Treatment of Gaseous Toluene by Cyclic-Feed Multi-ColumnBiofiltration

摘要

Until now, we have already shown experimentally that the performance of biofiltration wasimproved by supplying inlet gas evenly to the whole filter bed. In this study, a practical design,"Cyclic-Feed Multi-Column biofiltration" was proposed, and treatment of toluene gas wasperformed using this type of reactor. The reactor has plural filter beds which are connected inseries. Gas inlet position is switched periodically, and at the same time, each filter bed is washedby a “soak-and-drainage” process. Soaking the filter bed is not only for washing but also for thesupply of water, so this process can prevent the filter bed from excess water, which is oftencaused in usual biotrickling filters.Experimental result showed that only low efficiency of toluene was observed initially, but it wasimproved by increasing the ratio of nitrogen in the nutrient solution. Maximum eliminationcapacity (Ecmax) was increased with the elapse of time from the end of washing, whereassorption velocity (represented by the coefficient of first-order kinetics) was decreased in thesame period. It suggests that the washing process derives the improvement of gas-biofilmcontact efficiency but causes the loss of effective microorganisms.In this experiment, about 80% of inlet toluene was converted to CO2, and Ecmax was calculated33g m-3 h-1 as the highest value. This experiment was carried out sowing the filter bed withnight soil sludge initially. However, in the ongoing study, a stock of toluene-decomposingbacteria is being utilized to achieve much higher toluene removal. And we have just started aproject for the practical application of this system.