Study Of Biomass Accumulation In Biofilters And Biomass Control By Chemical Washing

Air pollution which attributes to the rapid development of industry is more and moreserious with the increase of people's material standard of living. As an important kind ofpollutants, the volatile organic compounds (VOCs) do great harm to people's health andnatural environment, so more and more attention has been focused on the purification andtreatment of VOCs. Biofilter is frequently used in the biological treatment of VOCs, andthis technology is simple, cost-effective and has minimum secondary pollution.Clogging of high-performance biofilters caused by excessive biomass growth is oneof the main obstacles to the industrial deployment of waste air biofilters,To extend thelife-time of biofilters, several strategies have been proposed to either prevent clogging orto remove excess biomass. Biomass control techniques are very important for biofilterstreating VOCs to enhance their long-term operation performance.In this study, four paralleled monolayer biofilters packed with wood chips were setup treating toluene gas,to investigate biomass accumulation and clogging in biofilters.The model was established to predict the changes in bioreactor performance as well asbiomass accumulation in different conditions with increasing operation time. Experimentalresults shows that as biomass accumulates in the reactor, the structure of the filter packedbed and the bioreactor performance will be changed. The specific surface area andporosity decrease with excessive biomass accumulation, causing an increase pressure dropof packed bed and a decline in removal performance .To the bioreactor of this study, themax biomass concentration to keep a steady drop is 15kg/m3.Chemical removal of biomass is an attractive technique for biomass control inbiofilters. In this study the chemical removal of excess biomass and its impact on biofilteroperation were investigated. The experimental results of circulating wash showed that theoptimal washing time for biomass removal was 2-3 hours by NaOH ranging from 0.2% to0.8%. The 0.4% NaOH solution was more effective to remove the biomass from thebiofilter and biomass shearing was the main process of the biomass removal under thiscircumstance. The monitoring results of the toluene removal performance demonstratedthat the impacts of NaOH solutions with different concentrations had little difference andthe toluene removal capacities could be recovered after 3-4 days.According to thecomparison results of three washing mode(circulating washing, filling/draining, airsparging), circulating washing was found to be the most suitable mode for biomassremoval. In the case of the water filling/draining treatment , the amount of biomassremoved was low compared to the other methods, the air sparging treatment removedhigher amounts of biomass but cause the destroy of packed bed structure.During the 500-days operation, the result shows that using chemical washingmethods for removing excess biomass can make the biofilter run stable under the averageloads more than 60gC/m3.h. After chemical washing, the toluene removal efficiencies ofbiofilter can be maintained about 70%, toluene removal velocity can be maintained morethan 40 g C/(m3·h) and pressure drop can keep less than 100pa.m-1.