Screening the Pollution-Tolerant Chlorococcum sp. (Chlorophyceae) Grown in Municipal Wastewater for Simultaneous Nutrient Removal and Biodiesel Production

Abstract

Over the last few years and with increasing global climatic change, the international energy crisis and shortage of freshwater resources have raised many inquiries about global water security and energy. Therefore, finding out alternative and sustainable energy sources has become an important universal requirement. Here, we assessed the viability of exploiting municipal wastewater (WW) as a nutrient-rich growth medium for cultivating the pollution-tolerant coccoid green microalga Chlorococcum sp. (Chlorophyceae) to simultaneously remove nutrients and produce biodiesel. Chlorococcum sp. was isolated from municipal wastewater sampled from Menoufia Governorate, Egypt. Under the standard growth conditions and until reaching the late exponential growth phase, it was cultivated at different concentrations (25%, 50%, 75%, and 100%) of the secondary treated WW, and the findings were compared to the control (grown in BBM). The study results revealed that the 50% WW treatment was the most suitable approach for removing NO3−, NH4+, and TP with percentages of 96.9%, 98.4%, and 90.1%, respectively. Moreover, the 50% WW treatment produced the highest algal biomass (1.97 g L−1) and productivity (82 mg L−1 day−1). In addition, it showed the highest lipid production (600 mg L−1), with 25 mg L−1 day−1 lipid productivity and lipid yield with 30.5% of the cell dry weight (CDW). The gas chromatography–mass spectrometry (GC-MS) technique was applied to characterize fatty acid profiling, and it was found that oleic (C18:1) and palmitic (C16:0) fatty acids were present in much higher concentrations in Chlorococcum sp. cells grown in 50% WW as compared to the control, i.e., 44.43% and 27.38% vs. 36.75% and 21.36%, respectively. No big difference was present in linoleic (C18:2) fatty acid concentrations. Importantly, the biodiesel properties of our Chlorococcum sp. grown in 50% WW were consistent with the international biodiesel standards. In light of our findings, Chlorococcum sp. has a great potential for utilization as a biodiesel feedstock and for bioremediation of wastewater.