Development of indigenous biofilm for pre-treatment of palm oil mill effluent and biogas production

Abstract

The process of producing crude palm oil required lots of water, creating a massive organic wastewater called palm oil mill effluent (POME). Current application favoured open ponding system which effectively treats POME to a safe level before release to the environment but have poor methane production. This research aims to develop indigenous biofilm for pre-treatment of POME in order to improve biogas production. Bacteria producing biofilm were isolated from local sources such as POME, palm kernel cake and food waste compost available in International Islamic University Malaysia (IIUM). Two bacterial isolates, Bacillus cereus and Bacillus substilis have been identified as biofilm producing bacteria with ability to excrete hydrolytic enzymes. Biofilm production was detected with crystal violet staining on the wall of the 96 well microplate containing bacterial cultures. Further study on biofilm screening showed better biofilm production for mixed bacterial cultures compared to the single culture. Addition of biofilm carrier, granular activated carbon (GAC) immobilized and mixture of identified Bacillus strains was found to 75% of removal of lipid content in POME compared to the control POME for hydrolysis analysis. Optimization of hydrolysis process of POME was done using Design Expert Software by Face Centered Central Composite Design (FCCCD) with two manipulated variables of total suspended solids (TSS) of POME and biofilm carrier (GAC) amount. Optimization of hydrolysis process indicated that the system was effective at 0.93% (volume of Total suspended solids/Total Volume) TSS value with no significant amount of biofilm needed. The analysis of variance (ANOVA) has showed value at R2 = 0.8968 which was significant to the regression line of this model. Anaerobic digestion of biofilm mediated hydrolysed POME for biogas production was done suing One Factor at a Time (OFAT) method with two variables tested, inoculum ratio and hydraulic retention time (HRT). Anaerobic digestion of POME was found to give highest yield of gas produced for inoculum ratio of 10% (volume of activated sludge/total volume) and HRT of 25 days. Comparison study showed significant increase in volume of biogas yield by 81.92% and 52.67% to anaerobic digestion of raw POME and non-biofilm mediated POME respectively. The COD removal of the effluent was obtained within range of 85-92%. The methane content in the biogas was found to be at 79 – 84% (v/v). Positive achievement of this study will be helpful in managing the POME waste in this country by having more enhanced biogas production as a new source of energy.