At a time of peak oil and peak coal, it is important to develop alternative energy resources. This study was conducted to optimize the process of anaerobic digestion (using microbes to break down activated sewage sludge and microalgae) to make it a viable replacement for fossil fuels.
Three anaerobic digesters are being used in this study; one is 100% activated sewage sludge, one is 100% microalgae, and one is a 50/50 mix based on the weight. The goal of the project is to look at the different contents in each digester and determine how this affects the amount and content of biogas produced. The hypothesis is that adding sewage to algae will increase the amount of gas produced and the content of methane in the biogas produced compared to algae alone.
The digesters are maintained on a semi-continuous basis and are fed and wasted 50mL four days a week. The digesters were seeded using sludge from an existing digester to get the correct environment of microbes. The Total Solids of the algae and activated sludge were determined to get the correct ratio for the 50/50 digester. The basic parameters used for the stability of the digesters, which is important in getting a constant supply of biogas, include pH, alkalinity, and COD.
The volume of gas released from each digester is measured using a vacuum pump. Samples of gas are taken periodically to test the contents of it using the GC machine. So far the tests have indicated normal stability and health of the digesters. However, the amount of gas has been small and variable. As the digesters stabilize it will become clearer if algae is a viable source for anaerobic digestion and if adding sewage increases its digestibility and gas production.