Removal of residual organic matter, phosphates and ammonium from thermofilically digested pig manure

Full-scale anaerobic digestion of pig manure often resulted in liquid effluents with considerably high organic matter, ammonia and phosphates content. If not enough agricultural land is available, the disposal of this effluent requires additional treatment. Different process scheme for reduction of the organic matter and nutrients from thermofilically digested pig manure were tested in full-scale and lab-scale conditions. The steps tested were membrane microfiltration, anaerobic post-digestion, phosphates removal as struvite (PRS), partial oxidation and oxygen-limited autotrophic nitrification-denitrification (OLAND) process. However, microfiltration was unsuitable for treatment of digested pig manure due to membrane clogging Combination of thermophilic anaerobic digestion with sequential separation by decanter centrifuge and post digestion in UASB reactor reduced the organic content by 80 %. PRS process employing MgO for struvite formation was used for almost complete removal (96 %) of phosphates from digested pig manure. OLAND process succeeded to remove ammonium only from highly diluted digested manure with low organic matter content (around 2.5 g COD/L). Based on the results obtained, a conceptual scheme for treatment of pig manure is suggested.