Heterotrophic Cultivation of Microalgae in Food Waste Digestate for Simultaneous Biomass Production and Nutrient Remediation

Abstract

As food wastage becomes an increasingly dire problem, research has been conducted on food waste management. Anaerobic digestion has been presented as an alternative to traditional methods of food waste disposal, as it is able to produce biogas as a renewable energy source. However, its byproduct, liquid food waste digestate, needs to be treated appropriately before disposal. Food waste digestate usually contains a high percentage of ammonia, phosphorus, and other organic compounds. Hence, microalgae cultivation in food waste digestate has been suggested as a treatment method, as various strains of microalgae are effective in removal of nitrogen, phosphorus, heavy metals, and toxins from wastewater, while using compounds present to synthesize valuable biomass. Thus, microalgae as a treatment for food waste digestate is promising. In this study, food waste was taken from a local anaerobic digester, filtered and used for the heterotrophic cultivation of three different strains of microalgae. Hetero-trophic cultivation was carried out as it does not require light and is easier to incorporate into biorefineries. From the three strains, Chlorella sorokiniana has been found to have the best growth rate, reaching a final dry cell weight of 0.144 g/L, and was thus used for subsequent experiments. C. sorokiniana was then cultivated in different glucose and food waste digestate concentrations to investigate microalgal performance and potential products. Results found that C. sorokiniana was effective in ammonia removal, with the highest removal at 250.8 ppm and had the highest protein and carbohydrate percentage contents at 47% and 57.1% respectively.