Study On Preparation And Characterization Of Sewage Sludge Biochar-based Ceramsite And Its Performance Of Phosphorus Removal

The eutrophication of water bodies caused by phosphorus pollution has become a problem in environmental governance.The key to alleviating eutrophication is reducing the discharge of phosphorus in wastewater.The adsorption method by utilizing ceramsite has become a research focus in the field of phosphorus removal due to its craft simplicity,running stability,low cost,and good effect in phosphorus removal.In addition,for now,the yield of environmentally hazardous excess sewage sludge is amazing and the treatment cost is expensive,which also increase the burden on the ecological environment.This study is based on the environmental protection concept of"turning waste into treasure and treating waste with waste",using sewage sludge biochar（SSB）,which is the solid residue from the pyrolysis of sewage sludge,and other materials to prepare sewage sludge biochar-based ceramsite（SSBC）.The prepared SSBC not only follows the standard but also demonstrates high-safety level and excellent adsorption effect on phosphorus.While absorbing hazardous waste sludge on a large scale,SSBC locks harmful substances such as heavy metals inside the body,and has good adsorption activity for phosphorus pollutants in the water body.It provides a new idea for dealing with solid waste treatment（sewage sludge）and water pollutant removal（phosphorus）at the same time.To prepare the SSBC,several materials were selected.SSB,whose properties had been characterized at the first time,was regarded as the basic material,kaolin（KL）,dried sewage sludge（DSS）and silica fume（SF）were as auxiliary materials.By mixing materials above,the silicon-aluminum&flux components of materials had been mutually complemented;the characteristic of pore-forming by burning loss of materials（SSB,DSS）had been used,and then,SSBC was successfully prepared.Single factor&orthogonal experiment were designed to determine the final calcination process parameters.The properties of SSBC prepared at the final calcination process parameters were as follows:density-1.569 g/cm³,apparent density-0.972g/cm³,piled density-0.464 g/cm³,water absorption rate-43.68%,porosity-33.70%,solubility in caustic soda-0.06%,void fracition-50.19%,solubility in hydrochloric acid-1.52%,breaking and wear rate-2.67%,silt carrying capacity-0.09%,specific surface area-1.2037×10⁴ cm²/g.SSBC,prepared at the final calcination process parameters,is a kind of ceramsite with ultra-light density,whose properties including void fraction,solubility in hydrochloric acid,breaking and wear rate,silt carrying capacity,and specific surface area meet the standard of CJ/T 299-2008"Artificial Ceramsite Filter Material for Water Treatment"and can be used as an artificial ceramsite filter material.The Toxicity Characteristic Leaching Procedure was used to access the toxicity characteristics of SSBC.The result indicated that leaching concentration of heavy metals were lower than the limit in the standard of GB 5085.3-2007"Identification Standards for Hazardous Wastes-Identification for Extraction Toxicity".The European Community Bureau of Reference Sequential Extraction Schemes was used to study the occurrence state of heavy metals in SSBC.The result indicated that heavy metals were mostly existed in residues state.SSBC,whose stability of heavy metals was higher than that of SSB and DSS,had a good effect of immobilization of heavy metals.The analysis suggested that the vitrification played an important role in the immobilization of heavy metals.SSBC was used to examine its performance of phosphorus removal in the static experiment.Its removal rate of phosphorus increased with the increase of ceramsite dosage,and its phosphorus adsorption capacity increased with the increase of initial phosphorus concentration.When the initial phosphorus concentration was 0.5～10 mg/L,after 24 hours of adsorption,the remaining phosphorus concentration in the solution was lower than 0.5 mg/L,meeting the standard of GB 18918-2002"Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant";When the initial phosphorus concentration was 0.5～200 mg/L,the phosphorus adsorption capacity and the phosphorus removal rate of SSBC were higher than clay ceramsite,biological ceramsite（BC）,and SSB,which suggested that the ability of phosphorus adsorption of SSBC was generally better.When p H=2～12,the phosphorus removal rate of SSBC was higher than 97.59%,which suggested that its ability to resist the influence of p H changes was stronger than that of BC and SSB.Different concentrations of Cl^-,NO₃^-,SO₄^2-,HCO₃^-had little effect on the ability of phosphorus adsorption of SSBC,which suggested that its ability of anti-coexisting ion interference was stronger than that of BC and SSB.Increasing temperature significantly increased the phosphorus adsorption capacity of SSBC.When the initial phosphorus concentration was 500 mg/L and the initial temperature were 298.15 K,308.15 K,and 318.15 K,the phosphorus adsorption capacity had reached 3.251mg/g,4.404 mg/g,and 5.147 mg/g respectively.The analysis of adsorption isotherm of SSBC suggested that it had the characteristics of co-existence of heterogeneous adsorption forces on its surface and monolayer adsorption in its adsorption process.The analysis of adsorption kinetics of SSBC suggested that the diffusion step had an important effect on the adsorption process.The adsorption rate is mainly controlled by the intra-particle diffusion step,but the step is not the only rate-controlling step.The analysis of adsorption thermodynamics of SSBC suggested that the adsorption of phosphorus was a spontaneously endothermic reaction,the rise of temperature strengthening the spontaneity of the adsorption process;the adsorption of phosphorus was mainly chemical adsorption,randomness increasing along with the adsorption process.The desorption experiment suggested that the phosphorus adsorbed by SSBC was hard to be desorbed,and there was chemisorption during the adsorption process.The characterization indicated that new phosphorus-containing crystals were formed after SSBC adsorbed phosphorus.