Avaliação do uso de coagulantes naturais no polimento de efluente de abatedouro e frigorífico de suínos

Abstract

Coagulation, an important process in the conventional treatment of effluents, promotes the removal of particles too light to sediment by gravity action (colloids). The settling of these particles becomes possible with the addition of coagulating agents, generally metal salts. However, the major drawback in the use of such salts are metallic residues remaining in the sludge, which can contaminate soil. Coagulant agents based on organic polyelectrolytes have been interesting for their ability to remove organic matter from effluents. This study aimed to test the efficiency of two natural polyelectrolytes, chitosan and Tanfloc®, As coagulants, for the reduction of COD, turbidity and apparent colour of effluent coming from a pig slaughterhouse, and to compare it with the efficiency of ferric chloride. The sequence of tests, conducted in Jar Test, was performed according to a predefined experimental design for each of the coagulants, with fractional planning followed by DCCR. Chitosan promoted a considerable increase in COD, rather than its reduction, proving ineffective in reducing this response. However, as a coagulation aid, chitosan favored the formation of larger flakes. Tanfloc® provided formation of large flakes at basic pH (7.75) and small flakes at acid pH (5.25). In optimum condition and at basic pH, a maximum reduction of 86% for turbidity and 34% for apparent colour was obtained. At acid pH, the reduction achieved for the responses was 96% for turbidity and 78% for apparent colour. The COD reduction was about 50% regardless of the pH. These results were satisfactory and consistent with that expected for the coagulant. Regarding ferric chloride, it generally presented a lower performance than Tanfloc®. The results showed that Tanfloc® performed very well the role of primary coagulant, favorably replacing ferric chloride in the treatment of coagulation, flocculation and sedimentation of the study effluent.