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ABSTRACT
In the present study, 100% centrate (wastewater generated in the sludge centrifuge of a municipal wastewater treatment plant) was used for the cultivation of microalga Nannochloropsis oculata in a lab scale externally illuminated photobioreactor. Cells were harvested at the end of the exponential phase and the resulting wet algal biomass (80 wt % moisture) was subjected to direct saponification in a low-cost microwave reactor using ethanolic KOH to convert the algal lipids to soap. The soap was separated from other unsaponifiable matter by precipitation using saturated KCl and subjected to simultaneous acidulation and esterification to form biodiesel of high purity (97.04% FAME in final biodiesel). Optimum values of esterification of fatty acids in microwave reactor were: microwave power-450 W, molar ratio of methanol to fatty acids -80:1, concentration of sulphuric acid-2.5 wt %, reaction time-11 min and reaction temperature-60 °C. Kinetics studies of esterification conducted under these conditions revealed that the rate constant was high (0.452 min−1). The final yield of biodiesel was 97.11%. Cetane number and oxidation stability index of biodiesel were evaluated to be 59.349 and 3.298 h respectively. Removal rates of Chemical oxygen demand (COD), total nitrogen and total phosphorous were 82.65%, 62.25% and 52.65% respectively.
Competing interests
The authors declare that they have no competing interests.
Acknowledgment
The authors gratefully acknowledge finanacial support from Visveswaraya Technological University, Belagavi, under "VTU Research Grants Scheme 2010-11 (Award No-VTU/Aca/2011-12/A-9/6380).
Disclosure statement
No potential conflict of interest was reported by the authors.
