Effect of chemical coagulation on anaerobic digestibility of organic materials

Abstract

Previous studies have indicated that coagulants used in wastewater treatment (principally alum or ferric chloride) cause 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. 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.