Study On The Preparation And The Phosphate Removal Performance Of River Sludge Ceramsite

Phosphate removal is the most important step in restoration of eutrophicated water body.Using river sludge and fly ash as raw materials,the optimum ratio of raw materials and sintering conditions were determined.The physicochemical properties of the ceramics were studied by a variety of characterization methods?XRD,SEM FT-IR?.The main mechanism of phosphate adsorption was further analyzed.Besides,the effects of dosage,initial phosphte concentration,pH,co-existing ions and humic acid on phosphate adsorption were studied by batch experiments.Then,the effects of flow rates on dynamic phosphate removal and the adsorption performance in actual wastewater were further investigated.In the study of preparation conditions,the best ratio of river sludge and fly ash was18g/2g.1g soluble starch was added as pore-forming agent.Before sintering,the raw materials were dried at 105?for 2.5h.The preheating temperature and time was 400?and 20min,respectively.The results showed that the structure stability was in proportion to the sintering temperature and time,while the removal performance exhibited the opposite performance.Finally,the sintering temperature and time was set as 950?and10min.The ceramsite was mesoporous structure with an average pore diameter of 12.5nm.It was concluded that the higher the dosage of ceramsite was,the lower the adsorption capacity,which reached the highest of 9.57mg/g at the initial phosphate concentration of 40mg/g.The inhibitory effects of coexisting ions followed the order of HCO₃^->F^->SO₄^2-,and humic acid also decreased the adsorption efficiency.In the pH range of 8-12,ceramsite could effectively remove phosphate and followed pesudo-second-order kinetic model.Besides,it also had a good fitting with Langmuir model and Tempkin model.Thermodynamic studies indicated that the adsorption of phosphate by ceramsite was endothermic and spontaneous process.In the fixed-bed study,the penetration volume decreased when the flow rate increased.The dynamic penetration curve model fitted well with Thomas model,Yan model and the Yoon-Nelson model.With a dosage of 5g/L,the concentration of total phosphate in influent of Townsend Lake Wastewater Treatment Plant decreased to 0.293 mg/L,which could comply with the Class A of Wastewater Discharge Standard for Municipal Wastewater treatment plants?GB18918-2002?.Ceramsite prepared by river sludge can be prepared with low cost and seprated easily.The idea of"treating waste with waste"was fully reflected in the selection of raw materials,and the adsorbed ceramsite could be recycled and used as agricultural fertilizer.It had great potential in practical application.