593 16 Design Basis The preliminary step in the design of a treatment wetland is to acquire a fundamental understanding of the site of the wetland. Site conditions dictate the physical, chemical, and biological environment of a wetland treatment system. Con- ditions that should be evaluated during planning of a wetland treatment system include climate, geography, groundwater and its chemistry, soils and geology, rainfall and runoff water chemistry, biology, and socioeconomic factors. The impor- tance of each of these conditions may vary, but all should be investigated to some extent. Detailed studies may be needed to determine the importance of those site conditions that affect technical feasibility. This book primarily considers performance-based design algorithms. The rst steps in the process require the assembly of the basis of the design, which includes the following steps: 1. Determine inlet concentrations and ows. 2. Determine target concentrations (regulatory limits and allowable exceedance factors). 3. Determine allowable inow and seepage rates. 4. Determine rain, ET, and temperature ranges for the project site. 5. Select wetland type (FWS or SSF). Often, the establishment of ows and concentrations will require the acquisition of data on ows and concentrations, at least to conrm estimates based on prior operations or knowledge of the technology of the source. There are, unfortunately, numerous examples of inappro- priate selection of the design basis for treatment wetlands. The difculty is often not the misunderstanding of current condi- tions, but rather incorrect assumptions about future conditions. This may involve actions outside the control of the designer. For instance the “failed” Gustine, California, system added wetlands to existing lagoons (Walker and Walker, 1990). The source water was a combination of municipal and milk processing wastewaters, the latter having very high bio- chemical oxygen demand (BOD). The design presumption was that milk wastewater would be discontinued, but this did not occur. Instead of the design inuent BOD of 60 mg/L, the wetland actually experienced BOD of approximately 600 mg/L. The wetland could not meet design targets for the unplanned tenfold-higher inlet concentrations. Another exam- ple is the “successful” wetland system treating potato waste- water at Connell, Washington (Kadlec et al., 1997; Burgoon et al., 1999). The system was built according to a design based on operating data from a xed-capacity processing plant. However, coincident with wetland start-up, the plant implemented water conservation. The loads of pollutants remained the same, but concentrations went up considerably as ows decreased. Fortunately, in this case the wetland sys- tem was robust enough to accommodate the change and still achieve goals. These anecdotes serve notice that the basis of design must be carefully set forth, and reasonable changes anticipated in inuent ows and loads. 16.1 PROJECT SETTING S PACE CONSIDERATIONS: LIMITED VERSUS UNLIMITED SPACE Free water surface (FWS) treatment wetlands are in the cate- gory of land-extensive technologies. At the end of this chapter, it will be seen that horizontal subsurface ow (HSSF) wetlands for the same purpose are not much different in size. However, the site conditions—primarily property boundaries and topog- raphy—can limit the potential size of a treatment wetland for a particular source-water volume. This is particularly true of urban stormwater wetlands, which need to be sited in built-up areas and which often utilize high-value lands. Siting of wet- lands inside the boundaries of major cities, such as Orlando, Florida (Palmer and Hunt, 1989), or Toronto, Ontario (Heleld and Diamond, 2004), means that the size of the wetland is dic- tated by existing streets, highways, and buildings, not by the size needed to achieve a particular performance goal. Topography may also limit the potential size of a treat- ment wetland. The presence of steep slopes adjacent to the site can preclude construction beyond a certain limit, dened by the practicality of earth moving (Figure 16.1). When the site demands, the treatment wetland may be established in terraces, with elevation drops occurring between the succes- sive cells of the system (Navarra, 1992; Inman et al., 2003). Land ownership can also constrain opportunities for wet- land construction. Above and beyond questions of acquisition costs, there is the issue of the willingness of the owner to sell property. Building a treatment wetland rarely falls into the category of eminent domain acquisition, although that has happened in connection with the phosphorus removal wet- lands of South Florida. For large wetlands, suitable parcels are often already in agricultural use. Wetlands are frequently viewed as valuable landforms across the regional landscape, but aquatic and terrestrial landforms are also valuable. The construction of a treatment wetland implies the removal of other types of plant, animal, and human communities. There- fore, competing uses may block the construction of a wetland on a particular plot of land. Perhaps the most serious potential constraint of preexist- ing landform is the presence of naturally occurring wetlands on property under consideration for a treatment wetland. In © 2009 by Taylor & Francis Group, LLC 