva lent sodium or potassium salts; more soluble in water. In the case of alkal ine salts of fatty acids (soaps) reported in the present work, we have obta ined a biodegradation of 80% average in anaerobic digesters, which is still significantly different from the expected value of 100% assumed theoretica lly for sodium or potassium derivatives. Soap biodegradation in anaerobic d igester was studied both in laboratory scale equipment as well as on commer cial scale digester of sewage treatment plants (STP). In the second case th e biodegradation was further monitored on sludge amended soils using the sl udge from STP's monitored in first step of the study. It was found that as a consequence of aerobic conditions prevalent in soil layer studied the rem aining soap further biodegrades up to nearly 100% after 150 days. (C) 1998 Elsevier Science Ltd. All rights reserved.