Urban Sludge And Municipal Solid Waste(MSW) Fly Ash For Co-processing And Resource Utilization

Discharge of city life sewage and industrial wastewater is increasing, thecontradiction between the growth and sludge disposal capacity and sewagesludge disposal costs have become increasingly prominent. At the sametime, Municipal Solid Wastes Incineration (MSWI) fly ash as a hazardouswaste landfill and fill capacity and duration of use is restricted, MSWI flyash disposal is also very difficult. Therefore, to explore the two kinds of the lowcost of waste disposal and resource utilization has multiple significance. Thispaper discuss the city sewage sludge and MSWI fly ash codisposal, first to explore thehigh-temperature volatilization characteristics of morphological characteristicsof heavy metals in sewage sludge and MSWI fly ash respectively, followed by theresearch of sludge and MSWI fly ash codisposal to improve sludge dewateringperformance of sludge, then fly ash mixed the volatilization of heavymetals complexes, industrialization demonstration project. Finally, carry out sewagesludge and MSWI fly ash to produce cement clinker collaborative resourcedisposal system. The main conclusions are as follows:1. The typical wastewater treatment plant sludge in Cu, Shanghai City, mainly inthe form of oxidized form (OX); Pb in sludge residue almost70%; Cd was mainlyassociated with the Fe-Mn oxide combination, reduced50%~70%; Ni exists mainlyin the form of soluble and oxidation state, a total of80%the above; Heavy metalsCr form is mainly the residue state and the oxidation state; Sludgeincineration process in Cu oxidation state, soluble and reducible transformed mainlyto residual Cu; Rate of burning10min essentially volatilization heavymetal Zn. Soluble, reduced and oxidized forms of Zn transformation to the residualform; The heavy metals of Pb form is almost all the residual state, withincreasing incineration time, almost no Pb volatilization; Incinerationprocess Ni soluble, all of the reduced and oxidized forms (including the new generation of soluble and reducible) mainly into the residue state.2. MSWI fly ash samples with1000℃high temperature burning, Pb content from2000mg/kg down to470mg/kg, volatile reached78wt%; Cd volatilization rate of80wt%; Zn volatilization rate of26.5wt%; Cr volatilization rate of7.8wt%. Theproportion of non stable form of heavy metals in MSWI fly ash is very high, Zn, Pb,Cd and Cr of the carbonate fractionwere65%,63%,86%and25%; Wetpretreatment (washing) after the heavy metals of Pb, Zn and Cd MSWI fly ash in thecarbonate bound by the original63%,65%and86%reduced to close to0%; Theleaching concentration of Pb in MSWI fly ash decreased from15.45mg/Lto0.229mg/L, Cd from2.31mg/L to0.018mg/L, much lower than the EPA standardand national standard. Wet MSWI fly ash stabilization increased heavy metalZn, Pb, Cr, Cd residue proportion have different levels of increasing.3. The dehydration properties of sewage sludge after conditioning by MSWI flyash has been significantly improved, and sludge system changed. With the increase ininvestment to increase the amount of MSWI fly ash, system pH from neutralenvironment raw sludge gradually transformed into a strong alkalineenvironment, pH reached12.5; system salinity rise in a straight line; Zetapotential change; extraction of EPS increasing volumes of sludge under high pH, Zetapotential of sludge increased upper suspension. Calcium addition has made improvingthe moisturecontentand the filtrate turbidity were SRF,sludge dewatering; salinity increase of the sludge SRF and the degree ofdehydration were improved; MSWI fly ash alumina, ferric oxide and siliconoxide onsludge chemical conditioning effect is not obvious.4. In the co-conditioning process of sludge and MSWI fly ash, threefactors (calcium ion, sodium ionand pH) composite conditioning, calcium ion and pHvalue has the most significant effect. With the increasing of pH and the increaseof calcium ion concentration, SRF and moisture content arereduced, conditioning effect is significant. Consistent with the characteristics of theMSWI fly ash and sludge conditioning system in the process of alkali, high calcium waste incineration. Adding sodiumion is conducive to sludge dehydrationbehavior in a certain extent, when the concentration of calcium/sodium ion concentration of>2~2.5times, no significant improvement.5. Co-conditioning of sewage sludge and MSWI fly ash, the volatilizationcharacteristics of heavy metals changed obviously. Pb and Zn at800℃volatilereduction, other heavy metals’ volatile with the increase of MSWI flyash dosage have stable inhibition. The conditioning of sludge and MSWI fly ash,heavy metal morphology change. Proportion of stable form of Pb, Ni, Crimproved. Cu with the addition of MSWI fly ash increased residual state increasedgradually, reduce the oxidation state; The Pb element is gradually increased with theadding amount of MSWI fly ash, Fe-Mn oxidation stategraduallyreduced, increasing the residual fraction, when the sludge and MSWI fly ashmixture of MSWI fly ash dosage is6%, residual content of up to79.8%; when thesludge fly ash mixture MSWI fly ash dosage is6%, residual Cr improved from73.3%to77.41%in the original sludge.6. In the demonstration project of cooperative resource disposal of sludge andMSWI fly ash to cement clinker production, MSWI fly ash conditioning after vacuumbelt filter dewateringthe sludge water content can be reduced from98%to42.8%, andthe dehydrated products after6days after natural drying moisture content is reducedto16.1%.7. Codisposal of resource utilization of Shanghai Shidong kou sewage sludge andMSWI fly ash, producing a four day trial in cement plant. Cement clinker prepared3days strength is7.2MPa, the28day strength is57MPa, the compressive strength ofcement clinker is better than the requirements of quality control in producing cementfactory. At the same time,the concentration of chloride ion in cement clinker is0.015%, far lower than the concentration of chloride ions in cement standards mustbe lower than0.06%of the requirements.