Straw-based Biochar Intensified Portulaca Oleracea To Repair Lead Pollution Study On The Effect Of Soil

Soil,as an integral part of the natural world,is the foundation of terrestrial ecosystems.With the rapid industrial and agricultural development,emissions of waste has resulted in increasingly serious heavy metal pollution in soil.Lead,one of heavy metals,is prone to migration and transformation and is difficult to degrade,causing great harm to soil.Nowadays,biochar has become a matter of great concern because of its loose and porous structure.Phytoremediation is a recently developed technology with minimal risk and without secondary pollution,but when applying it,its own enrichment effect have an negative impact.In this study,biochar,prepared from farm Land straw waste,was coupled with the highly enriched plant Portulaca oleracea,one type of hyperaccumulator widely grown in Northeast China,aiming at passivates lead pollution by biochar one the one hand and improving the Portulaca’s enrichment effect on the lead on the other hand,and then exploring the remediation effect of biochar and Portulaca on the soil contaminated with lead.（1）In the experiment to explore the adsorption effect of biochar on lead ions,biochar displayed a good absorbing property due to its tubular porous fibrous structure and a large number of oxygen-containing functional groups in it.Through the experiment of the adsorption system,it is found that the adsorption capacity of the biochar is 27.82 mg/g when reaching the adsorption equilibrium;Fitting results of kinetics showed that the biochar’s absorption to lead is a type of chemical adsorption.The adsorption isotherm of the lead ion impacted by the biochar follows the Langmuir adsorption equation,indicating that biochar’s adsorption to Pb²⁺is a type of monolayer adsorption.Three-dimensional fluorescence spectrum data showed that DOM is mainly composed of tryptophan-like proteins,aromatic proteins,humic acid,fulvic acid etc.Compared with the two types of protein components,humic acid and fulvic acid demonstrates more extraordinary ability to bind with lead.The data of synchronous fluorescence spectroscopy indicates that the higher the concentration of lead ions,the stronger the interaction between DOM and lead ions.Through the fitting by Stern-Volmer equation,the quenching rate constants were 2.023×10¹¹L/mol/s and1.004×10¹¹L/mol/s respectively,illustrating that Pb²⁺and DOM mainly occurres static fluorescence quenching.There are a kind of binding sites between the protein components of DOM and lead ions,and another ones between humic acid and lead and lead ions.（2）In the study of biochar’s regulation on the growth of portulaca oleracea,the test results of seed’s germination showed that biochar can promote the germination and the growth within the range of 2500 mg/L Pb²⁺.The experimental results of plant cultivation indicated that in 500 mg/kg of lead contaminated soil,biochar can increase the biomass of portulaca oleracea plants and restore the plant height and weight to the natural growth status of uncontaminated plants.By changing the dosages of biochar,it was found that when the proportion of biochar in the soil was 2%,the weight of plants in the treatment group reached the maximum of 4.996g,demonstrating that this addition of biochar words best.The measurement results of the indicators of plants’antioxidant defense systems showed that the addition of biochar improves the activity of antioxidant enzymes—purslane SOD,CAT,POD,etc.and effectively reduces the content of malondialdehyde（MDA）by 13.09%.（3）The co-application of biochar and portulaca oleracea effectively adjusted physicochemical properties of the soil,increased the total nitrogen of the soil,promoted the growth of organic matter,and also adjusted the p H value of the soil to a certain extent.When the dosage of biochar was 2%,the enrichment effect of portulaca oleracea on lead soil reached 1.807 mg/kg.The remediation of biochar coupled with portulaca oleracea significantly reduced the effective content of lead in the soil.As the dosage of biochar increased,a regular downward trend of the effective lead content emerged.It works best when applying 2%biochar coupled with portulaca oleracea to the soil contaminated by lead.In the treatment group of 3%biochar coupled with portulaca oleracea,the the effective lead content of soil was reduced to 303.9 mg/kg,and the restoration effect at this time was the best among all groups.Biochar plays an important role in regulating the occurrence state of heavy metal lead in the soil,transforming it to a residue state.Portulaca oleracea can be used to enrich the lead in acid-soluble state,reduced state or oxidation state,when the availability is greater.