Biofilm characteristics in biological denitrification biofilm reactors

The biological denitrification method applied to treat municipal sewage containing low levels of nitrogen compounds and contaminated groundwater is very popular. There are few studies in the literature an the treatment of industrial wastewater containing high levels of nitrogen compounds. To assess the feasibility of biofilm and immobilized cells for treating wastewater which contains high-strength nitrogen compounds, the biofilm characteristics of the biological denitrification process in attached-growth reactors were studied. The Richardson-Zaki relationship can adequately describe the bioparticle fluidization phenomenon developed in biological denitrification reactors. The terminal settling velocity of bioparticles was 1.88-5.14 cm/s for activated carbon and 2.98 cm/s for immobilized cells, respectively. The dry density of biofilm grown on activated carbon decreased as the biofilm thickness increased and ranged between 63 and 93 mg/cm(3). The biomass concentration in the reactor varied with the changes in both superficial velocity and biofilm thickness. The maximum biomass concentration occurred at the biofilm thickness of 400-700 mu m. Furthermore, a large amount of biofilm was grown on the surface of immobilized cells and there was only a small amount of microorganisms grown inside the cell beads.