TREATMENT WETLANDS - CHAPTER 11 ppt

403 In addition to the pollutants discussed in earlier chapters, wastewaters typically contain many other substances. Some of these elements can cause problems when discharged to receiving waters, and their removal must be considered dur- ing design. These additional materials include salts, acids, bases, macronutrients, micronutrients, and heavy metals, and may be categorized in a number of ways. Salts include com- pounds that readily dissociate in water to form charged ions that may or may not be used as nutrients for plant and animal growth. Common examples of salts are sodium chloride (NaCl) and gypsum (CaSO 4 ). Acids release a hydrogen ion when they dissociate (e.g., hydrochloric acid, HCl), and bases release a hydroxyl ion (e.g., ferric hydroxide—Fe(OH) 3 ). Spe- cic environmental conditions determine whether the cations (positively charged ions) and anions (negatively charged ions), formed when a salt, acid, or base is dissolved in water, are chemically or biologically active. Collectively, ionic materi- als contribute to the electrical conductivity (EC) of the water. When ionic materials are combined with dissolved nonionic materials, the result is the total dissolved solids (TDS) con- tent of the water. Nitrogen and phosphorus, discussed in Chapters 9 and 10, are examples of macronutrients, which have strong bio- geochemical cycles in a wetland. Sulfur also is typically present in variable but potentially high concentrations, and has just as powerful inuences on wetland functioning. The magnitude of these inuences is just emerging as a control- ling factor on wetland performance for a number of other pollutants. Most obvious is the role of suldes in immobiliz- ing trace metals. Iron, aluminum, and manganese are ubiquitous in wet- lands, but are present at elevated concentrations in mine drainage waters and the wetlands constructed to treat them. A trace metal can be either a required micronutrient or toxic, depending on the concentration. For example, copper and zinc are essential elements for plants and animals at low con- centrations, but they are toxic to some organisms at elevated concentrations. However, for some trace metals, such as cad- mium and lead, essentiality for plants or animals has never been found. In this chapter, many of the important elements are discussed, but the list does not include all the elements that may be found in waters, or all those that might require treatment. The use of a wetland treatment system to modify the concentration of elements depends on how the elements interact with the wetland environment and on the wetland designer’s knowledge of design factors that can enhance or diminish these processes. There is a rapidly growing body of knowledge about how wetland treatment systems affect specic trace elements. A thorough, updated review of the scientic literature is recommended for project design. A number of substances are considered measures of water quality, but are seldom of concern as pollutants to be treated in constructed wetlands. These include common metals (e.g., sodium, potassium, calcium, and magnesium) as well as halogens (e.g., uorine, chlorine, bromine, and iodine). Together with sulfate, these compounds often dominate the total ion content of natural waters and wastewaters. In total, they form the major part of EC and TDS. Sulfate is of spe- cial importance, because of its active biogeochemical cycle, and interactions with trace metal removal. In some treatment wetlands, several of these collective water quality parameters have become important in their own right. 11.1 HALOGENS Chloride and bromide are widely regarded as being “conser- vative” in wetland environments, meaning that they interact with the ecosystem to a very limited extent. Therefore, they can be used as tracers of water movement in the wetland. Usually, chloride is present at concentrations that preclude its use as an injected tracer, but it sometimes serves as a means of conrming the wetland water budget. Fluoride is usually a very minor trace constituent in aquatic systems, but there are industrial efuents that contain relatively high concentra- tions. The aluminum industry is one such source, including leachates from solid waste disposal sites. Bromide is often present at low background concentrations, and injected bro- mide may then be used to trace internal water movements. Very little is known about the fate and transport of iodine in freshwater systems. CHLORIDE AND CHLORINE U.S. EPA (2002a, 2006) sets a criteria maximum concentra- tion (CMC), which is an estimate of the highest concentration of a material in surface water to which an aquatic community can be exposed briey without resulting in an unacceptable effect. The value for chloride is 860 mg/L, and for chlorine is 19 µg/L. U.S. EPA (2002a, 2006) also sets a criterion con- tinuous concentration (CCC), which is an estimate of the highest concentration of a material in surface water to which an aquatic community can be exposed indenitely without resulting in an unacceptable effect. The CCC value for chlo- ride is 230 mg/L, and for chlorine is 11 µg/L. The chlorine content of wetland plant tissues has not been measured often. Results from two projects are shown in 11 Halogens, Sulfur, Metals, and Metalloids © 2009 by Taylor & Francis Group, LLC 404 Treatment Wetlands Tables 11.1 and 11.2. The Oxnard, California, systems were exposed to high chloride, and developed high leaf tissue