Preliminary Study On The Remediation Of Lead Pollution By Extracellular Polymer Substances Of Aspergillus Tubingensis F12

Extracellular polymeric substances（EPS）refers to a general term for high molecular polymers secreted by microorganisms into cells outside under certain environmental conditions.Studies have shown that EPS has an important protective effect on microorganisms,and can improve soil structure and promote soil aggregation after entering the ecosystem.Activated sludge EPS has the functions of flocculation,adsorption and sludge dewatering in wastewater treatment.At present,most of the research on EPS focuses on the adsorption of heavy metal ions in water,and there are few studies on the treatment of heavy metals in soil.In this paper,EPS was extracted from a self-preserved strain of Aspergillus tubingensis F12（Accession number CGMCC.NO.7174）to study its ability to repair lead pollution in water and soil systems,and the introduction of bentonite to build a synergistic system.First,extract the EPS from Aspergillus tubingensis F12 by EDTA method,Na OH-heating method,cation exchange resin（CER）method,ultrasonic method,centrifugation method,and compare the extraction efficiency of each method to confirm that the CER method is the most suitable.It was determined that the addition amount of resin per gram of dry mycelium was 30g,the temperature was 20℃,the rotation speed was 150 rpm,and the extraction time was 2 h.The extracted Fourier infrared spectra of EPS confirmed that the main functional groups in EPS were carbonyl,hydroxyl,amide,etc.The adsorption capacity of EPS of Aspergillus tubingensis F12 to heavy metal ions in water phase was investigated.The adsorption capacity of five heavy metal ions from large to small was:Pb²⁺>Ni²⁺>Cu²⁺>Cd²⁺>Zn²⁺.The adsorption capacity for lead ion is 241 mg/g when the equilibrium concentration is 50 mg/g.So lead is the object of study.EPS can enhance the adsorption performance of bentonite for lead ions.The adsorption behavior of EPS for lead ions is more suitable to be described by Langmuir equation.The theoretical maximum adsorption capacity for lead ions is 715.4 mg/g.The adsorption behavior of EPS-bentonite for lead ions described by the Freundlich equation is more suitable.The adsorption properties of bentonite modified by EPS have improved to a certain extent.The combination of EPS and bentonite was applied to the passivation treatment of soil lead pollution,and the change of soil lead morphology was analyzed by an improved BCR continuous extraction method.EPS treatment of 100 mg/kg lead-contaminated soil can increase36.7%of residual lead in 1 d.After adding bentonite,57%,while bentonite alone is only 5%,it can be seen that the two show a certain synergistic passivation.The proportion of residual lead and acid-soluble lead in the simulated soil increased with the increase of EPS usage,and the addition of bentonite could obviously inhibit the increase of acid-soluble lead.Prolonging the treatment time and acid rain treatment can increase the amount of passivation,but acid rain erosion under natural conditions will also increase the mobility of soil lead,which means that acid rain will increase the area of contaminated soil after passivation treatment.Different evaluation methods indicate that EPS is effective lead deactivators,but under simulated sulfuric acid rain extraction and Mehlich 3 extraction methods,it is not possible to confirm whether there is a synergistic passivation between EPS and bentonite,and further research is needed.