Synergetic Removal Of Sludge By Hydrothermal Dehydration And Heavy Metals

An improper treatment of sludge impose a great threat to the environmental protection and food security,due to excessive heavy metal pollution,in China.Incineration technology can quickly achieve volume reduction as well as optimize energy recovery.However the high contents of water and heavy metal in sewage sludge cause a great hurdles on achieving an efficient and pollution-free incineration process.Those eventually became a bottleneck of energy utilization form sludge.This paper puts forward a new idea of "the first time mechanical dewatering with hydrothermal coupling chemical pretreatment with the second time mechanical deeply dewatering",which is a new way to control the pollution of the source of the sludge,and the following research contents were carried out.Hydrothermal treatment experimentation on municipal sewage sludge was carried for examining the effects of reaction temperature,holding time,and chemical additives on the dewatering performance of the sludge.The optimal hydrothermal temperature and holding time was found to be 180°C and 30 min,respectively.Hydrothermal treatment with 0.04 MPa mechanical dewatering can reduce the initial sludge moisture content from 80% to 56.17%.The pressure of filter cake is only 51.15%.Compared the effect of NaCl,CaCl₂,Ca?OH?₂ and FeCl₃ on the dewatering performance,it showed that Na⁺ could replace the other surface of the sludge flocculation surface.The addition of chemical additives could improve the dewatering performance of the sludge.The effect of FeCl₃ coupling 2MPa mechanical dewatering effect and HT coupling 12 MPa mechanical dewatering are about 39%,By 0.04 MPa vacuum pumped out,the effect of sludge dewatering effect,?Ca?OH?₂? treatment and hydrothermal + non-alkaline flocculant?CaCl₂? treatment effect is worse,and under high pressure?0.2¹2MPa?,the effect is quite.Furthermore,the effects of initial reaction pressure?IP?and atmosphere on the characteristics of sewage sludge derived fuel were investigated.Reaction atmosphere of N₂,Air,or CO₂ were examined under initial pressure?gauge pressure?of 0MPa,1.2Mpa,or 3.0Mpa.The examined fuel characteristics included water content,heating value,organic content,drying rate and particle diameter.Sludge with low water content was produced under air atmosphere.The increase of IP decreased the dry-base heating value of the sludge while its maximum heat value was produced under CO₂ atmosphere.Minimum volatile content was obtained under Air atmosphere with same IP?3MPa?;IP promote the drying rate,decreased the sludge drying time,and the dewatered sample after CO₂ pre-treatment was fastest dried;as well as,the mean diameter of sludge particle decreased from 66.46?m?raw sludge?to 18.99?m?3.0MPaN₂?,and the minimum particle was detected under air atmosphere with same IP.The effects of EDTA on total heavy metal concentration and leaching concentration were studied under hydrothermal condition.The sludge solidification can be hydrolyzed by hydrolysis in sludge,so that the ratio of solid to liquid changes,and the total concentration of heavy metals in sludge increases.The effect of EDTA on the total concentration of most heavy metals in sludge was slightly worse than that in water treatment,which had a good effect on Pb.From the view of leaching toxicity of heavy metals,hydrothermal pretreatment can extract the heavy metals from the sludge,EDTA can improve the extraction efficiency,Zn showed the best effect,from the original 0.159 ug/L rose to 104.600ug/L.As the concentration is low,the effect is not significant.Pb decreased,Pb and organic matter of sludge can be well complexed into the liquid phase.