Comparative Study between Indigenous Natural Coagulants and Alum for Microalgae Harvesting

Abstract

The conventional jar test was used to evaluate the % mixed microalgae harvesting efficiency from domestic wastewater by using different natural coagulants such as de-oiled Jatropha curcas cake, Moringa oleifera, Conocarpus erectus and neem (Azadirachta indica) seeds compared to alum as a chemical coagulant. The highest microalgae removal efficiency (97.91%) was achieved with powdered neem (A. indica) seeds at 100 mg/L dosing, mixing speed 100 rpm, with 10 min agitation time and pH 9. Interestingly, it was observed that % removal of microalgae was found above 94% in all cases with neem (A. indica) seeds as compared to other coagulants. Then, the % removal is followed by C. erectus with 93.44 % and alum 91.62%. However, the consumption of alum was very high (200 mg/L) to achieve higher % removal efficiency making it uneconomical. Statistically, it was found that both coagulants neem (A. indica) and de-oiled cake of J. curcas seeds were having a percentage contribution of coagulant dosing on the harvesting results. The techno-economic analysis showed that the powdered neem (A. indica) and M. oleifera seeds were found the most economical in terms of mixed microalgae harvesting cost per litre of wastewater, i.e. (US$ 0.0068/L) and (US$ 0.0052/L), respectively. De-oiled cake of J. curcas seeds can effectively remove microalgae with % removal 84.98 %, but the cost analysis revealed that de-oiled cake of J. curcas seeds has higher harvesting cost per litre (US$ 0.0103/L) compared to neem (A. indica) and M. oleifera seeds. Thus, it is suggested to use the neem (A. indica) as coagulants for mixed microalgae removal from domestic wastewater with effective % microalgae removal in a cost-effective manner for biodiesel production.