Study On Treament Of Activated Sludge Of Municipal Sewage Treatment Plants By Supercritical Water Oxidation

Supercritical water oxidation is a highly effective oxidation technology in the treatment of organic waste and water,it get great attention both at home and abroad,when the temperature and pressure of the water is over a critical point(374℃,22.1MPa),the water is become to be supercritical water.The Supercritical water has a special character,it can dissolve with air, oxygen and organic matter in any proporti on,so it can eliminate the mass-transfer resistance.The oxygen can generate some violent oxidative radical with supercritical water,such as·HO₂,HO·,O·and so on.The organic matter can react with HO·by radical reaction in supercritical water,and it will turn into H₂O,CO₂,N₂ and Salt material.Most of the organic matter can be removed in a few minutes,the removal rate can reach 99%.The activated sludge of municipal sewage treatment plant of songjiang is the object that processed by scwo in this paper,the sludge Contain organic matter,humus,nitrogen,phosphorus, potassium,and other nutrients,and also contain abundant heavy metals,pathogenic bacteria and parasites.The domestic sewage and industrial waste water were treated in this plant,it use the technology of A/O,the sludge treatment use the technology of mesophilic anaerobic digestion, and then centrifugal dewatering.The treated water emit into the river of huangpu directly.The water content ratio of activated sludge is 99%,the Calorific value of drying sludge is 3479.36 Kcal/kg,it is equivalent to half of bituminite,the content of heavy mental is high in drying sludge, among which the content of elements of Cr,Ni,Zn are the highest.adequate experimental studies were made on the basis of understanding the nature,the technology characteristics and the research results of supercritical water oxidation at home and abroad.The oxidation behavior of activated sludge by scwo was be explored by changing the reaction factors,the removal ratio of composition of sludge was determinated in different reactive conditions,the relation of the concentration of harmful gases in the emitted gas with the impact factors of scwo was studied,the dynamics and chemical reaction heat of drying sludge that treated by scwo were be researched too.The activated sludge could be treated effectively by Supercritieal water oxidation,both the COD_Cr and SS could be greatly improved of the fluids.In the condition as:pressure was 26MPa, oxidant dose was 1.6,temperature was 520℃,resident time was 6 min,the COD_Cr removal efficiency could be reach 93.86%and the SS removal efficiency could be reach 96.82%,the chroma of fluids was little.The TN removal efficiency was less than the COD_Cr of sludge by scwo, as the material of organic nitrogen was difficult to be removed.The heavy metal ion concentration of fluids was low,only the Cr was exceed the integrated wastewater discharge standard in six monitored heavy metal ions,it was because that the Cr ion concentration was higher than the others in the sludge.The heavy metals pollution of sludge was a difficult problem in the Sludge Treatment,the heavy metal ions can be removed efficiently in sludge by scwo.The Pollutant gas of CO,SO₂,NO_x was be found in the emissions of activated sludge by scwo,and the CO was the main gas,the content of SO₂,NO_x was little.The gas of CO is toxic, its solubility is little in water,but it is soluble in ammonia.The gases of SO₂,NO_x are soluble in water,most of the gas was dissolved in water,some was in the exhaust.The produce of CO can be reduced through Improving the oxidative degradation efficiency of activated sludge by scwo.The activation energy is 64.95KJ/mol,the frequency factor(k₀) is 14.06×10³.A certain amount of heat was produced in the reaction of activated sludge by scwo.By calculating,the reaction heat was 68.00～86.47KJ/L which was released in the reaction of activated sludge by scwo when the oxidative rate was 90%in this paper,it can not maintain the required heat of reaction.It is because the total solid content of activated sludge is too little,only one percent in the activated sludge,the ideal total solid content of the activated sludge should be 6～9%,the COD value should be 100000～125000 mg/L,then it have sufficient heat to maintain continuous response.