This showed that higher reduction in efficiency of NH3-N was achieved and this is likely caused by the availability of microbial population in the POME, which aids the anaerobic bioconversion. It was reported by Angelidaki and Ahring [10] that process stability due to NH3 resulted in VFA accumulation and lowering of pH, thus decreasing the
concentration of free NH3 in the reactor. This explains the
observed ability of the operation to stabilize even with high ammonia concentration and with lower, but stable
biogas production.