The Influence Of Pb²⁺ And Physical-chemical Properties Of Carrier On Bioflim Extracellular Polymeric Substances （EPS）

With the development of industry, the heavy metal pollution is serious. Activated sludge process is not operated so good because of hydraulic retention time (HRT) and toxicity of heavy metal. The bioflim process has great effect for heavy metal wastewater treatment, becuse bioflim has more stabilized microecosystem. Besides, the extracellular polymeric substances (EPS) is the main component of bioflim, and not only dose it play an important role on keeping the structure and function of bioflim, but also keeps the mass transfer channels openning. However, the heavy metal could induce stress response of microoganism, and change the component, structure and function of EPS. Furthermore, it also could reduce the treatment effect of bioflim process. At present, the research of EPS mostly focus on the component, structure, extract methods and adsorption property, while the report which is about the influence of heavy metal on EPS is less to be seen.The surface physical-chemical properties of carrier are important to bioflim formation and EPS production. To research the influence of Pb2+and surface physical-chemical properties of carrier on EPS could (1) make the interaction between Pb2+and EPS;(2) show guiding significace by having a research on carriers selection and modification on heavy metal wastewater treatment.This research object on the interaction between EPS and Pb2+by Pb2+adsorption and stress culture with Pb+, and materials modification was uesd to study the influence of surface physical-chemical properties of carriers on EPS component. The research contents and results are as follows.(1) The active biomass and uonliving biomass both had the great adsorption effect. And the largest adsorption quantity of uonliving biomass was75.1%-87.8%of active biomass. With the culture time increased, the quantity of EPS increased as well. And the quantity of protein was more than that of polysaccharide all the time, and PN/PS was1.4-7.7. In this research, the C/N was3.3, and low C/N could promote microorganism to form protein through utilizing plenty of nitrogen. The resluts of stress culture showed that with Pb2+concentration increased, the quantity of EPS decreased firstly, and then increased. When Pb2+concentration was5-10mg/L, the active of microorganism decreased because of the toxicity of Pb2+. When the Pb2+concentration increased, plenty of EPS was produced for resisting the infringement from Pb2+.(2) The binding ability of organic and inorganic non-metal materials was stronger than metal materials, and the quantity of EPS was more much. Because the hydrophobic of organic materials was higher, the microorganism cell could adhere to the surface to growing and breed by hydrophobic interaction; the microorganism adhered tp the surface of glass and steel difficultly was because their surface were smooth, In addition there were more microorganism adhered to the surface of carriers after modification, including physical modification, NaOH modification, Fe2+modification and Mn2+modification. After physical modification, the EPS growth rate was189.9%, and the reason was that the roughness and specific surface area increased after physical modification, on the one hand, the contact area increased between microorganism and materials surface; on the other hand, roughened surface could protect the microorganism cell from sluicing. NaOH could remove the impurities which adhered to the surface of carriers and make internal functional groups be exposed, and it also increased the roughness of surface through alkali etch. After Fe2+and Mn2+modification, the EPS growth rate was202.76%and294.77%respectively. The surface of carriers would cover with Fe+and Mn+, and the microorganism could ahere to it through eletrostatic interaction. Furthermore, Fe2+and Mn2+were the component and activator of lots of bio-enzyme, so that they could improve the activity of microorganism and make more EPS be produced.(3) SEM (scanning electron microscope), FTIR(fourier transform infrared spectrometer) and XPS(X-ray photoelectron spetroscopy) were used to research the interaction mechanism between EPS and Pb2+. and the mechanism of the surface physical-chemical properties of carriers affecting component of EPS. SEM analysis results showed that bioflim was layered structure, the filamentous bacteria was the frame and there were lots of holes and channels. When EPS bonded with Pb2+, much of white precipitate appeared on the bioflim, distributed unevenly, and the number of holes and channels decreased. FTIR analysis results showed that there were lots of functional groups on bioflim,and some of adsorption peak skewed after EPS bonding with Pb2+. It indicated that Pb2+could bond with the functional groups of EPS but functional groups didn’t change. The functional groups which included the P and O were the main groups that interact with Pb2+. XPS analysis results showed that the characteristic peak of Pb appeared after bioflim adsorbing Pb2+, and the erea rate of characteristic peal of Ca and Mg decreased. It revealed that the quantity of Ca2+and Mg2+reduced on bioflim. Besides, when the steel was used as the carrier, the element content of bioflim changed after Fe2+and Mn2+modification. The quanity of Fe, Ca and Mg increased after Fe2+modification, and the quantity of Mn, Ca and Mg increased after Mn2+modification. It indicated that Fe and Mn could promote microorganism to absorb Ca2+and Mg2+.