Application of oxidation-reduction potential as a controlling parameter in waste activated sludge hydrolysis

In order to destroy the refractory structure of waste activated sludge (WAS) and increase its biodegradability, chemical pretreatment by adding NaOH was used in this study to enhance the hydrolysis of the WAS collected from the Taipei Min-Sheng Sewage Municipal Wastewater Treatment Plant located in northern Taiwan. Experiments were conducted with four total suspended solids (TSS) concentrations (0.5-2.0%) and four NaOH dosages (20-80 meq/l) at 25 degreesC. It was found that the optimal condition for WAS hydrolysis was TSS of 1% and NaOH dosage of 40 meq/l; 45% of soluble chemical oxygen demand (SCOD) was solubilized in the pretreatment time of 10 h. When the WAS was hydrolyzed by adding NaOH, profiles of oxidation-reduction potential (ORP) values were monitored on-line; also, a model covering the relationship between the change of ORP value and increase in SCOD was developed. This verified that the ORP monitoring technique is not only useful to investigate the solubilization rate but also suitable for the determination of optimal solubilization in WAS treatment. Considering the release of nitrogen by alkaline pretreatment, profiles of total Kjeldahl nitrogen, ammonia-nitrogen and amino acids were investigated. (C) 2002 Elsevier Science B.V. All rights reserved.