The Research Of The Medium Experiment Of Sludge Dewatering By Hydrothermal Method

The hydrothermal method of sludge dewatering medium-sized experiment mainly solves the problem of the moisture content of about 80% municipal sludge in the waste pit of landfill site on hold for a long time in Shanghai Laogang Waste Disposal CO. LTD. Firstly, the moisture content of 80% sludge can’t be disposed in landfill site directly otherwise it will produce plenty of rubbish leachate which is a huge challenge for anti-seepage disposal system. Secondly, the moisture content of sludge will not descend obviously after landfill in the result that reconstruction plan of landfill site can’t be implemented in decades.In the medium-sized experiment, the moisture content of 80.6% original sludge of Shanghai Zhuyuan sewage treatment plant from landfill pit is pretreated hydrothermally first. Then the pretreated sludge is dewatered by the plate and frame type double diaphragm filter press. Last it produces the sludge cake and the sludge dewatering filtrate.The hydrothermal-filterable experiment is completed by the method of control variable. The best hydrothermal conditions of the original sludge and working parameters of filter press are that hydrothermal temperature is 180℃ sustaining 45min;the temperature of the feedstock of the pretreated sludge is 80℃;the maximum pressure is 0.80 MPa sustaining 45 min and the time of vacuum drying is 30 min. The moisture content and the thickness of the sludge cake are 32.6% and 2.50 cm respectively in these best conditions and parameters.The moisture completely accords with the requirement of sludge incineration process. The resualt of the medium-sized experiment of the mixed original sludge of Shanghai Laogang landfill shows that the moisture content and the thickness of the sludge cake are 40.5% and 2.21 cm respectively in these best conditions and parameters. The moisture completely accords with the requirement of sludge incineration process too.The resualt of the biochemical methane potential(BMP) experiment of the sludge dewatering filtrate shows that the maximum removal of SCOD and TCOD are 87.23% and 86.54% respectively when hydrothermal temperature is 180℃. The shortest retention time of the sludge dewatering filtrate is 18 d when hydrothermal temperature is 180℃. The maximum biodegradable rate of the sludge dewatering filtrate is 85.76% when hydrothermal temperature is 180℃. The anaerobic digestion and treatment efficiency of the sludge dewatering filtrate are the easiest and best respectively when hydrothermal temperature is 180℃.The hydrothermal-incinerated system to do analog computation by Aspen Plus shows that the import of the sludge cake quality, the import of steam, the generation of steam, the output of steam and the effective energy utilization are 1.32kg/s, 1.63kg/s, 2.71kg/s, 1.08kg/s and 19.15% respectively in the conditions of the sludge daily capacity of 100 tons, the system stability of continuous running and the moisture content of 32.6% sludge cake in the best hydrothermal-filterable parameters. There is no need of additional fuel(coal) in the incineration process. The moisture content of original sludge is 87% at most in the best hydrothermal-filterable conditions otherwise it needs additional fuel in the incineration process to keep hydrothermalincinerated system running normally. Above of all, no matter how much is the moisture content of original sludge, the system makes the economic benefits of energy recovery and cyclic utilization.