Study On The In Situ Bioremediation Of Atrazine Polluted Groundwater

Atranex, also called atrazine, is a kind of triazine herbicides which iswidely used in the world. It has been considered in many reports as a kind ofenvironmental estrogen, and it would work as hormones to human beings andwildlife, retarding their reproduction, or causing cancer etc. Exposuring to lowdose atrazine(0.1μg/L)will lead to the increase of female hormone secretoryvolume in the body of frogs, destroying its endocrine system, bringing about thefeminization of male frog or hermaphroditism. Since the atrazine has been usedyear by year, the soil and groundwater is polluted in a large sale. Owing to thecomplexity, invisibility and difficulty in restoring of the groundwater pollution,once polluted, its natural recovery and purification process will take a long time.Therefore, it is necessary to find an economical and efficient in situ remediationmethod for it.To study the remediation method for atrazine will not only eliminate thepollution, insure the national environmental safety, promote the sustainabledevelopment of national social economy , but also improve the competitivepower of national agricultural products in the international trade.Therefore, atrazine in the groundwater is taken as the target substance,andits economic and efficient remediation method is studied in this paper.The study on the remediation of groundwater pollution in developedcountries began from 1970's, the treatment methods included isolation, pumplifting, adsorption, chemistry fencing, electrochemical process andbioremediation,etc. Among them, the bioremediation method had been used inthe remediation of groundwater pollution and been a clean and potentialemerging technology for its low investment, better efficiency and conveniencein use.In 1990's, the Canadian professor Gillim put forward PRB technique tothe remediation of point source pollution, and it has been developed rapidly inthe latest decade owing to its low investment, light ground disturbance,almostno energy requirement,etc. The technique mainly take zero valent iron as itsreactive media, to treat certain kind of halogenating organic matter and someheavy metals. And meanwhile add some adsorption materials such as absorbentcarbon and zeolite etc, to make the PRB for the insitu remediation ofgroundwater pollution. All among these studies, it is seldom the case that takingmicroorganisms as the reactive media to make the PRB.For the non-pointsource pollution, the natural remediation was used as a main method, it usedindigene microorganisms to degrade pollutants and also used diluting effect. Ifthere is no microorganisms which have the ability to degrade atrazine oratrazine only can be degraded partly, the dominance strains must be screenedand injected to the groundwater to degrade it.The achievement of the text included following three parts:1.The text studied on the regulation of atrazine's transformation inunsaturated zone and groundwater,and its conclusions are followings(1)The process of pesticides transfering downward the soil into thegroundwater were constrained by many complex factors. The static adsorptionexperiment showed that the three kinds of lithology soil didn't absorb muchatrazine, and the adsorption of atrazine completed in 24 hours.The fewer theorganic matter and ionic strength in the soil, the lower the absorption of atrazineis.whereas adsorptive capacity decreased when the pH increased.Natural degradation of atrazine in the soil and groundwater showed thatatrazine had a long half-life and long-term presence in groundwater andunsaturated zone.(2)The results of the soil column experiments showed:For three types of lithologies soil the atrazine could be strained out.Thefewer the organic matter in the soil, the lower the absorption of atrazine was,responsively,the leaching ability of the pesticides would increase.When theamount of rainfall was great and its intensity was low, or the time to apply thepesticides was short, were all in favor of pesticides leaching. Intermittentrainfall was more advantageous than continuous rainfall for the atrazineleaching.(3)The transfer simulation of atrazine in the groundwater showed that itmainly transferred in the crossrange direction and vertical direction, correspondto that of two dimension contraflow dispersion model. Owing to different kindsof physical, chemical and biological function,atrazine and groundwater ' smigration velocity was different.The atrazine 's retardation efficient was 2.45 ,migration velocity was 4.08 cm/d.2.After enrichment culture and domestication, four strains were screenedfor their high degradable abilities, and they were from pollution discharge portof pesticide factory in Jilin, leachate of Peijia landfill of Changchun, andactivated sludge of sewage disposal plant in Jilin. L1 was identified asEukaryota Fungi Basidiomycota Urediniomycetes Rhodotorulamucilaginosa.L2was identified as Bacteria Actinobacteria ActinobacteridaeActinomycetales Micrococcineae Microbacteriaceae Leifsonia.N8 wasidentified as Bacteria Proteobacteria Gammaproteobacteria XanthomonadalesStenotrophomonas maltophilia.The four strains which could degrade atrazinewere not reported at the home and abroad.W2 may be a new species whichbelonged to the Bacteria Proteobacteria γ-GammaproteobacteriaPseudomonadales Pseudomonadales Pseudomonas.Through the degradation experiment,the optimal degradation conditions ofodd and mixed strains were got. In cold condition, atrazine's degradationhalf-life of L1 is 4.4 day , L2 is 4.2day , W2 is 1.5day , N8 is 8.4day,thesedegradation half-life are shorter than other atrazine degradation strains whichwere reported.The starting concentration had no effect on the degradation ofmixed bacteria,and the mixed strains degradation rate reached 96.5% in 48h.Using PCR, the atrazine-degradation genes AtzABCD were identified inW2,AtzA was identified in N8.the AtzABCD genes revealed significanthomology (>99%) with the atrazine degradation genes of Pseudomonas sp.strain ADP.This result indicated atrazine degradation started with a hydrolyticdechlorination by W2 and N8.There were no atrazine-degradation genes instrain L1 and L2.Atrazine can be hydrolyzed and dehalogenated by mixedstrains.The biodegradation products of hydroxyatrazine ,deisopropylatrazineand deethylatrazine were comfirmed by GC/MS After quantitativedetermination of chloride ion and ammonia ion,it could be known that theatrazine were mineralized to CO2 and NH4+.3.The seepage tank was used in the lab to simulate the pollution ofgroundwater and the bioargumentation method was adopted . The resultsshowed that when the mixed strains at equal ration were injected into the pit,theatrazine's concentration of each sampling port was decreased rapidly, and for28#,29#,35#,41#, the degradation rate reached higher than 90%, after runningfor 21days, 28# reached 92.3%, 9# reached 94.9%, 35# reached 98.5% and 41#99.79%,the atrazine concentration was 1μg/L,which reached national drinkingwater hygienic criterion. The atrazine degradation rate in the outlet reached92.4%. With the increase of the flowrate, the concentration in the sample outletdidn't changed so much, which proved that to inject dominance microorganismsis an effective method for the remediation of groundwater pollution caused byno point source pollution.In the experiment , the bio-reactor was used for the rehabilitation of thegroundwater pollution caused by atrzine, and activated carbon was adopted asimmobilization carrier, and its optimal particle diameter is 0.5-1mm, pH is8.The activated carbon immobilized with microorganisms were filled in thereactor, another filled with activated carbon for comparison, the result showedthat the degradation rate reached higher than 99% in the 60 running days,however, the effluent concentration of the reactor filled with activated carbonincreased day by day when the absorption points were taken up.