Under conditions of high organic surface load and high hydraulic shear the influence of bulk water dissolved oxygen (DO) concentration on biofilm oxygen consumption, biofilm growth and sulfate reduction in biofilms was investigated using both domestic wastewater and synthetic glucose - yeast extract medium. The biofilm thickness apparently did not approach a steady-state value; instead biofilm thickness increased linearly until the entire biofilm eventually sloughed.
Potential activity of sulfate-reducing bacteria was highest when the biofilms were grown at low DO levels in bulk water. Potential sulfide production measured per biofilm volume remained fairly constant during the growth of the biofilms. Only at oxygen levels close to 0 ppm was sulfide production into bulk water under aerobic conditions evident; at higher oxygen levels, complete reoxidation of sulfide occurred within the biofilm. For biofilms growing at bulk oxygen conditions below 1 ppm, the sulfate reduction (and thus sulfide production) was of significance for the processes in the biofilm system in terms of oxygen consumption and COD removal.