Removal Of Benzo [a] Pyrene By Sludge Composting And Effects Of Compost Products On Remediation Of Lead-contaminated Soil

With the advancement of urbanization in China,the amount of sewage treatment is increasing,and the annual output of excess sludge is also increasing.The composition of sludge is complex and its moisture content is high,and the content of toxic and harmful substances in sludge from different sources varies greatly.If sludge is not properly treated and disposed of,it will cause secondary pollution of the environment.Composting is one of the effective means to realize sludge recycling,and the composting process can remove a variety of toxic and harmful substances.It has the advantages of meeting the requirements of sustainable development and minimal environmental hazards.In this paper,benzo [a] pyrene(BaP)contained in sludge was selected as the representative to simulate the composting experiment of sludge with different concentration of BaP mixed with sawdust and mushroom residue at a mass ratio of 10:2:1.The temperature,pH,conductivity,organic matter,moisture content and seed germination index of the compost were measured,and the effect of different concentrations of BaP on the composting was analyzed.The BaP residues in the compost were determined and the removal efficiency of different concentrations of BaP during composting process was investigated.The influence of different concentrations of BaP on the total amount and speciation transformation of heavy metals was analyzed by electric hot plate acid digestion method and BCR extraction.High-throughput sequencing was used to study the effect of different concentrations of BaP on microbial community structure in compost.The sludge after composting was prepared into compost products and applied to Pb-contaminated soils individually or combined with Scripus triqueter.The environmental benefits and remediation effects of compost products were analyzed,and the influence of compost products on soil enzyme activity and microbial community structure was studied.The main results of this paper are as follows:(1)BaP affected the temperature,moisture content and seed germination index of the compost,indirectly affected the microbial activity,organic matter degradation rate and the time required for compost maturity.(2)The passivation effect of compost on Cu,Pb,Cr and Ni in sludge was very significant.The decomposition rate of silicate and minerals,the formation of humus and the passivation of heavy metals were affected by different concentrations of BaP in the early stage of composting.(3)BaP affected the abundance,structure and composition of microbial community in the composting process.In the same compost,the higher the BaP concentration,the higher the similarity of microbial community structure in each stage of composting.The microbial community structure varied greatly between the same stages of different compost.(4)Compost products add in Pb-contaminated soils significantly improved soil fertility and microbial activity,and did not cause secondary pollution.When applied compost products alone,it was beneficial to the passivation of Pb in soil and greatly reduced its bioavailability and migration.When applied compost products combined with Scripus triqueter,it was beneficial to the activation of Pb in soil,the absorption and enrichment of Pb by Scripus triqueter.