Preparation Of Sewage Sludge Hydrothermal Charcoal And Its Removal Effect On Heavy Metals In Water

With the rapid development of social economy and the acceleration of urbanization,the problem of urban sewage treatment is becoming more and more serious.With the production of a large amount of activated sludge in the process of sewage treatment,sludge reduction has attracted wide attention in the society.Compared with traditional sludge technologies such as incineration and landfill,the current mainstream sludge reduction technologies include advanced oxidation technology,thermal decomposition,hydrothermal carbonization,and ultrasonic technology.Hydrothermal carbonization,as a new technology for sludge reduction,can not only realize the reduction and harmlessness of sludge,but also recycled the generated carbon-based products.It is of great significance to the protection of the ecological environment and has become a hot topic at home and abroad.In this paper,the sewage sludge hydrothermal charcoal?Fe-SSHC-A?and magnetic carbon?Fe-SSHC-B?were prepared by hydrothermal carbonization using original sewage sludge?secondary sedimentation tank sludge without additional iron during the process?and iron sewage sludge?the ferrous sulfate sludge?as raw materials.And Zero-valent iron SSHC?ZVI-SSHC?was further prepared by reduction reaction using Fe-SSHC-B as substrate.Using Cd²⁺and Pb²⁺as model pollutants,the effects of three kinds of hydrothermal carbon products on the removal of heavy metals in water were studied.The experimental content can be mainly divided into the following three parts:?1?Fe-SSHC-A was prepared by hydrothermal carbonization of sewage sludge?original sewage sludge?from the secondary sedimentation tank without additional iron in biochemical stage at 220?for 4 h.The physical properties of the samples were characterized by elemental analysis?EA?,field emission scanning electron microscopy?FE-SEM-EDS?,and Fourier transform infrared spectroscopy?FT-IR?.The adsorption properties of Fe-SSHC-A on Cd²⁺and Pb²⁺were investigated.The results show that the prepared sample has a non-uniform pore structure,and there is a small amount of iron on the surface.After 15 h of adsorption,the removal rates of Cd²⁺and Pb²⁺by Fe-SSHC-B were 51.7%and 41.9%,respectively.?2?Using the sewage sludge?iron sewage sludge?from the secondary sedimentation tank containing ferrous sulfate in the biochemical stage as the raw material,the magnetic carbon Fe-SSHC-B was prepared by hydrothermal carbonization at 220°C for 4 h.The physical properties of the samples were characterized by field emission scanning electron microscopy?FE-SEM-EDS?,Fourier transform infrared spectroscopy?FT-IR?,X-ray photoelectron spectroscopy?XPS?,and hysteresis loop?VSM?.Different single factor experimental conditions?Fe-SSHC-B dosage,solution pH,hydrothermal temperature,iron dosage?were investigated.And the adsorption process was explored by adsorption kinetics and adsorption isotherms.The results show that iron is successfully attached to Fe-SSHC-B surface,and coexists in trivalent Fe³⁺and bivalent Fe²⁺.Meanwhile,the samples showed strong magnetism.Using Cd²⁺and Pb²⁺as model pollutants,the optimal dosage of Fe-SSHC-B was 0.2g and 0.3g,and the pH of the solution was 5 and 6respectively.The adsorption performance of Fe-SSHC-B to target pollutants was enhanced by increasing hydrothermal temperature and iron dosage.The adsorption process of the sample is more consistent with the quasi-second-order kinetics and Langmuir model,which is mainly controlled by chemisorption,and there is monolayer physical adsorption at the same time.?3?Using synthetic Fe-SSHC-B as substrate material,NaBH₄ as the reducing agent and cetyltrimethylammonium bromide?CTMAB?as the surfactant,ZVI-SSHC was prepared by reduction reaction.Physical properties of the samples were characterized by field emission scanning electron microscopy?FE-SEM-EDS?,Fourier transform infrared spectroscopy?FT-IR?,X-ray photoelectron spectroscopy?XPS?,and hysteresis loop?VSM?.Zero-valent iron was detected in the samples,and the samples remained strong magnetic.Different single factor experimental conditions?ZVI-SSHC dosage,solution pH?were investigated,and the adsorption process was explored by adsorption kinetics and adsorption isotherms.Using Cd²⁺and Pb²⁺as model pollutants,the optimal dosage of ZVI-SSHC was 0.2g and 0.25g,respectively,and the optimal pH of the solution was 6and 5 respectively.ZVI-SSHC has stronger adsorption capacity than Fe-SSHC-B under the same adsorbent dosage and solution pH.The adsorption process of the prepared samples is more consistent with the pseudo-second order kinetic model and the Langmuir adsorption isotherm model.It is also mainly controlled by chemisorption.At the same time,there exists monolayer physical adsorption.