Study On The Efficiency And Mechanism Of Degradation Of Reactive Black 5 Dye Wastewater Via Sludge Hydrothermal Biochar Activating Persulfate

Azo dyes are the most commonly used and widely used dyes in printing and dyeing industry,and are the main components of printing and dyeing wastewater.Among them,reactive black 5（RB5）is the most representative azo dye.Azo dye wastewater has the characteristics of high chroma and toxicity.If it is discharged into the environment improperly,it will cause serious harm to the surrounding ecological environment and human body.In recent years,the advanced oxidation technology based on persulfate（PS）has been applied in the treatment of printing and dyeing wastewater for its advantages of fast reaction rate and wide p H application range.Biochar prepared from waste biomass,as a catalytic material of green economy,has been proved to be effective in activating persulfate and realizing the concept of"waste for waste".However,high temperature pyrolysis technology with high energy consumption is the main method for the preparation of biochar.In this study,the sludge hydrothermal biochar material with activated perdisulfate（PDS）performance was successfully prepared by using the residual sludge of secondary sink of sewage treatment plant as raw material and hydrothermal technology with relatively mild reaction conditions.On this basis,alkali modification and chitosan modification were used to further strengthen the catalytic performance of biochar and realize the rapid removal of RB5 dye wastewater.In addition,due to the presence of humus in sludge hydrothermal biochar,based on the photosensitization characteristics of humus,the effects of sludge biochar on the degradation efficiency of RB5 by activated PDS under light conditions were further studied.The main research contents of this paper are as follows:（1）Sludge hydrothermal biochar modification can effectively activate PDS to degrade RB5.By adding alkali,chitosan and alkali-coupled chitosan to the sludge,the sludge hydrothermal carbon was modified by hydrothermal heat treatment.The efficiency of activated PDS degradation of RB5by different biochar materials was compared,and the effectiveness of chitosan modification was confirmed.RB5 can be completely removed within 120 min of reaction time.On this basis,the optimum preparation conditions of chitosan modified biochar（hydrothermal time,hydrothermal temperature and optimal doping amount of chitosan）were further studied.The optimum preparation conditions of chitosan modified biochar were determined as follows:hydrothermal temperature200℃,hydrothermal time 6 h,and doping amount of chitosan 1%.（2）Study on influencing factors and mechanism of RB5 removal by chitosan modified biochar activated persulfate.For the chitosan modified sludge biochar,the effects of reaction conditions（biochar dosage,PDS dosage,initial p H,initial RB5 concentration）and different anions on the removal of RB5 dye wastewater were further studied.The optimal conditions for removing RB5 in1CBC/PDS system are determined as follows:When the dosage of biochar was 5g·L^-1,the dosage of PDS was 2 m M,the initial p H was acidic,and the initial RB5 concentrations(40 mg·L^-1,80mg·L^-1,160 mg·L^-1and 240 mg·L^-1)were different,1CBC could have a good removal effect.It is found that H2PO4-and HCO3-have great influence on the system by exploring the influence of different anions.In the mechanism study,the important role of ¹O₂ in the system was confirmed by the addition of various free radical quenchers and the auxiliary detection of EPR,and·OH,SO₄^-·and O₂^-·did not play a role in the system.（3）Effect of light on biochar activated PS degradation of RB5 dye wastewater and its mechanism.The degradation of RB5 wastewater by light conditions（darkness,visible light and ultraviolet light）was further studied as to whether light would stimulate humus substances in biochar to further accelerate the decomposition of PS.It was found that,compared with the dark condition,the effect of light on the degradation of RB5 was little,and the degradation rate of RB5was increased from 0.020 min^-1 in the dark condition to 0.087 min^-1 in the ultraviolet condition.The active particles in UV/BC/PDS system were determined to be O₂^-·and ¹O₂ by free radical quenching experiment and EPR experiment,and the main active particles in the system were¹O₂.