Effect of C/N ratio on the PHA accumulation capability of microbial mixed culture fed with leachates from the organic fraction of municipal solid waste (OFMSW)

Abstract

Activated sludge was submitted to the aerobic dynamic feeding strategy in a Sequencing Batch Reactor (SBR) to evaluate the effect of the carbon/nitrogen (C/N) ratio on the polyhydroxyalkanoates (PHA) accumulation capability. The SBR was operated for 233 days using leachates from the stabilization of the organic fraction of municipal solid wastes (OFMSW) as carbon source, with a Volatile Fatty Acids (VFA) content of 13.95 ± 7.81 g COD/L. The influence of the C/N ratio on PHA accumulation capability was evaluated by supplementing the leachates with acetate or ammonium, then applying C/N ratios within the range of 13.3 to 42.1. Low C/N ratios of 13.3 and 23.3 promoted PHA accumulation in form of polyhydroxybutyrate (PHB), reaching a maximum of 16.8 % stored, whereas the application of the highest C/N ratios led to a reduction on the PHA accumulation capacity, this probably due to an inhibition induced by the high carbon concentration. Moreover, during the experimental period it was observed that the reduction on the respiration activity of the culture, reflected in a decreasing on the Specific Oxygen Uptake Rate (SOUR) from 1.67 down to 0.42 mg O2/g VSS min This phenomenon could be the result of the continuous exposure of the microorganisms to long famine periods as well as the inhibitory effect of specific organic compounds commonly found in leachates. Overall, the PHB production is negatively affected when the MMC is submitted to the operation at high C/N ratios along with long famine periods.