Adsorption And Biodegradation Of Atrazine In Soils By Clay Minerals Immobilized A Degradation Bacterium

Adsorption and biodegradation of atrazine in soils by clay minerals immobilized a degradation bacterium were studied. Fourier Transform Infrared Spectroscopy (FTIR) technology was applied to analyze the mechanism of atrazine adsorption on clay minerals. A bacterium was isolated from activated sludge by enrichment using atrazine as sole source of carbon and nitrogen. The bacteria were immobilized by clay minerals which had special micro-crystalloid structure and huge surface area. The growth situation of immobilized microorganism was observed by Environment Scanning Electron Microscope (ESEM). We conducted laboratory studies to examine the effect of biodegradation of immobilized carriers in different soils, reveal synergism mechanism between the adsorption of carriers and biodegradation of the microorganism. The findings will provide the theory for biological remediation of pesticide pollution in farmland, also will provide the new way for fast degradation of residual chemicals in soil. The concrete research contents and results were as follows:1. Adsorption and desorption of atrazine on clay minerals and soils were studied using the batch equilibration technique. Adsorption isotherms of atrazine were fitted to the Freundlich equation. Adsorption of atrazine on clay minerals increased with increasing concentration. The smaller the particle size of clay minerals, the more the adsorption of atrazine. The nanoscale clay minerals had higher adsorption capacity for atrazine than those of the corresponding clays. The adsorption capacity of clay minerals for atrazine followed the order nano-SiO2 > nano-montmorillonite > attapulgite > montmorillonite > SiO2. Desorption of atrazine showed significant hystersis which was indicated by the higher adsorption slope (1/nads) compared to the desorption slope (1/ndes). The desorption rate followed the order SiO2 > attapulgite > nano-montmorillonite > nano-SiO2 > montmorillonite. Average desorption rates of atrazine were 8.58%, 23.28%, 44.32%, 20.03%, 33.44% on montmorillonite, nano-montmorillonite, SiO2, nano-SiO2 and attapulgite.The adsorption of atrazine on soils was smaller than on clay minerals significantly. The adsorption capacity of the soil for atrazine followed the order red soil > vertisol > alfisol. The adsorption of atrazine was influenced by the physical and chemical properties of the soil. Organic matter content of red soil was higher, the adsorption of atrazine was more. 2. A bacterium which was isolated from activated sludge by enrichment using atrazine as sole source of carbon and nitrogen was preliminarily identified as Ochrobactrum sp., according to its physiological-biochemical characteristics, photos of ESEM and the similarity analysis of its 16S rDNA gene sequence.The bacteria reached logarithmic phase at 48 h, and degradation of atrazine was 47.08%. The bacteria were cultivated on the optimal ingredient of medium and the optimal method of cultivation. When the inoculum size was 4%, the value of OD600 was 3.97 after 48 h. When pH was 8, the value of OD600 was 2.79. When the optimal conditions were 6 g?L-1 glycerin, the other ingredient of medium were 2 times than common medium, the value of OD600 was 3.50. When adding 4 mL new medium after 24 hours, the value of OD600 was 3.46. Under those optimal conditions, the effect of bacteria's growth was better. 3. A bacterium was immobilized by clay minerals. The strains growed well on clay minerals and reached logarithmic phase at 48 h. The degradation rate of atrazine was larger significally when adding degradation bacteria into soils. The biodegradation capacity by immobilized microorganism on clay minerals was improved compared with free microorganism. The smaller the particle size of clay minerals, the more the biodegradation of atrazine. The effect of immobilized nano-clay minerals was better than corresponding clays.Atrazine degradation in soils can be described by first-order kinetic equation. The effect of degradation varied from different soils. The degradation rates of atrazine were 42.47%, 46.19%, 56.31% respectively, after adding free microorganism into vertisol, alfisol and red soil 28 d. When adding immobilized microorganism by montmorillonite, nano- montmorillonite and attapulgite, the degradation rates of atrazine were 52.16%, 63.97%, 65.78 % in vertisol, 59.28%, 63.91%, 65.16% in alfisol, and 68.03%, 76.59%, 72.09% in red soil. The degradation rates of atrazine in the soil without microorganism was 29.16% in vertisol, 30.63% in alfisol, 41.47% in red soil. The (t1/2) of atrazine was 36.9 d in red soil,49.1 d in vertisol,and 55.0 d in alfisol without microorganism. When adding immobilized microorganism by nano-montmorillonite, half-life was 16.3 d,25.3 d,21.7 d respectively.