Waste utilization and biodiesel production from Desmodesmus maximus grown in swine wastewater using waste eggshells as a catalyst

Abstract

Desmodesmus maximus is a potential candidate for algal biofuel production. It was cultivated for lipid enhancement in four different types of wastewater used as algal growth media. After growing Desmodesmus maximus for period of 10 days in four different types of waste water, it was found that swine wastewater collected from Swine Research Center of Oklahoma state university was the best media because of the faster biomass yield and lipid content in the algal biomass. The specific growth rate of algal strain grown in swine waste water was found to be 0.88 µ/d with doubling time T2 of 1.3 h which shows the better quantity of algal biomass. Algal lipids comprised 72.3 % (dry weight %) of the biomass. In our study wastewater was used as a nutrient source for biofuel production while remediating the waste. Calcined waste eggshells doped with lanthanum and switchgrass biochar were used to catalyze the conversion of algal lipid to biodiesel. Our study found that Biochar doped 950 degree Celsius CaO provided the optimal catalyst. The physicochemical characteristics of wastewater were analyzed and it was found that swine wastewater contains all the vital macro and micronutrients required for the optimal growth of this microalgae. The catalyst synthesized from waste eggshells was characterized by FTIR-ATR, SEM-EDX techniques and N2 physisorption by Brunauer–Emmett–Teller (BET) theory. The resulting produced biodiesel was analyzed by 1H NMR, 13C NMR, GC-MS techniques. Conversion to biodiesel was 99 % efficient with the optimized catalyst. The catalyst was subjected to 10 runs of transesterification to study reusability. After 10 runs the reused catalyst still provided 77 % conversion efficiency. The result obtained shows that Desmodesmus maximus grown in swine wastewater yields a very good quality and quantity of biodiesel. The waste eggshells and switchgrass can be utilized as renewable heterogeneous catalysts because of their highly porous nature and a more specific surface area that acts as a catalyst in the transesterification reaction of biodiesel.