Pós-tratamento físico-químico de efluentes pré-tratados anaerobiamente.

Abstract

The Upflow Anaerobic Sludge Blanket (UASB) reactor is quite efficient in the removal of suspended solids and organic material from sewage. However, anaerobic digestion does not affect significantly the nutrient concentration, so that the post treatment of the anaerobic effluent is of great importance. In addition to the removal of nutrients the post treatment will complement the removal or suspended solids and organic material, thus producing an effluent that is compatible with the environmental standards and assures environmental protection of receiving waters bodies. In this dissertation the technical and economic feasibility o f using physical chemical processes for the post treatment of UASB effluent is evaluated. Through the addition of an adequate coagulate, phosphate is precipitated and any particulate material is flocculated. Samples of UASB effluent were collected and submitted to batch experiments in the Jar Tester equipment. The experimental investigation was divided into two phases. Initially tests were carried out using commercial quick lime (calcite) as coagulant (First phases). The doses varied between 200 and 450 mg/L. Subsequently aluminium sulfate was tested for post treatment of anaerobic effluents (Second phase). The doses of aluminium sulfates were between 50 and 300 mg/L. The obtained results were very promising and revealed an average removal efficiency o f organic material in terms of COD and BOD of 53,4 % and 62,7 % respectively for an addition of 250 mg/L o f quicklime. It was shown that under these conditions the removal efficiency o f phosphate was very high and (81,8 % ) . The removal efficiencies of COD and BOD were 60,4 and 69,4 % respectively, for a dose of 150 mg/L of this salt per liter of digested sewage. The phosphorous removal for the same dose, was found to be 93,1 %. h i both eases the final phosphorus concentration was less than 1 mg/L of treated sewage.