Sulphate and Manganese Removal During Sulfitogenesis in a UASB Reactor

Sueli Moura Bertolino, Nayra Quites, Flávia Reis, Versiane Leão

The treatment of sulphate-containing wastewaters is a major issue for the mining, metallurgical and chemical industries. The reasons for such a contamination are the widespread use of sulphuric acid in these industries, in addition to natural oxidation of sulphide minerals in mining operations – the so-called acid mine drainage (AMD). Thus sulphate removal is one of the main issues for water recirculation in metallurgical plants due to gypsum precipitation.

Because of its large content, environmental agencies worldwide set a maximum between 250 mg/L and 500 mg/L for discharge, requiring effluent treatment when sulphate concentrations are above such values. Manganese is a toxic metal which is very common in effluents of hydrometallurgical plants and mine waters as well. Sulphate removal by sulphate reducing bacteria (SRB) has already been demonstrated and applied industrially. Therefore the purpose of the current study was to couple the removal of both sulphate and manganese in an anaerobic bioreactor (UASB).

The UASB reactor was fed with an industrial wastewater (mine water) containing manganese supplemented with synthetic Postgate C medium using lactate as a carbon and electron source. It achieved sulphate and COD removal efficiencies of 80 ± 8 % and 48 ± 13 %, respectively, whereas an alkalinity of 1246 ± 283 mg HCO3-/L was produced during lactate oxidation and the pH remained between 7.3 and 8.3. The biologically produced hydrogen sulphide was used to precipitate copper and nickel for recycling, whereas the produced alkalinity removed manganese as MnCO3. Under such conditions, 86 % manganese removal was observed with an average residual concentration of 15 mg/L. Therefore, it was demonstrated that sulphate, manganese and other metals can be removed concomitantly in an anaerobic process.