concentrations (5–40 g/kg dry weight, or 0.5–4.0%). Presumably, much of the chlorine associated with the dry matter was originally in solution in the plant water content, which is 70–80% of the wet weight. Therefore sap concentra- tions would be about ve times lower. Interestingly, Salicor- nia spp. is a hyperaccumulator of chlorine (Table 11.1). It is also notable that roots contain much less chlorine than the shoots. Standing dead and litter of Typha latifolia were found to contain much less chlorine than live leaves at the Hough- ton Lake, Michigan, treatment wetland (Table 11.2). Chlorine is biologically interactive in wetland eco- systems. It is inuential in the osmolality salinity balance, but metabolic utilization does not usually cause changes in water concentrations (Wetzel, 1983). However, there are cir- cumstances in which utilization can be measured. Xu et al. (2004) measured chloride and sulfate proles in vertical ow mesocosms with Typha latifolia in sand, during growth of the plants. The hydraulic loading rate was low (0.66 cm/d), and consequently, transpiration was an important effect (about 0.3 cm/d). Sulfate was added at concentrations far in excess of any potential plant requirements (80 mg/L SO 4 -S). As the water traversed the root zone, sulfate concentrations increased to about double their inlet value, which was strictly attributed to transpiration losses. No increase occurred in unvegetated controls. However, the proles of chloride were very different: virtually all of the inlet chloride was absorbed in the mesocosms, from a starting concentration of about 5.0 mg/L. Given the biomass increase of the plants, chloride removal would have produced a chloride content of the cat- tails of about 4,000 mg/kg, which is at the low end of the range measured for Typha (Tables 11.1 and 11.2). The more typical situation is an overabundance of chlo- ride entering the wetland. Because of the relatively low biological demand for chloride, the total chloride mass is usually relatively constant between the inows and outows and storages of a treatment wetland (Table 11.3). Therefore, the wetland chloride mass balance can be used to conrm the water budget. TABLE 11.2 Halogen Content of Biomass Compartments for Typha latifolia in the Houghton Lake, Michigan, Treatment Wetland in 1991 Water Live Leaves Standing Dead Litter Roots + Soil Control Zone Chlorine 5–15 13,300 195 727 300 Bromine — 25 2 43 37 Iodine — — 3 13 9 Disc harge Zone Chlorine 100–125 34,700 369 1,105 858 Bromine — 46 11 50 51 Iodine — — — 17 11 Note: Units are mg/kg for tissues, and mg/L for water. Source: Unpublished data. TABLE 11.1 Chlorine and Fluorine Concentrations in Plant Tissues at Oxnard, California Chlorine Fluorine Plant Water Shoot Root Water Shoot Root Typha latifolia 300–340 8,910 7,650 2.5–2.8 352 155 Scirpus americanus 300–340 19,100 2,920 2.5–2.8 232 343 Juncus balticus 300–340 6,040 2,490 2.5–2.8 280 453 Anemopsis california 300–340 28,600 7,080 2.5–2.8 3,290 160 Jaumea carnosa 300–340 36,500 5,330 2.5–2.8 690 389 Distichlis spicata 300–340 5,820 4,470 2.5–2.8 336 518 Potemogeton pectinatus 300–340 4,910 9,910 2.5–2.8 134 389 Salicornia virginica 300–340 67,300 7,570 2.5–2.8 402 110 Monothochlore littoralis 300–340 4,400 1,360 2.5–2.8 204 213 Note: Units are mg/kg for tissues, and mg/L for water. Source: Data from CH2M Hill (2005) Additional testing for the Membrane Concentrate Pilot Wetlands Project. Report to the City of Oxnard Water Division, Oxnard, California, United States. © 2009 by Taylor & Francis Group, LLC TABLE 11.3 Examples of Conservative Materials Entering and Leaving FWS Treatment Wetlands System Wetland Years HLR (m/yr) EC In (µS/cm) EC Out (µS/cm) Chloride In (mg/L) Chloride Out (mg/L) TDS In (mg/L) TDS Out (mg/L) Pass-Through Tres Rios, Arizona Hayeld 1 8 41.2 1,559 1,497 259 257 902 Tres Rios, Arizona Hayeld 2 8 55.8 1,558 1,511 254 253 913 Tres Rios, Arizona Cobble 1 8 119.5 1,500 1,494 264 272 934 Tres Rios, Arizona Cobble 2 8 65.2 1,500 1,488 263 264 934 Brawley, California All 4 33.9 4,503 4,713 — — — Imperial, California All 4 24.9 2,718 2,642 — — — Orlando Easterly, Florida WP1–MM7 10 11.5 550 522 66 65 — Estevan, Saskatchewan All 10 10.5 2,332 2,457 198 201 1,644 Isanti-Chisago, Minnesota All 3 36.5 1,367 1,147 79 76 770 ENRP, Florida All 6 11.3 1,033 1,037 160 167 — Connell, Washington Full scale 1 21.8 2,890 2,740 — — — Purdue University, Indiana 15 wetlands 2 15.5 4,658 3,788 — — — Newton, Mississippi 12 wetlands 2 — — — — — 710 Richmond, New South Wales Myriophyllum 2 26.8 772 707 — — — Benton, Kentucky Cattail 1 19.7 324 362 — — — Benton, Kentucky Woolgrass 1 20.8 324 348 — — — Albright, West Virginia All 10 26.4 — — — — 1,334 Springdale, Pennsylvania All 10 35.8 — — — — 1,818 Oxnard, California Train 1 1 19.8 4,500 4,650 215 255 4,200 Pensacola, Florida 6 pulp and paper 2 18.4 2,125 1,931 — — 1,458 Boney Marsh, Florida River 8 7.4 — — 16.5 15.9 — A nomalies New Hanover, North Carolina Full scale 1 0.79 6,256 1,468 2,753 411 5,742 Incline Village, Nevada Full scale 5 0.54 — — 39 155 269 Ouray, Colorado Full scale 5 95 — — — — 326 © 2009 by Taylor & Francis Group, LLC 406 Treatment Wetlands Chloride can serve as a tracer of water movement, espe- cially in the analysis of the very slow underground movement of water. For instance, the progress of a chloride front from rapid inltration basins, underground to a monitoring well on the edge of the receiving wetland, and then out into that