1998 Volume 21 Issue 6 Pages 367-375
The vertical zonation of 02 respiration, NO3- respiration, H2S oxidation and SO42- reduction in microaerobic biofilms grown on rotating biological contactors (RBCs) of treating domestic wastewater was studied by measuring concentration profiles in the biofilms with microelectodes for 02, NO3-, H2S and pH. From those profiles, in situ specific reaction rates and substrate fluxes were calculated by using a simple one-dimensional deffusion reaction model and were related to population densities of sulfate-reducing bacteria (SRB) and potential sulfate reduction rates determined by standard batch experiments. The maximum population densities and the highest potential sulfate reduction rates were found in the outermost biofilm. On the contrary, the in situ sulfate reduction rates were restricted in a narrow zone located in the middle biofilm incubated DO=100 μmol·l-1. An increase in the O2 and/or NO3- penetration depth in the biofilm induced a shift of sulfate reduction zone to the deeper biofilm and a decrease in the specific sulfate reduction rate. This is probably because that the potential sulfate reduction rate decreased toward the depth and addition of nitrate enhanced oxidation of the produced sulfide or increased competition for electron donor with denitrifiers, or both. The microelectrode measurements with the high spatial resolution enable us to quantitatively measure in situ SO42- reduction rate in microaerobic biofilms, which could not be detected measureing sulfide or sulfate flux across the water-biofilm interface.
