Iron-containing clay and hematite iron ore in slurry-phase anaerobic digestion of chicken manure

Abstract

It is shown in this review that addition of clay minerals and hematite iron ore can significantly enhance anaerobic digestion of chicken manure. Liquid-phase anaerobic digestion of chicken manure consumes a lot of fresh water and energy to keep waste as a suspension. Meanwhile, anaerobic digestion of chicken manure in clay slurry without stirring could minimize energy and water consumption because the initial acceptable content of organic solids can be increased. For example, this content can be increased from 5% (w v-1) in suspension of chicken manure for liquidphase anaerobic digestion up to 15% (w v-1) in the slurry of chicken manure for slurry-phase anaerobic digestion than can save up to 13.3 L of water per kilogram of dry organic solids. The slurry-phase anaerobic digestion of nitrogen-, sulphur-, and fat-containing organic wastes can be enhanced using microbial reduction of Fe(Ⅲ) in clay or in hematite iron ore. This is due to adsorption or precipitation of such inhibitors of microbial acidogenesis and methanogenesis as ammonium, sulphide, long-chain fatty acids, humic and fulvic acids with clay or ferrous ions. For example, maximum concentration of ammonium decreased from 11.4 g L-1 during liquid-phase anaerobic digestion to 1.4 g L-1 during slurry-phase process due to adsorption of ammonium ions on clay. Addition of iron-containing clay to slurry-phase anaerobic reactor removed dissolved sulphide totally due to its precipitation with ferrous ions that are produced by bioreduction of Fe(Ⅲ) in clay. Slurry-phase anaerobic digestion enhanced with bioreduction of Fe(Ⅲ) minerals is also more effective process in terms of environmental safety than widely used liquid-phase anaerobic digestion because of an absence of water supply and wastewater effluent.

Keywords

• clay slurry
• anaerobic digestion
• organic waste
• chicken manure
• ferric bioreduction
• ammonium adsorption