Experimental Study On Heavy Metal Remediation By Quaternary Ammonium Compounds Induced Hyperaccumulative Plant Endophytes

Since the 21st century,a large amount of wastewater containing heavy metals has entered the ecological environment,which has caused great harm to the ecosystem and human health,and attracted much attention.The remediation methods of heavy metal wastewater mainly include physical method,chemical method and biological method.Bioremediation of heavy metals has many advantages,such as low cost,less secondary pollution hazard,high tolerance and high efficiency of remediation,due to the shortcomings of physical and chemical methods,such as high cost and difficult to be separated.Therefore,bioremediation of heavy metals has become a new treatment technology.Bioremediation of heavy metals has achieved good results,but because the discharge of surfactants from hospitals and laundries will affect the survival of microorganisms,and then affect their ability to repair heavy metals,this paper mainly focuses on the effect of QACs on endophytic bacterial remediation of heavy metals.This paper mainly studies the effect of heavy metal remediation by QACs hyperaccumulative endophytic bacteria and draws the following conclusions through experiments:1.The endophytic bacteria LSE01 and LSE02 extracted from the stem of hyperaccumulative plant Solanum nigrum showed that the endophytic bacteria could secrete catalase and 16S rDNA identification showed that they belonged to Bacillus bacteria.2.To explore the effects of low and high concentrations of heavy metals on the growth of Two Endophytic Bacteria and do-E.coli,we can find that the biomass of bacteria in the presence of low concentrations of heavy metals is larger than that of non-inoculated heavy metals at the same time,showing a toxic excitation effect;high concentrations of heavy metals inhibit the growth of the three bacteria,affecting their growth.3.The resistance and adsorption of three strains to heavy metals were better after QACs induction than before induction.After induction of semi-inhibitory concentration of QACs C₁₂2 and C₁₄,the resistance of strain LSE01 to heavy metal cadmium increased from 140 mg/L to 160 mg/L.After induction of semi-inhibitory concentration of QACs C₁₂2 and C₁₄,the resistance of strains LSE02 and do-E.coli to heavy metal cadmium increased from 120 mg/L to 140 m/L.4.The removal efficiency of the three strains increased first and then decreased when they repaired low concentration of heavy metal cadmium,which may be due to the intracellular mechanism playing a major role in the early stage of heavy metal repairing and the release of some heavy metals into the environment due to cell lysis and death in the later stage,resulting in the increase of heavy metal concentration.However,in the presence of QACs,the concentration of heavy metals did not increase in the later stage of Endophytic bacteria.It may be that QACs or degraded QACs residues were embedded on the surface of cell membranes,forming a group with lysed cells to form a stronger adsorption of heavy metals.5.Infrared spectra of strain LSE01 before and after cadmium adsorption showed that the amino,carboxyl and hydroxyl groups on the cell surface played a certain role in the repair of heavy metals by strain LSE01.In addition,compared with the presence or absence of QACs,when strain LSE01 repaired heavy metals,the infrared spectra of strain 12 hours later showed that the position of carboxyl group peak changed most significantly.6.In QACs degradation,do-E.coli is superior to endophytic bacteria.When the strain do-E.coli degraded both C₁₂2 and C₁₄4 QACs,it was found that the strain preferentially degraded QACs with small molecular weight.On the basis of improving the ability of phytoendophytic bacteria to repair heavy metals,this paper strengthens the resistance to QACs and the ability to degrade QACs,which is of great significance to solve the problem of combined pollution of heavy metals and QACs in wastewater and promote the practical application of microbial remediation technology.