Changes In Physical And Chemical Properties Of The Medium During CO₂ Enrichment By Fermentation Of Organic Wastes And The Effect Of Its Residues On Improving Soil Fertility

Composting of organic wastes (crop straw and animal manure) is a process of fermentation and microbial decomposition under the conditions of artificial regulation of water, C/N ratio, pH, and ventilation to produce organic fertilizer. It is the fundamental way to achieve the reduction, recycle and safe treatment of the organic wastes. Compost with maturity and stability characteristics can not only improve the soil physical and chemical properties, but also increase crop yields and the quality of agricultural products. This research investigated the effects of fermentation process of organic wastes for CO2 enrichment in greenhouse on the antibiotics degradation and the changes of temperature, pH, C, N, microbial population and pathogenic bacteria in the fermentation medium. After modifying the extraction method of tetracyclines (TCs) in soil and compost, as well as the detection method of TCs using HPLC, the degradation of TCs during composting and the sorption of TCs in soils with addition of compost were studied. The reaserches on the inhibition and mechanism of antagonistic bacteria on cucumber and tomato were also carried out by a series of experiments such as sitzkrieg testing of antagonistic bacteria to pathogenic bacteria, the effect of fermentation residues inoculated with antagonistic bacteria on improving soil fertility and promoting crop growth and so on. The main results obtained from experiments are as follows:1. Modification on the extraction method of TCs in soil and compost and determination method using HPLCThe Oxytetracycline (OTC), Tetracycline (TC) and Chlortetracycline (CTC) in soil and compost could be extracted by a mixture solution of 1 mol·L-1 NaCl/0.5 mol·L-1 oxalic acid/ethanol (25/25/50, v/v/v), with the recoveries from 76.0% to 92.5%. The HPLC method was used to determine the three TCs at the same time. The results indicated that the three TCs could be completely separated in 20 min by a column of Agilent Eclipse XDB-C8 (4.6×150 mm,5μm). The mobile phase was 0.01 mol·L-1 oxalic acid-ACN-MeOH (79/10.5/10.5, v/v/v) at a flow rate of 1.0 mL·min-1. The injection volume of sample solution was 5 pL and the UV detector wavelength was at 268 nm. An external standard method was employed for the quantification. The linear correlation coefficients for three TCs under the concentration of 0-10 mg·L-1 were all larger than 0.999.The sorption experiment showed that the adsorption of OTC, TC and CTC to Haplaquents, Kandiudox, and/or mixtures of compost and soils fit Freundlich model well. The adsorption quantity increased with the increasing concentration of TCs. The adsorptivity of TCs in matrices was in sequence:CTC>TC>OTC. The adsorptivity of TCs in compost was significantly in soils and mixtures of compost and soils. The adsorptivity of Kandiudox was higher than that of Haplaquents. The adsorption of TCs in soils was affected by pH, content of organic carbon and content of CEC. Compost added into soils could enhance the sorption of TCs. The more compost was added, the higher sorption of TCs happened. When the OC content in the soil amended with compost reached 5%, the influence of OC and CEC on sorption became dominant. The trend of sorption of TCs in different electrolyte solutions was 0.01 mol·L-1 KCl≥0.01 mol·L-1 CaCl2. Degradation test showed that the reversible isomerization reaction occurred to TCs. The degradation rate was affected not only by characteristic of soil, but also by the structure and characteristic of tetracycline.2. The changes of temperature, pH, C, N, microbial population, pathogenic bacteria and antibiotics in the medium during CO2 enrichment by fermentation of organic wastesIt was showed by the results of temperature continuous record that the temperature of fermentation medium increased very quickly. It reached the highest temperature of 64.5℃at the 5th day of fermentation. Finally, the temperature higher than 50℃was lasting for 12 d, hiher than 55℃for 7 d. The quantities of fecal coliform group were between 10-1-10-2 after 35 days'composting, which completely met the demand of hygienic standard for innocent treatment of feces (GB7959-87).At the beginning of compost, decomposition occurred to the organic waste due to the microbial activity. NH4+ and NH3 were produced, which resulted in the pH rising rapidly from 7.09 to 8.06 of the maximum at the 14th day. After that, pH decreased gradually, and it increased slightly again to 7.53 at the end of composting. The concentration of NH4+-N also increased first and then decreased rapidly, stable at 0.45 g·kg-1 at last. The concentration of NO3--N reached to 0.67 g·kg-1 finally and the content of organic carbon was 233 g·kg-1. The C/N ratio declined to 18. At the end of composting, the losses of total C and N were 69.8% and 38.0%, respectively.During composting, the trends of changes in bacteria, actinomycetes and fungi were slightly different. The number of bacteria presented in a trend of increase, then decrease and increase again, while the trends for actinomycetes and fungi were increase first, then decrease, and at last reached a plateau. Experiment of germination indices (GI) showed that the GI of fermentation residues reached 98%. In addition, the tetracyclines could be reduced rapidly by composting. CTC and both of OTC and TC could be completely degradated by the composting for 14 d and 42 d, respectively. These results indicated that composting for CO2 enrichment could achieved the aims of reduction, recycle and safe treatment for organic wastes. The results of sorption test demonstrated that soil by adding compost could significantly enhance the sorption ability of tetracyclines and reduce their environmental risks.3. Inhibitory effect of Bacillus cereus, Bacillus subtilis Cohn and effective microorganisms (EM) against Fusarium oxysporum f.sp.The sitzkrieg experiment results showed that the Fusarium oxysporum f.sp. was inhibited obviously by Bacillus cereus, Bacillus subtilis Cohn and EM. Bacillus cereus had the greatest inhibition effect against the four Fusarium oxysporum f.sp., with the inhibition ratio between 20%-50%. The ratio of Bacillus subtilis Cohn and EM against Fusarium oxysporum f.sp. was 6.7%-34.8%. The results of spore germination tests showed that the spore germination of Fusarium oxysporum could be effectively inhibited by the solution of antagonistic bacteria or EM with dilution rate less than 20 times, and completely suppressed by the antagonistic bacteria or EM with the concentration of 108 cfu·mL-1.4. Effects of the fermentation residues inoculated with antagonistic bacteria on the remediation and improvement of continuous cropping soil in greenhouseThe results obtained from the experiments of tomato carried out on a grayey clayed paddy soil and fluvo-aquic soil with continuous cropping for 5 and 10 years, respectively, showed that the application of fermentation residues inoculated with Bacillus cereus, Bacillus subtilis Cohn and/or EM could significantly increase the pH and decrease the EC of the degradation soils, especially in the treatment inoculated simultaneously with three kinds of microbes, which would effectively alleviate soil acidification and secondary salinization. The content of available N, P, K and organic matter were also increased significantly, which could facilitate crops on nutrient absorption and utilization and be beneficial to soil fertility. Furthermore, the application of fermentation residues could also improved and promoted soil microflora and enzyme activity, which played a role in resolving the continuous cropping obstacle in greenhouse. Pot experiment showed that the plant height, fresh weight and dry weigh of tomato were increased, indicating a good effect of the fermentation residues inoculated with beneficial microorganism on promoting tomato growth and development.