594 Treatment Wetlands the United States, it is generally not allowed to build any proj- ect that destroys existing wetlands. But what if the project is a constructed wetland? That situation is obviously confusing and unclear, and it is therefore not surprising that a variety of rules and regulations apply in various states. Sometimes the constructed treatment wetland may be viewed as self-mitigating; that is, it inherently compensates for the loss of preexisting wetlands. That situation has occurred at the West Jackson County, Mississippi, constructed wetland site. It is probably most acceptable when the preexisting wet- land is degraded, and of low regional value. However, in many other circumstances, construction in wetlands must be avoided. For instance, HSSF and vertical ow (VF) wetlands do not offer the same type of habitat that occurs in natural wetlands, and construction of these systems in natural wetlands is often blocked by regulatory constraints. Of course, the extreme cir- cumstance is the use of natural wetlands for wastewater treat- ment, which is outside the scope of this book. For these area-constrained situations, the design methods described herein are not used to select wetland area, but rather are used to forecast performance of the available wetland area. This predictive mode is readily accommodated in a rate coef- cient approach, but is very awkward, if not impossible, for a loading design approach due to the data scatter inherent in loading charts. SOILS AND GEOLOGY For planning purposes, site soils in the United States can be characterized by using USDA Soil Conservation Service soil surveys, which are generally available for most coun- ties within the United States. Other countries often have similar mapping resources. Soil surveys typically include maps of soil types as well as summaries of soil properties, groundwater conditions, climatic information, and plant community information. Soils are classied by soil scientists based on a complex array of physical and chemical characteristics. Soil informa- tion that might be important during project planning includes the presence of hydric soils, which occur in natural wetlands (even if formerly drained) and could be a potential regula- tory constraint for a constructed wetland site; soil texture and composition as a suitable medium for berm construction or for impeding leakage to the groundwater; depth to seasonal high groundwater; and depth to conning layers of clays or rock horizons. On-site soils are typically preferred for the rooting media in FWS wetlands. In some cases, the sorption potential of these rooting soils will be a design variable, such as for metal removal. The construction of wetlands entails the excavation of the wetland basin, including any deep zones, possibly together with conveyance and seepage interception canals. Therefore, the soil thickness above bedrock is an important piece of design information, because that material is movable without blasting. The characteristics of the bedrock are important if s u ch blasting is required (Figure 16.2). Construction in rock is extremely expensive, and is to be avoided if possible. At the other extreme, on-site materials may be unsuitable for the construction of embankments, because they cannot withstand exposure to the water (Figure 16.3). GROUNDWATER Inltration of wastewater to the groundwater is important because inltration affects the wetland water balance and could pose regulatory problems under some conditions. Soil inltration rates published in soil surveys typically overesti- mate the actual inltration rates under sustained, saturated soil conditions and are not reliable for project planning or design. Surface inltrometer tests or well slug tests provide better estimates of the groundwater leakage that can be FIGURE 16.1 The treatment wetlands in the Tucush valley of the high Andes Mountains of Peru (4,100 masl) are constrained to a xed area by extremely steep slopes. They treat the drainage com- ing from the wasterock dump of a mine operation. (Photo courtesy Compañía Minera Antamina. Reprinted with permission.) FIGURE 16.2 Deep zones and canals for South Florida’s storm- water treatment areas require blasting of the limestone bedrock. A thin veneer (0.3–1.0 m) of peat overlies the limestone. © 2009 by Taylor & Francis Group, LLC Design Basis 595 expected from a full-scale wetland treatment system. Meth- ods for measuring inltration rates are described by the Soil Conservation Service (SCS) (Hansen, 1980; U.S. Bureau of Reclamation, 1993). Field tests are the most reliable method of estimating groundwater inltration rates. For constructed wetlands, it may be necessary to construct pilot wetland basins on a proposed site and then instrument inows and outows to develop an accurate water balance. Wetlands can be built on leaky soils as long as regulatory requirements can be met and adequate hydroperiods can be maintained with the wastewater addition and net rainfall. In fact, wetlands have been designed with groundwater recharge as a specic project goal (Ewel and Odum, 1984; Knight and Ferda, 1989). Groundwater inltration can be eliminated as a project concern for constructed wetlands by using a clay or synthetic impervious liner. Although this approach may not be necessary if the wastewater has received