wet- land, is shown in Figure 11.1. The wastewater treatment plant at Genoa-Oceola, Michigan, received very high chlorides (about 400–550 mg/L) because of the widespread use of water softeners in the region. The treated water was discharged onto rapid inltration basins on a hilltop adjacent to a wetland. The hydrologic gradient moved the water slowly toward the wet- land, and the high chloride arrived in wells at the wetland edge after about three years. After about six years, the wetland sur- face waters reected the chloride of the wastewater, with some dilution from the other ows in the aquifer. Di sinfection: Chlorine in Wetlands Free chlorine is toxic to most life forms, and is one of the most frequently used wastewater disinfectants. There are implications for treatment wetlands that receive chlorinated efuents, because the residual toxicity may negatively inu- ence the microbial communities within the system. Some of the free chlorine added during disinfection is converted in solution to chlorides or chloramines, the lat- ter being regarded as an undesirable pollutant. The products that result from disinfecting water by the addition of chlorine are: Free residual chlorine—the portion of chlorine remaining as molecular chlorine, hypochloride (HOCl), or hypochlorite ion (OCl – ) Combined residual chlorine—the portion of chlo- rine that combines with ammonia or nitrogenous compounds, forming chloramines Total residual chlorine (TRC)—the sum of free residual plus the combined residual chlorine • • • Chlorine reduction in wetlands can occur via sev- eral pathways, such as photodegradation, and reaction with organic and inorganic material in the water, as well as ammonia. Wetlands have enough organic matter to pro- mote formation of trihalomethanes (THM) (Gallard and von Gunten, 2002), but other organic halides may also form. Total organic halides (TOX) and halo-acetic acids (HAA) may also form (Rostad et al., 2000). The photochemical pro- cess is initiated by production of oxidants such as peroxides. These oxidants then oxidize the chlorinated compounds. Volatilization, adsorption, and interactions with aquatic plants and the soil system may also contribute to the decay of residual chlorine. Studies of the loss of TRC were conducted in the Tres Rios, Arizona, FWS wetlands (Wass, Gerke, and Associ- ates, 2004). Disappearance was approximated by rst-order behavior. The rate constants were calculated to be 0.86 d −1 for the Cobble C1 and Hayeld H1 wetlands, based on tran- sect data. Thus there would be more than 90% reduction in TRC for a three-day detention time. Surveys of organo-chlo- rine compounds in the wetlands showed decreasing gradients fr om inlet to outlet for TOX, THM, and HAA (Table 11.4). BROMIDE AND BROMINE Bromide is not commonly measured as a constituent of natural freshwaters or wastewaters. It is a common choice for a water movement tracer, and a number of studies have therefore determined the background bromide in treatment wetland waters. Example values were 0.2–0.3 mg/L at Tres Rios, Arizona; 0.13–0.18 mg/L at Orlando Easterly, Florida; 0.05–0.15 mg/L at Hillsdale, Michigan; and 0.3–0.4 mg/L at Des Plaines, Illinois. Bromine is, therefore, also found in only minor trace amounts in vegetation. Concentrations of 25–46 mg/kg dry mass were measured in Typha latifolia at the Houghton Lake, Michigan, treatment wetland. Parsons et al. (2004) added a uniform sudden dose of bromide to 0 100 200 300 400 500 600 0123456789101112 Years of Operation Chloride (mg/L) WWTP Edge well Wetland FIGURE 11.1 Progress of chloride from the inltration beds of the wastewater treatment plant (WWTP), underground to a well on the wetland edge, and then out into the wetland at Genoa-Oceola, Michigan. (From unpublished data.) © 2009 by Taylor & Francis Group, LLC Halogens, Sulfur, Metals, and Metalloids 407 establish an initial surface water concentration of 100 mg/L in a prairie pothole in Saskatchewan. The wetland had no surface inow or outow, and thus the dose remained con- ned to the system except for inltration. They measured 20–90 mg/kg dry mass in aboveground tissues of Heracleum lanatum, Polygonum spp., and Carex spp., with localized values ranging up to 12,700 mg/kg dry mass. The fraction of the dose retained in vegetation was estimated to be 8.7%, as determined by areal averaging for the diverse species. Bromide sorbs to soils to about the same extent as nitrate (Clay et al., 2004), which is negligible in most situations. Bromine does not have a role in plant metabolism; however, bromide can be taken up by plants, to help satisfy the anionic component of the charge balance in the plant internal water. In that respect, bromide competes with chloride, as docu- mented by Xu et al. (2004) in Typha and Phragmites sys- tems. Plant uptake is, therefore, presumably greatest during the growing season, during which new plant water is building within the wetland. FLUORIDE AND FLUORINE Fluorine in water exists primarily in the form of sodium and calcium salts. Calcium uoride is used as a ux in steel manufacturing. Sodium uoride is used as a drinking water additive for prevention of dental cavities (tooth decay). The recommended optimum level ranges from 0.7 mg/L for warmer climates to 1.2 mg/L for cooler climates. Median concentrations are 0.2 mg/L in surface water and 0.1 mg/L in groundwater (U.S. EPA, 2002a). The current Maximum Contaminant Level set by the U.S. EPA in 1986 is 4 mg/L. Fluoride levels typically range