REMEDIATION OF WASTEWATER AND BIOFUEL PRODUCTION USING MICROALGAE

Abstract

Increasing concentrations of carbon dioxide and other harmful gases into the environment from various sources like combustion of fossil fuels and thermal power plants, etc. are posing threat to the environment continuously. Fast growing population, urbanization and industrialization have led towards increase in energy demands across the world. Increasing energy demands have drawn attention of researchers towards the development of renewable energy sources. Fuels derived from biomass like biodiesel, bioethanol and biogas, etc. could be the possible substitutes of traditional energy resources in the near future. Increasing population, urbanization and industrialization are the major factors behind different types of environmental problems with generation of huge volume of wastewaters from municipal and industrial areas. Safe disposal of these wastewaters is a tedious task. Globally the consumption of water for domestic and industrial purposes is 450 billion m3 year-1, where domestic sector alone contributes to 315 billion m3 year-1 which is 70% of total water consumption. Usually wastewater discharges from industries have high organic loading, nutrients, toxic organics (xenobiotics), and heavy metals, etc. These pollutants have serious impact on human health, aquatic life and soil microbiology. However, inorganic and organic nutrients present in the wastewaters can be used as substrate for the of growth microorganisms. Biomass obtained from such micro-organisms can be utilized in the production of value added products like biodiesel, bioethanol, pharmaceuticals and proteins, etc. Open literature indicates that significant work has been accomplished to enhance microalgal biomass and lipid production. This thesis is focused on evaluating and demonstrating potential of microalgae for remediation of wastewaters and production of biodiesel. Four freshwater microalgae namely Chlorella minutissima (C. minutissima), Scenedesmus abundans (S. abundans), Nostoc muscorum (N. muscorum) and Spirulina sp. have been used for remediation of dairy, distillery and secondary treated wastewater contaminated with phenols. Batch experiments were performed in laboratory using conical flasks as photobioreactor. Among the four microalgae species C. minutissima was found the most efficient and promising microalga for production of biodiesel. Optimum temperature and light intensity observed for C. minutissima were 27 ± 2 ℃ and 9000 lux, respectively. At these conditions C. minutissima obtained highest biomass and lipid yield of 1840 and 405.36 mg/L, respectively when grown on modified CHU-13 medium. Remediation of distillery wastewater in combination with secondary treated domestic sewage was also performed using C. minutissima. Increase in biomass and lipid yield was observed with the addition of glucose in the cultivation medium. C. minutissima iv achieved highest biomass and lipid yield of 5.23 ± 0.065 g/L and 976 mg/L, respectively, when cultivated on 25% distillery spent wash containing 20 g/L of glucose. Furthermore, remediation of secondary treated wastewater contaminated with different phenols (1,2-dihydroxy benzene, 2,4-dinitrophenol, 2,4-dichlorophenol and 2-chlorophenol) was also assessed using C. minutissima. Removal of phenols by C. minutissima and effect of different phenols on biomass and lipid yield of microalga were observed in presence and absence of additional organic carbon sources like glucose and glycerol. Highest removal of phenol (1,2-dihydroxy benzene) was achieved at 25 mg/L concentration in cultivation medium. Dairy wastewater remediation was also performed using different poly-microalgae cultures of C. minutissima, S. abundans, N. muscorum and Spirulina sp. Polyculture (C. minutissima + N. muscorum + Spirulina sp.) achieved 75.16, 61.37, 58.76, 84.48 and 84.58% removal of BOD, COD, total nitrogen (TN), total phosphorus (TP) and suspended solids (SS), respectively when cultivated on dairy wastewater diluted with 30% secondary treated domestic sewage at 12:12 h photoperiod along with biomass and lipid yield of 3.47 ± 0.07 g/L and 496.21 mg/L, respectively, in 10 days of cultivation period.