Degradation Of Environmental Hormones4-tert-octylphenol By A Bacterium Isolated From Sewage Sludge And Its Immobilized Cells Application

In recent years, Chinese researchers have been focusing on the waste water treatments, but with no attention to the sewage sludge for a long time. Some reports on sewage sludge discuss the heavy metal pollution issues instead of the problem of environmental hormones and other organic pollution. With the increase of Chinese population and economic development of urban areas, sewage disposal facilities are widespread, and their treatment effects are continuously improved, to meet the demand of the amount of sludge daily produced by human beings. If discharge these sludges without proper treatments, it would cause serious pollution to the environment.As an environmental hormone, OP (Octylphenol, OP) is a kind of important fine chemical raw materials and intermediates, which would be a tremendous threat to human health and ecological safefy. Therefore, how effectively removing and degrading OP and other environmental hormones from the environment to reduce the hazards towards the environment and human beings has become a focus of attention of foreign and domestic scholars.Biological treatment has several advantages in environmental hormones in waste water and sewage sludge treatments, such as low cost, simple operation, high removal efficiency, no secondary pollution. To achieve this goal, we started from the perspective of biological treatment, to carry out the study on screening biodegradable strains to obtain highly effective strains. It provieds technical assurance to the environmental pollution control and ecological restoration projects regard to OP. This study includes findings as the following aspects:(1)Obtain a high efficiency4-t-OP degradation bacterium. A bacterial strain was isolated from activated sludge samples collected from the secondary sedimentation tank in the Tangwang Sewage Treatment Plant of Yangzhou City, and was designated as TW30. At40℃and pH6.0 and with addition of5mg/L4-t-OP and2%(v/v) inoculums of TW30,99.03%of initial4-t-OP was biodegraded after120hours culture.(2)Identify strain TW30by molecular biological approach. According to the analysis of its16S rRNA gene sequence, strain TW30was preliminarily identified as Acinetobacter sp. Because its similarity to Acinetobacter sp. JPB-1.07(EU652468) is99.9%.(3) Screen the optimal growth conditions of strain TW30. Its optimal conditions for4-t-OP biodegradation in the shaking flasks were at40℃and pH6.0and with addition of5mg/L4-t-OP and2%(v/v) inoculums of TW30. It is also proved that TW30can use4-t-OP as sole carbon source by setting the control of the solvent acetone.(4) The biodegradation kinetics of the degradation process by strain TW30. It is determined that4-t-OP degradation rate constants and half-lives at various4-t-OP concentrations and inoculum amount, different pH values and temperatures, and additional minerals and carbon sources. The biodegradation reaction fitted well with first-order kinetic model, with a degradation rate constant of0.875d"1and half-lives of0.8d. It fitting equation is y=-0.8929x+8.2202, r2=0.9831.(5) Investigate different environmental factors on the influence of degradation efficiency of strain TW30. Culturing5d under the optimal conditions, the degradation rate could reach99.03%, when the remaining4-t-OP concentration was48.3μg/L. Furthermore, degradation rate for4-t-OP was enhanced by increased level of temperature, addition of Ca2+or Mn2+, and was inhibited by the increase of4-t-OP initial concentration from5to25mg/L, and additional phosphates, NH4+, Mg2+, Fe2+, Na+, Zn2+, Cu2+, NaAc, or glucose.(6) Detect degradation products of4-t-OP and presume the degradation path. According to the GC-MS test results, the degradation products of4-t-OP were4-Isopropyltoluene, tert-Butylbenzene and4-Acetylbenzoic acid. It is inferred that the degradation pathway of4-t-OP is made of two parts:1)the break of Alkyl chain on the benzene;2)the break of hydroxy on the benzene; and generating some free activative groups which re-combined into the alkylbenzene, short-chain alkylphenols, Acetyl phenol, Alkyl acid, Alkyl aldehydes and other intermediates.(7) Investigate immobilized cell beads on the influence of degradation efficiency of strain TW30. The4-t-OP biodegradation by alginate immobilized cells of Acinetobacter sp. was compared with its respective free cells in different media. The effects of different bead densities, pH values and practical applications of artificial seawater and wastewater on the biodegradation rate of4-t-OP were investigated. The immobilized TW30cells could enhance the efficiency of4-t-OP degradation. The degradation rate and4-t-OP half-life were97.6%and0.7d, respectively.(8) Apply the immobilized cells in artificial seawater and wastewater to detect the removal of4-t-OP. Increasing level of bead amount could also improve the degradation effects. The immobilized TW30cells could degrade4-t-OP both in artificial seawater and wastewater. The degradation rates were87.7%and84.3%, respectively, besides their degradation rate constants are1.257d"1and1.305d-1and half-lives are0.5d and0.4d, respectively, indicating its potential application of removing and biodegrading4-t-OP under practical environment. Because of its simple operation, mild reaction conditions, less impact on the activity of microbial cells, higher cell capacity, high mechanical strength of this kind of immobilized cells beads, good stability and impermeability, this method is valuable in soil repair, sewage treatment, environmental protection and management measures.According to our findings, such as an efficient degradation bacterium TW30to degrade4-t-OP, elaborating the degradation rule, we provide strong support to environmental hormones pollution control and ecological restoration technique, of an extremely important environmental and social significance.