Heavy Metals Treatment By Combined Fenton Oxidation And Constructed Wetland In Sludge

The city sewage treatment capacity has been sharply increasing with more and more municipal sludge in China.Sludge disposal of wastewater treatment plant is an important subject issue urgent solution in environmental science.The heavy metals in the sludge are main obstacles which restrict the resource utilization of the sludge.At present,Fenton oxidation mostly used in domestic sewage treatment and special wastewater treatment,municipal sludge treatment.In particular,Fenton oxidation treatment of sludge has the advantage of improving the flocculation and dewatering performance of sludge and crack EPS of sludge.But the disadvantage is that the Fenton oxidation of sludge with low pH value,in sludge filtrate the TN,TP and COD concentration is high,At the same time,the heavy metal still exists in the sludge solid-liquid phase.Therefore,the sludge of Fenton oxidation need further dehydration and the increase of pH and The removal efficiency of heavy metals,in order to facilitate resources.Based on this,Considering the advantage of wetland in sewage and sludge treatment,the heavy metals in sludge treated by combined Fenton oxidation and constructed wetland to make it harmless and useful.The main research contents and results are summarized as follows:1.Study on removal of Fenton oxidation sludge optimum condition and heavy metals.The results showed that Fenton oxidation has apparent effect on the migration and variation of heavy metal,and the key influence factors were the initial pH,H2O2 dosage,H2O2/Fe2+ratio and temperature.However,the reaction time has no apparent effect on the migration and variation of heavy metal.According to the orthogonal experiment results and base on the acid soluble fraction concentration,the proper reaction conditions were recommended as follows:initial pH=1,H2O2 dosage=12 g·L-1,H2O2/Fe2+ratio=10 and T=50?.Under these conditions,the acid soluble fraction of Cu,Zn,and Mn can reached the highest concentration,which was 72.7%,90.1%,87.5%and 53.9%,respectively.After Fenton oxidation,the heavy metals Cu,Mn,Zn and Ni were decreased by 186.20,34.80,358.55 and 73.17mg kg-1,the removal rate reached 67.2%,79.7%and 37.0%,respectively.2.Fenton oxidation combined with artificial wetland removal efficiency of heavy metals in sewage sludge.The results indicated that the removal rates of Cu,Zn,Ni and Mn of Fenton oxidized sludge after the constructed wetland treatment were 67.2%,79.7%,37.0%%and 17.0%,respectively 27.5%was increased of the average removal rate that compared with the control treatment.The bioavailability of heavy metals in Fenton oxidized sludge and original sludge was Simultaneously significantly reduced after constructed wetland treatment.There are obvious differences in the removal of sludge load under the condition of different Fenton oxidation sludge heavy metals.The results showed that except for heavy metal Mn,heavy metals removal rates ofThe sludge loads were 1,2,3,4 L·d-1 and in the control systemwere 48%,34.5%,35.8%,and 18.9%,respectively,and the content of heavy metals increased first and then decreased with the increase of sludge load.3.Study on the migration in the artificial wetland system in the transformation of Fenton oxidation sludge.The results showed that the removal rates of Cu,Zn an d Ni were 78.3%,63.3%and 25.4%,respectively,but the Mn was less than the others.The biological availability of Cu,Mn,Zn and Ni in the Fenton oxidation sludge was reduced after the constructed wetland treatment,which were 23.16,130.04,97.44 and 14.40 mg·kg-1,respectively.The heavy metals concentration in the substrate of Fenton sludge treated constructed wetland were increased with the increase of substrate depth.The average concentrations of Cu,Mn,Zn and Ni in the substrate were 18,382.75,127.25,121.75 mg·kg-1.The contribution rate of plant to heavy metal enrichment was 0.23%-0.43%in Fenton oxidation sludge treatment system.It's remarkable that Fenton oxidation sludge inhibited plant growth,and the dry weight of the plant roots and stems decreased by 77.8%and 83.2%,respectively,compared with the control of 50.68 g and 30.26 g,respectively.