Potential of coal fly ash as low-cost culture medium for cultivation of microalgae chlorococcum and sustainable nutrient recovery from CFA culture medium

Present study evaluated the susceptibility of essential nutrients available in thermoelectric coal fly ash (CFA) for the cultivation of screened microalgae maintained in demineralized water - CFA (DMW + CFA) as culture medium. Different concentration of CFA culture medium was prepared from 0.5 to 4.0 g/L of CFA, but the low nitrate and phosphate content in culture medium was not plausible for growth of cells; therefore, additional NaNO3 and KH2PO4 were added. Culture mediums were inoculated with characterized microalgae chlorococcum sp. and placed in ambient dark/light period for growth study which was measured with time by optical density. Max. OD @ 680 and @750 nm observed as 0.396 +/- 0.073 and 0.306 +/- 0.072 for 0.5 g/L culture medium, respectively. Max. biomass yield was 562.21 +/- 95.54 mg/L for 0.5 g/L culture medium; however, yield was 40.00% low as compared to BG-11 culture. Max. sp. growth rate observed was 0.253 +/- 0.007 d(-1) for 0.5 g/L. The max total lipid was 139.0 +/- 7.5 mg/L for 1.0 g/L culture, which was comparable with BG-11. NO3-N and PO4-P concentration reduced > 90% whereas Na+, K+ and Ca+ content was reduced > 75.00-90.00%. ORP was also intriguingly measured for oxidative state of culture medium during growth phase and found to be maintained between + 350 and + 25 mV. Max. total chlorophyll analysed was 4.64 +/- 0.56 mu g/ml. The results support that CFA may be used as culture medium for chlorococcum sp. for biomass and lipid production and subsequent nutrient recovery from CFA.