Reduction of odorous compounds emissions from swine slurry by electrolytic treatments and copper addition

Swine livestock farms represent potential sources of emissions of gaseous compounds and odors in relation to slurry management, manure treatment, and particularly, storage. Electrolytic treatments of slurries were proposed to solve this pressing problem. Electrolytic treatment consists of the passage of a low electric current through the liquid phase of swine manure in storage basins determined by two or more electrodes with alternated polarisation. We investigated the mechanisms of odour reduction and evaluated the effects of current intensity and of anodically dissolved copper (Cu²⁺) ions. Fresh swine slurry was subject to electrolytic treatment in a bench top experiment, at 25 mA and 75 mA for 32 days with either copper or graphite electrodes. Emissions of methane, hydrogen sulphide, and volatile fatty acids were measured. Effects of copper addition to fresh swine slurry were also monitored in a bench top scale trial. Reduction of emissions was found to be due to both current passage and copper dissolution. Reduction of foul emissions in graphite electrodes assays resulted lower than in copper electrodes assays, although the direct additions of Cu²⁺ ions had a much larger effect than could be predicted from the results of electrolytic treatments with copper electrodes, probably due to the greater uniformity in distribution in swine manure. A simple empiric odour threshold value normalised index, odour offensiveness index of slurries, was found to be effective in differentiating treatments.