Mechanistic and kinetics of carbon dioxide fixation in aerobic biogranules developed from palm oil mill effluent

Abstract

Palm oil mill effluent (POME) generated from oil palm industries is a major source of water and air pollution. Ineffective wastewater treatment results in excessive production of carbon dioxide (CO2) that contributes to global warming. In this study, photosynthetic aerobic biogranules (PAG) were develop in a lab-scale phototrophic sequencing batch reactor (PSBR) using POME as substrate. The capability of PAG for CO2 fixation was determined and the biokinetic parameters were estimated from the chemical oxygen demand (COD) fractionation of POME. The PAG were developed in a four litre column reactor that was operated with four hour per-cycle time for 40 days. After six weeks of development process, it was observed that, compact-structured PAG were formed in sizes between 1.0-3.0 mm and a maximum settling velocity of 97 m/h. The mass liqour suspanded solid (MLSS) and the mass liqour volatile suspanded solid (MLVSS) were found to increased from 2.0-8.0 g/L and 2.5-7.0 g/L, respectively. The field emission scanning electron microscope (FESEM) analysis showed the presence of spherical-shaped bacteria (cocci) with sizes ranging from 1.86-2.57 μm. The removal performance achieved was 55 % for COD, 85 % for total nitrogen (TN) and 72 % for total phosphorus (TP). In additon, the CO2 fixation was analysed in terms of carbon content of the PAG. The CO2 fixation rate was 0.0967 g/L/d and for one year application the result was estimated to be 4.178 g/L/d. The stoichiometric and kinetic parameters were determined to describe the bioprocess of PAG development using the PSBR system. The COD fractionation of POME indicated the biodegradable substance was 72.9 % with the largest fraction of 46.8 % for slow biodegradable substances (XS). The biokinetic parameters for the maximum specific growth rate of heterotrophic biomass (μmaxH) was 3.36 d-1 while the half-saturation coefficient for the readily biodegradable substrate (Ks) was 40.1 gm-3. The biokinetic parameters obtained were verified for the development process of PAG in the PSBR system.