Enhanced nutrients removal in conventional anaerobic digestion processes

One of the main challenges for one phase anaerobic digestion processes is the high concentration of NH ₄ ⁺ and PO ₄ ^3- ions in the digested sludge supernatant. This project focuses on enhancing the removal of nutrients during the anaerobic digestion process through fixing both NH ₄ ⁺ and PO ₄ ^3- ions in the form of struvite (magnesium ammonium phosphate, MAP, MgNH ₄PO ₄.6H ₂O) within the anaerobic sludge. Batch anaerobic digestion tests showed that Mg ²⁺ concentration in the range 279 - 812 mg/L had insignificant effect on CGP but incurred a slight increase in COD removal. The reactor that had soluble Mg ²⁺:NH ₄ ⁺:PO ₄ ^3- at a molar ratio of 1.28:1:00:1:00 achieved the best performance enhancement of 8% increase in COD removal and 32% reduction in NH ₄ ⁺ in the reactor supernatant. Overall, the results show that there is a potential to optimise conventional anaerobic digestion such that supernatant lean in P and N, and sludge rich in nutrients are obtained.