Study On Integrated Sludge Thickening And Digestion Reactor

Sludge produced by municipal wastewater treatment plant contains organic matter, heavy metals, pathogens, etc. If the sludge was not appropriatly treated, it would cause secondary pollution to the environment, and the sewage treatment plant can not play its functions. In the Three Gorges reservoir area, many sewage treatment plants have been in running, but sludge disposal, reduction and stabilization are lacking, Therefor, research of the new sludge treatment technology, especially the stability of sludge and sludge volume reduction technology is extremely urgent.Combining modern high-rate anaerobic reactor theory with gravity concentration tank for the first time, the research group has successfully designed the Two-phase Integrated Sludge Thickening and Digestion reactor (TISTD), to achieve integration of thickening and digest.The TISTD reactor has a capacity of 110L,with design sludge feeding rate of 30%. To startup TISTD, using 10% sludge feeding rate, under the condition of mid-temperature, 28 days later, the TISTD reactor was running persistently. Hydrodynamic experimental results showed that the flow pattern of outer chamber was close to plug flow, while the flow pattern of inner chamber was close to completely mixed flow.The operation performance were studied when the sludge feeding rate was 20%, 30%, 40%, 50% respectively. Results showed that the optimal sludge feeding rate was 30%, and the hydrolic rentention time was 3.33d. When the rate of water content of influent sludge, the ratio of VS/TS was in the range of 99.4⁹9.6%, 0.62⁰.77, the rate of water content and the ratio of VS/TS of effluent sludge was in the range 89.5%⁹3.5%, 0.21⁰.28 respectively. The suspended solids in effluent water were in the range of 0.15⁰.6g/L, and the thickening and digestation effects of the TISTD were separately better than conventional gravitational thickening tank and anaerobic digestor. Scanning electron microscopy sludge check showed that these bacteria in the reactor included the basic shape of bacteria in anaerobic environment, reflecting a stable microbial ecosystem and rich in bacteria.From begingning in the reactor to the stable operation, the sludge activity has a significant change in coenzyme content from 0.076mol/gVSS×10^-3 to 0.180 mol / gVSS×10^-3. During stable operation, the coenzyme content of sludge is significantly different in the different sampling. PH, alkalinity, VFA in the Integrative Reactor were basically within the range of anaerobic digestion,which indicated that Integrative Reactor had the ability against shock loads and could meet the requirement of anaerobic digestion. With the sludge feeding rate from 20% to 50%, ORP is from -355 mV to-340mV during the stable operation. Under dosing ratio of 20%, after studying on balance of N and P found that after the response 31.0%⁵0.6% of total nitrogen of inlet sludge back to the medium, 54.1%⁶4.3% of total nitrogen in the discharge of sludge in anaerobic; 28.7%⁴7.6% of total phosphorus back to the medium, 49.3%⁶5.6% of total phosphorus in the discharge of sludge in anaerobic. Under dosing ratio of 30%, after the response 18.6%³2.6% of total nitrogen of inlet sludge back to the medium, 64.6%⁸1.0% of total nitrogen in the discharge of sludge in anaerobic; 23.5%²8.3% of total phosphorus back to the medium, 70.7%⁷5.1% of total phosphorus in the discharge of sludge in anaerobic. TISTD has a very good separation efficiency of TN, TP.After anaerobic digestion, the three types of specific resistance of sludge are also reduced in medium temperature conditions. The specific resistance of primary sludge is small. After digestion,the specific resistance of primary sludge reduced slightly from 8.0×10¹²m/kg 9.2×10¹²m/kg down to 7.6×10¹²m/kg 8.9×10¹²m/kg, and the specific resistance of waste sludge decreased obviously from 145×10¹²m/kg 225×10¹²m/kg to 62×10¹²m/kg 88×10¹²m/kg, whereas the specific resistance of mixed sludge dropped sharply from 71×10¹²m/kg 120×10¹²m/kg to 40×10¹²m/kg 75×10¹²m/kg. Test of different sludge digestion at different temperatures showed that the temperature increasing have impact of sludge differently. Test indicated the primary sludge was less affected at different temperatures. The specific resistance of waste sludge and mixed sludge changed greatly, the specific resistance increased significantly. At the same time, dynamic models of sludge digestion were deduced according to the TISTD experimental data, and parameters, i.e. K s andνmax were given. The results showed that the VSS degradation of three kinds of sludge was consistent with a kinetic equation, but waste sludge and mixed sludge digestion can be described better than primary sludge.