Effect of additives on volatile fatty acid production in anaerobic digestion

Abstract

Laboratory-scale experiments were conducted to study the effect of additives on the process of anaerobic digestion in general and on the production of volatile fatty acids in particular. Twelve reactors with a working volume of 3-litres were operated as anaerobic digesters and were loaded daily with 150 ml of the primary sludge with an average volatile solids content of about 3%. Five commercial additives - Biocope, Medina d-part, MPC, Alken Murray and Biosep - were added in duplicates to the total ten reactors and two reactors were operated as control. The influent and effluent from each reactor were analyzed for total volatile solids, volatile fatty acids and pH. The volatile fatty acids were analyzed by using gas chromatography. The addition of Biocope resulted in the greatest reduction of the volatile solids of 47.5% This was 8.1% greater (P< 0.05) than the reduction of volatile solids in control reactors, which did not receive any additives. Acetic and propioiuc acids were the only major acids present in the reactors receiving Biocope and Medina d-part. The reactors receiving MPC, Aiken Murray and Biosep produced considerable amounts of six major fatty acids. The reactors receiving MPC developed unbalanced conditions and hence resuhed in the lowest destruction in volatile solids and highest concentrations of volatile fatty acids. It was found that only Biocope affected the anaerobic digestion process in a significant manner by causing the highest destruction in volatile solids. A cost analysis performed for a wastewater treatment plant using Biocope as an additive gave a benefit to cost ratio of 2:27, indicating the potential economic advantages associated with its use.