Comparison of different granular solids as biofilm carriers

Abstract

Biofilms grown on three different carriers (Biolite™, Perl™ and zeolite) in municipal wastewater were examined and their biochemical properties like dehydrogenase enzyme activity (DHA) and nutrient removal efficiency were studied. The artificial Biolite™ and Perl™ carriers were produced from ceramics and glass waste, respectively. The physico-chemical properties of carriers such as specific surface area, composition, methylene blue and protein adsorption capacities were also measured.According to DHA values, two different colonization periods were identified for each carrier. During the first 45days, DHA values were between 0.1 and 0.9mg TPF/g dry carrier and varied together with the chemical oxygen demand and total Kjeldahl nitrogen ratio of the influent wastewater. During this period, the biofilm on Biolite™ had more intensive dehydrogenase enzyme activity than those grown on Perl™ and zeolite. After the 45th day, the DHA values increased and were about three times higher on each carrier. In both colonization periods, DHA values were higher in the case of biofilm grown on artificial carriers than on zeolite.Biofilms attached to carriers and activated sludge were compared and related to total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) removal efficiencies during municipal wastewater treating experiments. Nutrient removal was more effective in the case of biofilms grown on artificial carriers. Biofilm on Perl™ carrier was very successful in organic matter removal, too. The highest total carbon and NH4+N removal efficiencies in the case of activated sludge indicated active nitrification process, while biofilms produced more effective TN and TP removal than activated sludge. Since the oxygen diffusion into the biofilm layer is limited to about 40μm, as described in a number of studies, both aerobic and anaerobic transforming processes can occur, which implies that denitrification and nitrification can be present at the same time, meanwhile in the case of activated sludge the aerobic converting processes are predominant. Among the carriers—on the basis of the biofilm DHA and TN removal data—the artificial ones seem to be more promising than natural zeolite for wastewater treatment technologies.