Development,production And Application Of Fly Ash-based Phosphorus-removing Particulate Filler

For a long time,due to the shortage of treatment funds and the weak awareness of environmental protection of rural water bodies,the random discharge of rural domestic sewage is more common,which seriously damages human health and the ecological environment.The treatment of rural domestic sewage is urgent.The effective treatment of rural domestic sewage depends on the development and application of new technologies and methods.The compound humus packing biological filter technology previously developed by the research group can better reduce the Chemical Oxygen Demand（COD）and Total Nitrogen（TN）in rural domestic sewage.However,the removal effect of Total Phosphorus（TP）is not good.Fly ash has great potential value in the removal of total phosphorus,but there are few studies on the use of fly ash as an adsorbent for phosphorus removal.In this thesis,fly ash is used as a matrix to prepare a new type of fly ash-based phosphorus-removing particulate filler for rural sewage treatment technology.The main research contents and conclusions of this paper are as follows:In this paper,the degree of excitation and gelation of the fly ash of each sample under different dosages of activator and curing conditions at different temperatures are studied.The results show that:The mixing of quicklime alone can not stimulate the activity of fly ash well,and the mechanical strength of the particles after curing is very low;Single-doped strong alkali activator can better stimulate the fly ash activity,but due to lack of Ca²⁺,gelation reaction cannot occur;Mixing quicklime and strong alkali activator can not only stimulate the fly ash activity but also make the particles form better mechanical strength,but the particles are easy to fall off the slag and the particle alkalinity is too high,resulting in pan-alkali phenomenon;Under low temperature conditions,cement alone cannot stimulate the activity of fly ash,however,when the temperature is higher than 40℃,the fly ash activity excitation is better and produces gelled products;Mixed lime and cement also can’t stimulate the fly ash activity under low temperature conditions,but it can better stimulate the fly ash activity and form gelation products under the temperature above 40℃,so that the particles have a certain mechanical strength.In order to increase the phosphorus adsorption capacity of the phosphorus-removing particulate filler,the final selection of the raw material ratio is fly ash:cement:lime is 7:1:2,curing temperature is 50℃,curing time is 5 days.The phosphorous particulate filler was prepared by the above method,and the physical characteristics of the phosphorous particulate filler were tested and characterized.The results showed that:The apparent density of the phosphorus-removing particle filler is 2.03g/cm³,the bulk density is 0.73g/cm³,the porosity is64.04%,the specific surface area is 5.3320m²/g,and the pore volume is 0.02cm³/g.The pore diameter in the particles is mainly 7.8nm and 12.6nm.SEM characterization results show that the surface of the particles is relatively dense,the surface of the fly ash particles inside the particles is wrapped by C-S-H,and the C-S-H are bonded to each other to form mechanical strength.XRD analysis showed that the particle composition mainly includes C-S-H,Si O₂,Ca CO₃,Al2O₃,Ca（OH）₂,mullite and so on.The results of the adsorption experiment showed that the adsorption capacity of the particles under the conditions of 25℃,35℃and 45℃were 6.01mg/g,6.97mg/g and7.78mg/g,respectively.Because the surface of the phosphorus removal particles is relatively dense and the internal components of the particles cannot play a role,it is necessary to optimize the ratio and maintenance scheme to prepare porous phosphorus removal particle fillers.The effects of 1%,2%and 3%straw blended and calcined at 300℃on the compressive strength and pore size distribution of phosphorus-removing filler particles were studied.The results showed that the particles mixed with 2%and 3%straw were cured at 50℃for a period of time,and the strength of the particles was far less than that without straw.The particles mixed with 1%straw were cured for 5 days at 50°C and then calcined.The particle strength decreased compared with the particles without straw,but the specific surface area increased to 9.4501m2/g and the pore volume increased to 0.035cm3/g,the pore diameter is mainly 4nm,7nm,10nm.The reason for the formation of porous structure is that the partial dehydration of C-S-H to form steam and carbonization of straw to form gas under the calcination condition at 300℃makes the pores increase,and at the same time the volume of straw carbonization decreases,the original straw filling part becomes hollow,which further increases the pores.The reason for the decrease in particle strength due to the addition of straw is that the saccharides released by the straw in the alkaline environment inhibit the hydration of the cement.At the same time,the addition of straw also reduces the volume fraction of other components,which in turn leads to a reduction in the strength of the particles.Therefore,the optimal solution was finally determined by mixing straw with 1%and curing at 50℃for 5 days and calcining at 300℃for 10 minutes.The results of adsorption experiments show that the adsorption capacity of the particles at 25℃,35℃and 45℃is 21.93mg/g,22.22mg/g and 23.20mg/g,respectively,and the adsorption capacity is greatly improved.Finally,the granulation effect of the disc granulator,the pair of roller extrusion granulator and the tooth stirring granulator is compared,and a comprehensive comparison is made according to the cost and effect,and finally the YGZL-1200 disc granulator is determined as the production process.The phosphorus concentration in the effluent is less than 0.5mg/L,which meets the Grade A standard of"Emission Standard for Pollutants in Urban Sewage Treatment Plants"（GB18918-2002）.