Study On Development And Application Of A New Sludge-based Filter Material

A new type of filter material is made from coagulation sludge in drinking water treatment. Based on its strength, composition of raw materials and the preparation process were optimized. The ratio of the raw materials composition is as following: dry coagulation sludge: kaolin: humic acid = 10:7:2. The ratio of water in the raw mixed material was maintained at approximately 65±5%, with a average particle size of 2~5 mm. The optimized preparation process was suggested with calcination temperature under 700? for 2h in the muffle. Then decrease the reaction temperature to 200 ? gradually. Then the prepared filter material was stored in a drying oven before conducting the following experiment. It was determined that the average particle size, BET specific surface area, and density of the prepared filter material was 1.4 mm, 91.74 m2/g, and in the range of 1800~2300 kg/m3, respectively. Meanwhile, the concentrations of heavy metals leached from the novel filter were also proved to be in an acceptable level, without secondary pollution risk.The adsorption performances of the novel filter material on the removal of ammonia nitrogen and total phosphorus were investigated using static adsorption experience, under different p H, temperature, and initial dosage conditions. It was determined that both total phosphorus and ammonia nitrogen showed notable adsorption capacity on the surface of the filter material, and above adsorption processes were highly depended on the solution p H. The highest removal rate of total phosphorus was achieved at p H 7.0; while the removal rate of ammonia nitrogen was higher under basic conditions. Further study showed that the adsorption of phosphos on the filter material would be finished in 200 min, much faster than that of ammonia nitrogen, usually more than 6 hours. Both the adsorption processes of ammonia nitrogen and total phosphorus followed the pseudo-second order kinetics(R2>0.999). Meanwhile, both Freundlich and Langmuir adsorption isotherm could be used to decribed above adsorption processes(R2>0.99). Thermodynamical calculation results proved that the adsorption of PO43-(?G?<0, ?H?>0) is a spontaneous, endothermic chemical process, and the adsorption of NH4+-N is mainly a physical sorption process.The pollutants removal performances of a filter filled with the novel filter material developed in our study were investigated in one filtration period with influent at different solution p Hs. It was determined that the filter bed showed a good performance on the removal of both turbidiy causing materials and nutrient materials, such as ammonia nitrogen and total phosphorus for the influent at p H 7.0-8.0. Meanwhile, the filter material also showed a p H buffering function; the p H value of the effluent was approximately 8.4. The concentration of total phosphorus in the effluent could be controlled below 0.3 mg/L, meeting the requirement of the treated wastewater discharging standard. This might not only be contributed to the physical adsorption process, but also is related to the chemical composition of the novel filter material. The existence of large amounts of available metal elements could enhance the removal of total phosphorus as the occurring of chemical exchanging and precipitation processes(x PO43- +3Mx+ = M3(PO4)X).From the experimental results obtained in this study, it was determined that the noval filter material could be easily made, has good physical and chemical characteristics, and shows a good performance on the removal pollutants during filtration. Meanwhile, the work done in this study also provided an alternative choice for the reuse of the coagulation sludge produce in drinking water purification process and the simuteniously removal of suspended solids with nutrient elements in wastewater treatment process. Accordingly, the conclusions obtained in this study also show great potential in application.