The Experiment And Dynamics Research On Purification Of Methanol Phenol Mixed Organic Wastewater By Non-thermal Plasma Combined With Adsorption

With the rapid development of industry and the improvement of environmental protection standards,the large amount of industrial organic wastewater requires efficient purification treatment.Due to traditional treatment technology has different defects,searching an effective,efficient and low energy consumption treating method of industrial organic wastewater is one of research hotspot in this field.Non-thermal plasma(NTP)is one kind of advanced oxidation process(AOPs).The discharge phenomenon occurs when electric field is loaded between anode and cathode.The active groups,include high-energy electrons,excited atoms/molecules,free radicals,molecules,cation and anion,generated during the discharge process.The collision between active groups and pollutant molecules leads to bond breaking,thus,the contaminant can be degraded.However,there are still some drawbacks if NTP technology was used independently such as long discharge time,low energy utilization rate,etc.Adsorption method has the disadvantages of low purification efficiency and high running cost.This paper will carry out the research of organic wastewater purification by dielectric barrier discharge NTP combined with adsorption.The degradation rules and kinetic equations will be analyzed and compared under the three conditions of adsorption,NTP and NTP combined with adsorption.With methanol as small molecular organic matter,phenol is refractory organic matter,the purification rules and reaction kinetics models of single component and two-components wastewater will be studied respectively.Intermediate product of organic wastewater purification by NTP combined with adsorption will be detected.Based on the experimental data and theoretical analysis,the macroscopic mass transfer and kinetics model is explored.In adsorption experiment,four types of adsorbent,4A molecular sieves,ceramsite,ceramic raschig ring and ?-Al2O3,can adsorb methanol and phenol effectively.The adsorption purification effect of 4A molecular sieves is better than the others in the same stacking volume.The adsorption process of 4 types adsorbent on methanol follows the pseudo-second order adsorption kinetic equation.The adsorption process of ceramsite on phenol follows the pseudo-second order adsorption kinetic equation,while adsorption process of other three adsorbents on phenol follows the pseudo-first order adsorption kinetic equation.Under the same experiment condition,the adsorption velocity and equilibrium absorption capacity of methanol is higher than phenol.In non-thermal plasma oxidation experiment,the results of single factor experiments and multifactorial response surface analysis indicate that:the methanol and phenol simulated wastewater can be degraded effectively by non-thermal plasma.During the degradation process,the colour of methanol wastewater has not changed while the colour of phenol wastewater changes from colourless to brown to almost colourless.With the prolongation of discharge time,COD concentration decreased while COD degradation rate increased,and the effective energy yield decreased.Compare with methanol wastewater,phenol requires longer discharge time to reach the same degradation rate even the initial COD concentration is similar.This indicates that phenol is more difficult to degrade than methanol.The discharge voltage can improve COD degradation rate in unit time.However,much higher discharge voltage requires higher energy consumption and the improvement of COD degradation rate is not obvious due to the structure of reactor.With the increasing of initial concentration and air flow rate,COD degradation rate increased firstly and then decreased.For the initial concentration,this change is mainly affected by maximum degradation capacity of different reactor.For air flow rate,much higher air flow rate leads to the stripping of active groups and short retention time.In different factors,the discharge time and discharge voltage have the higher influence on the degradation rate,while the initial concentration and air flow rate have lower influence on the degradation rate.The kinetics of degradation process indicates that,the decrease of contaminant concentration in liquid phase leads to the increase of macroscopic reaction order.However,the overall degradation process conforms to the first-order kinetics model,and the reaction rate constant increases with the increase of discharge voltage.In the synergistic degradation process of methanol,under the same experiment condition,the purification effect of combination process is better than single process.In the initial stage of synergistic process,the degradation of COD dominated by adsorption process.However,NTP plays a main role in degradation process with the prolongation of discharge time.The degradation reaction is not a complete first or second order kinetic equation,the reaction order changes with the variation of reaction time and initial concentration.In the synergistic degradation process of phenol,the improvement of COD degradation rate is not obvious in the initial stage compare with NTP oxidation process.In the late stage,the degradation effect of NTP combined with adsorption is better than NTP alone.Adsorption can enrich concentration of organic matter in liquid phase,and leads to higher fitting degree of first order kinetic equation.In the mix wastewater of methanol and phenol experiment,the larger phenol proportion,the longer reaction time to reach the same COD degradation rate,and the lower effective energy yield.According to the response surface analysis,COD degradation rate is positively correlated with discharge voltage and discharge time,while negatively correlated with phenol proportion.The discharge voltage has the greatest influence on the degradation effect,followed by discharge time and phenol proportion.Degradation kinetics shows that,with the increase of phenol proportion,the fitting degree to first order kinetic model increases.The COD degradation velocity of mix wastewater of methanol and phenol can be influenced by reactor structure.From quick to slow:coaxial nebulization>coaxial liquid film>wire-plate>multi-needle-plate>single needle-plate.The coaxial DBD reactor reaches the highest effective energy yield,followed by wire-plate DBD reactor and multi-needle-plate DBD reactor,the effective energy yield of single needle-plate is lowest.The degradation effect of coaxial nebulization NTP combined with adsorption is better than multi-needle-plate NTP combined with adsorption.The LC analysis indicated that the main intermediate products of phenol oxidation process are dihydroxybenzene and benzoquinone.The intermediate products of methanol and the intermediate products of phenol can produce new intermediate substances.In the mix wastewater of methanol and phenol experiment,the larger methanol proportion,the faster COD degradation velocity.The degradation rate of phenol is lower in mix wastewater than one-component phenol wastewater under the same experiment condition.The degradation process of NTP to contaminant is a complex mass transfer-reaction process.The active groups generated by discharge in gas phase need to pass through the gas-liquid interface to get into the liquid phase.In liquid phase,the oxidation degradation reaction occurs by molecular diffusion and encounter.The degradation rate of contaminant in liquid phase is influenced by gas-liquid mass transfer rate,molecular diffusion rate and chemical reaction rate.By increasing discharge voltage,the gas-liquid mass transfer rate can be enhanced.The concentration of active groups increases by aeration.