Process And Mechanism Of Improved Biotechnology To Remove Waste Gas Containing Dichloromethane And Toluene

At present,China is facing dual pressures of fine particulate matter(PM2.5)pollution and ozone(O3)pollution.Volatile organic compounds(VOCs)are one of the important precursors that form PM2.5 and O3 pollution,which are harmful to both of human health and ecological environment.Strengthening the treatment of VOCs is an effective policy to control atmospheric pollution at this stage.Biotechnology is one of the widely used technologies in the treatment of VOCs.However,for the treatment of aromatic hydrocarbons and halogenated hydrocarbons,the representative VOCs discharged from pharmaceutical industries,the removal performance of traditional biotechnology is not ideal due to their hydrophobicity and recalcitrance.This study taking biotechnology as the core treating technology,optimized the bioreactor configuration,improved the degradation ability of microorganisms,and fixed catalytic ozonation pretreatment,etc.,to enhance the removal of hydrophobic and recalcitrant VOCs.The effect of different enhancing methods on the biological treatment characteristics and mechanism of VOCs degradation was analyzed to provide a reference for the industrial application of VOCs treatment technologies.Specific conclusions were described as follow:At first,an airlift packing bioreactor(ALPR),which combined the suspended and fixed-film microbial growth system,was set up to remove dichloromethane(DCM)and toluene.The maximum elimination capacity(ECmax)of the ALPR for DCM reached 108 g m-3 h-1,increased by 145%if compared to the ALR.The biodegradation ability of the microorganisms in the liquid-phase of the ALPR is significantly better than that in the ALR.However,the ECmax of toluene of the ALPR decreased by 25%compared with the ALR.In the face of fluctuations in pH,operating temperature,empty bed residence time(EBRT)and transient inlet concentration that may be encountered in industry,ALPR shows higher removal performance and stability more than ALR in the removal of both DCM and toluene.A factorial design was used to analyses the interaction of multiple factors and their influence on the removal of DCM and toluene in the ALPR and ALR.It shows that pH value has the most significant influence,and plays a crucial role in maintaining high RE of DCM and toluene in both of the ALPR and ALR.Temperature has a great effect on the removal of toluene.EBRT has certain effect on the removal of DCM.The transient concentration of a single substrate has a significant negative effect on the RE of this substrate,and the steep increase of DCM concentration has an adverse effect on the RE of toluene in the ALR.The overall RE of both toluene and DCM by the ALPR are much higher than that of the conventional ALR under unsteady operation conditions.The results of high-throughput sequencing showed that the microbial composition on the packings of the ALPR had a large difference from its liquid-phase or the liquid-phase of the ALR.Rhizomicrobium,Chitinophaga,Vampirovibrio and Fodinicurvata that found with great abundance fixed on the packings are first to be reported in VOCs biological removal.The richer microbial community diversity and stronger biodegradability in the ALPR are the key to maintain efficient removal of VOCs under drastic changes in different operating parameters.However,during the steady-state operation of the ALPR,the ECmax of recalcitrant DCM has been greatly improved,but the removal performance of toluene has not been effectively enhanced compared with the ALR.Therefore,a novel catalytic ozonation-biodegradation coupled system was developed for enhancing the removal of toluene.An in-depth investigation on the treatment of toluene by single catalytic ozonation technology was conducted.The effect of nitric acid modification on activated carbon(AC)and on the properties of Mn/AC ozone catalyst were studied,and the ozone catalytic performance of toluene on catalysts modified with different concentrations of nitric acid was investigated.Nitric acid modification can greatly increase the acidic oxygenated groups content of the catalysts and the overall valence of Mn element.Among the catalysts modified by nitric acid with different concentrations,the Mn/AC modified by fuming nitric acid with a 43%vol.have the highest electron affinity and the best lattice oxygen mobility,and have the highest toluene conversion rate,CO2 selectivity and ozone conversion rate.Furthermore,a new toluene catalytic ozonation intermediates conversion and accumulation mechanism at low temperature is proposed.This study combined ozone catalysis and biotechnology to develop a catalytic ozonation-biodegradation coupled system to remove toluene.Results showed that when the ozone catalytic temperature is 70 ? and the ozone concentration is 250 ppm,it can ensure that the coupled system has a relatively high RE of toluene,while it can effectively control the accumulation rate of the biomass on the packing layer,and no ozone is discharged.Under this condition,the ECmax of the catalytic ozonation-BTF coupled system were 442 g m-3 h-1,increased by 39%if compared to the single BTF.The pressure drop of the packing layer can be maintained at relatively stable low pressure for the BTF in the coupled system,while the single BTF was blocked several times during the operation due to the increase of the biomass on the packing layer.The analysis of ozone catalytic intermediates showed that toluene was convert into intermediate products of carboxylic acids,aldehydes and ketones,which can be effectively removed through the biodegradation and without more toxic pollution emissions.The above research showed that the catalytic ozonation-biodegradation coupled system is a feasible and promising VOCs treatment technology that could be used.