Effects of Composting Swine Manure on Nutrients and Estrogens

Application of raw manure to fields can contribute ammonia, pathogens, and volatile organic compounds at concentrations that may give rise to adverse odors and environmental concerns. In addition, raw manures contain reproductive hormones that could impact the endocrine systems of sensitive organisms. Composting manure, in which aerobic microorganisms destroy pathogens and convert organic compounds into more stable forms, may reduce its potentially harmful effects. Two piles of swine (Sus scrofa domestica) manure with corn stalk bedding were monitored for temperature, inorganic N, total N, P, K, pH, electrical conductivity, and the hormones 17 beta-estradiol (E2) and estrone (E1). A compost pile was mixed periodically, resulting in internal temperature increases to the thermophilic range (40 degrees C-60 degrees C) after each mixing. A static manure pile was not mixed, and the temperature stayed close to ambient throughout. After 92 days, the compost resembled a humus-like material with very little odor, whereas the manure pile had maintained much of its original physical characteristics. After 92 days, the compost had a pH closer to neutral, a lower electrical conductivity, and slightly lower total N content than the static manure pile. Both piles had greatly reduced ammonium concentrations. 17 beta-Estradiol concentrations did not decline, but rather fluctuated with time, and were much lower than E1 concentrations, which were initially high but decreased during the study. Static manure storage appeared to be just as effective in reducing total estrogenicity (estrogenicity = E2 + 0.1 x E1) compared with aerobic composting, in that estrogenicity was reduced by 74% in the static manure pile and 79% in the composted pile.