Bioenergy production of wastewater remediated (nitrogen and phosphorus) algal biomass-feasibility and evaluation.

Abstract

Microalgae are unicellular aquatic microorganisms that can utilize light and carbon dioxide through photosynthesis and produce biomass. Nowadays, they can be used as a source of alternative food, animal feed, biofuel, fertilizer, cosmetics, and for nutraceutical purposes. Additionally, the use of microalgae in wastewater treatment has gained considerable interest recently for its ability to combat environmental pollution and provide cost-effective remediation. However, the high cost of the chemical nutrient medium required for microalgae growth leads to economic inefficiency, while using aquaculture and municipal wastewater could be a viable alternative to synthetic nutrient media in practical applications. This thesis explores the potential of using aquaculture wastewater (ACWW) and municipal wastewater (MWW) as substitutes for synthetic nutrient media in microalgae cultivation. The study involved cultivating two common microalgae species, Scenedesmus, and Chlorella sp., using various nutrient media compositions. These included a mixture of 50% raw wastewater, 50% filtered wastewater, and a control Bold’s Basal Medium (BBM) for batch cultivation. However, in lab-scale cultivation, only 50% of raw wastewater was utilized as the nutrient media for the cultivation process. Various growth parameters such as optical density (OD), dry cell weight (DCW), and specific growth rate (µ) were assessed to meet the research objectives for both batch and lab cultivation. The highest biomass concentration was observed in filtered ACWW, with values of 0.407 g/L for Scenedesmus sp. and 0.503 g/L for Chlorella sp. in batch cultivation. Additionally, parameters related to wastewater treatment efficiency, such as chemical oxygen demand (COD), total phosphorus (TP), and total nitrogen (TN), were monitored every third day during the cultivation process. The overall TP removal efficiency was observed higher in filtered ACWW compared to MWW with the removal of 94.1 % in Scenedesmus sp. and 94.4% in Chlorella sp. Similarly, the overall TN removal efficiency was found to be 68.9% in Scenedesmus sp. and 88.5% in Chlorella sp. in the filtered ACWW sample.