The effects of algae pre-treatment on the biomethane potential of swine wastewater

Anaerobic digestion is a common method of waste treatment in the agro-industrial and municipal sectors, which utilizes microbial metabolisms that take place in an environment closed to the atmosphere to convert the organic content of wastewater into gas composed of approximately 65% methane and 35% carbon dioxide. This gas can be used as a combustible fuel for the production of heat and/or electricity. Anaerobic digestion is not typically used to treat swine waste because of its low carbon to nitrogen ratio being below the ideal range of 20-30:1. This high nitrogen content of swine waste results in ammonia inhibition of the methanogen microbial consortia, which are responsible for the production of methane. A periphytic algae cultivator (PAC) is a system in which high nutrient wastewaters; such as swine waste, can be circulated over a bed of algae. In this process, all ammonia nitrogen is taken out of solution through volatilization into the atmosphere and uptake by the algae. Also, the algae facilitate the conversion of carbon dioxide into organic compounds, increasing the carbon to nitrogen ratio of wastewater. The goal of the project was to test the hypothesis that treating swine wastewaters with a PAC results in a significant increase in biomethane potential of the waste by increasing its carbon to nitrogen ratio and overall organic content, making it a more suitable feedstock for anaerobic digestion. This is significant because, if successful, the research could contribute to the development of a more economically feasible method of utilizing and recycling nutrients in agro-industrial and municipal wastewaters for the cultivation of algae to be used as a renewable energy source. It was found in the project that algae pre-treatment of swine wastewater results in a lower ammonia concentration and higher VS and COD contents, which leads to a better conversion of the substrate into methane and a larger reductions of VS and COD contents of the wastewater resulting from anaerobic digestion