from 0.03 to 0.57 mg/L in eastern U.K. rivers (Neal et al., 2003a). Fluoride differs from chloride and bromide, because it has been a target of treatment wetland design. The aluminum industry relies upon molten salt electrolytes that contain uo- rides. Solid wastes from the industry are usually landlled, and produce leachates that contain elevated concentrations of uoride (up to 100 mg/L). Fluoride partitions more strongly to soils and sedi- ments than do bromide and chloride. The Langmuir adsorp- tion capacities of soils ranges from 100–400 mg/kg for silts and loams (Bower and Hatcher, 1967). However, the oxyhydroxides of iron and aluminum have much higher bind- ing capacities, 30,000–50,000 mg/kg. This property causes uoride to be a poor tracer. For instance, LeBlanc et al. (1991) found: “Fluoride was abandoned as a tracer early in the test because uoride concentrations were rapidly attenuated by adsorption…” in the mineral soils of the site under study. Similarly, Jamieson et al. (2002) found only 57% recovery on a uoride tracer test of a dairy wastewater treatment wet- land in Nova Scotia. Fluorine is taken up by plants to a moderate extent (see T a ble 11.1), with tissue concentrations typically in the 100– 500 mg/kg range. But because it is not a macronutrient or a micronutrient, it is probable that such uptake is driven by the plant water ionic balance. The result of limited uptake and sorption is a limited overall reduction of uoride in treat- ment wetlands (Table 11.5). Data are too sparse to determine whether seasonal effects are present, or to elucidate possible differences between wetland types or plant varieties. TABLE 11.4 Inputs and Outputs of Chlorination Byproducts in the Tres Rios, Arizona, Demonstration Wetlands (µg/L) Location TOX THM HAA Input 170 11.0 31.0 C1 Out 76 0.3 7.2 C2 Out 97 1.4 8.2 Input 140 11.0 31.0 H1 Out 101 1.8 8.7 H2 Out 127 1.8 11.0 Input 178 11.0 70.0 R1-R12 Out 123 1.4 10.9 Note: TOX = total organic halides; THM = trihalomethanes; HAA = halo-acetic acids Source: Adapted from Rostad et al. (2000) Environmental Science and Technology, 34: 2703–2710. TABLE 11.5 Example Performances of Treatment Wetlands for Fluorine (mg/L) Location Water Treated Inlet Outlet Reference Brookhaven, New York Domestic 0.24 0.24 NADB database (1998) Tucush, Peru Metal mine 0.24 0.17 Unpublished data Imperial, California Agricultural runoff 0.54 0.56 Unpublished data Brawley, California River 0.71 0.83 Unpublished data Oxnard T1, California Backwash 2.80 2.90 CH2M Hill (2005) Oxnard T2, California Backwash 2.80 3.10 CH2M Hill (2005) Alcoa, Tennessee Aluminum waste leachate 5.80 4.90 Gessner et al. (2005) Russelville, Kentucky Aluminum processing 15.4 8.50 Rowe and Abdel-Magid (1995) Lambton, Ontario Gypsum leachate 16.0 15.3 Unpublished data Australia Power station 11.4 11.7 Jensen et al. (2006) © 2009 by Taylor & Francis Group, LLC 408 Treatment Wetlands 11.2 ALKALI METALS Sodium, potassium, calcium, and magnesium are rarely the object of regulatory concern, because under most circum- stances they do not pose any toxicity threat. Nevertheless, each of these has a role in wetland functioning, and can yield valuable information about pollutant processing and the wet- land water budget. SODIUM Sodium is important in plant and animal physiology. Sodium ions help to regulate osmotic pressure in cells, and therefore affect the diffusion of all essential growth nutrients between the external environment and the protoplasm of the living cells. A “sodium pump” fueled by the conversion of energy- bearing adenosine triphosphate (ATP) maintains internal cell sodium concentrations at optimal levels. The sodium content of wetland plant aboveground tissues ranges from <0.05% to more than 1.3% dry weight (Table 11.6). The median across the 13 species is 0.28%, or 2,800 mg/kg. Because most freshwater wetland species have low sodium requirements, the dissolved sodium content of waste- water passing through wetlands changes little (Table 11.7). Thus, sodium concentrations can be used as a conservative tracer for calculating dilution and concentration and for track- ing groundwater discharges from wetlands. For instance, the concentration of sodium in arid land treatment wetlands is likely to increase during the summer season due to evapora- tive concentration. Sodium is useful as a marker for added salt (NaCl), which may enter wastewater treatment systems because of its use in water softening and road de-icing. For example, the Cumberland County, Pennsylvania, data in Table 11.7, show a large increase in sodium during a spring ushing event, which was also accompanied by a large pulse of chloride (data not shown: C i = 14 mg/L and C o = 140 mg/L). The ori- gins of the sodium may have been the accumulation of road de-icing salt, contributed by the highway runoff the wetland was designed to treat. At the Genoa-Oceola, Michigan, site, discussed in the section on chloride, the water softener salt also had elevated sodium (150 mg/L), compared to the wet- land background of about 5 mg/L. The underground plume reached the wetland after about six years, at which time the wetland surface water sodium had increased to 95 mg/L. POTASSIUM Ionic pumping maintains potassium levels in plants at con- centrations of 1.0–4.0%. Potassium regulates the open- ing and closing of stomata on plant leaves. Stomata are the valves that allow gases inside the plant to be exchanged with the atmosphere. Potassium also is used as an