Study On The Remediation And Soil Utilization Of Lead And Cadmium Contaminated Sediment Based On Ryegrass/biochar Combinatio

A significant amount of domestic sewage and industrial wastewater are dumped into rivers and lakes without being treated or treated in an efficient manner due to China’s economy’s rapid development.Sediment becomes the primary"source"and"sink"of heavy metal contamination in water bodies as heavy metals and other toxic compounds in sewage build up over time.In order to investigate the effects of straw biochar on the aggregate structure of sediment soil and the mechanism by which ryegrass restores heavy metals in sediment,batch tests were used to study the preparation of straw biochar and its adsorption properties on Pb²⁺and Cd²⁺and to discuss the restoration effect of ryegrass on heavy metals in sediment under various ratios of biochar,sediment,and soil.First,wheat straw primary carbon（BC）was prepared by pyrolysis at 500℃for2h,and modified carbon（MBC）was prepared by sodium hydroxide.Its structure and composition were characterized by thermogravimetric analysis,elemental composition analysis,Fourier infrared spectroscopy and scanning electron microscopy.The findings demonstrate that wheat straw biochar has good pore structure,a big specific surface area,a lot of functional groups,and can offer good heavy metal adsorption sites.The static adsorption properties of BC and MBC on Pb²⁺and Cd²⁺were investigated.Under the solution system,the adsorption capacity of Pb²⁺and Cd²⁺of the two biochars under different proportions of modifiers,different dosages,initial solution p H value and ionic strength was determined by single-factor test,and the results showed that both biochars were superior at adsorbing Pb²⁺and Cd²⁺under the identical test conditions,with MBC biochar having a higher adsorption capacity than BC biochar.According to the Pb²⁺and Cd²⁺adsorption isotherm features by BC and MBC,Freundlich equation fitting（R²=0.85～0.95）performed worse than Langmuir equation fitting（R²=0.91～0.99）.The adsorption of BC and MBC for Cd²⁺was compatible with the quasi-second-order kinetic model（R²=0.94～0.99）,whereas the adsorption of BC and MBC for Pb²⁺was more consistent with the quasi-first-order kinetic model（R²=0.96～0.98）,according to the adsorption kinetics experiments.A pot experiment was employed in this work to investigate the repair impact of ryegrass on heavy metals in sediment in varying quantities of BC,sediment,and soil.According to the growth situation of ryegrass,heavy metals had certain inhibitory effect on its development,while the addition of biochar had a promotion effect.In terms of physicochemical properties,the electrical conductivity,p H,organic matter,nitrogen and phosphorus elements of each test group were significantly increased.In terms of heavy metal morphology,the proportion of acid extractable state decreased and residue state content increased in all experimental groups at the end of the 90d experiment.Compared with the initial stage of the experiment,acid extractable state decreased from 35.0%to 28.6%and residue state increased from 20.8%to 26.4%in experimental group S7.The conversion effect of heavy metal in experimental group S7 was better.In the experimental group,the extractable state of S8 acid reduced from 38.6%to 32.6%,while the residue state increased from 21.4%to 25.4%.In terms of toxic leaching,the concentration of all experimental groups had a significant downward trend.In terms of aggregate structure,the average weight diameter（MWD）and geometric mean diameter（GMD）were S7>S8>S5>S3>S1 after the 90d.The decrease in the proportion of particle size<0.25mm indicates that the presence of biochar can promote the transformation of small particle level to large particle level of agglomerates.After the improvement of 90d,the destruction degree of agglomerates（PAD）changed from large to small is>S1>S8>S3>S5>S7,and the structure of S7 soil aggregates was the most stable.The downward trend of shape dimension of each test component was also obvious.In terms of microbial analysis,at the phylum level,the primary bacteria are Proteobacteria,Bacteroidetes,Acidobacteria and Actinobacteria.At the genus level,the community was mainly composed of Pseudomonas,Phenylobacterium,Chitinophaga,Sphingomonas and Sediminibacterium.After 90 days,the species composition of experimental group S7 became more abundant.The early community structure of the two test groups groups S3 and S7 was similar at both phylum level and genus level.