secondary pre- treatment, it is recommended when wastewater is less than secondary quality, or is known to contain contaminants of concern for the regional groundwater and its intended uses. Percolation tests are often used as the basis of sizing inltration elds for septic tank efuent disposal, although such tests are probably insufcient for ensuring adequate performance of the eld (Crites and Tchobanoglous, 1998). The allowable hydraulic loading for the inltration eld is set according to a published table or curve, relating the allowable loading to the time for the water level in a test pit to drop a specied amount (usually 2.5 cm). Data collected from perco- lation tests are then typically related to a prescriptive hydraulic loading that is usually much less than the observed percolation rate. The reduction in hydraulic loading is to account for the long-term accumulation of microbial biomass and particulate matter in the soil, which substantially reduces the inltration rate (Tyler and Converse, 1994). Allowable hydraulic load- ings are usually in the range of 1–5 cm/d. Additionally, there must be a specied vertical travel distance to the groundwater table, typically about 1 m of unsaturated soil (to allow for the removal of pathogens). These requirements are commonly set forth in local codes and rules, and are enforced as a condition for acceptability of new on-site (septic) systems. These codes are typically intended for single-home treatment systems, but are often extrapolated to larger systems due to a lack of more appropriate regulatory guidelines. The focus of on-site (septic) system codes is the dis- posal of primary efuent into the soil matrix. When water is pretreated, organic and pathogen loads are substantially reduced, and soil-based treatment is less critical for regula- tory compliance. Given this basis, constructed wetlands are frequently viewed by the on-site regulatory community as a means for justifying higher loadings or lesser unsaturated travel dis- tances in the inltration bed, or both. For example, the state of Indiana allows reduction in the size of the absorption eld associated with a subsurface-constructed wetland based on the soil loading rate (Indiana Department of Environmental Management, 1997). For soil loading rates less than or equal to 5 cm/d but greater than 2 cm/d, the allowable reduction in eld size is 50%. For soil loading rates of less than 2 cm/d but greater than or equal to 1 cm/d, the allowable reduction in the eld is 33%. Similar reductions in inltration area are allowed in other states. In general, it is benecial to understand the directions and ows of regional groundwater under the project site. Dif- ferent levels of hydrogeological surveys may be performed, depending on the requirements of the specic project. Con- siderable detail is necessary for groundwater remediation wetlands that intercept a plume of contamination, because those studies provide the ows and concentrations needed to determine wetland size or performance. For instance, the design of the Hillsdale, Michigan, project involved multiple monitoring wells, studied over several years, and three- dimensional computational uid mechanics (Ecology and Environment Engineering, 2004). Modeling at a similar level was necessitated at the Columbia, Missouri, project, because of proximity to the city’s potable water well eld (Brunner and Kadlec, 1993). If the water leaving the system is trans- ported by unsaturated ow, more complex models will be required (Langergraber, 2001; Davis, 2007). ALTITUDE As the use of treatment wetland technology has grown across the planet, the site conditions have broadened to include a wider range of conditions, among which is the altitude of the project. A few experiences have identied special issues, such as the types of wetland plants that are adapted to high-altitude conditions: Phragmites is not a mountain plant! (Navarra, 1992). Other concerns have yet to be explored. For instance, treatment wetlands have now been built at up to 4,000 m above sea level (see Figure 16.1), at which altitude the atmosphere is approximately at half sea-level density. Therefore, the partial pressure of oxygen is half that at sea-level, with potential con- sequences on the ability of the wetlands to process reactions that require dissolved oxygen, such as nitrication. FIGURE 16.3 This collection canal in the Lakeland, Florida, FWS system was built using unstable materials from on site. Despite the attempt to reinforce the embankment with concrete matting, ero- sion caused the discharge structure to drop into the water. © 2009 by Taylor & Francis Group, LLC 596 Treatment Wetlands BIOLOGICAL CONDITIONS The addition of any type of water or wastewater will alter biological conditions at a site. Constructed wetlands fre- quently replace upland habitats with wetland vegetation. The upland habitats that are lost might include plant communi- ties such as grassland, forest, scrub, desert, or agriculture. The environmental values of these upland habitats should be assessed during project planning. Likewise, wastewater dis- charge to natural wetlands can cause biological changes of varying magnitudes (see Chapter 3). Existing plant and ani- mal communities in natural wetlands will change depending on the degree of changes to surface water quality and hydrol- ogy. Construction-related impacts will result in replace- ment of part of the existing vegetation by distribution pipes, boardwalks, and monitoring structures. For most constructed wetland projects, site-specic biological conditions do not represent a major technical constraint. 