Enhanced Removal Of Hydrophobic VOCs From Waste Gases In Biotrickling Filters

Volatile organic compounds?VOCs?emitted to the ambient atmosphere from municipal and industrial represent a major environmental problem.In recent years,more and more VOCs have been dicharged into the environment due to human activities and biogenic emissions.VOC concentration varies considerably.Moreover,VOCs are closely correlated with the formation of fog and haze,and pose a great threat to public health and ecological security due to their toxicity.Therefore,close attention has been paid to VOC emissions.Among available technologies of air pollution control,biological process is becoming an established technology because of its cost-effectiveness and environmental friendliness.However,a biotrickling filter?BTF?for VOCs removal exists some disadvantages such as a deterioration in degradation performance over a long period operation due to clogging within biofilter beds,and BTF for hydrophobic VOCs removal usually performs poorly due to low solubility and mass trans fer of hydrophobic VOCs between gas phase to liquid phase.Based on problems mentioned above,n-hexane is chosen as model VOCs and removed in BTFs with polyurethane sponge.The effects of operational parameters,surfactants,hydrophilic VOCs on the removal performance of n-hexane were discussed.The biofilm was preliminarily analyzed during a long-term operation and the recycle of biofilms in wastewater was investigated.The effects of operational parameters including nitrate concentration,n-hexane inlet concentration,temperature and gas empty bed contact time?EBCT?on the long-term removal performance of n-hexane were investigated.Biofilms characteristics over long-term operation in the BTF were also studied.Results showed that 160 mg L^-1 of N-NO₃^-was sufficient for n-hexane removal at a constant inlet concentration of 350 mg m^-33 and gas EBCT of 30 s.With increasing inlet concentration and decreasing EBCT,the removal efficiency declined.The elimination capacity?EC?maximized at 45.36 g m^-3 h^-1 for an inlet concentration of 900 mg m^-3 and gas EBCT of 30 s.The zeta potential of biofilms became less negative due to an increase in protein concentration.Protein concentration in biofilms increased while polysaccharide concentration changed slightly.The chemical composition of EPS and the protein concentration changed in long-term BTF accordingly,possibly resulting in the deterioration of performance in the long-term BTF.The partition coefficient?K?of n-hexane in surfactant solutions?SDS,Tween20,Triton X-100?,the biodegradability of surfactants,and the toxicity of SDS to microorganisms were examined by using batch experiments.The optimal concentration of SDS for enhanced n-hexane removal was investigated using two BTFs?BTF 1 without SDS,BTF 2 with SDS?.The K of n-hexane in surfactant solutions was much lower than that in water,and the K in SDS was lower than that in Triton X-100 and Tween 20.SDS could be degraded by microorganisms,and it was non-toxic to microorganisms within the experimental range.The optimal concentration of SDS added into the BTF was 0.1 CMC.EC of 50.4 g m^-33 h^-1 was achieved at a fixed loading rate?LR?of 72 g m^-33 h^-1,and the removal efficiency?RE?of n-hexane increased from 50%?BTF 1?to 70%?BTF 2?at SDS of 0.1 CMC.The concentration of protein and polysaccharide in the second packing medium of BTF 1 was higher than that in the first and third packing medium of BTF 1 and lower than that in the second packing medium of BTF 2.The removal performance of n-hexane in two BTFs?BTF 1 without SDS,BTF2 with SDS of 0.1 CMC?was investigated under different operational parameters?inlet n-hexane concentration and EBCTs?.When an inlet concentration of n-hexane increased from 600 to 850 mg m^-3,the RE decreased from 67%to 41%by BTF 2 and from 52%to 42%by BTF 1.SDS could enhance the n-hexane RE from 43%?BTF 1?to 60%?BTF 2?at EBCT of 7.5 s and an inlet concentration of200 mg m^-3.The removal of n-hexane in the presence of a hydrophilic compound was investigated.Acetone has been introduced and mixed with n-hexane in order to increase the bioavailability of n-hexane in a BTF.LRs and RE of n-hexane and acetone varied from 10.7 to 73.7 g m^-3 h^-1 and 4.3 to 148.8 g m^-3 h^-1,and the RE ranged from 33%to 100%and 80%to 100%,respectively.Results showed the presence of high acetone concentration negatively affected the n-hexane removal and led to excess biomass accumulated on packing media.However,the degradation of acetone was not impacted by the presence of n-hexane.Moreover,for n-hexane LR less than 24 g m^-3 h^-1,the RE of n-hexane was quickly restored from 55%to 85%¹00%in the presence of acetone(<18 g m^-3 h^-1)when the BTF restarted after 12 h,and the removal performance of the BTF for n-hexane was quickly enhanced to>90%after 24 h due to using backwashing.A dried biomass wasted from biotrickling filters has been prepared for removing lead?Pb?II??ions from aqueous solutions.The kinetics,isotherms and thermodynamics of Pb?II?ion adsorbed by the dried biomass were investigated.The maximum Pb?II?ion adsorption capacities of a dried biomass was 160.0 mg/g at 25?according to an evaluation using the Langmuir equation which was fitted well to the adsorption data.The results of kinetic studies reveale d that the adsorption process followed the pseudo-second-order model.The calculated thermodynamic parameters of?S°,?H°and?G°suggested that the adsorption of Pb?II?ion was endothermic and spontaneous.Fourier transform infrared spectroscopy?FT-IR?analysis illustrated that amide group and hydroxide group affected Pb?II?ion removal significantly.This study demonstrated that a dried biomass wasted from biotrickling filters for removal n-hexane could be successfully used as adsorbent for the treatment of Pb?II?ion from aqueous solutions and have a higher adsorption capacity.