Abstract:
Crude glycerol is the major byproduct of the biodiesel industry. In general, around 10 percents of
crude glycerol are generated during biodiesel manufacturing process. Since purification of glycerol
to use in food, pharmaceutical, or cosmetics industries is too costly, an alternative method for its
disposal is strongly required. Applying crude glycerol as a carbon source for biogas production is a
promising alternative use for this high-strength waste. In this study, effect of COD:N ratios in cosubstrates
of crude glycerol and treated palm oil mill effluent (as nitrogen source) on biogas
production were investigated. The experiments were divided into 4 phases. The characterization of
crude glycerol and palm oil mill effluent were characterized in the first phase showed that crude
glycerol is high carbon substrate but lacked of nutrients for anaerobic digestion (300:0.05). On the
other hand, the COD:N ratio of palm oil mill effluent (300:30) was higher than anaerobic
requirement. Next, the methane potential of crude glycerol on biogas production was studied by
biochemical methane potential (BMP) experiment. From the results, it is found that the methane
accumulation and methane yield were 42 mL and 280 mL CHi g CODrcmovcd' respectively, which is
equivalent to 81 percent methane efficiency. In third phase of this study, the suitable nutrient ratio
was investigated in a laboratory-scale stirred tank reactor. When vary COD:N ratios from 300:10,
300:7, 300:5, to 300:3, no significant difference among methane yield and methane production rate
was found among ratios of 300:10,300:7 and 300:5. However, the 300:3 COD:N ratio affected the
methane yield and production rate. The suitable COD:N ratio for biogas production from crude
glycerol was hence, 300:5. The last phase of experiment was the study in semi continuous operation
at an HRT 4 days. The semi continuous operation was more stable than batch operation. The daily
methane production of 513.1+-19.4 mL. The methane production efficiency and COD removal were
62 percent and 85+-2 percent, respectively. From the results, it can be concluded that crude glycerol
is a good alternative carbon source for biogas production.