enzyme acti- vator in protein synthesis in most cells. Potassium typically comprises about 2.6% of the dry weight of wetland plants. Potassium concentrations in water of surface ow treatment wetlands are typically between 1.0 and 40 mg/L (Table 11.7), with an average world river concentration of about 3.4 mg/L (Hutchinson, 1975). Potassium has not been the target of treat- ment wetland design. In general, there is not much change in po tassium from wetland inlet to outlet (Table 11.7). CALCIUM Calcium is biologically active because it is used as a nutri- ent by invertebrates and vertebrates, and because of its role in the carbonate cycle. Calcium is required by, and present in sizeable amounts in, angiosperm plants (Vymazal, 1995). The median concentration in a variety of wetland plants is TABLE 11.6 Examples of Major Ion Content of Wetland Plants Plant Type Sodium (% dw) Potassium (% dw) Calcium (% dw) Magnesium (% dw) Typha latifolia 0.28 2.65 0.76 0.15 Juncus effusus 0.40 0.89 0.38 0.11 Phragmites australis (W) 0.06 2.60 0.17 0.08 Glyceria maxima (W) 0.12 0.81 0.48 0.15 Scirpus americanus 0.09 2.83 0.50 0.22 Sagittaria latifolia 0.14 4.04 0.55 0.18 Nymphaea odorata 1.35 1.28 1.06 0.14 Nelumbo lutea 0.66 0.99 1.79 0.26 Ceratophyllum demersum 1.16 4.01 0.77 0.42 Najas guadalupensis 0.61 3.49 0.98 0.47 Myriophyllum heterophyllum 1.30 3.03 0.88 0.26 Eichhornia crassipes 0.01 — 6.12 3.90 Pistia stratiotes 0.02 — 4.46 5.25 Median 0.28 2.65 0.77 0.22 Note: The letter “W” denotes a treatment wetland. Sources: Data from Boyd (1978) In Freshwater Wetlands: Ecological Processes and Management Potential. Academic Press, New York, 155–167; and Vymazal (1995) Algae and Nutrient Cycling in Wetlands. CRC Press/Lewis Publishers, Boca Raton, Florida, 1995. © 2009 by Taylor & Francis Group, LLC TABLE 11.7 Examples of Major Cations Entering and Leaving Treatment Wetlands Sodium Potassium Calcium Magnesium System Wetland Years HL R (m/yr) In (mg/L) Out (mg/L) In (mg/L) Out (mg/L) In (mg/L) Out (mg/L) In (mg/L) Estevan, Saskatchewan All 10 10.5 353 364 25.7 23.5 87 90 65 ENRP, Florida All 6 11.3 110 119 — — 84 69 — Oxnard, California Train 1 1 19.8 405 465 20 20 490 475 210 Imperial, California All 4 24.9 371 348 11.2 8.9 182 160 82 Brawley, California All 4 33.9 698 774 18.6 18.7 181 183 88 Columbia, Missouri All 3 49.0 — — 36.6 32.8 — — — Musselwhite, Ontario All 4 190 55 71.2 19.0 22.5 93.8 112.5 9.63 Monroe County, New York FWS 2 3.5 410 430 269 196 180 70 160 Hidden River, Florida Urban runoff 2 3.8 0.477 0.828 0.069 0.106 7.08 8.35 0.094 Pensacola, Florida 6 cells pulp and paper 2 18.4 — — — — — — 9.3 Brookhaven, New York MMP 2 5.48 19.97 19.05 4.42 3.16 25.52 16.69 4.58 Boney Marsh, Florida River 8 7.4 9.79 10.28 1.2 1.26 13.83 13.77 2.73 Norco, Louisiana Renery, West Cell 1 17.8 360 430 8.4 9.1 140.7 46.7 23.4 West Lafayette, Indiana Urban stormwater 1 Event — 110 85 2.5 2.7 95 54 28 Cumberland County, Pennsylvania Highway runoff 1 Event — 28.1 62.7 6.54 7.93 16.6 16.2 1.15 San Tomé, Argentina, FWS Tool factory 3 18.3 — — — — 175 86 17.2 Mor˘ina, Czech Republic, HSSF Municipal sewage 1 9.3 127 102 19 20 98 89 21 Br˘ehov, Czech Republic, HSSF Municipal sewage 1 24.6 39 31 62 49 42 33 18 Slavošovice, Czech Republic, HSSF Municipal sewage 1 9.8 43 16 36 18 41 17 16 Australia Power station 6 24.3 238 245 — — — — — © 2009 by Taylor & Francis Group, LLC 410 Treatment Wetlands 0.77% dry mass (see Table 11.6), and is similar in fresh- water planktonic algae. However, levels in oating plants and lamentous green algae range upward to 5–7% dry mass (see Table 11.6; Vymazal, 1995). The photosynthetic organs of plants and algae may develop calcium carbonate (calcite) encrustations in hard water environments. Because there is generally an excess of calcium in surface water and waste- water, calcium concentration does not change appreciably in many wetland treatment systems (see Table 11.7). In some treatment wetlands, there is an iron deciency, and calcium biogeochemistry is dominant. When this occurs, the wetland sediments contain a high proportion of calcium carbonate, which is referred to as calcitic mud or marl. The southern Everglades contain extensive areas of these calcitic muds, which form under conditions of shorter hydroperiod, as a result of calcium carbonate precipitation mediated by periphyton. These materials are very dense, low in organic content, and are typically low in phosphorus content. Calcar- eous periphyton in the south Florida environment contributes to high soil calcium, with concentrations ranging from 3–4% in peats to 20–40% in calcitic wetland sediments (Reddy et al., 1991; DeBusk et al., 2004). Calcium is also important in constructed wetlands receiv- ing some types of leachates. Municipal landlls may contain construction materials including gypsum wallboard (calcium sulfate), and the waste piles from phosphate fertilizer manu- facture contain mostly calcium sulfate as well. MAGNESIUM Magnesium is an essential micronutrient because of its role in phosphate energy transfer and because it is a structural component in the chlorophyll molecule (Wetzel, 1983). Because magnesium concentration of surface water almost always exceeds the requirements for plant growth, elevated magnesium concentrations are not affected when waste- water travels through wetland treatment systems. Magne- sium is more soluble than calcium, and precipitate formation does not occur (see Table 11.7). Plant tissue concentrations are approximately 0.25% dry weight, but may be higher for oating plants and lamentous algae (see Table 11.6). 