Optimization of biodiesel production from palm oil mill effluent using lipase immobilized in PVA-alginate-sulfate beads
Introduction
Biodiesel is a non-toxic, easy storage and transport, sustainable diesel fuel to substitute petroleum-based diesel [1]. Biodiesel have several improved value-added properties including less CO2 emissions, fewer carcinogenic particulate matter and biodegradability that can be obtained from numerous renewable sources [2]. Biodiesel typically composed of mixture alkyl esters of fatty acids usually synthesized by catalyzed transesterification of biological oils such as triacylglycerol (TAG) and free fatty acids (FFA) with short-chains alcohols like ethanol and methanol. Animal fats and vegetable oil such as sunflower oil, soybean oil, rapeseed oil and waste cooking oils have been used to produce biodiesel [2]. The reaction process can be catalyzed under suitable conditions by acids, bases or enzymes. Alcohols and vegetable oils transesterification is the most widely recognized approach to produce biodiesel, but the high cost of crude materials especially refined oils remain the primary disadvantage in the production of biodiesel. Therefore, feedstock such as waste cooking oils and microalgae oil were being assessed as substitutes of refined oil in biodiesel production [1].
Palm oil mill effluent (POME) is an agro-industrial wastewater from palm oil processing; it has a very high suspended organic component such as nitrogenous compounds, simple sugars, free organic acids as well as lipids. Common sewage is hundred times less polluting than the POME, treatment of this organic pollutants fulfills the demand for sustainable palm oil productions [3,4]. Several technologies for the treatment of POME have been reported, the system requires further exploration which gives a sustainable solution to the polluted water, by taking the waste and using it to produce value added products [4]. There are around 3000–6000 mg/l of oil and grease in POME [5,6], that shows similar characteristics to that of Jatropha oil and commercial palm oil that can be converted into biodiesel [7].
These less expensive feedstocks could be an alternative, despite the fact of being prone to appear relatively unclean [8]. The amount of saturated and unsaturated FFA varies from 3 to 40% in acidic oils [9]. The used of traditional alkali as catalyst is not recommended at point when the amount of FFAs exceed 0.5% in the feedstock, this is because saponification reaction might be favored quickly. However, the FFA could be change to ester by immediate esterification reaction as well as enzymatic methods [10].
Lipases are enzymes that catalyze the synthesis or esterification of free fatty acids alkyl esters (biodiesel) from useful, waste oil or industrial wastewater such as POME [11]. Apart from showing more tolerance and efficiency towards short chain alcohols, Candida rugosa lipase are non-regiospecific lipases capable of hydrolyzing triacylglycerol completely into FFA and glycerol, which give these enzymes a profound effect on transesterification [12]. In recent years the biodiesel production has gained importance because of its ability to replace fossil fuels by blending with conventional fossil diesel [13], since it is environmentally friendly and taken as alternative approach in recycling the waste. Free lipase like all other free enzymes faces the problem of discarding after single use, loss of activity and stability after usage, which necessitate their immobilization for continuous process, ease separation of product and usage in industries. Immobilization of an enzyme such as lipase is the entrapment and movement restriction of the enzyme in a confined space with retention of its catalytic activity [14]. This restriction of movement gives much advantage over free enzymes; these include lipase reusability, easier downstream processing, longer activation period and easier continuous process [[15], [16], [17]]. This approach is easier to operate and can reduced the high cost of enzymes when compared with chemical catalyst.
A number of enzymes had been immobilized as biocatalyst in Poly vinyl alcohol (PVA) and its derivatives [15,18], PVA is a non-toxic, high strength synthetic polymer, with the ability to stabilize and preserve protein activity that has been extensively applied in biotechnology for immobilization of enzymes as well as complete cell [19]. PVA-alginate-sulfate beads are stable microspheres of high quality, rubber like elasticity and strength both mechanically and chemically. The beads do not agglomerate in aqueous solution, which make it a suitable carrier for transesterification reaction [20]. Lipases play a key role and applied in biotechnology in wider spectrum [21]. The production of biodiesel and hydrolysis of oils by incorporating lipases in PVA-alginate-sulfate beads has been reported to yield positive results [22].
In this present study, the following parameters agitation speed, reaction time, oil/methanol molar ratio and weight of the immobilized beads, which were involved in the production of biodiesel from palm oil mill effluent (POME) were optimized using Box-Behnken design (BBD) of experiments. The study concludes with measurements of fuel properties of the biodiesel produced at the optimum conditions.
Section snippets
Materials
POME was obtained locally from Sedenak Palm Oil Mill, Kulai, Johor. Candida rugosa lipase (3.1.1.3) used for the immobilization was purchased from Sigma–Aldrich (Japan). All other reagents used were of analytical reagent grade and used without further purification.
Extraction of oil from POME
Solvent extraction process using n-hexane as reported by Ahmad et al. [5] and Primandari et al. [7] was adopted. The n-hexane and raw POME were mixed in a conical flask in the ratio of 1:1. The mixture was then stirred for 20 min at
Analysis of FESEM-EDX and characterization of PVA-alginate-sulfate beads
PVA-alginate-sulfate beads was characterized using Field Emission Scanning Electron Microscopy (FESEM), this is to detect the entrapment of Candida rugosa lipase in the matrix of the beads. Fig. 1a shows an immobilized bead without lipase and Fig. 1b revealed that the lipases are entrapped in the PVA-alginate-sulfate matrix. The image was taken at magnification of 5.00KX at 5.00 kV. The native globular shapes of Candida rugosa lipase was clearly seen, which are similar to the previous
Conclusion
The highest yield OAME 65% of the initial 40.0% w/w Oleic acid and PAME yield of 44% of the initial 43.5% w/w palmitic acid of the extracted POME oil were obtained from methanol/oil molar ratio of 6:1, agitation speed of 300 rpm, reaction time of 5 h and weight of the immobilized beads of 2 g. The fuel properties of the biodiesel produced from POME when compared with American Standard for Testing of Materials (ASTM) specification, European Union Biodiesel (EN) standards and Commercial Standard
Acknowledgement
The author would like to thank Universiti Teknologi Malaysia for Tier 1 Research University Grant (GUP) – 11H02 entitled ‘Biodiesel Production from Palm Oil Mill Effluent using Immobilized Lipase in PVA-Alginate-Sulfate Matrix’. The authors are grateful to Mahamurni Plantations Sdn. Bhd. for constant supply of the sample. The authors also thanked Prof. Ir. Dr. Dominic Foo for talks on manuscript anatomy and preparation.
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