Study On The Biological Utilization Of Iron Sludge From Fenton Oxidation

Iron compounds are widely used in sewage treatment,not only can be used as flocculant,phosphorus removal agent,decolorization agent,but also an essential raw material of Fenton oxidation process.However,the wastewater treatment process involving iron,especially Fenton oxidation,will produce a large amount of iron sludge,which is expensive to treat.The resource utilization of iron sludge can greatly reduce the cost of sewage treatment and save iron resources.In this paper,the strategies of biological regeneration and recycling were used to recycle iron sludge.The main contents of the paper are as follows:（1）Feasibility study on biological regeneration and recycling of Fenton iron sludge.Based on the artificial iron mud and the actual Fenton iron sludge,the feasibility of the strategy and the optimization of the conditions of each link are verified.The FIS is firstly experienced an anaerobic biological digestion process to convert the Fe（III）to Fe（II）by Fe-reducing bacteria,then the Fe（II）was acidified by a weak acid（p H>3.0）and entered the solution phase as free Fe²⁺,while the activity of Fe-reducing bacteria is still maintained;finally,the Fe²⁺is in-situ cyclic utilized for Fenton oxidation and the residual sludge containing abundance of iron reducing bacteria flows back to the anaerobic digestion tank.Thus,the resource utilization of iron sludge can be realized.It is found that the Fe/organics ratio,PO₄^3-level and solid content show great effect on the conversion efficiency and product of Fe（II）during anaerobic digestion of the iron sludge.The optimal p H for extraction of Fe（II）by acidification was around 3.5,under which not only over 94%of the regenerated Fe（II）could be extracted in the form of Fe²⁺from the digested sludge,but also the activity of the iron reducing bacteria in the residual sludge could be preserved.The extracted Fe²⁺could be recycled for Fenton oxidation and show comparable performance to that of the pure specification Fe²⁺.Based on the artificial iron mud and the actual Fenton iron sludge,this paper verifies the feasibility of the strategy and the optimization conditions of each link.This strategy has been tested in wastewater treatment plants and can reduce the cost of homogeneous Fenton oxidation wastewater treatment technology by about 60%.（2）Study on separation and recovery of phosphorus resources from phosphorus-containing iron sludge.The Fe²⁺and PO₄^3-obtained from the anaerobic digestion biological treatment of phosphorus-containing iron sludge will react to produce vivianite（Fe₃（PO₄）₂·8H₂O）with recycling value,and the vivianite will be separated by fractional precipitation.Through the control test,it is concluded that when n（Fe）:n(PO₄^3-)in the system is less than 6.5,the system will generate the vivianite particles which can be successfully fractional precipitated,after 10 days of anaerobic digestion,the recovery efficiency of vivianite can reach 73%.However,in actual sewage,the concentration of PO₄^3-cannot reach the optimal ratio.Therefore,the low concentration phosphoric acid in the system can be concentrated by using cyclic anaerobic oxidation aeration,and then the resultant vivianite can be separated by fractional precipitation.The results show that the vivianite particles obtained by cyclic oxidation-aeration for12 times(n（Fe）:n(PO₄^3-)is less than 6.5)can be precipitated by stages,but the vivianite particles are relatively small and clustered into flower clusters compared with the vivianite particles obtained by adding sufficient amount of PO₄^3-at one time.