Improvement of sludge quality by iron-reducing bacteria

Abstract

Sewage sludge can be used in agriculture as organic fertilizer. However, one of the obstacles for this use is the high concentration of heavy metals and the presence of sulphides (acidifying soil or compost). The aim of this research was to develop the biotechnology for improving the quality of sewage sludge that would be used as organic fertilizer. Microbial reduction of inexpensive sources of Fe(III) in anaerobic digester is proposed as a means of preventing the accumulation of sulphide and of enhancing the accumulation of phosphate in sewage sludge. Industrial grade iron hydroxide can serve as a suitable source of Fe(III) The results show that almost all dissolved phosphate is recovered by the reaction with Fe2+. Additionally, the activity of iron-reducing bacteria inhibits the production of sulphide by sulphate-reducing bacteria and the growth of these bacteria in anaerobic digesters.