The use of pretreated palm oil mill effluent for acetone–butanol–ethanol fermentation by Clostridium saccharoperbutylacetonicum N1-4

Palm oil mill effluent (POME) was used as an acetone–butanol–ethanol (ABE) fermentation medium using Clostridium saccharoperbutylacetonicum N1-4. Various pretreatment methods were applied on POME to increase the amount of fermentable sugars leading to enhanced ABE production. Sulfuric acid-treated POME (SA-POME) method was found to give the highest yield of total reducing sugars (glucose, cellobiose, xylose, and arabinose) as compared to other pretreatment methods. An increment in the concentration of H2SO4 from 1 to 2% resulted in the enhanced release of reducing sugars (18.3, 26.3 g/L, respectively). However, the treatment of POME with 3% H2SO4, decreased the reducing sugars to 21.6 g/L and consequently, the total ABE production was also reduced. The highest yield of ABE was observed from a culture grown with POME treated by 1% H2SO4. The total ABE production from 1, 2, and 3% SA-POME was obtained as 2.2, 0.45, and 0.41 g/L, respectively. Although, enzymatically treated POME (EH-POME) could produce 4.42 g/L glucose, sulfuric acid treatment (1%) was able to liberate only 1.76 g/L glucose, ABE production was higher when 1% SA-POME was used. Low yield of ABE from enzymatically treated POME can be attributed to the production of some inhibitors during hydrolysis of POME. When EH-POME was treated with XAD-4 resin to nullify the inhibitors, the production of ABE was increased to 4.29 g/L, and ABE yield was also increased to 0.29 g/g. In conclusion, enzymatic hydeolysis of POME followed by elution to XAD-4 column can be proposed as the best pretreatment method for highest productivity of ABE. It was found that addition of P2 medium to the POME hydrolysates was able to improve the production of butanol except in raw POME and sulfuric acid hydrolysates.