11.3 COLLECTIVE PARAMETERS H ARDNESS Hardness measures the concentrations of divalent cations in a water sample. The prevalent divalent ions in most surface waters are calcium and magnesium. Rainwater typically has low hardness (soft water) with a calcium concentration between 0.1 and 10 mg/L, a magnesium concentration of about 0.1 mg/ L, and a hardness value less than 30 mg/L as CaCO 3 . Surface water hardness is variable, depending on the soil and rock con- centrations of calcium and magnesium, and on the degree of contact with rocks, soils, and pollution. Inland surface water hardness varies from 10 to 300 mg/L as CaCO 3 , with a calcium concentration between 0.3 and 70 mg/L and magnesium con- centration between 0.4 and 40 mg/L. TOTAL ION CONTENT Two chemical parameters are commonly used to indicate the collective concentrations of dissolved substances: TDS and specic conductance. These parameters do not specify the distribution of contributing ions and organic compounds that contribute, but they are helpful in support of the wetland water budget. Further, the TDS content of water is sometimes a regulated parameter, especially in arid regions, where salt buildup is a water quality concern. Total Dissolved Solids TDS is used to quantify the degree of pollution in many industrial wastewater efuents, including textile wastes, food processing wastes, and pulp and paper wastes. When dis- charged to surface or groundwaters, these dissolved solids may represent a signicant pollution source. The total quan- tity of dissolved solids in a water sample is measured by ltration followed by sample evaporation. This quantity con- tains both inorganic ions and organic compounds. TDS is nearly as conservative in wetlands as specic conductance and chloride. Because TDS concentrations are high in many wastewaters and the individual components of these solids greatly exceed the biological requirements for growth, wet- lands generally have a negligible effect on this parameter (see Ta ble 11.3). Electrical Conductivity EC, also called specic conductance, of an aqueous solu- tion is the reciprocal of the resistance between two platinum electrodes, 1 cm apart and with a surface area of 1 cm 2 . The reciprocal of EC is equal to resistance, and is a function of the total quantity of ionized materials in a water sample. Specic conductance usually is reported at a temperature of 25°C and in units of µS/cm, or µmhos/cm. Measurements can be made with pocket-portable, inexpensive meters. Specic conductance is nearly proportional to the TDS in many sur- face waters and is a convenient measure of the salt content of wastewaters. Total ionic salts in wetlands, as measured by specic conductance, may be somewhat altered by biological con- ditions in wetlands, but physical processes of dilution and evaporation represent the major inuences. Therefore, EC is a relatively accurate indicator of dilution and concentration effects by rainfall and runoff and evapotranspiration in wet- land treatment systems. Treatment wetlands are usually, but not always, domi- nated by the introduced ows. Rainfall and evapotrans- piration are minor in comparison, except possibly for the duration of extreme events. Therefore, in the long run, EC of the inlet and outlet waters are close to the same. For the 17 pass-through systems of Table 11.3, the outlet EC averages © 2009 by Taylor & Francis Group, LLC Halogens, Sulfur, Metals, and Metalloids 411 98% o 2% of the inlet EC. This represents long-term mean performance, over an average of ve years. Those wetlands receive an average annual hydraulic loading of 31 m/yr, which is far greater than precipitation or evapotranspiration, which is about 1 or 2 m/yr. There are circumstances in which conductivity, chloride, and TDS change from inlet to outlet, and data then present a challenge for nding the cause. Three such anomalies are listed in Table 11.3. The rst of these is data from the rst 17 months of operation of the New Hanover County, North Carolina, system. This FWS wetland treats landll leachate that has a high EC (>6,000 µS/cm), and during the start-up period produced an average outlet EC = 1,468 µS/cm. Chlo- ride and TDS exhibit similar large decreases. The reason in this case is a very low hydraulic loading (0.79 m/yr), coupled with large rainfall. However, the larger effect was the long time required to replace the low conductivity water used to initially ll the wetland. Both factors produce large dilution of the incoming leachate. The second illustration is for the Incline Village, Nevada, wetland. This arid-climate system does not receive water in the summer, because it is used to irrigate fodder crops. The design of the wetland was for disposal, primarily (y90%) to evaporative losses, and secondarily (y10%) to inltration. The hydraulic loading is very small, and large concentra- tion increases in chloride and TDS are produced as the water moves through the sequence of cells (Kadlec et al., 1990). The third illustration is the Ouray, Colorado, wetland, which exhibits twofold increases in TDS over a ve-year averaging period (HDR/ERO, 2001). This is a strong signal of secondary sources of water entering the treatment wet- land. This has been identied as a maintenance issue: “The wetland system experiences an outside ow problem with sulfates, which concentrate.