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Introduction Fernando L. Rosario-Ortiz* Department of Civil, Environmental, and Architectural Engineering, University of Colorado, Boulder, Colorado 80309 *E-mail:
[email protected].
The study of dissolved organic matter (DOM) has fascinated researchers in different fields of science and engineering for many decades. The impact that DOM has on a wide array of environmental processes has resulted in the development of a multidisciplinary community of researchers all focusing on using different analytical techniques and experimental design to better understand DOM. This book offers select case studies focusing on the advanced characterization of DOM in differet environments and with respect to different processes.
Organic Matter The study of the physicochemical properties of dissolved organic matter (DOM) focuses on answering one key question: How do we accurately predict (and potentially minimize) the effect that DOM has on a wide array of processes? These processes include metal binding, fate and transport of organic compounds, formation of disinfection byproducts, light penetration in ecosystems, etc. Given the broad scientific impact of these processes, the study of DOM extends over many different disciplines ranging from ecology, environmental engineering, organic geochemistry, marine and atmospheric sciences, and analytical chemistry. As a result, the study of DOM may represent one of the most interdisciplinary topics in basic and applied sciences and engineering. Perhaps the key to the multidisciplinary nature of the study of DOM is the lack of a fundamental understanding of the chemical structure of this material. The concentration and physicochemical properties of DOM are a function of the source of the material (e.g., terrestrial vegetation and biological processes within the water column) and the different processing mechanisms that occur in the environment (e.g., photolysis, settling, and microbial degradation). In spite of the chemical © 2014 American Chemical Society Rosario-Ortiz; Advances in the Physicochemical Characterization of Dissolved Organic Matter: Impact on Natural and ... ACS Symposium Series; American Chemical Society: Washington, DC, 2014.
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complexity of DOM, there have been advances in understanding its effects on specific processes. For example, it is well known that the degree of aromaticity (as measured by NMR and characterized as the specific UV absorbance or SUVA) is a good predictor of the relative DOM source and of the formation of disinfection byproducts during water chlorination. Although there have been great advances in understanding, the development of a chemical model that could be used in a priori predictions of DOM physicochemical properties remains a distant goal. While historically the focus has been on the characterization of DOM from either terrestrial or aquatic origins, there has been a shift to include other sources of organic matter that are important for understanding different environmental processes. For example, the contribution of algae-derived organic matter to the DOM pool in source waters for potable water production has gained attention over the past decade. This source of organic matter, termed algogenic organic matter (AOM), includes both intracellular and extracellular organic matter (IOM and EOM), and is characterized by differences in molecular weight and composition. In addition, the characterization of wastewater-derived organic matter, known as effluent organic matter (EfOM), has also gained attention, especially as the field of water reuse has gained importance. EfOM includes background DOM plus contributions from biological processes within wastewater treatment and as such is described as closer to aquatic-derived DOM in terms of aromaticity and fluorescence properties. Another interesting extension of DOM research is the characterization of organic mixtures in aerosols and fog. When the organic carbon in aerosol samples is extracted in water and characterized using typical DOM analytical tools, the results indicate the presence of what has been termed HUmic-LIke Substances, known as HULIS, or in more general terms water-soluble organic carbon. HULIS, which is formed in part by the chemical reactions involving secondary aerosol formation, is a relatively new field and has important implications for the understanding of carbon transport in the atmosphere. These are just a number of examples where the study of DOM is being redefined to characterize other material, which shares some of the same complexity and importance that first motivated the study of DOM.
Book Organization The development of any book focusing on DOM faces the immense challenge of defining a scope that is somewhat representative of the larger universe with regards to DOM research. In addition, there are other volumes being published that focus on specifc aspects of DOM, including fluorescence characterization and physicochemical properties. The objective of this volume is to give the reader an overview of a select number of case studies where advanced understanding of DOM has resulted in a better understanding of a specific process. Following this introductory chapter, the book includes three main sections. The first section of this volume, titled “Characterization of Dissolved Organic Matter,” deals with the topic of DOM characterization in general. The first chapter offers a detailed examination of the most impactful publications with regards to DOM characterization over time. The authors offer their interpretation 2 Rosario-Ortiz; Advances in the Physicochemical Characterization of Dissolved Organic Matter: Impact on Natural and ... ACS Symposium Series; American Chemical Society: Washington, DC, 2014.
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of the importance of different publications through the analysis of the number of citations and the Hirsch-index. The authors also provide what they term “classical papers” over the past five decades. The second chapter is an excellent review of the application of fluorescence for the characterization of DOM. The authors review the use of PARAFAC models for DOM characterization in surface and ocean waters. The third chapter explores the acid/base properties of DOM. The last chapter in the first section of the book offers a detailed review of water soluble organic carbon in aerosols, an emerging field within atmospheric research. The second section is titled “Impact of Dissolved Organic Matter on Environmental Processes.” This section offers the reader a glimpse into the impact that DOM has on environmental processes, including interactions with contaminants, oxidants, and photochemical processes in wastewater-derived EfOM. The first chapter in this section is a review of the role organic matter plays as a natural xenobiotic. This work summarizes different aspects of DOM that are important for biological processes in the water column. The second chapter describes recent work on the sorption of hydrophobic organic contaminants to DOM, specifically focusing on DOM impacted by storm runoff. This chapter is followed by recent work on the study of the interactions between DOM and hydroxyl radicals using polymers to evaluate the role of molecular weight on the reaction rate constant. The next chapter focuses on the characterization of organic phosphorous in the Everglades region. The last chapter in this section describes the study of DOM and EfOM photochemical and photophysical properties as a function of molecular weight. This work focuses on measuring quantum yields for the formation of different reactive intermediates, including hydroxyl radical and fluorescence. The last section of the book is titled “Impact of Dissolved Organic Matter on Water Treatment.” The first chapter describes new work on the role of molecular weight on the formation of DBPs. This is an interesting topic as there are potential differences in the chemical composition of the different molecular weight components. The second chapter investigates the sources and sinks of DBPs in DOM during treatment, focusing on coagulation. The third chapter examines changes in DOM and reactivity towards DBPs for samples collected during extreme weather events. Lastly, an evaluation of fluorescence for DOM removal by coagulation compares different data analysis methods and their resulting interpretations.
Concluding Remarks As we move into the next decade of work in DOM characterization, we will continue to uncover different aspects of this mixture’s complex chemistry. The advent of ever more powerful analytical techniques and the vast amount of knowledge already amassed will continue to allow scientists and engineers to investigate different processes. Even though we may never be able to offer a complete chemical model representative of all DOM properties, continuing advances will allow researchers and engineers to fine tune our understanding of DOM and its impact on the numerous processes which are of interst to us. 3 Rosario-Ortiz; Advances in the Physicochemical Characterization of Dissolved Organic Matter: Impact on Natural and ... ACS Symposium Series; American Chemical Society: Washington, DC, 2014.
