Avaliação do produto gerado na hidrólise alcalina de carcaças

Abstract

The deposition of animal carcasses in the environment, if inadequately done, brings contamination risk to the soil, as well as surface and subterranean water. Among the alternatives available for depositing carcasses in the environment are burial, incineration, composting and alkaline digestion. All present economic and environmental advantages and disadvantages. Thus, the objective of this work was to monitor the carcass digestor installed at the Pathology Sector of the Department of Veterinary Medicine at the Universidade Federal de Lavras (UFLA), and physically and chemically analyze the liquid effluent generated in the digestor, as well as the possibility of its use in agriculture as organic fertilizer. For characterizing the carcass digestor liquid effluent (CDLE), three samples were collected and sent to the Residual Water Analysis Laboratory of the Environmental and Sanitary Engineering Center of the Department of Engineering – UFLA. The variables analyzed were: pH, electric conductivity (EC), total (TS), fixed (TFS) and volatile (TVS) solids, total Kjeldahl nitrogen (TKN), total phosphorus (TP), total sodium (Na), total potassium (K), total calcium (Ca), total magnesium (Mg), sulfur (S), total manganese (Mn), total copper (Cu), total zinc (Zn), total iron (Fe), and total and thermo-tolerant coliforms. We determined the content of organic matter (OM), and calculated the sodium absorption ratio (SAR) and potassium absorption ratio (PAR). Near 97% of all mass that enters the digestor produces liquid effluent, while only 3% are considered solid residue, formed by bones, which lose its consistency and crumbles with finger pressure. The pH of the CDLE was of 11.2, while electric conductivity was of 36.5 dS m-1. The average values for TKN, P, K, Na, Ca, Mg and S were of 0.33, 0.47, 2.80, 2.12, 0.83, 0.23 and 0.38 g L-1, while the concentrations of Mn, Cu, Zn and Fe were of 0.035, 0.90, 6.96 and 30.6 mg L-1. We verified that, in average, the values for SAR and PAR were of 17.46 (mmol L-1)1/2 and 13.4 (mmol L-1)1/2, respectively. In conclusion, the traits of the digested animals had little influence over the traits of the generated CDLE, which is rich in organic matter (69.5%), and in macro (TNK, P, K, Ca, Mg and S) and micronutrients (Mn, Cu, Zn and Fe), in addition to Na. The CDLE cannot be launched directly in to watercourses, given that it is not in accordance to the legal directives established for its final destination in the state of Minas Gerais, Brazil, allowing the use as soil acidity corrector and as source of nutrients, remaining aware to possible damages caused to the soil-plant relation due to the contraction of K and Na in relation to other minerals.