…” Conductivity has also been used as a diagnostic tool for internal processes in treatment wetlands in a number of ways. For example, EC is often much higher in the pore waters of FWS wetland soils and sediments than it is in over- lying waters. DBE (2003) measured the EC of surface waters and pore waters in Cell 1 of the ENRP in 2001. The pore water EC was higher than that of the overlying surface waters ( T able 11.8). Among the potential reasons is that rooted plants extract their transpiration requirement from pore water, but reject some or all of the associated salts. The result is an upward positive gradient in EC in the top soil layer. That gradient may continue into the overlying water, and pro- duce stratication of the EC of the water column. The pattern of these results indicates an internal recycle loop, in which dissolved substances are drawn down into the root zone by transpiration or other ows, only to be rejected by the plants to avoid buildup of TDS within their tissues. This creates an upward gradient, which causes diffusive solute movements back into the water column from the pore water. Density-Induced Vertical Stratification Conductivity is also a tool to understand the phenomenon of density stratication in constructed and other wetlands. Wetlands are typically too shallow to stratify due to thermal gradients, but the same is not true for density segregation, which may exist due to the character of incoming wastewater, rainfall, or added tracers. Two examples will serve to illus- trate the potential for vertical stratication. Salt Plumes in FWS Wetlands Various salts, such as sodium bromide and lithium chloride, are convenient tracers for water movement. Considerable quantities are needed, and consequently it is tempting to add concentrated solutions, in order to deal with manageable tracer solution volumes for addition. However, when dense solutions are introduced into the bottom of wetlands, there may be a strong energy barrier to vertical mixing, resulting in the dense material remaining on the bottom of the wetland. Concentrations used in a South Florida Water Management District (SFWMD, 2002) tracer study were 7.5% LiCl (density = 1.04 g/cm 3 ) (Söhnel and Novotny, 1985). Concentrations of sodium bromide in a Tres Rios, Arizona (Whitmer, 1998), tracer study were about 20% NaBr (density = 1.16 g/cm 3 ) TABLE 11.8 Pore Water Concentrations of Alkalinity, Calcium, and Electrical Conductivity in Cell 1 of the ENRP Wetland in Florida Community Location EAV SAV FAV Mean Alkalinity (mg/L) Surface water 213 204 209 209 Pore water 634 598 631 621 Calcium (mg/L) Surface water 67 63 67 66 Pore water 152 136 146 145 Conductivity (µS/cm) Surface water 1,038 1,008 1,045 1,030 Pore water 1,830 1,899 1,740 1,823 Note: EAV = emergent aquatic vegetation; SAV = submerged aquatic vegetation; FAV = oating aquatic vegetation. Source: Data from DBE (2003) Assessment of hydraulic and ecological factors inuencing phosphorus removal in Stormwater Treat- ment Area 1 West. Final report to Florida Department of Environmental Protection, Contract No. WM795, April 2003. © 2009 by Taylor & Francis Group, LLC 412 Treatment Wetlands (Söhnel and Novotny, 1985). It is noteworthy that demonstra- tion of stratication in limnology laboratory courses utilizes densities of 1.105 and 1.05 g/cm 3 (Wetzel and Likens, 1991). More directly, the work of Schmid et al. (2003, 2004b) shows that both tracer injections would lead to stable, unmixed layers of tracer on the wetland bottom. Both tracer studies showed very poor tracer recovery, suggesting that the tracer “got stuck” in the wetland sediments. Further evidence of vertical stratication was reported by Chimney et al. (2006), for a constructed wetland in the Florida Everglades (Figure 11.2). In this case, a likely cause is the back-diffusion of salts from the concentrated pore water, as described in Table 11.8. Stratification in HSSF Wetlands The presence of a gravel matrix in a HSSF wetland serves to exacerbate the potential for vertical stratication. It is well known that ows through clean porous media are suscep- tible to layering. For example, Wood et al. (2004) found that density effects occurred when the invading solution concen- tration was greater than approximately 13,000 mg/L. It is not surprising that Drizo et al. (2000) found that tracer bromide at 20,000 mg/L sank to the bottom of HSSF wetlands. Rash and Liehr (1999) have also reported stratication effects in HSSF wetlands. The Grand Lake, Minnesota, wetland exhibited large vertical stratication during a start-up period of two years, as evidenced by much higher EC in the bottom water samples than in the top samples (Figure 11.3; Kadlec et al., 2003). These wetlands were initially lled with water from an adja- cent natural bog, which had lower EC than the incoming wastewater. The stratication persisted, as a result of the very low ow over the summer and fall of 1996. The stratica- tion was mitigated in the fall of 1996 by pumping bottom water to the surface, although it restratied the next spring but not as strongly. After about two years of operation, only mild stratication existed, with 21% higher EC in the bottom water samples than in the top samples. –70 –60 –50 –40 –30 –20 –10 0 800 900 1,000 1,100 1,200 1,300 Conductivity (µS/cm) Depth (cm) Emergent SAV FIGURE 11.2 Vertical stratication of electrical conductivity in the ENRP, Florida constructed FWS wetland. Points represent the averages for 141 dates during May 1995 to October 1997. (Data from Chimney et al. (2006) Ecological Engineering 27(4): 322–330.) 