Development and microbial characterization of aerobic granulation using palm oil mill effluent

Abstract

Palm oil is widely used for food and non-food manufacturing industries and as a biofuel. The production of palm oil generates a large amount of solid and liquid wastes in the form of empty fruit bunch (EFB) and palm oil mill effluent (POME), respectively. As POME contributes to a high pollution process waste, the need to find an efficient and practical approach to preserve the environment is essential. Novel aerobic granular sludge is a compact consortium of self-immobilized bacteria with high rate biological wastewater treatability. This study is aimed at investigating aerobic granular sludge formation in lab-scale sequencing batch reactor (SBR) using POME as substrate. The efficiency of aerobic granular sludge developed for the treatment of POME in corresponds to the structure of bacterial population is monitored. Aerobic granular sludge was developed at volumetric exchange rate (VER) of 50% and cycle duration of 3 hours at flow rate of 3 Lm-1 in reactors R1, R2 and R3 operated at OLR of 1.5, 2.5 and 3.5 kgCOD m-3d-1, respectively. Shock load conditions were introduced by increasing the OLR in R2 from 2.5 to 19 kgCOD m-3d-1. Aerobic granular sludge was successfully formed at an OLR of 2.5 and 3.5 kgCOD m-3d-1, respectively while bioflocs remained dominant in R1. Under shock loading rate, aerobic granular sludge was partially disintegrated due to mass transfer limitation within the granule. The average sizes of granules were between 1.0 mm to 4.0 mm. Upon steady state, COD removal efficiency of greater than 80% was recorded for all reactors. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and fluorescence in situ hybridisation (FISH) techniques were used to show that the bacterial population changes during aerobic granular sludge formation at different OLRs. The average Raup and Crick similarity indices obtained during the acclimation/granulation and the maturation phases were 0.95 ± 0.02 and 0.72 ± 0.06, respectively. Mature granules maintained good settling property and dominant granular morphology as evidenced by low SVI of 19.9 mL g-1 SS at 3.5 kgCOD m-3d-1. Visible bands from the DGGE profiles indicated the shift of bacterial population during the aerobic granulation process. Comamonadaceae sp., Leadbetterella sp. and Runella sp. are dominant bacteria that consistently present throughout the granulation process. Distribution of AOB in mature granule was confirmed by FISH technique thus contributing to efficient removal of ammonia in POME of > 80%. Despite the different OLRs, aerobic granular sludge formation was successfully achieved for the treatment of high strength wastewater such as POME.