Acid Sludge Fermentation Products Vary with the Type of Sludge

In this experiment primary sludge (PS), waste activated sludge (WAS) and a mixture of WAS with PS were fermented at 21°C. The sludges were collected from two plants: the biological nutrient removal (BNR) WestEnd Water Pollution Control Center (WEWPCC) and carbon-removal only SouthEnd WPCC (SEWPCC). The batch fermentation test showed that the primary sludge fermentation generated significantly higher amount of soluble COD than WAS. WAS fermentation released considerable amounts of phosphate and ammonium. Co-fermentation of WAS with the PS enhanced soluble COD production as well as increased the release of phosphate and ammonium. The semi-continuous flow fermenters showed that regardless of the sludge source, with a similar total COD load, there was no significant difference in soluble COD production observed during co-fermentation between the two plants. Volatile fatty acids (VFA) were the primary components of the soluble COD generated during fermentation. 20-22% volatile solids destruction was achieved due to sludge fermentation. The WEWPCC sludge released higher concentration of phosphate than the SEWPCC sludge - the latter originating from a non-BNR process. Fermentation of combined sludge from both plants generated concentration of phosphate high-enough to allow phosphorus recovery as struvite.