Performance, bacteria counts distribution, and biofilm flora of biotrickling filter treating styrene-polluted gaseous streams

摘要

Build biotrickling filter treating styrene-polluted gaseous streams using the enriched sludge bacteria, perlite and liquid medium flow. A biodegradation experiment on treating styrene waste gas was run in a biotrickling filter. A microbiological study and a measurement of biodegradation activities were simultaneously carried out on four identical perlite-packed columns. For four reactors, the spatial structure of the microbial communities was investigated by means of plate count method. The experimental data of styrene gaseous stream, gas velocity, liquid flow and bacterial counts obtained at different biofilter heights were used to evaluate the pollutant concentration profiles as well as the influence of styrene load on biomass distribution along the packing medium. This work highlights the spatialization of biodegradation functions in a biofilter. The distribution of biodegradation activities correlates with the spatialization of microbial density and diversity. The vertical structure of microbial communities must be taken int℃onsideration when dealing with the malfunctioning of bioreactors.When the concentration of styrene ranged from 200 mgm -3 to 1 000 mgm -3 , the gas flow ranged from 0.2 Lh -1 to 0.25 Lh -1 , the liquid flow ranged from 10×10 -3 m 3 h -1 to 12×10 -3 m 3 h -1 , the gas residence time was 50 s to 65 s, the PH ranged from 6.5 to 7.5, the styrene removal efficiency could be arrived at 90%～99 %. When the concentration of styrene was below 1000 mgm -3 , the gas flow was 200Lh -1 and the liquid flow was 10Lh -1 , the styrene removal efficiency could be arrived at 90% and elimination capacity was 30mgL -1 h -1 . The maximal volumetric styrene elimination capacity could come up to 35 mgL -1 h -1 , whereas styrene was removed nearly completely under milder conditions. An inhibiting effect due to high pollutant load was observed mainly in the first sections of the column, whereas a decrease in biomass concentration took place in all the sections of the column when decreasing the apparent gas residence time. Perlite is a suitable packing material for biofilters as it showed a sufficiently low pressure drop and good immobilization properties for mixed microbial cultures. The dominant micropopulations in moist biofilm include Pseudomonas putida, Bacillus fusiformis, Acinetobacter lwoffii, et al. The maximal living bacterial cells of Pseudomonas putida in biofilm was 5.5×10 7 CFUg -1 , and the living cells decreased with increasing duration of biotrickling filter operating period (Table 1).The experimental data for styrene and bacteria concentration measured along the filter height under variable operating conditions demonstrated that the bacterial count along the packing material depends on both styrene load and gas residence time. At relatively low inlet pollutant concentrations, bacterial counts reached a maximum value at the bottom and decreased progressively along the column regardless of the apparent gas residence time due to the progressive decrease in styrene availability. By progressively increasing inlet pollutant concentrations, its distribution became relatively homogeneous, whereas the opposite behavior was observed beyond this threshold. (Table 2).