Phototrophic anaerobic lagoons as affected by copper and zinc in swine diets

Odor emissions from anaerobic lagoons containing large populations of photo trophic bacteria are usually minimal. This study was conducted to determine whether copper (123 ppm) and zinc (2,310 ppm) in diets fed to weanling pig s for therapeutic purposes affect phototrophic conditions within lagoons. C olumn reactors containing 47 L of swine lagoon sludge and supernatant were used to represent lagoons. The reactors were placed in an environmental cha mber maintained at 24 degrees C. Copper zinc, and control manure were added to the reactors at a volatile solids loading rate of 128 g(vs) m(-3) da(-1 ) using a hydraulic retention time of 32.5 days. Bacteriochlorophyll a, cop per, reduction-oxidation potential, salinity, sulfate, sulfide, and zinc we re then measured for at least 99 days. Sulfide, total copper and total zinc were the only parameters to be significantly impacted. The copper and zinc concentrations in the sludge increased but that of supernatant in the indi vidual reactors changed little during the study period. However the additio n of dietary copper significantly increased the concentrations of sulfides in the supernatant, creating a condition that appeared tonic to phototrophi c bacteria. In contrast, a decrease in sulfide concentration resulted from the addition of dietary zinc, resulting in an environment that may have bee n favorable to phototrophic bacteria. Thus, to minimize potential odor conc erns, zinc rather than copper may be the best choice as a dietary supplemen t for weanling pigs.