| Currently, sludge treatment and disposal has become one of the urgent problemspresented in the field of wastewater treatment, especially in small towns of China. Dueto the unstable quantity and quality of inflows in wastewater treatment plants (WWPTs)in small towns, which result in a low sludge production and the unsteady properties, it isrequired that some simple, cost-effective and innovative sludge treatment technologiesand facilities should be developed. Aiming at the problems in sludge treatment in smalltowns, our research team has developed an integrated sludge thickening and digestionreactor. Three generations of the reactor have been modified and improved successfullythrough investgiations of small-scale experiments. Moreover, on the basis of thenumeric simulation and optimization of flow condition, the pilot-scale reactor has beendeveloped. Study on the pilot-scale experiment has been carried out in a WWPT.Optimized operation conditions have been obtained and the disadvantages of the reactorhave been analyzed simultaneously. After improvement of the pilot-scale reactor, thefull-scale reactor has been developed and studied in Dadukou WWPT of Chongqing.The efficiency of sludge thickening and digestion, stabilization of heavy metals andmacrobiotic population diversities in the full-scale reactor have been investigated andstudied. The results are shown as follows,①The flow test is carried out to study the characteristics of flow condition in thepilot-scale reactor using NaCl as tracer. The results illustrate that the dimensionlessvarianceσ (σ_θ~2) in the lower section and base of inner reactor are0.63,0.67and0.34,0.44in the upper section and mid-upper section under no gas recirculation. The innerreactor from upper section to base under8L/min,12L/min and16L/min are0.60-0.63,0.64-0.68, and0.65-0.66, respectively. And the flow condition has a tendency to amixing flow condition completely. For the purpose of completely mixing in innerreactor and the operation cost,12.0L/min of gas flow has been adopted in the operationtest of the pilot-scale reactor.②The efficiency of sludge treatment of the pilot-scale under mesosphericcondition（35±2℃）is studied under four different excess sludge inflows of12%,18%,24%, and30%. The results indicate that the biogas production per unit (325L/kgVS)under sludge inflow of24%is the highest. The methane content of biogas is62.7%.VS/TS has been dropped down from25%to20%and the water content in the outlet sludge has been decreased from99%to93%. The efficiency of sludge thickening anddigestion is better than that of thickener and digester in the WWPT.③The efficiency of sludge treatment of the full-scale under ambient temperature（25-35℃）is studied under the four different excess sludge inflows of10%,15%,20%,and24%. The results demonstrate that the biogas production per unit (110.5L/kgVS)under sludge inflow of15%is the highest. The methane content of biogas is61.4%.VS/TS has been decreased from36%to29%and the water content in the outlet sludgehas been decreased from98.5%to91%. The specific methane activity of sludge under15%of sludge inflow is20.5and20.5mgCODCH/gVSS·d tested by automated methanepotential system.④Chemical fraction of heavy metals in the full-scale reactor is studied bysequential extraction using the BCR method. Compared to the sewage sludge, thepercentage of Cu, Mn, Pb, and Cd in acid soluble/exchangeable fraction is reduced by73.6%,32.0%,40.7%,19.0%, respectively, whereas the percentage of Ni in acidsoluble/exchangeable fraction is increased by27.6%. The percentage of Fe in reduciblefraction is reduced by30.5%. The percentage of Zn and Cd in oxidizable fraction isincreased by37.0%and55.0%, respectively. The index of mobile ability about Mn, Cd,and Zn are reduced from0.68,0.62,0.92to0.53,0.50, and0.77. The results show thatafter the treatment of the full-scale reactor, the mobile and easily available heavy metalfractions (acid soluble/exchangeable and reducible fractions) are transformed mainlyinto the relatively stable heavy metal fractions (oxidizable and residual fractions).⑤The microbial population diversity in the full-scale reactor has beeninvestigated by the PCR-DGGE technology. The results illustrate that microbialdiversity distribution is shown in the reactor. Amount of microbial in the area of outletsludge is more than that in the inner reactor, so the outlet sludge can be recircled intothe inner reactor to increase the amount of microbial. The microbial population diversityis similar under different inlet sludge ratios. In fact, the only difference is the quantity. Itis concluded that the microbial population diversity do not change with inlet sludgeratio. The microbial population diversity is more than that in the outer reactor, and it canbe concluded that there is functional difference between the inner reactor and outerreactor. The same microbial populations exist both in the inner reactor and anaerobicdigester, but four special microbial populations are found in the inner reactor.The results from this study can be the basis of practical application for theintegrated sludge thickening and digestion reactor, including design, start-up and operating of reactor, which will be of great significance to engineering application ofintegrated sludge digestion and thickening processing technology in the future. |
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