Growth Regularity And Adsorption Characteristics Of Important Components In Surface Coatings Developed In Natural Waters

Natural water system is one of the most important ecosystems that have being contaminated by heavy metals. The speciation and transformation of heavy metals in the aquatic environments are affected significantly by many factors. It is recognized that adsorption at the solid-solution interface is important in determining the residence time and aqueous phase concentration of toxic metals in most aquatic systems. As one of the typical multi-phases, surface coatings have drawn great interest. They are ubiquitous in the environment, forming on all surfaces in rivers, lakes and wetlands, such as rocks and sediments, and account for a wide range of microbial organisms on earth. Iron oxides, manganese oxides, microorganisms and particulate organic materials in surface coatings have been identified as the most prominent solid phases controlling the behavior, transport, bioavailability and ultimate fate of trace metals in aquatic environments because of their high surface reactivities and large surface areas. The characteristics of natural surface coatings developed in different environments are diverse, while the metals associated with the surface coatings depend on not only the amount of the heterogeneous assemblages, but also the character of the surface materials. The researches concerning the growth behavior of important components in natural surface coatings and relevant determinative, as well as their characters, will give a great contribution to the mechanism understanding of the formation of freshwater surface coatings, the chemical reactions and transportation of trace heavy metals in aquatic environments. The particular research work focused on the growth regularity and characteristics of main components in natural surface coatings. In this thesis, the growth rules and trace metals binding behaviors of ferromanganese oxides and organic materials in surface coatings, which were developed under different conditions including development time, depths, seasons and waters, were studied firstly. Two expressions of organic materials (COD, TOC)and their correlativity were discussed, while the speciation, biomass and the corresponding changes of microorganisms phases in the heterogeneous surfaces were investigated. Additionally, the effects of suspended particulates in water on the amount and growth of iron, manganese oxides and Pb, Cd adsorption to surface coatings were evaluated. Finally, the influence and potential control of certain parameters such as water temperature, dissolved oxygen, photic intensity and pH value on the growth and behavior of main constitutes in the mixed mineral-organic assemblages were analyzed. To study the distribution of ferromanganese oxides in natural surface coatings, glass slides were submerged in Nanhu Lake at different depths for different time and in different seasons. The amounts and rates of iron, manganese oxides accumulating on surface coatings along with the influencing factors were studied. Pb and Cd adsorption was measured under controlled laboratory conditions, and the nonlinear least squares fitting was applied to estimate the corresponding Langmuir adsorption parameters to investigate the seasonal variation of iron, manganese oxides and organic materials in surface coatingsdeveloped periodically over three seasons, and to understand their influence on trace metals adsorption to heterogeneous surface materials. It was obvious that there was a significant increase in iron, manganese oxides in surface coatings with extending the development time scope, during which iron oxides were observed on the slides prior to manganese oxides, while manganese oxides would assembled gradually and exceeded iron oxides on a certain time. The amounts of metal oxides decreased with developing depths dropped. The accumulating rates of iron oxides were higher than those of manganese oxides, and the latter decreased in increase of water depths where surface coatings were collected with significant correlation, while no similar trend was found for iron oxides. In general, components in the surface coatings varied greatly with seasons altering and obtained higher concentrations in summer, following the order of summer > spring > fall, which was similar to Pb, Cd binding on the surface coatings. Correlation analyses results indicated that Pb phase association with manganese oxides and Cd phase association with iron oxides as well as manganese oxides in natural surface coatings developed in different seasons were statistically significant. The importance of ferromanganese oxides for Pb, Cd adsorption was evidenced. Two current expressions of organic materials in natural surface coatings, i.e. chemical oxygen demand (COD) and total organic carbon (TOC) were compared and researched theoretically to understand the growth and distribution regularity of organic phases. It was concluded that COD and TOC values of natural surface coatings varied notably with development time, depths, seasons and waters. Organic molecules adhesion was prior in the first stage of biofilm formation, and the relative concentrations of organisms were in descending order with timesequentially, while the entire COD and TOC were in ascending order with time. Generally speaking, the contents and proportions of organic materials in