Inhibition of anaerobic biological processes either by toxic components of the wastewater or by products of the microbial reactions has always been a concern to the process design engineer. A typical example is hydrogen sulfide gas (H₂S). It is a product of the reduction of sulfates (S0₄) by sulfate reducing bacteria (SRB) and is a concern, particularly in the pulp and paper, fermentation, and edible oil industry where sulfate concentration can reach several thousand milligrams per liter.