Anaerobic Ammonia-oxidation Coupled with Fe Reduction by an Anaerobic Culture from a Piggery Wastewater Acclimated to NH_4~+/Fe~(3+) Medium

摘要

The oxidation of ammonia coupled with the reduction of iron is a unique pathway mostly reported in soils and sediments. An anaerobic sludge from a piggery wastewater treatment plant had been acclimated to an NH_4~+/Fe~(3+)-rich environment to secure an enrichment culture and investigate an anaerobic ammonia oxidation coupled with an iron reduction. The enrichment culture showed an average pH of 6.8 and the concentration of mixed liquor volatile suspended solid was measured as 1,120 mg/L. The mol ratio of oxidized NH_4~+ and reduced Fe~(3+) was 0.33 mol NH_4~+/mol Fe~(3+). It was suggested that the culture acclimated to NH_4~+/Fe~(3+) contained the anaerobic ammonia oxidizing bacteria as well and thus NH_4~+ was fully oxidized to NO_3~- by the bacterial consortia. In a batch experiment using the culture, the oxidation of NH_4~+ was increased as the initial concentration increased. However, it was suspected from the experimental results that other iron reducing bacteria had grown under the environment applied for the enrichment culture. As a result, it was observed that heterotro-phic and autotrophic iron reducers were competing for Fe~(3+).