POTENTIAL USE OF ALGAE FOR NUTRIENT REMEDIATION OF WASTEWATER AND PRODUCTION OF CLEAN ENERGY

Abstract

The reliance on fossil fuels as a source of energy has led to environmental degradation and a myriad of health problems leading to a need for renewable source of energy that is economical and sustainable. Likewise, eutrophication of water bodies is a matter of concern because it disturbs normal functioning of such an ecosystem. The release of improperly treated wastewater is one major cause of this problem. The objective of this study was to utilize nutrients present in wastewater for algal growth and later produce biofuel from the harvested biomass of the algae. Individual algae cultures of locally dominant genera Spirogyra, Oedogonium and Zygnema, collected in Kesses area of Uasin Gishu County were grown in laboratory conditions at Moi University. A 10g portion of the algae were grown in 250 ml Erlenmeyer flasks containing 100ml of sewage in an incubator set at 260C with continuous light provided by a 5 W fluorescent tube. The flasks were stirred once daily to prevent settling of algal cells. 0.05 mg of CO2 was bubbled to the flasks once. The control consisted of algae grown in Bold Basal media. Algal growth was monitored for seven days using daily measurements of chlorophyll a. Daily uptake of nitrate from the wastewater by the algae was also determined through automated hydrazine reduction method. After the seven days, the algae were harvested and dried. Lipids were obtained from the dried biomass by Soxhlet extraction using a mixture of hexane and ethanol, and weighed in grams. The quantities of starch were estimated using enzymatic-colorimetric method and given as a percentage of the sample. The lipids obtained were utilized to determine the calorific value of the fuel using a bomb calorimeter. All the data obtained were statistically analyzed using the SPSS program. Friedman test was utilized to check whether there was a statistical difference exhibited by the various taxa in amounts of nitrates reduced, as well as in the accumulation of chlorophyll a. Wilcoxon test was employed to check whether there was a statistical difference in the amounts of lipids, starch and calorific values between those algae that grew in sewage and those that had been grown in the growth medium. Results showed that all the algae genera grew better in Bold Basal Medium than on sewage. For all the genera that were grown on sewage, growth declined after the fourth day and Zygnema showed the highest growth in sewage. On nitrate removal from the wastewater, the length of contact time between the algae and wastewater was of paramount importance. After four days the studied Spirogyra decreased the quantities of nitrate in 100 mL sewage by 90.7%, Oedogonium by 89.48% and Zygnema by 83.84%. On lipid productivity, results obtained showed that growth of algae on sewage led to accumulation of higher quantities of lipid. Spirogyra increased lipid quantities when it was cultured on sewage by 73.99%, Oedogonium by 91.38 and Zygnema by 89.04%. However, those results acquired from estimation of starch illustrated that growth of the algae on sewage led to accumulation of less amounts of starch. Growth of Zygnema on the sewage reduced the quantities of starch by 82.11%, 79.63% in Spirogyra, and 58.13% in Oedogonium. In Spirogyra and Zygnema, lipids obtained from algae that grew in sewage had higher calorific values than those that had grown in the growth medium. From the results of this study, it can be concluded that sewage may be used as an alternative growth media for algae. The problem of eutrophication can also be counteracted using local genera of algae. The results also illustrate that sewage grown algae can produce biomass suitable for production of biofuel. v