Anaerobic Degradation of Synthetic Wastewaters at Different Levels of Sulfate and COD/Sulfate Ratios in Horizontal-Flow Anaerobic Reactors (HAIB)

Treatment of synthetic wastewaters containing sulfate in concentrations of 500 to 3,000 mg SO₄ ^{− 2}/L at chemical oxygen demand (COD)/sulfate ratios of 5.0, 3.0, 2.4, 1.7, and 1.0 was evaluated in two horizontal anaerobic fixed bed reactors (HAIB) filled with wood charcoal (WC) as support material. Ethanol, acetate, propionate, and butyrate were used as carbon sources to obtain synthetic wastewaters with COD ranging from 1,100 to 6,200 mg/L. Sulfate removal efficiencies exceeding 90% were achieved with the lowest sulfate concentrations up to 1,965 mg SO₄⁻² /L and COD/sulfate ratios higher than 1.7. The sulfate removal rate tended to remain constant (1.55 g SO₄⁻² /L · day) at sulfate concentrations equal to or higher than 1,960 mg SO₄⁻² /L. Organic matter removal efficiencies were always higher than 85%. Sulfidogenesis was the predominant process associated with organic matter removal in the first section of the reactor with the higher sulfate loads. In these cases, methane was not detected in the biogas.