Study On The Treatment Of Pnp Wastewater By Microwave Assisted Cu(Ⅱ)-fenton Catalytic Oxidation Process

In order to resolve the increasingly serious environmental problems brought byorganic wastewater which is toxic or hazardous to microorganisms, this studyestablished a new microwave catalytic oxidation process in nearly neutral solutionbased on universally accessible Fenton oxidation. And investigated the removal of p-nitrophenol（PNP） in simulated wastewater which is bad biodegradability due to itspoisonous to the growth of microorganisms. MW-Cu-Fenton system and microwaveirradiation-standing process was established, static experiments and continuous flowprocess was investigated, and then the oxidation mechanism of MW-Cu-Fenton wasalso studied in this paper.In static experiments, MW-Cu-Fenton system was established because microwaveirradiation could obviously reduce the reaction time, and assistant catalyst Cu²⁺couldaccelerate the reaction rate, the removal efficiency was enhanced at the same time.Microwave irradiation-standing process was proposed later based on MW-Cu-Fentonsystem, which could largely save much microwave energy. Under optimal conditions of[Cu²⁺]=0.8mg/L,[Fe²⁺]=3.0mg/L,[H₂O₂]=0.2g/L, microwave power=250W,irradiation time=2.0min, standing time=4.0min,50mL synthetic wastewatercontaining100mg/L PNP was treated and over95%of PNP was removed when initialpH was5.0in the solution. The optimal range of pH in Fenton reaction was extendedfrom2.0-3.5to2.0-5.5successfully. Overall, the presented process not only extentsnarrow pH range of traditional Fenton reaction to a nearly neutral condition but alsoyields a dramatically high removal efficiency in a short time.In continuous flow process, orthogonal tests indicated that the importance of mainfactors are in sequence as: system temperature（T）＞H₂O₂concentration＞standingtime＞hydraulic retention time（HRT）, and99.67%of PNP was removed in optimalcase of T=70℃,[H₂O₂]=200mg/L, standing time=2.0min, HRT=2.5min. Takingpractical utility into consideration, further study was implemented, results indicatedthat under conditions of pH=5.5, the optimized operating parameters for continuousflow system were [Cu²⁺]=0.5mg/L,[Fe²⁺]=3.0mg/L,[H₂O₂]=0.2g/L, T=60℃,HRT=2.0min, PNP concentration≤100mg/L, standing time=10.0min, over95%ofPNP was removed. This system realized the efficient treatment of PNP-containingwastewater under continuous flow when initial solution pH was nearly neutral.Obvious kinetic experiments were conducted that first-order constant of reactionrate of MW-Fenton system31.781times Fenton system, and half-life period wasreduced from38.51min to2.65min; first-order constant of reaction rate of MW-Cu-Fenton system2.826times MW-Fenton system, and half-life period was reduced from2.65min to0.94min; The generation of·OH is improved obviously by the addition of Cu²⁺. Fe²⁺played as a key role while Cu²⁺played as an assistant role in the catatlyticprocess of H₂O₂, OH generation was strengthened by the cooperation of Cu²⁺and Fe²⁺.This effect is probably controlled by some concealed mechanism.