Author: Brian Anthony Foulkes

Publisher:

Published: 2002

Total Pages: 170

ISBN-13:

Zinc and copper are supplemented into a swine's diet in relatively large concentrations and then further concentrated in sludge by anaerobic digestion. Anaerobic digestion, which produces energy and organic fertilizer, is gaining popularity as a treatment of swine manure. Land application can be used for disposal, although these sludges can contaminate the soil with heavy metals. The concentrations of zinc and copper in anaerobically digested swine manure are approximately 2,900 mg/kg and 1200 mg/kg respectively. These concentrations greatly exceed the regulations for many European countries and are on the borderline for the EPA 503 land application limits. Metals when released into the environment can accumulate to high concentrations and can contaminate soils, groundwater and living organisms. Bioleaching is a process that removes metals from solids or biomass, by acidifying the sludge and therefore solubilizing the metals attached to biosolids. Bioleaching has been successfully applied to many other waste streams but has yet to be applied to anaerobically digested swine manure, which contains both high ammonia and organic compounds both are toxic to sulfur oxidizing bacteria. Traditional physical and chemical methods for metal removal are expensive. Removal of heavy metals by bioleaching has the potential to be highly efficient and economical. A Thiobacilli culture was established by acclimating the bacteria to anaerobically digested swine manure using elemental sulfur. The bioleaching batch tests used this inoculum in the bioleaching experiments. Experiments were completed to test the effects of inoculation, substrate, and solids concentration. ORP, pH, sulfate, nitrate, pathogen reduction, copper and zinc were measured regularly in this study. Results showed that bioleaching is feasible to remove copper and zinc from anaerobically digested swine manure. Inoculation proved to be valuable in increasing the rate of acidification. The results also showed that at high concentrations above 6% TS, the potential for using bioleaching decreases and that higher sulfur concentration yield greater metal removal efficiencies. Using 6% TS and 10,000 mg/l of elemental sulfur in the batch experiments, 94% of Zn and 72% of Cu was solubilized.