heterogeneous surfaces decreased with increase in water depths. Organic materials expressed as per mass surface coatings developed in Nanhu Lake in September were the highest, while total organisms amounts achieved the maximum in June, 2003, and those of surface coatings in different waters were dissimilar. There was a significant linear correlation between the data of COD and TOC, and a uniform regression equation was determined by comparison and test statistics, therefore appropriate characterization of organic materials would be employed according to actual material conditions. Moreover, the significant correlation between COD and TOC was proved theoretically in the work, and organisms in surface coatings would be quantified with COD effectively though there were other deoxidants in the composite mass besides carbonic organic compounds. The microorganism phases on natural surface coatings were analyzed qualitatively and quantificationally. The microbial species, including algae, protozoa and some metazoa, and the dominant organisms were determined. The changes of microbe fraction on surface coatings under photic conditions, as well as their aquatic microbial community parameters were investigated. It was revealed that the microorganisms and extracellular polymers they produced were essential materials forming natural surface coatings. Organisms on surface coatings were various, with diatom, green algae and infusorian identified as dominative microorganisms. The amounts of microorganisms ascended with time. Algae occupied the dominant fraction of the microbe in surface coatings and its concentration was higher than 105 unit/cm2, while that of protozoa was relativelower although the protozoa was crucial for the characters of biofilm. The speciation and the biomass were diverse along with the development of surface materials, with the dominant organism was diatom firstly and green algae sequentially, but the change of protozoa was negligible. The accumulating rates of microorganisms on surface coatings were relatively slower, and the microbial systems on the glass slides developed for about 10 d were basically mature. There were more species and higher biomass of organic materials in surface coatings developed in summer. In addition, relative higher temperature accelerated the propagation of diatom, and lower temperature benefited green algae. Study on the effect of suspended particulates in Nanhu Lake on the growth of ferromanganese oxides in surface coatings and their characteristic was conducted in two ways. Firstly, fresh suspended materials in the water were collected directly by filtration, and the relationship of crystallogram and organic/inorganic carbon concentrations between particulates and surface coatings in the same water were discussed. Secondly, surface coatings developed in waters with different particulates were obtained by means of stepwise filtration of water, to assay the effect of the amounts and diameter of suspended particulates in water on iron, manganese oxides and associated trace metal binding behavior. The comparison analysis showed that both of surface coatings materials and suspended particulates in water were amorphous, or little crystalloid mixtures. Moreover, relative concentrations of organic materials of both samples were similar. Thus it would be plausible that natural suspended particulates in water would contribute to the formation and the characteristics of surface coatings. There was a statistically significant correlation between thecontents of iron and manganese oxides on surface coatings and those in water. Noticeable, surface concentrations of manganese oxides were influenced obviously by particulates suspended in waters, and consequently greater particles was subject to form manganese oxides while iron oxides were affected insignificantly by the size of particulates. It was deduced here that surface coatings developed in water with particulates of greater diameters were apt to consist of constituents with greater size, and smaller the particulates in the water, smaller the possible components size in the surface coatings. Meanwhile, it was observed that all of the iron oxides in the surface coatings contributed to Pb adsorption, while manganese oxides in surface coatings developed in water containing suspended particulates with a greater diameter contributed most to Cd adsorption. In summary, Pb, Cd adsorption capacities of per mole ferromanganese oxides in surface coatings increased with the decrease of diameter of suspended particulates in water. In this thesis, some environment variables such as water temperature, dissolved oxygen content, photic condition and pH value in cultivation medium were also measured to determine their influence on the development of the main components in a heterogeneous matrix and associated trace metal scavenging abilities. The results suggested that there was a significant correlation between water temperatures and iron, manganese oxides accumulating on natural surface coatings, and relative higher temperatures facilitated microbial activity and the growth of metal oxides, especially for manganese oxides, whose optimal temperature was determined as 26 ℃. The concentrations of dissolved oxygen decreased with water depths increased. The amounts of ferromanganese oxides and organic materials in certain surface coatings were in direct ratio with DO in...