Laboratory And Pilot Studies Of Sludge Dewatering In The Ninth Beijing Drinking Water Treatment Plant

The water treatment residuals (WTR) are characterized by high turbidity, highcolor and high organic content. In most waterworks, WTRs are reduced with chemicalconditioning with organic polymer with high molecular weight followed by lowpressure dewatering (belt press filter or centrifuge). The moisture content of sludge cakeis always higher than80%. Sludge cake with high moisture content results in difficultiesin transportation, treatment and recycling and high cost for final disposal. In addition,due to high organic content, turbidity and color, the filtrate from dewatering can not bereused, leading to wasting of water resource. Direct discharge of WTR would produceserious pollution for receiving water body. In order to solve problems mentioned aboveand realize advanced sludge dewatering and filtrate recycle, the integrated process forsludge dewatering was tested in laboratory and pilot scale. This study emphasized theeffects of chemical condition on sludge properties (dewaterability and filtrability) andfiltrate quality.According to laboratory test, the SRF was effectively reduced by adding inorganiccoagulants, FeCl3and PAC. However, chemical conditioning with inorganic coagulantalone had limited effect on sludge dewatering property, raw sludge could be onlyconverted into that of medium sludge dewaterability, and combined use of lime andinorganic coagulation could lead to further decrease in SRF and enhancement of sludgedewaterability. FeCl3and PAC mainly played roles through charge neutralization. SRFis linearly correlated with lime dosage, skeleton building of lime can reduced thecompressibility and improve permeability of cake, providing passage for water release.Furthermore, the effects of chemical conditioning on supernatant quality were alsoinvestigated. When dosage of both FeCl3and PAC was0.35g/L, the turbidity and DOC was reduced to below3NTU and2.5mg/L, which were lower than influent quality ofwaterwork.3DEEM analysis indicated that fluorescence intensities of aromatic proteinII, humic acid, fulvic acid and SMP were reduced, while removal efficiency of themvaried considerably. The50%of protein II, humic acid, fulvic acid was removed afterchemical conditioning with inorganic coagulants, while only20%of SMP was reducedafter treatment.Pilot test indicated that cake blocking was avoided with all conditioning methods,but the dewatering efficiency was still limited and cake moisture was around70%underFeCl3and PAC used alone. Combined use of inorganic coagulation and lime showedsynergistic effect, could further improved solid content of dewatered cake.