Comparative Study on the Use of Untreated Water of Mahananda River in West Bengal, India and Household Gray Water for Cultivation of <i>Desmodesmus elegans</i>

This is the first study that has compared the use of untreated river and household gray water to obtain high-density cultures of the microalga Desmodesmus elegans under natural sunlight and at room temperatures. Cultivation of microalgae for all downstream applications requires the use of fresh water, inorganic nutrients, light, and energy to maintain optimal temperatures and harvest the biomass. To minimize our environmental footprint in terms of water, nutrients, and energy, untreated wastewater from two different sources were used. The Mahananda River receives unrestricted discharges of pollutants from urban activities, including the free movement of livestock. The household gray water produced from the laundry and kitchen sink consisted of a mixture of detergent, soap, oil, grease, and dirt from legumes, vegetables, and fruits. The gray water sample with high turbidity was filtered through an in-house dual-media filter made of sand and activated carbon. The filtration process significantly reduced the chemical oxygen demand (COD) of the gray water sample from 1,260 ppm to 546 ppm. Prior to algae cultivation, the initial measurements of pH, total dissolved solids (TDS), COD, phosphate, and ammonium for river and gray water were 7.44 and 8.5, 115 and 141 ppm, 350 and 546 ppm, 0.44 and 2.4 ppm, 2.5 and 1.7 ppm, respectively. The COD reduction of 74.89% and 54.31% in the river and household gray water respectively was achieved. The novelty of this study is that the cultivation of D. elegans was carried out under natural light and temperature conditions.