The Effect Of Biochar/white-rot Fungi On Stability Of Heavy Metals During Sediment Composting

With the rapid development of society,the problem of sediment contaminated by heavy metals is becoming more and more serious.Sediment dredging,a technology with a strong maneuverability and rich engineering practice,is the most widely used technology in river endogenous pollution control.Meanwhile,composting technology is considered to be one of the most effective ways for resource utilization of dredged sediment.However,the existence of heavy metals greatly limits the resource utilization of compost products from composting of dredged sediment.Therefore,studying the effect of biochar/white-rot fungi on the stability of heavy metals in the composting of sediment and understanding the relationship between Diethylene triamine penta-acetic acid(DTPA)-extractable heavy metals and functional components of dissolved organic matter(DOM)are not only of great significance to explore the mechanisms of biochar/white-rot fungi inactivating heavy metals during composting of dredged sediment and to develop the ex-situ methods of remediating heavy metals contaminated sediment,they also provide a theoretical reference to apply biochar/white-rot fungi to remediate heavy metals that contain in composting of sediment.In this experiment,based on the sediment from the river in SX Town,QJ District,SG City,GD Province,a co-composting of sediment,rice straw,vegetable and bran was constructed.There were four different trials in this experiment,which includes control group,white-rot fungi group,biochar group,and the combination white-rot fungi with biochar group.It was performed to evaluate the influence of white-rot fungi,biochar,and the combination of white-rot fungi with biochar on the composting process of dredging sediment and the contents of DTPA-extractable Cu,Zn,and Cd in each pile during 60 days of composting.During this experiment,the temperature,moisture,p H values,TOC/TN,and seed germination index(GI)were investigated first,following dividing the dissoluble organic matter(DOM)into fulvic acids(FA),humic acids(HA),and hydrophilic(Hy I)fractions and employing the fluorescence excitation-emission matrix spectra combined with parallel factor(PARAFAC)analysis to identify the fluorescent components of DOM from different sediment composting samples.Then the effect of white-rot fungi,biochar,as well as the combination of white-rot fungi with biochar on the composting process of dredging sediment and the fluorescent components of DOM in four different trials were analyzed.Lastly,the changes of the total and DTPA-extractable contents of Cu,Zn,and Cd in each pile were detected and analyzed,then estimating the effect of white-rot fungi,biochar,and the combination of white-rot fungi with biochar on the toxicity of heavy metals during composting process of sediment.What's more,the mechanisms of white-rot fungi,biochar,and the combination of white-rot fungi with biochar affecting the toxicity of heavy metals during the composting process of ex-situ sediment were researched by analyzing the relationships among the fluorescent components of DOM and the available contents of heavy metals(extraction with DTPA).The main research results are shown below:At the end of the composting,all four piles reached the mature stage,and their p H values were all within the range of suitable p H values(6.5-7.5)for plant growth.Although the temperature,moisture content and TOC/TN of each heap had no obvious difference during composting,the addition of biochar/white-rot fungi to composting significantly lowered the plant toxins of compost products compared with the control group.After composting,the GI values of white-rot fungi group,biochar group,and the combination of white-rot fungi with biochar group increased by 28.13%,49.85%,and 49.41%,respectively,compare with that of control group.The total amount of target heavy metals in the four heaps increased.Except for DTPAextractable Cu,the contents of DTPA-extractable Zn and Cd decreased at the end of the composting.Meanwhile,biochar/white-rot fungi effectively reduced the contents of DTPA-extractable Zn and Cd in the piles during this process.Compared with the first stage of composting,the extraction efficiency of DTPA-extractable Zn in the control group,white-rot fungi group,biochar group,and the group combining by white-rot fungi and biochar decreased by 38.98%,45.72%,42.55%,and 43.22%,respectively,while that of DTPA-extractable Cd decreased by 27.5%,45.20%,37.15%,and 44.45%.Composting can lead more stable and complex structures(e.g.,benzene and quinone organic compounds)to form.Compare with control group,the addition of both white-rot fungi and biochar could promote the production of benzenoid and quinone compounds in the heap.The addition of white-rot fungi can promote the rapid formation of benzenoid organics in DOM and its biostabilization during curing.The addition of biochar mainly promoted the formation of benzenoid organic compounds and quinone containing compounds in FA,HA,and Hy I,and increases the content of aromatic condensation or conjugated chromophore in protein organic compounds in Hy I.The combination of biochar and white-rot fungi also promoted the increase of benzenoid organic matter and quinone.During the process of composting,the effect of fluorescent components in FA,HA,and Hy I on DTPA extractable heavy metals depends on their types.Benzenoid organics and quinone compounds and quinone compounds in Hy I were not conducive to the decrease of DTPA-extrable Cu in composting.However,benzenoid organics and quinone containing substances in FA as well as quinone containing substances in Hy I reduced the activity of DTPA-extrable Zn and Cd.The results above showed that the passivation effect of composting was selective for heavy metals;biochar/white-rot fungi exerted passivation effect on specific heavy metals during sediment composting,but there was no synergy between biochar and white-rot fungi.