Phosphorus dissolution from dewatered anaerobic sludge: Effect of pHs, microorganisms, and sequential extraction

Phosphorus (P) and iron mass balance from Limassol Wastewater Treatment Plant showed that the major removal and accumulation occurred at the aerobic secondary stage and at Dewatered Anaerobic Sludge (DWAS), respectively. The purpose of this study was to examine various parameters that effect the P dissolution under low pH from DWAS. The parameters that significantly contribute to P extraction were the exposure to pH 2.5, the anaerobic conditions and the sequential extraction. The addition of chemolithotrophic acidophilic bacteria has negatively influenced P dissolution, whereas the addition of acidophilic Heterotrophic Iron Reducing (HIR) bacteria has slightly increased P dissolution but they contributed to pH maintenance at lower levels compared to no addition of HIR. P fractionation of the residual sludge after sequential extraction pointed out that the organically bound P was hardly dissoluted from DWAS. The residual DWAS after acid treatment generated around 45% less methane compared to the initial DWAS.