16.2 CHARACTERIZATION OF DOMESTIC AND MUNICIPAL WASTEWATER Wastewater quality varies widely among domestic, municipal, industrial, agricultural, and stormwater categories. Different wastewater sources have unique mixtures of potential pollut- ants, so that even a single wastewater source category, such as municipal wastewater or urban runoff, may vary considerably depending on local, site-specic circumstances. However, for some chemical constituents, the qualitative and quantitative composition of wastewaters from different sources varies less. In general, any summary of “typical” wastewater concentra- tions and loads must be considered cautiously. Site-specic wastewater data showing historical ows and mass loads provide the best information for wetland treatment system design. However, because many treatment systems are designed for new facilities or because historical monitoring may be nonexistent or insufcient, it is useful to know the typical concentrations of major constituents in similar wastewaters. This section summarizes information from a number of sources on the typical pollutant composi- tion of wastewater applied to engineered wetlands. These “typical” concentrations and loads should only be used when site-specic information is not available. The total municipal wastewater ows from municipal sources undergoing treatment in the United States is 45 × 10 9 m 3 per year, serving approximately 72% of the popula- tion (U.S. EPA, 2007). In addition to industrial and munici- pal wastewaters, nonpoint source pollution contributes about two thirds of the total pollution load to U.S. inland surface waters (U.S. EPA, 1989). Sources of nonpoint ows include urban and suburban runoff, diffuse agricultural runoff, forestry activities, runoff from concentrated agricultural activities such as feedlots, mine drainage, and runoff from undisturbed areas. However, in certain areas urban runoff or other stormwater sources provide the greatest percentage of uncontrolled pollutants. Wetlands are often used in con- junction with other treatment devices, including septic tanks, lagoons, and mechanical treatment plants (Figure 16.4). In those circumstances, the water quality of interest for the wet- land design is that exiting a pretreatment step. The amount and timing of the water to be treated is the rst and foremost item of the design basis. This informa- tion should include the possible seasonality of ows and the anticipated progression of ows over the life of the design. This is more important for treatment wetland design than for conventional concrete and steel treatment plants, because of the implied life cycle of the process and the nature of urban and industrial growth. It is customary to plan for a 20-year life expectancy for conventional wastewater treatment plants, because mechanical equipment often wears out during this period. But wetlands clearly can continue to function for far longer periods than two decades; for example, there are receiving wetlands that have been in operation for periods of 70 years (Great Meadows; Yonika et al., 1979) and 90 years Surface Discharge Infiltration Bed Subsurface Discharge Sludge Reed Bed VF Wetland HSSF Wetland FWS Wetland Settling Basin Lagoon Oxidation Pond Activated Sludge Biofilm (RBC) Source Septic Tank Sludge Bed Combination Wetland FIGURE 16.4 Simplied options for treatment trains involving treatment wetlands. © 2009 by Taylor & Francis Group, LLC Design Basis 597 (Brillion; Spangler et al., 1976). Projecting ow estimates far into the future is risky, so it is necessary to be explicit about ow capacity at the time of design. Most of the pollutants that are common to many of these wastewater sources can be effectively treated by wetland sys- tems. The normal concentration range of these pollutants is an important consideration in evaluating wetland treatment system options. This section compares and contrasts these wastewater sources to facilitate initial alternative evaluation. WATER QUANTITY The information on water quantities and timing is assembled into the annual and monthly water budgets for the design, including any seasonal or event storage that may be necessary. Such water budgets are easily prepared within the framework of a spreadsheet program on a personal computer. This infor- mation is later linked to the computation of the expected reduc- tions in pollutant concentrations. Interestingly, the addition of a wetland to any of the several forms of pretreatment provides dampening of ow pulses. Although it is necessary to account for the diurnal cycles in the inows for hydraulic purposes, the wetland will typically “hold” several such daily pulses, because of the extended detention time used in the wetland. SMALL DOMESTIC SYSTEMS Most design information in engineering textbooks is based on large-scale sewer networks that have a continuous base ow. Small-scale wastewater treatment systems often do not have a continuous base ow. On the contrary, low ows are zero (no ow), and peak ows are many times larger than