PHOTOTROPHIC ANAEROBIC LAGOONS AS AFFECTED BY COPPER AND ZINC IN SWINE DIETS

Abstract

Odor emissions from anaerobic lagoons containing large populations of phototrophic bacteria are usuallyminimal. This study was conducted to determine whether copper (123 ppm) and zinc (2,310 ppm) in diets fed to weanlingpigs for therapeutic purposes affect phototrophic conditions within lagoons. Column reactors containing 47 L of swinelagoon sludge and supernatant were used to represent lagoons. The reactors were placed in an environmental chambermaintained at 24 C. Copper, zinc, and control manure were added to the reactors at a volatile solids loading rate of128 g vs m 3 da 1 using a hydraulic retention time of 32.5 days. Bacteriochlorophyll a, copper, reduction-oxidationpotential, salinity, sulfate, sulfide, and zinc were then measured for at least 99 days. Sulfide, total copper and total zincwere the only parameters to be significantly impacted. The copper and zinc concentrations in the sludge increased butthat of supernatant in the individual reactors changed little during the study period. However, the addition of dietarycopper significantly increased the concentrations of sulfides in the supernatant, creating a condition that appeared toxicto phototrophic bacteria. In contrast, a decrease in sulfide concentration resulted from the addition of dietary zinc,resulting in an environment that may have been favorable to phototrophic bacteria. Thus, to minimize potential odorconcerns, zinc rather than copper may be the best choice as a dietary supplement for weanling pigs.