Volatile fatty acids and methane production from organic wastes using anaerobic digestion

Abstract

The abundance of organic waste poses environmental issues as it is disposed of into landfills resulting in the emission of greenhouse gases. Industries have been seeking environment-friendly solutions, as waste handling is expensive due to the bulk volume of the waste. One of such solutions is resource recovery using anaerobic digestion (AD) process. AD process can be used to produce methane and volatile fatty acids (VFAs). AD process performance can be enhanced using thermal hydrolysis pretreatment (THP). The effect of solubilization of waste potato starch due to THP was studied on methane and VFAs production. A relationship was established between THP temperature and potato starch solubilization (R[superscript 2] = 0.74-0.90). The AD reactors were fed with raw starch and starches pretreated at 100 (THP_100) and 140 °C (THP_140) for VFAs production. VFAs production from THP_140 starch fell significantly, but raw starch and THP_100 samples showed no changes. A maximum VFAs yield of 0.482 mg-VFAs/mg-COD was obtained at an organic loading rate of 9 kg-COD/m[superscript 3] ∙day and at hydraulic retention time (HRT) of 2 days for THP_100 starch, 6% higher than VFAs yield using raw starch. The methane production was carried out using raw starch, THP_70, THP_100, and THP_140 starches. The highest methane yield of 0.32 mL-CH[subscript 4]/mg-COD was obtained from THP_70 starch, in comparison to 0.33 mL-CH[subscript 4]/mg-COD for the co-digestion of starch and pre-hydrolysis liquor obtained from the dissolving pulp mill. The alkalinity requirements went down by 25% during co-digestion compared to single substrate digestion. The food waste was found to be a good source of methane production. A continuous lab-scale bioreactor was used to evaluate VFAs production. The optimal HRT of 0.26 d provided the maximum VFAs production of 0.78 mg-VFAs/mg-COD.