Research On The Selection Of The Bacterium Degrading Hexachlorocyclohexane In Lower Temperature

The temperature is the important environment factor in themicroorganism vital activity, according to grows the temperaturecharacteristic, the microorganism may divide into 3 kindsapproximately: High temperature fungus, center warm fungus andlow temperature fungus. On the Earth, the cold environment occupiesthe very big area, even if in the tropics area, its winter temperature isalso low. Therefore studies on how is the microorganism under thelow temperature condition have the profound significance to thepollutant degeneration. This article take HCHs as the degenerationsubstrate, the research the low temperature microbial inoculumswhich degrades HCHs effectually under the low temperature . HCH, short for Hexachlorocyclohexane, is one kind ofpesticides which are toxic, fat-soluble. Although the use of it hasbeen banned in recent years, its residues in the environment is stillharmful to people , animals , other living things or even to ourecosystem., it is extremely difficult to break down, isomers of HCHsin the soil have long hydrogen half-life. Half-life of the isomerα is26 years;of the isomerγ is 42 years;and half-life of the isomerβ isthe most stable and the most toxic, it has the longest half-life, so it isthe main environmental pollution emission. On the degradation ofchlorine pesticide residues, there were reports about selectiondegradability microbial organisms and pure training degradation. Butthese research reports are rare about methods of degradation ofHCHs in low-temperature environment and selecting bacteriacategories. For an example, in Changchun city, the annual averagetemperature is 4.6 ℃. According to several years outdoorobservation, we found that remaining organ chlorine pesticides in thesoil and surface water in suburbs haven't depredated for six monthsin winter. Therefore, in low-temperature microbial degradation ofHCHs has broad prospects. This method not only can be used in thebiological restoration in cold soil and surface water but also can beused to break down organic pollutants in the deeper soil andgroundwater in warm areas.Through experiment, the effective microorganism for thedegradation of HCHs under lower temperature(≤9℃)among 18known strains in the lab were selected using HCHs as sole carbonresource,and by means of orthogonal experiment respetively ,theresults showed that the optimal conditions in which the HCHs wasdegraded by three effective strains includes:pH7.5, biomass ofinoculation6%,NH4Cl0.8g/L, KH2PO40.6g/L for strain No1;pH5.5,biomass of inoculation4%,NH4Cl0.8g/L, KH2PO40.6g/L for strain No2;pH6.5,biomass of inoculation2%,NH4Cl1.2g/L, KH2PO40.8g/L forstrain No3.Under the optimal conditions,the biodegradation rate forthree strains had already reached 39.62%,48.63% and 40.12% .respectively For the most effective stain No2,the isomerαandδ ofHCHs always reached 48.63% and 40.07%。Based on the above results,the amount of other influencingfactors such as the additional nitrogen source NO3-, trace elementFe2+and Ca2+ were also studied.It showed that the HCHs wasdegraded better under the proportionment of NO3-1.00g/L, Fe2+0.02g/L,Ca2+为 0.03g/L.In the paper, the cell grows were measuredas well,and the degradation curve,cell grows curved weredescribed.The identification of basic characteristics of variousstrains, including colony character,strains form and size of cells,andgram staining were given in the paper.In contrast experiments, In contrast experiments, under thecondition of pH=6.5,NH4Cl0.8g/L, H2PO40.6g/L,MgSO40.04g/L ,twostains were mixed each other in three stains, we configured 12 typesof vote plus. When the total vote bacteria of degradation was 8%,and Num 1:Num 2 is 1:3,the rate of degradation is thehighest ,reaching 56.3%.We also mixed the three stains under thecondition of pH=6.5,NH4Cl0.8g/L, KH2PO40.6g/L,MgSO40.04g/L.respectively in 9% and 6% of the volume formed four types ofbacteria vote ratio .when vote bacteria volume is 9%, and Num 1 :Num2 : Num 3 is 1:5:3, the highest rate of degradation was 63.27%,;when vote bacteria volume was 6%, and Num 1 : Num2 : Num 3 is1:3:2 ,the highest rate of degradation is 61.87%. Finally we knew,degradation rate of the three mixing stains is higher than degradationrate of one stain and any two mixing stains. The concerted effectbetween the various stains reduced the negative feedbacksuppression of intermediate product .and used abject materials morethoroughly. Moreover the use of mixing strains can enhance capacityof the resistance to bad conditions overall to and made the systemoperation more stable. The result showed that Num 2 play a primaryrole on degradation of HCHs both in the double stains mixed andthree stains mixed, and other stains have collaboration effect ondegradation. Therefore, it is significance to degrade HCHs incryogenic conditions by further study Num 2 stain.According to early reports, under the anaerobic conditionbiological degradation is feasible;various isomers of HCHs wererapidly degradable in flooding territories or lake mud. But in theconditions of, biological degradation was very rare reports, Ma Aizhiand other people got one microbe which able to get carbon sourcesonly from HCHs by separating HCHs from long-term soil pollution. Intheir test on cucumber basins and bowls, degradation rate of HCHs is84.3% in 15 days. But under the low-temperature and adequateoxygen conditions, studies on biological degradation of HCHs haven'tbeen reported. Therefore, this study should be a national innovation.It will open a new field for persistent organic pollutants biologicaldegradation under the low-temperature conditions.