Microbial lipid accumulation through bioremediation of palm oil mill effluent by co-culturing yeast and bacteria

• Main Author: Md Ahasanul, Karim
• Format: Thesis
• Language: English
• Published: 2020
• Subjects: TP Chemical technology
• Online Access: http://umpir.ump.edu.my/id/eprint/33721/1/Microbial%20lipid%20accumulation%20through%20bioremediation%20of%20palm%20oil%20mill.wm.pdf; http://umpir.ump.edu.my/id/eprint/33721/
• Institution: Universiti Malaysia Pahang

The discharge of palm oil mill effluent (POME) on arable land causes large amounts of environmental distress due to its high concentration of phenolic compounds, chemical oxygen demand (COD), and biochemical oxygen demand (BOD). On the other hand, the progressive depletion of fossil fuels and mineral resources have also been identified as a future challenge. The approach of simultaneous microbial lipid production through the wastewater treatment could be a potential option to address both renewable energy production and environmental resilience. This study aims to produce microbial lipids using robust oleaginous bacteria and yeast of Bacillus cereus (B. cereus) and Lipomyces starkeyi (L. starkeyi) through the bioremediation of POME in batch mode fermentation. Different concentrations of POME substrates (25%, 50%, 75%, and 100%) were used as nutrients to determine the optimum POME concentration for achieving maximum yield of biomass as well as lipid production. It was observed that among the different dilutions, the moderately diluted solution of POME (50% POME) showed higher microbial growth and lipid accumulation and offered a significantly higher degree of bioremediation. The degree of bioremediation was assessed by evaluating several wastewater parameters (i.e., BOD, COD, total phenol, total organic carbon, etc.) and determining the seed germination index (GI) of Mung bean (Vigna radiata). POME treated with a co-culture inoculum (B. cereus and L. starkeyi) substantially reduced the pollution load, particularly, in COD for 50% POME, thus demonstrating a removal efficiency of 83.66%. Furthermore, POME treated with co-culture inoculum obtained a higher GI value than the other samples (treated by pure cultures and untreated) due to the significant remediation of detrimental organics present in the POME as evidenced by Gas Chromatography-Mass Spectrometry (GC-MS) analysis. Nevertheless, the co-culture inoculum was found to have potential for the highest biomass growth (9.16 g/L) and lipid accumulation (2.21 g/L), with a lipid content of 24.12% (dry weight basis) in the 50% (v/v) POME. Lipid composition was analyzed in terms of fatty acid methyl esters using GC-MS. C16 and C18 were found to be the predominant fatty acids in the lipid of co-culture inoculum suggesting the potential of microbial lipid to be used as a biodiesel feedstock. A novel lipid extraction method, namely electroporation (EP) was used to extract microbial lipid and the efficiency of EP was compared with some other conventional methods. The EP demonstrated a higher lipid extraction efficiency of 31.88% (wt.%) compared to the ultrasound (11.89%), Fenton’s reagent (16.80%), and solvent extraction (9.60%). Finally, the influence of several process parameters such as inoculum compositions, pH, temperature, and time on the performance of the COD removal efficiency and lipid accumulation were optimized using response surface methodology. Optimization of co-culture inoculum showed that the inoculum composition, pH, temperature, and time had a significant effect on the performance of the COD removal and lipid accumulation. The maximum COD removal efficiency of 86.54% and lipid accumulation of 2.95 g/L could be obtained while the inoculum composition, pH, temperature, and incubation time were 50:50, 6.50, 32.5 ℃, and 90 h, respectively. Therefore, the results of this study suggest that the co-culture of B. cereus and L. starkeyi could be a promising inoculum for attaining higher biomass growth and lipid production in conjunction with the bioremediation of POME. This combined approach of achieving dual objectives (bioremediation of POME and microbial lipid production) that is utilized in the present study provides a novel strategy for palm oil millers.