Biofiltration Of Trichloroethylene From Air Streams

Biofiltration has won researchers’ favor because of simplicity of processes andequipments, low costs, facility of operate and control, high removal efficiency andlimited negative environmental effects in seeking a efficient and economicaltreatment technology for waste gases. Most work about biological removal of volatileorganic compounds （VOCs） was reported with low concentration waste gas underlow gas velocity. For the research on removal of waste gas with high concentrationunder high gas velocity has been proven to have bad processing effect, weak shockresistance and unstable in the long term run.In this work, the biofilter packed with the mixtures of chicken manure compostand modified polyethylene （PE） were employed to removal trichloroethylene wastegas under high gas velocity in a continuous operation and in a intermittent operation.The removal efficiency of trichloroethylene and influencing factors were evaluated bymeasuring concentrations of trichloroethylene waste gases, the characteristics of thepacking materials and pressure drop.The following main conclusions were obtained:（1） Trichloroethylene waste gas was successfully removal in a biofilter in a co-ntinuous operation.The removal efficiency of70％¹00％could be obtained with trichloroethyleneinlet concentration of50¹500mg·m^-3at the empty bed retention time （EBRT） of120s. The elimination capacity of32g·m^-3·h^-1had been achieved with the inlet load of44g·m^-3·h^-1. The biofilter has not received maximum capability of the trichloroethyleneremoval.（2） A good performance of the biofilter was obtained in a intermittent operatio-n.The removal efficiency of90.43％¹00％could be obtained with trichloroethy-lene inlet concentration of15³00mg·m^-3at EBRT of90s. The elimination capacityof23g·m^-3·h^-1had been achieved with the inlet load of30g·m^-3·h^-1. The biofilter has not received maximum capability of the trichloroethylene removal.The removal efficiency of86.17％¹00％could be obtained with trichloroethy-lene inlet concentration of15³00mg·m^-3at EBRT of36.2s. The eliminationcapacity of26g·m^-3·h^-1had been achieved with the inlet load of30g·m^-3·h^-1. Thebiofilter has not received maximum capability of the trichloroethylene removal.（3） Water content, pH and nitrogen content of packing media, pressure drop c-hanged in the biofilter where trichloroethylene was continuously and intermittently r-emoval.The method of artificial spray has been used to keep humidity, when the watercontent of packing media was dropped a little aside from optimal range. The stableremoval efficiency could be maintained.pH of packing media was dropped because trichloroethylene was degraded to Cl-and carbonic acid. The removal efficiency has not been changed obviously.Microorganisms has great tolerance for the acidification.The nitrogen nutrients were sufficient and the compression and blocking of beddid not occur during the long term run of biofilter.In conclusion, trichloroethylene waste gas under high gas velocity were succ-essfully eliminated in a biofilter packed with the mixtures of chicken manure compostand modified polyethylene （PE）. The results showed that the biofilters has highremoval efficiency, stable performance and higher potential of the trichloroethyleneremoval in the long term run.