Process optimization of aquaculture wastewater treatment using a mycoalgae biofilm

The current challenge in intensive aquaculture is to control the level of nutrient pollutants in the wastewater and provide sustainable sources of proteins for feed. A novel lichen type biofilm was developed, comprised of a fungus, Mucor indicus, and a microalga, Chlorella vulgaris, growing symbiotically on a polymer matrix termed a “mycoalgae biofilm”. Previous studies established that the mycoalgae biofilm can reduce ammonia levels in synthetic aquaculture wastewater. In this study, different cultivation conditions as relate to various forms of aquaculture wastewater were studied, including glucose, ammonia concentrations, and process time, in a central composite design experiment. Growing Chlorella vulgaris and Mucor indicus in simulated aquaculture wastewater reduced levels of ammonia while producing an easily harvestable mycoalgae biomass which is possible for fish feeds. Experimental results showed that the biofilm readily formed over a range of ammonia conditions (6.14 mg L⁻¹ to 124 mg L⁻¹) albeit with varying algae to fungi compositions (14.8 % to 0.5 % algae composition of the biofilm). Glucose concentration was the strongest predictor of significant ammonia removal, with time being a non-significant variable over the range of values tested (56 h to 136 h) indicating a shorter process duration as acceptable. Amino acid quantities in the mycoalgae biomass align with simple additive values of amino acids present in the algae and fungi alone. The mycoalgae biofilm was confirmed to grow in actual aquaculture wastewater both sterilized and unprocessed. These continued studies demonstrated the efficacy of the biofilm under a wide range of aquaculture conditions thus confirming its application in real aquaculture wastewater.