Environ. Sci. Technol. 2001, 35, 4805-4816
Nature and Transformation of Dissolved Organic Matter in Treatment Wetlands L A R R Y B . B A R B E R , * ,† JERRY A. LEENHEER,‡ TED I. NOYES,‡ AND ERIC A. STILES§ U.S. Geological Survey, 3215 Marine Street, Boulder, Colorado 80303, U.S. Geological Survey, P.O. Box 25046, MS 408, Denver, Colorado 80225, and U.S. Bureau of Reclamation, P.O. Box 25007, D-8570, Denver, Colorado 80225
by filtration/adsorption, volatilization, photolysis, and microbial transformations, the relative significance of each process being a function of chemical concentrations, environmental factors, and hydraulic retention time (HRT). A hierarchical analytical approach (12-16) is necessary for measuring the chemical characteristics of DOM when evaluating wetland transformations. Four treatment wetlands in the western United States (Table 1) were selected to evaluate the effects of climate, wastewater characteristics, and operating conditions on the nature and fate of DOM. The focus of the study was analysis of water collected during synoptic samplings at the wetland sites. The analytical measurements provided data on the concentrations and molecular characteristics of the DOM and were used to monitor changes during wetland treatment.
Experimental Methods This investigation into the occurrence, character, and transformation of dissolved organic matter (DOM) in treatment wetlands in the western United States shows that (i) the nature of DOM in the source water has a major influence on transformations that occur during treatment, (ii) the climate factors have a secondary effect on transformations, (iii) the wetlands receiving treated wastewater can produce a net increase in DOM, and (iv) the hierarchical analytical approach used in this study can measure the subtle DOM transformations that occur. As wastewater treatment plant effluent passes through treatment wetlands, the DOM undergoes transformation to become more aromatic and oxygenated. Autochthonous sources are contributed to the DOM, the nature of which is governed by the developmental stage of the wetland system as well as vegetation patterns. Concentrations of specific wastewaterderived organic contaminants such as linear alkylbenzene sulfonate, caffeine, and ethylenediaminetetraacetic acid were significantly attenuated by wetland treatment and were not contributed by internal loading.
Introduction Dissolved organic matter (DOM) plays a major role in biogeochemical processes in natural and treatment wetlands (1) and influences the transport characteristics, chemical interactions, and biological availability of trace elements and synthetic organic compounds (2). DOM consists of a continuum of macroscopic particles, biotic and abiotic colloids, dissolved macromolecules, and specific compounds (3). Wetlands are highly productive ecosystems, and DOM is simultaneously assimilated and produced; however, little is known about the chemical nature and fate of DOM in treatment wetlands (4, 5). Biological transformations can result in the formation of stable metabolites or complete degradation of specific components of the DOM (6). Free water surface treatment wetlands consist of semiaquatic emergent marshes that support a variety of biological, chemical, and physical functions and have been used to treat municipal, industrial, and agricultural effluents (7-11). Removal of contaminants by treatment wetlands is achieved * Corresponding author phone: (303)541-3039; fax: (303)447-2505; e-mail:
[email protected]. † U.S. Geological Survey, Boulder. ‡ U.S. Geological Survey, Denver. § U.S. Bureau of Reclamation. 10.1021/es010518i Not subject to U.S. Copyright. Publ. 2001 Am. Chem. Soc. Published on Web 11/03/2001
Sampling. Sampling at each site involved field measurement of temperature, pH, specific conductance, and dissolved oxygen (DO). Water was collected for analysis of total organic carbon (TOC), dissolved (5 yr) April 1995 sampling (Table 4); collect samples from primary clarifier (WWTP effluent); lagoon 1 effluent; lagoon 2 effluent; combined treatment marsh effluent; final enhancement marsh effluent Halsey, OR treatment wetlands at the Pope and Talbot non-chlorinated oxygen delignification Kraft pulp mill, located in western Oregon; operated by Oregon State University (OSU); secondary treated effluent is discharged into 10 pilot cells (∼0.01 ha each) in paired configurations (subsurface flow rock bed, fully vegetated with cattail, fully vegetated with bulrush, open water) all run in parallel; effluent from treatment wetlands is discharged to Willamette River; inflow to each cell, ∼6.5 × 104-3.3 × 105 L/d; HRT, ∼2-10 d; inflow BOD, ∼25 mg/L cool-wet climate, immature system (C9 aliphatic carboxylic acids and amines; >3-ring aromatic carboxylic acids and amines; chlorophyll and related pigments; LAS and optical brighteners
