| The major problems facing humans are the global energy crisis caused by the depletion of traditional energy and the environmental pollution caused by its burning.In recent years,hydrothermal carbonization technology has been widely used in the treatment of municipal sewage sludge and the recovery of solid fuels.The sorts of biomass,reaction temperature and pH are considered to be an important factor affecting hydrothermal carbonation.In view of the present situation and shortcomings of the research on the hydrothermal carbonization of municipal sewage sludge,the following research work has been carried out in this paper.First,the effect of temperature on the hydrothermal carbonization municipal sewage sludge was explored.We were carried out at five temperatures of 180?,210?,240?,270? and 300?,respectively.The effects of temperature on the yield,moisture content,functional group,morphology and combustion characteristics of hydrochars were investigated.Secondly,the effect of pH on hydrothermal carbonization was discussed.The experiments set two temperatures at 210? and 270? and set seven pH at two temperatures,respectively.The effects of pH on the yield,water content,functional groups,morphological characteristics and combustion characteristics of hydrothermal carbonized municipal sludge were investigated.Thirdly,the degree of stabilization and distribution fractions of heavy metals and the change of environmental risk was investigated before and after the hydrothermal carbonization.The experimental results show that with the increase of temperature,the yield of hydrothermal carbon produced by the process of hydrothermal carbonization decreases,the ash content increases and the water content decreases.Among them,the highest yield was obtained at 180?.The optimum temperature of hydrothermal carbonization is 270?.Changes in temperature and pH of hydrothermal carbonization have little effect on the sorts of functional groups of hydrochar.With the increase of temperature,the stretching vibration peak of OH increases,the higher the temperature,the more complete the carbonation reaction.And the stretching vibration peak of CHn is weakened with the increase of pH value.Indicating that in the acidic environment is more conducive to the formation of fat substances.The ignition temperature and burnout temperature of the hydrothermal carbon are elevated relative to the sludge,indicating that the combustion of hydrochars is more durable.The results show that the stability of heavy metals Pb and Zn after hydrothermal carbonization is less than 100%.The stabilization rates of heavy metals Cd,Ni and Cu are higher than 100%,and these three heavy metals are enriched in hydrothermal carbon.Heavy metal Cu content is better stabilized in an alkaline environment,heavy metal Zn,Cd,Ni,Pb content in acid and alkaline environment than the neutral environment for better stability.The alkaline reaction environment has a significant effect on the heavy metals of the bioavailable fraction.The results show that the order of pollution of hydrochar is 180-7>300-7>210-7>240-7>sludge>270-7.The change in temperature of the hydrothermal carbonization is favorable to the reduction of the risk of heavy metal pollution.When the temperature rises to 270 ?,the change of pH value has a positive effect on the risk of heavy metals pollution.The comparison of Igeo Eir.values,RI values and their corresponding pollution levels of 270-2,270-3,270-5,270-7,270-9,270-11 and 270-12 can be found in the pollution of hydrochars levels order is:270-11<270-7<270-12<270-9<270-3<270-2<270-5.The most suitable treatment conditions of hydrothermal carbonization of municipal sewage sludge to treat heavy metals are 270-11. |
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