Low pH anaerobic digestion of waste activated sludge for enhanced phosphorous release

This paper assesses anaerobic digestion of waste activated sludge (WAS) at low pH to enhance phosphorous solubility. Batch biochemical methane potential tests were conducted at a pH range of 5 to 7.2 in two separate sets (two different WAS samples collected from municipal WWTP). Low pH (<5.7) caused a significant (p = 0.004) decrease in methane potential (B0) up to 33% and 3.6 times increase in phosphorus release compared to neutral pH (7-7.7), but with no major change in methane production rate coefficient (khyd). The loss in methane yield was mainly due to decrease in hydrolytic capability rather than inhibition of methanogenesis with volatile fatty acids being <300 mgCOD L(-1) and soluble COD <1300 mgCOD L(-1) even at low pH. While pH did not influence the acetoclastic community (Methanosaeta dominated), it was the primary driver for the remaining community (p = 0.004), and caused a loss of diversity and shift to Clostridia.