Abstract:

       In order to identify the sewage irrigation pollution of unsaturated zone and groundwater in the suburb of Shijiazhuang City, common bacteria in the soil and water of sewage irrigation area were cultivated through maximum probable number method(MPN method). Iron-oxidizing bacteria were cultured and analyzed by the change of the number of iron-oxidizing bacteria in the soil and water and its relationship between environmental factors,this paper indicates that the best aqueous environment for the growth of ironoxidizing bacteria in the study area is pH=7.4,showing in the alkaline and neutrality condition, ORP=318 mV,meaning in an oxidation environment, temperature=15 ℃, DO=4.7-7.8 mg/l and depth=40 m,and the amount of bacteria is up to 1.1 × 10⁵ cells/ml;the best soil environment is that pH is 8.07-8.28, water content is 19.0%-22.9%, lithology is silt, depth is less than 3.5 m,and the amount of bacteria is up to 5.1 × 10⁷ cells/g. The result shows that the shallow groundwater and the surface soil(depth<3.5 m)in the study area are polluted at different degrees because of long-term sewage irrigation. Iron-oxidizing bacteria quickly rear in soil and water environment, and constantly oxidize water-soluble  Fe ²⁺ into water-insoluble Fe ³⁺ , this process affects the water and soil environment of the study area, then changes the ecological environment of the study area.

Key words: sewage irrigation, iron-oxidizing bacterium, influencing factor, oxidation