Study On The Screening Of Degradable Microorganisms For Organophosphorus Pesticides And Degradation Conditions

The use of pesticides can ensure stable production and increase production of agriculture. However, it may bring some influences on soil, air and water environment. Some organophosphorus pesticides have some characteristics of strong toxicity, slow degradation and long action time, and may exist in the soil for a long time, which causes pesticide residues to be superstandard and does harm to human health through food chain. Therefore, it is of great significance to study the degradation of organophosphorus pesticides. Conventional chemical degradation method is to hydrolyze organophosphorus pesticides using strong base, but it is low efficiency, and many hydrolysates are also the environment pollutants. Microorganisms are important bio-resources in bioremediation because they have many kinds, and are fast variation and easy to manipulate. Some studies indicated that it is effective to dispose organophosphorus pesticides in the environment using microorganisms or degradation enzymes produced by microorganisms and has shown promising application prospect. However, microbial degradation abilities have large differences between the laboratory and natural environment. How to sufficiently display the performance is a problem to be deep studied.In order to reduce the hazards to the organisms and environment owing to organophosphorus pesticides, and decrease some unnecessary losses, it is increasingly urgent to study the degradation methods. Wherefore, many researchers in the world has developed effective methods to degrade organophosphorus pesticides, such as biological method, activated carbon absorption, alkaline hydrolysis, wet oxidation, and photocatalysis. At present, biodegradation is commonly used in our country, and it is particularly important to screen and purify the strains. Therefore, it is urgent to find predominant strains to degrade organophosphorus pesticides effectively, and study the optimal growth conditions of microorganisms and the optimal degradation conditions for organophosphorus pesticides in detail, which is the problem to be solved in this thesis.In this study, gas chromatography method was used to determine organophosphorus pesticides, while spectrometry to investigate the growth status of microorganisms. The retention times of rogor, omethoate and methamidophos are 8 min, 4 min and 2.5 min, respectively. The external standard method was used to analyze organophosphorus pesticides quantitatively.In order to get microorganisms which can degrade organophosphorus pesticides effectively, the active sludge of swage disposal pool in a pesticide plant was used as bacterial source, 14 strains was separated by domestication and screening, and the culture characteristics and individual shape were observed. Thirteen strains were preliminarily identified as Pesudomonas, and one strain was Acinetobacter according to Berger's System Bacteriological Handbook. Among them, Pesudomonas had better degradation effect for organophosphorus pesticides.The results showed that L₁, M₁, and N₁ strains had good degradation effect for rogor, omethoate and methamidophos, respectively. After 7 h, the degradation rates were 46.99%, 46.71% and 45.45% for the three pesticides, respectively. Moreover, the degradation effects of the strains were good for low concentration of organophosphorus pesticides. With the concentration of organophosphorus pesticide increasing, the degradation rate decreased gradually, but the absolute amount could be increased. This may be related to the toxic action of organophosphorus pesticides with high concentration to the strains and short disposal time. Because the residual amount of pesticides in soil is far lower than the use amount in this study, it is hopeful to obtain good degradation effect if the strains are used to dispose the residual organophosphorus pesticide in soil. Therefore, L₁,M₁ and N₁ strains were used as experimental strains, their growth conditions and the gradation conditions for organophosphorus pesticides were studied further.The growth conditions of L₁, M₁ and N₁ strains, such as temperature, pH and NaCl concentration were studied using orthogonal experiment. The results showed that temperature has great influence, i.e. the strains grew rapidly at 30-40℃, while slowly at 20℃, and low temperature could inhibit the growth of the strains. The initial pH also had distinct influence, i.e. the strains grew rapidly under the condition of neutrality and alkalinity (pH≥7). Therefore, it is very important to adjust pH for the growth of the strains. The influence of the concentration of NaCl solution was very low. No interaction of the three factors could be found. The growth status of the strains was good at 30-40℃, pH of 7.0, NaCl concentration of 0.5 g/L.Under the conditions of 125 mg/L-1000 mg/L of organophosphorus pesticides, 25℃-30℃, pH of 7-9, and degradation time of 3 d, the degradation effect was good using the strains. No interaction of the factors could be found. Thus, control the degradation conditions can improve the degradation rate of organophosphorus pesticides. The strains could tolerate 2500 mg/L of organophosphorus pesticides, and could degrade 1000 mg/L of the pesticides which was higher than the maximum amount (800 mg/L) in the operating instruction for organophosphorus pesticide. These results indicated that the strains could degrade organophosphorus pesticide effectively.How to create the optimal growth conditions of the 'strains and metabolic environment for organophosphorus pesticide is necessary to obtain the optimal effect removing phosphorus. Many factors can influence on the biologically removing phosphorus, and different factor can obtain different effect. Only to find the optimal combination of all the factors, the best disposal effect can be achieved.