A Study On Treatment Of Off-gases Containing BTX By Fungual Biofilter

The gaseous volatile organic compounds(VOCs)pollution and its controlling methods are paid more and more attention nowadays. Fungi in biofilter can grow better at low water activity, low pH than bacteria and the aerial mycelia of fungi in direct contact with gases can facilitate more rapid mass transfer of hydrophobic compounds than agueous bacterial biofilms.The aim of this study is to find certain kind of fungus that can treat benzene, toluene and xylene (BTX) efficiently and optimize the performance of fungual biofilters for gaseous treatment. Activated carbon and ceramic pellets were chosen to set up the biofilters. Performances of biofilters containing ceramic pellets, activated carbon, and three mixtures that ceramic pellets/activated carbon are 1/2, 1/1 and 2/1 under different conditions were evaluated during more than 100 days. The results show:(1) After isolated and cultivated from sewage activated sludge, the fungus was selected by changing pH and identified as Trichoderma viride Pers.ex Fr. The fungus has much mycelium on the packing surface, forming complex reticular which enable direct contact of the fungus and BTX.The ceramic pellets have more rough surface and more hydrophilicity than activated carbon, so they are better for biofilter setting up.Two kinds of biofilter starting up method were evaluated, one is domesticating the fungus in liquid and then inoculating onto packing media, another is domesticating and inoculating simultaneously on the packing media. The results shows that the latter started in about 28 days, about a month shorter than the former, and much longer than that of bacteria(7～18 days). The best environment for the fungus is in C:N as 5:1, nutrition liquid 24mL·mL^-1, 25℃,pH at 5.5.(2) Toluene is the most biodegradable pollutant, followed by benzene, then by xylene. (3)When the inlet load is lower than 100g·m^-3·h^-1, each biofilter can gain a purifying efficiency of nearly 100%. When the empty bed retention time is 84.8s, 42.4s, and the inlet load is in 97～200g·m^-3·h^-1,80～144g·m^-3·h^-1, the outlet load in the five biofilters can reach 88～180g·m^-3·h^-1,72～130g·m^-3·h^-1,with a purifying efficiency of more than 90%. While when the empty bed retention time is 21.2s, more outlet load and bad purifying efficiency are gained.Compared with other bacterial biofilters, for the same purifying efficiency, the fungal biofilters have an about three times elimination capacity.(4)Purifying efficiency decreased with increasing of inlet pollutants concentration. When the empty bed retention time is 84.8s,42.4s and the inlet pollutants concentration is in 7～14g·m^-3,1.5～5.5g·m^-3, the purifying efficiency in the five biofilters can reach more than 90%. When the empty bed retention time is 21.2s, bad purifying efficiency is gained.Water content is different on different packing height, resulting in different purifying efficiency on different packing height. The height of 200～400mm gains the best purifying efficiency with a water content of 35～55%. It shows that fungi have more drying adaptability than bacteria. Feasible surface area and porosity of the packing media for the fungus is 600～1000m²Â·m^-3 and 0.5 in this research.(6) The biofilter packed with activated carbon gain the best purifying efficiency and the highest pressure drop, then followed by ceramic pellet/activated carbon as 1/2, ceramic pellet/activated carbon as 1/1, ceramic pellet/activated carbon as 2/1, that of ceramic pellet has the worst purifying efficiency and lowest pressure drop. This indicates that adding ceramic pellets into activated carbon could prevent bed compaction effectively and increase the void fraction of the filter beds.After the inhibitition constants were determined, Monod kinetics for multiple VOCs was established, then a theoretic model of biofilter treating multiple VOCs gas was set up, numerical solution was obtained through C language finally. Under different inlet concentrations and velocities, the model can predict the outlet concentration. The model successfully simulated biofilter's BTX removal performance. These simulation results could supply theoretical guide for biofilter design and operation optimization.