Mechanisms of Decreased Digestibility in Chemically-Coagulated Wastewater Sludges

摘要

Previous studies have indicated that coagulants used in wastewater treatment (principally alum or ferric chloride) caused resulting sludges to be less biodegradable in subsequent anaerobic digestion. The objectives of this research were: to determine the types of organic materials whose digestibility is most affected by coagulants; and to investigate the effect of coagulants on enzymatic hydrolysis of complex organic material. Substrates studied included: raw wastewater, activated sludge, three proteins, glycine, cellulose, glucose, butyric acid, and palmitic acid. In general, those substrates whose digestibilities were most affected were those that are insoluble in water and/or are known to form complexes with iron or aluminum. Thus, amino acids, proteins, and long-chain fatty acids were particularly affected, while glucose and butyric acid were not. Cellulose was moderately affected, suggesting that physical enmeshment, as well as chemical interactions may be important in determining extent of coagulant effects.