Effect Of Trace Ozone Strengthened Biological Trickling Filter Treating VOCs

The biological treatment is the mainstream technology for VOCs control with high efficiency,low consumption,mild reaction conditions and low secondary pollution.The excessive growth and non-uniformal distribution of biofilm lead to layer clogging and deterioration of operating performance.Therefore,it is necessary to control the biomass within reasonable limits,and to ensure its long-term degradation activity.Setting two sets of bio-trickling reactor with and without trace ozonation(O3-BTF&BTF)to explore the changes of the biofilm phase composition and surface characteristics by measuring and comparing their operating performance,packed bed characteristics,biomass accumulation and distribution pattern.Trying to clarify the primary causes of clogging and performance deterioration.Trying to ues trace ozone technology to control the growth and distribution of biofilm and clogging in the biotrickling filter,thereby strengthening its continued operation efficiency.The performance of the two sets of biological trickling filter differentiated during their running which was similar to each other in the early time.The BTF stopped running because of its deterioration of performance at 150th day.03-BTF kept high efficiency even at 180th day since its start.During operation time,the removal efficiency of toluene was gradually reduced with the shorter EBRT and increased inlet concentration.In the initial operation period(40th day),the toluene elimination capacity and removal efficiency of BTF and O3-BTF were both around 24 g/m3·h and 97%when the inlet concentration was 200 mg/m3 and EBRT was 30 s;In the later operation period(140th day),the toluene elimination capacity and removal efficiency of BTF was 48.96 g/m3 h and 69.2%when the inlet concentration was 600 mg/m3 and EBRT was 30 s while that of O3-BTF was 66.12 g/m3 h and 89.4%.The removal efficiency of upper and lower segments in O3-BTF kept high and is almost the same,however,that in BTF had remarkbly declined.It was obviously that in the same operation condition,O3-BTF showed great strengthening effect in the later operation time.The yields of CO2 and toluene elimination capacity were linear related.The maximum mineralization rate in O3-BTF was about 87%which was higher than that in BTF of 80%.Toluene purification in BTF fit the Michaelis-Menten kinetic model,The maximum unit volume degradation rate(rmax)of O3-BTF was 174.2 g/m3·h which was higher than BTF of 156.3 g/m3 h.During the long operation period,the pressure drop in BTF rose greatly while the porosity decreased.The pressure drop in O3-BTF whose porosity of upper and lower segmants were higher than BTF remained at 4.5 mmH2O at the 180th day since its start.It showed that the O3-BTF was more advantaged in operating performance and extending the operation time than BTF by regulating the characteristic of packing layer.It showed that trace ozone had a great effect on controlling the excessive accumulation and non-uniform distribution of biomass.The biomass concentration decreased in the radial direction up along the reactor.The biomass in BTF accumulated seriously,neared the inlet and outlet was respectively 60.32 mg VSS/g and 10.25 mg VSS/g in the later period(150th)while it was less serious and more evenly in O3-BTF,The biomass neared the inlet and outlet was respectively 40 mgVSS/g and 13.5 mgVSS/g at the 180th day.The analysis of biolog showd that trace ozone would not reduce the activity of microbe in BTF.The monitoring of relative hydrophobicity of biofilm surface and zeta potential which was closely related with acculating ability between biofilm showed that trace ozone could effectively slow down the increase of hydrophobicity and the decrease of electronegativity on biofilm surface.The change of EPS secretion and main chemical components might be one of the causes leading to the operation deterioration of biotricling filter and trace ozone could effectively slow down the change speed.The secretion of total EPS and extracellular protein in later period(140th day)gradually increased up respectively to 2.7 and 2.6 times that of the initial period(40th day)in BTF while the secretion in the O3-BTF was basicly the same as that of the initial period.Polysaccharide secretion did not changed obviously in biotrickling filter.The increase of PN/PS in EPS would cause the increase of relative hydrophobicity of biofilm.Trace ozone could control relative hydrophobicity by regulating PN/PS.Electronegativity of the biofilm and EPS decreased with the running of the reactor,and it was greater in upper segment.Electronegativity of the biofilm and EPS in O3-BTF decreased more slowly.The change trend of the average molecular weight of EPS was the same as zeta potential.The result of FTIR further showed that the main chemical components of EPS changed in the operation period.Ozonation strengthened the long-term operation efficiency of the biotrickling reaction system by changing the biofilm phase.With the increase of the distance from the inlet,the toluene concentration and biomass decreased gradually in the radial direction of the reactor which were linearly related.The biomass in the O3-BTF changed mitigantly while toluene concention changed fiercely along the diameter.The removal efficiency of unit microbial biomass in O3-BTF was higher than that in the BTF.It was showed that the toluene degradation ability of microbial biomass in O3-BTF was greater than that in the BTF.The porosity,biomass concentration and pressure drop were linearly related whose correlation coefficients were above 0.92.It was showed that the biofilm characteristics and packed bed properties within the biotrickling reactor were closely related.