Fe(Ⅱ) Activated Persulfate-assisted Hydrothermal Conversion Of Dewatering And Denitrification Of Sewage Sludge:Experimental And Principle Investigations

The output of municipal sludge increases year by year,which puts forward higher requirements for the treatment and disposal of municipal sludge.Therefore,the sludge pyrolysis has become an effective sludge treatment method because of its obvious advantages,such as greatly reducing the volume of sludge and large processing capacity.However,due to the large water content of the sludge,and the pyrolysis process of a large number of proteins i n the sludge will release nitrogen-containing polluted gas,causing environmental pollution.It is necessary to pretreat sludge to make pyrolysis more realistic and feasible.In this study,free radical hydrothermal and pure hydrothermal sludge were compared at four temperatures.Explored the advantages of improving the efficiency of nitrogen removal and reducing the water content of sludge of ferrous activated persulfate-assisted hydrothermal treatment under low temperature conditions（temperature 150℃,reaction time 20min）.Explored the effects of free radical types and effects on the nitrogen conversion process,and the mechanism of free radical assisted hydrothermal treatment of sludge dehydration and denitrification.The total N content in the solid residue was used to evaluate the N removal efficiency.The types of free radicals activated by ferrous persulfate and the effect of free radical hydrothermal sludge denitrification were explored.The sludge moisture content and sludge dewatering rate were used as indicators to evaluate the sludge dewatering effect.Further,the redistribution of nitrogen in solid and liquid products was characterized and quantified,and the destruction of various extracellul ar polymers in sludge with free radicals was obtained to explore the relationship and mechanism of dehydration and denitrification during free radical hydrothermal treatmen t.The experimental results show that,compared with the results of hydrothermal treatment of sludge,the removal efficiency of fre e radical hydrothermal treatment of sludge at a relatively mild temperature（temperature:150℃;time 20 min）increased the nitrogen removal of sludge by 35.0%Increase dehydration rate by 32%.Using ferrous iron to activate persulfate radical hydrothermal sludge,persulfate/carbon=0.085 molar ratio,ferrous iron/persulfate=1.25 molar ratio,can obtain a higher nitrogen removal rate,and sludge dehydration rate.In addition,electron paramagnetic resonance（EPR）and scanning electron microscopy（SEM）results show that the sulfate radical(SO₄^-·)produced by ferrous activated persulfate destroys the sludge structure.The fixed extracellular polymer（TB-EPS）is destroyed by free radicals and converted into free extracellular polymer（S-EPS）,which is further decomposed.In the absence of the EPS protection,the water in the sludge is released to promote the hydrothermal hydrolysis process,and the protein is directly exposed to the extreme hydrothermal environment and decomposes and transforms.The free radicals also provided energy for the denitrification of Heterocycle-N.Consequently,a high N removal efficiency was obtained.