This project delivers an energy positive and water neutral, closed-loop biorefining system that converts organic wastes into renewable energy and reduces the overall impacts on the environment. The research consisted of three major stages: The first stage of this project was conducted in an anaerobic co-digestion system. Effects of the ratio of dairy manure-to-food waste as well as operating temperature were tested on the performance of the co-digestion system. Results illustrated an increase in biogas productivity with the increase of supplemental food waste; fiber analysis revealed similar chemical composition (cellulose, hemicellulose and lignin) of final solid digestate regardless their different initial feedstock blends and digestion conditions. The molecular genetic analyses demonstrated that anaerobic methanogenic microorganisms were able to adjust their community assemblage to maximize biogas production and produce homogenized solid digestate. The second stage utilized electrocoagulation (EC) pretreated liquid digestate from previous stage to culture freshwater algae. Kinetics study showed a similar maximum growth rate (0.201-0.207 g TS day-1) in both 2× and 5× dilutions of EC solution; however, the algal growth was inhibited in original EC solution (1×), possibly due to the high ammonia-to-phosphate ratio. Algal community assemblage changed drastically in different dilutions of EC solution after a 9-day culture. The following semi-continuous culture in 2× and 5× EC media established steady biomass productivities and nitrogen removal rates; in addition, both conditions illustrated a phenomenon of phosphorus luxury uptake. Biomass composition analyses showed that algae cultured in medium containing higher nitrogen (2× EC medium) accumulated more protein but less carbohydrate and lipid than the 5× EC medium. The last stage involved hydrolyzing the algal biomass cultured in anaerobic digestion effluent and analyzing the effects of the neutralized algal hydrolysate on the performance of enzymatic hydrolysis of acid or alkali pretreated lignocelluosic substrates (poplar, corn stover, switchgrass, and solid fiber from anaerobic digestion). Results found that algal hydrolysate significantly improved the efficiency of enzymatic hydrolysis of lignin-rich, structurally recalcitrant biomass such as poplar and solid fiber from anaerobic digestion. This discovery broadened the potential application of algal biomass besides direct use for biofuel production.
Read
