Study On Kinetics Of Treating Methylene Blue Wastewater With Sludge Derived Activated Carbon And Its Composite Material

With the growth of my country’s population and the improvement of the level of urban industrialization,the amount of sewage treatment has continued to increase,and the output of sludge has also continued to grow.The environmentally sound treatment and resourceful use of sludge from municipal sewage plants have become a challenge in the field of environmental protection applications.The preparation of sludge-derived activated carbon（SDAC）from sludge can fully recover the organic carbon in the sludge,which can also be used for the treatment of dye wastewater to achieve sludge resource reuse.In recent years,the molten salt method has become another research hotspot in carbon material preparation.The adsorption process of activated carbon treated dye wastewater simply transfers contaminants from the liquid phase to the solid phase,and the contaminants are not broken down into simpler substances.Advanced oxidation technology can degrade organic pollutants in wastewater into harmless substances,which has become a research hotspot in the field of wastewater treatment.Among them,titanium dioxide（TiO₂）photocatalytic oxidation technology has developed rapidly in the field of dye wastewater treatment,but TiO₂ can be used in a narrow spectral range,is easy to agglomerate,and difficult to separate and reuse,which greatly increases the cost of treatment.Therefore,broadening its usable spectral range,enhancing its photocatalytic performance and reuse performance has become the key to the promotion and application of photocatalytic oxidation technology in dye wastewater treatment.In this thesis,SDAC with its good adsorption performance was prepared by the Zn Cl₂ melt salt method using sludge from an urban sewage plant as raw material.The adsorption performance of SDAC on methylene blue（MB）dye wastewater was studied by adsorption experiments,and the carbon quality of recovery and adsorption was calculated;the process of SDAC adsorption of MB molecules was simulated from a microscopic perspective by using molecular kinetics simulation method to explain the microscopic adsorption mechanism;finally,the TiO₂/SDAC composite visible catalytic material integrating adsorption and photocatalysis was prepared by hydrothermal synthesis,and the experiment of photocatalytic degradation of MB molecules was carried out under visible light.The visible photocatalytic performance and photocatalytic oxidation mechanism of composite materials were preliminarily explored.The specific research content and results are as follows:The characterization results show that SDAC with different pores can be prepared by changing the mass ratio of Zn Cl₂ and dry sludge;the surface of SDAC has hydroxyl,carboxyl,carbonyl,and other functional groups,which can promote the adsorption of organic pollutants.The heavy metal content in SDAC leachate is much lower than the concentration specified in the national standard,and it is safe and feasible to be used for wastewater treatment.Under the conditions of a roasting temperature of 500°C,roasting time of 2 h,and mass ratio of Zn Cl₂ to dry sludge of 1:1,the specific surface area of SDAC was 549.72 m²/g,and the adsorption capacity of MB was 0.0792 mg/mg_（SDAC）,the recovered and adsorbed carbon quality can reach203.18 mg_（carbon）/g_（sludge）,thereby reducing carbon emissions.The adsorption behavior of SDAC for MB accords well with Langmuir isothermal equation.The experimental equilibrium adsorption amount is close to that calculated by the pseudo-second-order rate equation.SDAC has good regenerative stability,and the removal rate of methylene blue remains above 90%after five times of alkali regeneration of saturated SDAC.The adsorption mechanism is explained from a microscopic perspective through molecular dynamics simulations.According to frontier orbital theory,the presence of surface functional groups reduces the energy gap value of SDAC and increases molecular activity.The SDAC model has intermolecular,electrostatic,and van der Waals interaction energies in the adsorption of MB.Due to the existence of functional groups such as hydroxyl,carbonyl,and carboxyl in SDAC,the relative affinity between SDAC and MB molecules is increased and the binding ability of the two molecules is enhanced.The structure is stable and not suitable for desorption.The TiO₂/SDAC composite visible photocatalytic material was prepared by hydrothermal synthesis,and the prepared composite material has certain visible photocatalytic activity.The optimal preparation conditions for TiO₂/SDAC composite were as follows:mass ratio of TiO₂to SDAC was 0.4,the hydrothermal temperature was 180°C,and hydrothermal time was 4h.Under this condition,the removal rate of MB by TiO₂/SDAC composite was 95.00%,and the visible light catalytic degradation efficiency of MB was the highest,reaching 39.00%.The Elovich model described the adsorption-photocatalytic degradation kinetics of TiO₂/SDAC to MB well and confirmed that due to the strong adsorption of SDAC,photocatalytic degradation of TiO₂ and the synergistic effect between the two,the degradation effect of the target pollutant was significantly improved.The above results show that the urban sewage plant sludge can be prepared the SDAC excellent adsorption performance,and can be with TiO₂ preparation of TiO₂/SDAC visible light catalytic composite materials,as a kind of efficient,safe,economic,and feasible commercial activated carbon alternatives for refractory pollutants such as dye,to realize the goal of sludge harmless and recycling,and expand the application range of TiO₂ under visible light.