Simultaneous Removal of Organic Matter and Nitrogen Compounds in Autoaerated Biofilms

Abstract

This paper describes the simultaneous removal of organic matter and nitrogen compounds carried out using an autoaerated multispecies biofilm growing on gas-permeable hollow-fiber membranes. In order to perform the aerobic heterotrophic oxidation and nitrification processes, the biofilm absorbs atmospheric oxygen through the inside walls of hollow fibers and consumes substrate from the bulk liquid. A mass balance calculated the consumed oxygen. Depending on the removed organic and nitrification rates, the oxygen flux through the hollow fibers can reach up to 90% of the total oxygen consumed, whereas the remaining 10% pertains to the dissolved oxygen from the influent wastewater. Without the biofilm the oxygen transfer rate through clean hollow fibers is 3.5gm−2day−1, whereas the oxygen transfer rate through the biomembrane (hollow fiber+biofilm) achieves a maximum value of 25gm−2day−1. The enhanced oxygen transfer using the biological pathway may be attributed, among many other factors, to the mobility of the microorganisms generating microturbulence, which produces more active bioturbulent diffusiveness than the molecular diffusion in the biofilm. It has also shown that the oxygen utilization efficiency was affected by the substrate utilization rate.