0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 0 365 730 1,095 1,460 Days Conductivity (µS/cm) Inflow Outflow Top Bottom FIGURE 11.3 Electrical conductivity for Grand Lake, Minnesota, HSSF wetland cell #1. Introduction and removal were at the cell bottom. High conductivity water persisted at 45 cm depth for about two years, and low conductivity water persisted at 15 cm depth. The inuence of snow melt can be seen in the lower conductivity values on the top in each early spring. (Adapted from Kadlec et al. (2003) In Constructed Wet- lands for Wastewater Treatment in Cold Climates. Mander and Jenssen (Eds.), WIT Press, Southampton, United Kingdom, pp. 19–52.) © 2009 by Taylor & Francis Group, LLC [...]... 11. 23) Vertical flow constructed wetlands due to higher oxygenation of the bed exhibit good removal of manganese (Table 11. 23) There are two popular methods of interpreting performance data for metal removal in wetlands: the areal load removal and the first-order removal model These are both explored in detail for iron and manganese in a 35-wetland data set by Tarutis 436 Treatment Wetlands TABLE 11. 22... Rios, Arizona, treatment wetlands (Table 11. 19; Wass, Gerke, and Associates, 2002) Sediments generated in treatment wetlands are often high in aluminum, with values in treatment wetlands ranging from 1.4% (Tres Rios, Arizona) to 4% (Sacramento, California) (Nolte and Associates, 1998b) The process of phosphorus adsorption onto aluminum hydroxides has seen extensive application to water treatment and... phosphorus In wetlands, without coagulation, this floc settles slowly or not at all, leaving particulate aluminum and phosphorus in suspension (Bachand and Richardson, 1999) However, alum addition is a pretreatment step for waters sent to wetlands for further polishing Wetlands are also the recipients of water treatment backwash and sludge (Kaggwa et al., 2001) Consequently, 432 Treatment Wetlands TABLE 11. 19... sulfate reduction (Equations 11. 1 and 11. 2), iron may form insoluble ferrous sulfides (Equation 11. 27) and is deposited in the bed Coal Mine Drainage Wetlands Information on iron removal in wetlands is available primarily from acid mine drainage (AMD) wetland treatment systems in the United States (Girts et al., 1987; Kleinmann and Hedin, 1989; Hedin, 1989) However, treatment wetlands also became widely... Vymazal (1995) Samecka-Cymerman and Kempers (2001) Vymazal and Krása (2005) Samecka-Cymerman and Kempers (2001) Vymazal and Krása (2005) Samecka-Cymerman and Kempers (2001) Vymazal (1995) Vymazal (1995) Samecka-Cymerman and Kempers (2001) Ye et al (2001a, b) Samecka-Cymerman and Kempers (2001) DeVolder et al (2003) Obarska-Pempkowiak et al (2005) Obarska-Pempkowiak et al (2005) Obarska-Pempkowiak et al... wetlands were net sinks for iron in all seasons Performance of Wetlands for Iron Removal Wetlands interact strongly with iron in a number of ways, and thus are capable of significant metal removal Three major mechanisms are operative: 428 Treatment Wetlands TABLE 11. 17 Iron Content of Above- and Belowground Plant Parts in a Variety of Wetlands Location Wetland Plant TVA Mussel Shoals, Alabama New York... bound in calcium-rich materials, or in organic components of soils and sediments Two effects have been reported: (1) a reduction of phosphorus uptake due to sulfide toxicity, and (2) sulfide binds iron and interferes with that component of phosphorus storage that relies upon the iron–phosphorus link (Lamers et al., 1998) 418 Treatment Wetlands TABLE 11. 11 Example Performances of Treatment Wetlands for... m/d) FIGURE 11. 14 Outlet manganese concentrations from treatment wetlands at various loading rates © 2009 by Taylor & Francis Group, LLC Reference 438 Treatment Wetlands Aerobic FWS Wetland Flow in Flow out Organic material Anaerobic FWS Wetland Flow in Flow out Organic material Limestone Aerobic VF Wetland Flow in Organic material Flow out Limestone FIGURE 11. 15 Three types of constructed wetlands used... in the Mediterranean climate at Meze, France (Paing et al., 2003) The pond reduced sulfate TABLE 11. 10 Hydrogen Sulfide in the Listowel, Ontario, Constructed Wetlands, 1980–1984, in mg/L Total H2S System Annual 2 3 4 5 In % Un-ionized 1.81 72% 1.81 72% 1.81 72% 0.23 57% 0.23 57% Out % Un-ionized Jan-Feb-Mar 1 1.19 76% 4.44 67% 1.00 65% 1.28 63% 3.10 69% In Out 3.93 0.75 3.93 3.41 3.93 0.72 0.46 0.66... circumstances, treatment wetlands have been observed to turn purple, as happened in a FWS treating high-strength potato processing wastewater (P Burgoon, personal communication) In any case, these microbially mediated reactions suggest that elemental sulfur may be found in treatment wetlands Anecdotal reports of elemental sulfur have been made for the Houghton Lake, Michigan, system; the Tres Rios, Arizona, wetlands; . Demonstration Wetlands (µg/L) Location TOX THM HAA Input 170 11. 0 31.0 C1 Out 76 0.3 7.2 C2 Out 97 1.4 8.2 Input 140 11. 0 31.0 H1 Out 101 1.8 8.7 H2 Out 127 1.8 11. 0 Input 178 11. 0 70.0 R1-R12 Out 123. and evapotranspiration in wet- land treatment systems. Treatment wetlands are usually, but not always, domi- nated by the introduced ows. Rainfall and evapotrans- piration are minor in comparison,. rhizosphere of constructed wetlands, even in the case of treatment of domestic wastewater, has been underestimated. Extreme variations of removal pro- cesses in large-scale treatment wetlands may reect