Effect of Dietary Arsonic Acids on Performance Characteristics of Swine Waste Anaerobic Digesters2

A completely random design experiment was conducted to determine the effect of dietary arsonic acids on the performance of laboratory swine waste anaerobic digesters. Fortified corn soybean meal diets containing no arsonic acids (control), 100 ppm arsanilic acid or 75 ppm roxarsone were fed to growing-finishing pigs. Fresh waste (including urine) from all treatments were collected daily for 74 days and loaded at a rate of 2.4 kg volatile solids/m3into nine 25-liter anaerobic digesters heated to 34 C with continuous agitation and total gas collection. After a 60-day acclimation period, daily gas production and composition and nutrient composition data were obtained from the anaerobic digesters. Inclusion of the arsonic acids in swine diets reduced dry matter and volatile solids content. Dietary arsonic acids also increased nitrogen in the ammonium form. Alkalinity was high in all the digesters; however, arsonic acids decreased alkalinity. Dietary arsonic acids reduced the ratio of methane to carbon dioxide in the gas compared to the control. Significant amounts of arsenic accumulated in the digesters. Acetic, propionic and butyric acids were increased by roxarsone, and arsanilic acid increased the butyric acid concentration over the percentage in both the roxarsone and control digesters.