Biological reactor for odorous fatty acids treatment

Abstract

A fibrous bed bioreactor was applied for treatment of odorous gas. The column reactor was packed with spirally wound fibrous sheet material on which a consortium of microorganisms selected from activated sludge was immobilized. The first stage of this work comprised a preliminary study which aimed at investigating the feasibility of the fibrous bed bioreactor for treatment of odorous volatile fatty acids (VFAs). In this part, the microbial kinetics in the selection culture and the performance of fibrous bed bioreactor at increasing mass loadings ranged from 9.7 to 104 g/m3/hr were studied. VFA removal efficiencies above 90 % were achieved at mass loadings up to 50.3 g/m3/hr. At a mass loading of 104 g/m3/hr, removal efficiency was found to be 87.7 %. In the second stage of the work, the process was scaled up with design and operational considerations, namely packing medium, process condition and configuration selections. A biochemically inert, synthetic fibrous material was employed as the packing medium. The submerged biofilter configuration failed to operate due to the shear force generated by the gas bubbles, which hindered microbial attachment on the packing medium. The selected trickling biofilter configuration was operated under counter-current flow of gas and liquid streams. Odorous VFAs were introduced into the bioreactor at various inlet concentrations and flow rates. The effect of inlet concentration was studied by increasing the gaseous VFA concentrations at fixed empty bed retention times (EBRTs) of 90, 60, 45 and 30 seconds. While the effect of EBRT was investigated by increasing the gas superficial velocity or shortening the EBRT, at different inlet VFA concentrations of 0.08, 0.2, 0.4 and 0.7 g/m3. The bioreactor was effective in treating odorous VFAs at mass loadings up to 32 g/m3/hr, at which VFAs started to accumulate in the recirculation liquid indicating the biofilm was unable to degrade all the VFAs introduced. Although VFAs accumulated in the liquid phase, the removal efficiency remained above 99 %, implying that the biochemical reaction rate, rather than gas-to-liquid mass transfer rate, was the limiting factor of this process. The bioreactor was stable for long term operation; relatively low and steady pressure drop, no clogging and degeneration of the packing medium were observed during the 4-month operation.