Strategies To Cultivate Microalgae On Eutrophic Wastewater For Nutrients Recycling And Biomass Production

Abstract

Wastewater generated from industry may contain excessive nutrients, including nitrogen, phosphorus and organic carbon. On one hand, excessive nutrients in wastewater could cause environmental pollution and ecological disaster. On the other hand, these nutrients could be utilized for algae growth and algal biomass production. Unregulated discharge of eutrophic wastewater not only poses threats to water body, but also wastes the valuable nutrients in wastewater. This dissertation research focuses on the technologies and mechanisms to improve the efficiency of nutrients utilization by algae grown in eutrophic wastewater. The lack of ammonia limits algae growth in wastewater from food industry. In this study, a potential solution is to mix the wastewater from different resources to balance the nutrients profiles and promote the algae growth. The results showed that appropriate mixture of food industry wastewater effectively mitigated the bottleneck to algae growth and improved the nutrients removal efficiencies. Ammonia toxicity is a serious concern in the treatment of some wastewater. In this study, comparison of three common carbon sources, glucose, citric acid, and sodium bicarbonate, indicated that in terms of ammonia assimilation, glucose is the best carbon source. This result could be applied to the toxicity of ammonia enrichment to algae cultivation in eutrophic wastewater. A cooperation model between algae and wastewater-borne bacteria was reported by this dissertation research. Such a cooperation model increased the nutrients removal efficiencies and promoted the algae growth. A strain of beneficial aerobic bacteria, Acinetobacter sp., was isolated and its biochemical characteristics were explored. After treatment by co-cultivation of Acinetobacter sp. and Chlorella sp., residual nutrients in municipal wastewater were reduced to be under the permissible discharge limit. To fully utilize the nutrients in swine manure, it is always exploited to produce biogas by anaerobic digestion. However, the treatment of residual nutrients after anaerobic digestion is a critical issue. High turbidity and ammonia toxicity are two factors limiting the algae growth in anaerobically digested swine manure. This research developed a strategy to pretreat the anaerobically digested swine manure by cationic starch-assisted turbidity reduction and air bubbling-driven ammonia stripping.