Lipid production from POME using microalgae grown in hybrid photobioreactor (HPBR)

Abstract

Palm oil mill effluent (POME) is one of the wastewaters with the highest organic content which can be converted into useful materials. Improper discharge may create adverse effects to the environment. Conventional treatment including the use of ponding systems which requires large scale of land, biological treatment is insufficient to solve the problem. Microalgae are known to assimilate organic pollutants into cellular constituents and grow on non-arable land with high aerial productivities Therefore, this study was conducted to find an alternative method to balance between environmental protection and sustainable reuse of nutrient available in POME. Initial study includes screening and isolation of microalgae from POME. Studies on the effect of photo periods, Carbon:Total Nitrogen ratio and organic loading rate on the lipid production and biomass were performed. A 5 litre laboratory scale reactor known as Hybrid Photo-Bioreactor (HPBR) was fabricated and used. The operation of the reactor was based on the Sequencing Batch Reactor (SBR) system, specially designed to be operated for 24 hours continuously at 24 ºC ± 1ºC, using batch mode. All analytical measurements performed in this study were conducted according to Standard Methods for the Examinations of water and wastewater (APHA, 2005). Modified Bald’s Basal Medium was used to selectively enhance the growth of microalgae screened from Palm Oil Mill Effluent (POME). Once screened and isolated, Chlorella pyreniodosa was found to be dominant over other existing species and was used in further experiments. Initial study on the effects of concentration showed growth was inhibited at 1000 mg COD/L. Several cultural characteristics in terms of carbon to total nitrogen ratio (C:TN), different photoperiod cycle and organic loading rate were determined using a fabricated Hybrid PhotoBioReactor (HPBR). Chlorella pyrenoidosa was found to produce the highest biomass and lipid productivity under continuous illumination which was 0.58 g/L.d and 0.044 g/L.d respectively. The study indicated that high biomass and lipid productivity can be achieved when Chlorella pyrenoidosa was grown under low nitrogen concentration, C:TN of 100:6. The lipid productivity obtained was 115 g/L.d. High biomass productivity (0.155 g/L.d) can be obtained under high organic loading rate, in contrast, lipid productivity (0.101 g/L.d) was highest when the microalgae was grown at the lowest organic loading rate. In conclusion, highest lipid production from Chlorella pyrenoidosa in POME required low nitrogen concentration with C:TN ratio of 100:6, under continuous illumination of 24 hours and low organic loading rate of 36 kg COD/m3.d