Microbial structure and functions of biofilm during wastewater treatment in the dairy industry

Abstract

The microbial structure and activity of biofilm are two important parameters for the successful operation and control of fixed film processes in wastewater treatment. However, the constant interaction between fixed and suspended biomass requires the parallel investigation of these two biological components. The aim of the present article is to study the key microbiological and enzymological parameters of biofilm and suspended biomass from an anaerobic sequencing batch biofilm reactor for dairy wastewater treatment. The effectiveness of organic matter (measured as COD) removal and nitrates removal was determined. The microbial structure of biofilm and suspended biomass was investigated by the quantity of anaerobic heterotrophs, anaerobic spore-forming microorganisms and denitrifying bacteria. The total dehydrogenase activity and the nitrate reductase activity were used as indicators for biomass activity. The obtained data showed that the enzyme activity of the fixed biomass was higher in comparison with that of the suspended biomass. This result is related to the more heterogenic media of the inert carrier and more dynamic conditions in the biofilm inner layers. The total dehydrogenase activity of the fixed biomass was four times higher and the nitrate reductase activity of the fixed biomass was two times higher than that of the suspended biomass during stable biofilm functioning. The investigated biological system mineralized the organic matter with high effectiveness (to 90 %) and removed 67 % of the nitrates from dairy wastewater as a result of the controlled water treatment process.