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 equivalent sodium or potassium salts; more soluble in water. In the case of alkaline salts of fatty acids (soaps) reported in the present work, we have obtained a biodegradation of 80% average in anaerobic digesters, which is still significantly different from the expected value of 100% assumed theoretically for sodium or potassium derivatives. Soap biodegradation in anaerobic digester was studied both in laboratory scale equipment as well as on commercial scale digester of sewage treatment plants (STP). In the second case the biodegradation was further monitored on sludge amended soils using the sludge from STPʹs monitored in first step of the study. It was found that as a consequence of aerobic conditions prevalent in soil layer studied the remaining soap further biodegrades up to nearly 100% after 150 days.