Effect of iron dosing on metal and phosphorus behaviour in anaerobic digesters

Iron salts are used at wastewater treatment works to remove phosphorus for the final effluent as the excess of phosphorus in this effluent can result in eutrophication. The sludge rich in iron and phosphorus generated after the addition of iron must be stabilized before disposal usually by anaerobic digestion. This research investigated the effect of different iron salts at different ratios iron:phosphorus on anaerobic digestion of iron and phosphorus rich sludge by measuring biogas and methane production and the destruction of organics as well as the effect on phosphorus removal. Iron and phosphorus inorganic profiles were also studied of samples generated before and after digestion in order to establish any relationship between the content of iron and phosphorus in the bioavailable fraction and biogas and methane production. The approach used in this research was direct comparison of iron-dosed activated sludge and non iron-dosed activated, using the iron-dosing laboratory method developed for Smith and Carliell-Marquet (2009). Results from this research showed that iron has not always a detrimental effect on anaerobic digestion as biogas and methane production. The phosphorus removal efficiency was greater in all the experiments within the range 91.5-99.69%