Performance And Enhancement Of VOC Removal In Biotrickling Filters

Emissions of volatile organic compounds (VOCs) resulted in environment pollution and human health threat, which have paid close attention. Among various technologies for controlling VOCs, biofiltration is bocoming an established technology because of its reliability, cost-effectiveness and environmental friendliness. However, biotrickling filters (BTFs) for VOCs treatment exist some disadvantages, such as performance decrease caused by excess biomass in media over a long period operation and BTF treat difficultly for hydrophobic VOCs. In addition, media affect BTF performance to a large extent.Two identical bench-scale biotrickling filters (BTFs) were employed and designated as BTF1and BTF2in this research. Toluene and hexane were chosen as model VOCs. Polyurethane sponge was used as packing media in BTF, and the activated sludge from a secondary sedimentation tank was used for seeding the BTFs. Furthermore, BTF performance was investigated and evaluated at different operating conditions such as which different organic loading rates, gas empty bed contact times (EBCTs), nitrogen resource and surfactant over a long period of continuous operation. Biofilm within the sponge media of BTF was also primarily analysis after running over a long period. In this research, gas choromatograph was used for determining the concentration of VOCs. In particular, in order to check the reproducibility and reliability of BTFs in each operation stage, a set of reference condition was used in this research.When toluene was used as model VOC, BTF1and BTF2were packed with structured and cubic synthetic polyurethane sponges, respectively. BTF1and BTF2could start up successfully and exceeded99%in removal efficiency using19and27d, respectively. At a constant toluene loading rate of16g/(m3·h), toluene removal efficiencies decreased from98.8%to64.3%for BTF1and from98.4%to74.1%for BTF2as gas EBCT decreased from30to5s. When the toluene load increased from35to140g/(m3·h) at a gas EBCT of30s, the removal efficiencies decreased from99.1%to77.4%for BTF1and from99.0%to81.5%for BTF2. Moreover, BTF2displayed higher removal efficiency even under shorter EBCT or higher loading rate than BTF1when other operation conditions were similar, while showed lower pressure drop than BTF1during the whole period of operation. The high performance could recovery in3～7d after excessive biomass was removed from the BTFs by washing.When NH4Cl was used as sole nitrogen resource at a constant toluene concentration, toluene removal efficiencies decreased from98.0%to57.9%and51.6%for BTF1when gas EBCT decreased from30s to15s and5s, respectively. However, NaNO3was used as sole nitrogen resource when BTF runned at a constant toluene loading rate. When gas EBCT was setted at30,15,10and7.5s, the corresponding removal efficiency reached99.0%,79.8%,70.8%and61.2%. Either NH4Cl or NaNO3was used as sole nitrogen resource at a gas EBCT of30s, the removal efficiencie for toluene decreased with increase in inlet loading rate. BTF presented a better performance when toluene load was less than70g/(m3·h) and NH4Cl used as the sole nitrogen source. In contrast, BTF2used NaNO3as the sole nitrogen source reached higher removal efficiency when toluene load was more than140g/(m3·h). Afer long period running or media washing, BTF could resume to previous high performance in a relatively short period when NaNO3was, but the BTF used NH4Cl as the sole nitrogen source could not.When hexane was used as model VOC, when the hexane load increased from15to30,60g/(m3·h) at a gas EBCT of30s, the corresponding removal efficiencies and elimination capacities were92.9%,86.7%,63.8%and14.3、26.1、39.3g/(m3·h), respectively. At a constant hexane concentration of260mg/m3, removal efficiencies and elimination capacities were87.0%,46.4%,31.7%and28.028.8、41.0g/(m·h) when gas EBCT decreased from30to15s and7.5s, respectively. Moreover, biofilm formed in reticulated polyurethane sponges could resist shorck loading, and BTF could also maintain stable performance after long period operation.The effect of surfactant on BTF performance for hexane removal was also investigated in this research. When the concentration of was1.0and0.2mL/L at influent organic loading rate of15g/(m3·h), the removal efficiencies reached40.0%and53.1%, respectively. When the hexane load increased to30g/(m3·h) at Triton X-100concentration of0.2and0.1mL/L, the corresponding removal efficiencies were58.8%and81.7%. At a constant Triton X-100concentration of0.1mL/L, the removal efficiency increased to83.7%under the hexane load of60g/(m3·h), and it was higer than the value in chapter5at the same condition. Subsequently, the removal efficiency decreased and stabilized at72.8%after the surfactant removed from nutrition solution. Particularly, during the whole duration of126days, Triton X-100introduced could control efficiently excess biofilm growth, which will be a novel control strategy for biofilm control.This dissertation researched on the optimization of packing materials, excessive accumulation and control strategy for biofilm, the removal performance of hydrophobic VOCs over a long period. These reseach results would contribute to expand the adaptation range of VOCs removl by BTF, and provide a novel control strategy for excessive accumulation of biofilm with media. At the same time, it is helpful for understanding the mechanisms of gas biofiltration process.This study provides theriotical basis on the practical application of BTF and polyurethane sponges.