| In the case of heavy metal pollution becoming serious increasingly,it's an urgent task to develop water treatment technology with low cost,simple equipment operation,high efficiency to remove heavy metals.Due to microbial treatment technology has significant advantages of smaller investment,lower operating cost than the traditional physical and chemical technology,it is widely used to study the removal of heavy metals.But there are some problems,such as,smaller microbial cells,easy activity loss,and the difficulty to separate from aqueous solution that could easily lead to secondary pollution.Also,Heavy metals in wastewater to some extent are toxic to microorganisms,which inhibits the metabolic activity of microorganism,thereby affects removal efficiency of heavy metals.So,how to improve the microbial treatment efficiency of heavy metals becomes a key of microbial treatment technology applications.Microorganism immobilization technology has maintained a strong activity of microorganisms,strong stability and feasibility to separate bacteria,which is an ideal choice.In addition,the microbial metabolism plays a key role in the detoxification process of heavy metal for microbial treatment technology.Therefore,white rot fungi,Bacillus subtilis and Pseudomonas aeruginosa that have favorable removal efficiency of heavy metals were used as objects to study the performance of biological adsorbent for heavy metals,and to discuss the mechanism between microbial metabolism and pollutant stress.Finally,a method to improve the removal efficiency of heavy metal for microbial treatment technology was proposed by studying the interaction of metal and organic compound in wastewater,and the role of surfactants in heavy metal detoxification mechanism.In this paper,the main research work and achievements mainly include the following five aspects:The first section focused on the absorption peformance and mechanism of Pb(?)by immobilized biological adsorbent prepared by embedding chitosan,activated carbon and Phanerochaete chrysosporium(P.chrysosporium).Firstly,we successfully prepared the biological adsorbent that can be applied in removal of Pb(?),and then studied the effect of pH,time and metal ions initial concentration on removal efficiency.Finally,recycle of biological adsorbent and a possible adsorption mechanism were investigated.The results can be concluded as follows:(1)the optimal pH for biological adsorbent in the treatment was about 5.0,adsorption equilibrium time was 7 h with maximum adsorption quantity of 167.36 mg/g;(2)the adsorption isotherm fits well with the Langmuir model,indicating that the biological adsorbent surface is homogeneous,adsorption sites are equal,and the adsorption of Pb(?)is a monolayer adsorption;(3)the adsorption kinetics of Pb(?)on biological adsorbent was primarily elaborated by the pseudo-first-order model,which means the internal mass transfer is limiting factor;(4)the removal efficiency of Pb(?)is affected by other coexisting ions.(5)This biological adsorbent has a good capacity of repeatability,even after recycling 5 times,adsorption efficiency was only reduced by 6.13%.The second section describes the competitive adsorption of Cu(?)and Pb(?)with magnetic biological adsorbent prepared by sodium alginate embedding P.chrysosporium and Fe3O4 nanoparticle.Main research includes the activity of magnetic biological adsorbent,the effects of pH value and adsorption time on the adsorption of single and double components of Pb2+,Cu2+.The results showed that:(1)the magnetic biological adsorbent not only has a strong magnetization,but also has enhanced metabolic activity;(2)the optimal pH for magnetic biological adsorbent in the treatment was about 5.0,and adsorption equilibrium time was 7 h;(3)the adsorption isotherm fits well with the Langmuir model,meaning that the adsorptions of single and double components of Pb2+,Cu2+ are monolayer adsorption;(4)The adsorption kinetics of single and double components of Pb2+,Cu2+ on magnetic biological adsorbent fit well the pseudo-second-order model,and chemical adsorption is adsorption rate limiting factor.In the third section,we mainly discussed the influence of heavy metals on P.chrysosporium metabolism to reveal the detoxification mechanism of heavy metal.The results found that heavy metal ions have a certain influence on intracellular and extracellular metabolites of P.chrysosporium:(1)The amount of intracellular reactive oxygen free radicals decreased with the increase of Cd(?)concentration and contact time.The quantity of malondialdehyde(MDA)reached maximum(9?mol/g)in 8 hand minimum value(0.6 ?mol/g)in 24 h.The amount of intracellular protein increased and then decreased.Under the stress of short time(2 h),the SOD activity was proportional to Cd(?)concentration,but when contact time increased to 8 h,the SOD activity decreased.Low concentration of Cd(?)and contact time stimulate the production of the CAT and the higher enzyme activity,but increasing Cd(?)concentration or time,the situation was exactly opposite,which implied the effects of Cd(II)on P.chrysosporium are both stimulative and suppressive with contact time and Cd(II)concentration increase,the increase trend of glutathione disulfide(GSSG)concentration was more obvious than that of glutathione(GSH);(2)In the culture medium and extracellular polymers(EPS),sugar concentration decreased and then tended to reach balance.Protein concentration showed a trend of increase and then decrease.Cd(?)stimulated the production of oxalic acid with 0-0.8 mM,but when the concentrations of Cd(?)exceed 1.0 mM,the secretion of oxalic acid decreased.The fourth section describes the effects of Cd(?)concentration,pH on the degradation of pyrene with bacillus subtilis by studying the influence of Cd(?)on bacillus subtilis cell membrane protein and polysaccharide content and the amount of pyrene inside and outside of cell membrane,to discuss the role of Cd(?)on degration of pyrene with bacillus subtilis.It was found that:(1)the optimal pH for bacillus subtilis in the treatment of pyrene was about 8.0.(2)Cd(?)inhibited the degradation of pyrene for bacillus subtilis,and the concentration of Cd(?)was inversely proportional to the biodegradation efficiency.(3)Cd(?)could inhibit the production of protein and polysaccharide in bacillus subtilis membrane;(4)the concentration of intracellular pyrene increased with the increase of concentration of Cd(?),and then reduced,but extracellular situation is the opposite.So,Cd(?)hinders the transmembrane process of pyrene,the strongest inhibition occured when the concentration of Cd(?)to 20 mg/L.The fifth section studies the effects of surfactant(diRL,CTAB,Triton X-100)on reduction of Cr(?)with Pseudomonas aeruginosa.The results were as follows:(1)diRL can be absorbed by Pseudomonas aeruginosa as carbon source,and thus promote the growth and metabolic activity of Pseudomonas aeruginosa,which is beneficial to the reduction of Cr(?).But the cation ionized by CTAB reduced the the activity of Pseudomonas aeruginosa,resulting in inhibition of Cr(?)reduction.Triton X-100 has no effect on the reduction of Cr(?).(2)The reduction of Cr(?)is more suitable in alkaline conditions,and the higher the solution pH value,the greater the reduction rate of Cr(?).(3)Among three surfactants,only diRL could promote the dispersion of Pseudomonas aeruginosa.(4)Cr(?)reduction efficiency is inversely proportional to the contact time,and proportional to the microbial quantity.Cr(?)removal effeciency increased from 17%to 62.5%when the microbial quantity increased from 0.5%to 0.5%.(5)Cationic Cu2+ promoted the reduction of Cr(?),Zn2+ inhibited reduction of Cr(?),and anionic NO3-and SO42-almost did not affect the reduction of Cr(?).To some extent,this article reveals the mechanism of interaction between microbial and heavy metal ions,and analyzes the reasons of low efficiency in the microbial treatment of heavy metal wastewater,also figures out the optimal operating parameters,improves the repeatability of microbial by immobilization of microbial and the treatment efficiency by addition of surfactant,which has certain guiding significance for improving efficient use of microbial treatment technology in heavy metal contaminated water. |
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