the average ow. These differences in water use patterns raise issues that are not encountered in the design of larger sewage treatment works. SMALL FLOWS For design of single-family home treatment systems, the accepted practice in the United States is to base the design ow on the number of bedrooms within the home. These pre- scriptive ow determinations (typically ranging from 455 to 568 L/d per bedroom) are used to provide a sufcient factor of safety for soil inltration of septic tank efuent. They do not represent actual water use. Prescriptive ow determina- tions are commonly interpreted as representing the maximum expected occupancy of the home (two occupants per bedroom) and a corresponding peak ow rate. As a result, peaking fac- tor determinations and inltration/inow allowances are typi- cally not necessary when using prescriptive ows based on a bedroom count. Special provisions may apply in some cir- cumstances (Minnesota Pollution Control Agency, 1999). Flow projections may be based on population for small communities. A prescriptive criterion of 379 L/d per person is commonly used in North America (Great Lakes UMRB, 1997). This per-person ow guideline is intended to repre- sent an average dry weather ow from domestic wastewater sources plus a “normal” amount of inltration for gravity sewers built with modern construction techniques. If the only available information is the number of homes, an aver- age number of people per household may be used to approxi- mate the total population. The average household size in the United States is 2.7 people (American Housing Survey, 2003), although this varies by geographic location. An appropriate peaking factor must be applied to determine peak ows. PATTERNS OF SMALL FLOWS Wastewater ow from individual residences is delivered to a small-scale treatment system via a series of discrete pulses triggered by ush toilets, washing machines, dishwashers, etc. Low ows in small systems will be zero (no ow). Most water use occurs in the morning, evening, and at mealtimes. In the United States, water use from single-family homes has been idealized for design purposes, as indicated in Figure 16.5. As more and more homes are added to the system, ow pulses overlap. If there are enough homes in the collection network, ow pulses overlap to form a continuous base ow, and ow peaks start to attenuate. 10% 15% 5% 0 0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 24:00 Percent of Daily Flow Time of Day FIGURE 16.5 Idealized water use pattern for an individual home. (Adapted from NSF International (2000) Residential wastewater treat- ment systems. NSF/ANSI 4–2000, NSF International: Ann Arbor, Michigan. Reprinted with permission.) © 2009 by Taylor & Francis Group, LLC 598 Treatment Wetlands For single-family homes, the ratio of the peak ow to the average ow (peaking factor) can be ve or higher. Larger treatment systems will experience lower peaking factors due to overlapping ow pulses and the presence of a continuous base ow. In the United States, Recommended Standards for Wastewater Facilities (Great Lakes UMRB, 1997) suggest a formula based on population to determine the ratio of the peak hourly ow to the average daily ow (Equation 16.1). For small populations (less than 100 people), this relation- ship results in a peaking factor of approximately 4.5. Q Q P P peak hourly average day    18 4 (16.1) where Flow rate, any units Population in Q P   tthousands The pattern of peak ow events can be altered dramatically if wastewater is collected and pumped into the treatment system, as might be the case for septic tank pretreatment. Sources of inow and inltration from homes (sump pumps, footing drains, roof leaders, and furnace drains) can easily produce much higher ows unless they are identied during the design process with a home plumbing survey program and subsequently separated from the wastewater collection system. ACTUAL WATER USE Water use studies in the United States estimate an average daily water use of 189 to 265 L/d per person for homes built before 1994; implementation of standards for water-efcient appliances since then has reduced water use in newer homes to approximately 161 to 227 L/d per person (U.S. EPA, 2002c). Water use is strongly inuenced by cultural practices and varies widely from country to country. Across Europe, typical ow rates in small communities (less than 500 people) range from 80 to 120 L/d per person (IWA Specialist Group on Use of Macrophytes in Water Pollution Control, 2000). In Germany, water use rates are much lower than in the United States (Gesellschaft zur Förderung der Abwassertechnik d.V (GFA), 1998), at 100–150 L/d per person. In urban areas of developing countries, water use is approximately 60 L/d per person (Nhapi et al., 2003). Lagoons There are many variants on the concept of aquatic units for wastewater treatment, ranging from single-pond units (Water Environment Federation, 2001) to complex arrays of multiple units (Craggs, 2005). Often, other treatment process units are added to complement the pond itself (Middlebrooks et al., 2005). The combination of a pond followed by a wetland has been explored at a number of locations (Horne, 1995; Stein- mann et al., 2003; Tanner and Sukias, 2003; Kadlec, 2003d; Polprasert et al., 2005; Wang et al., 2005; Kadlec, 2005e). Because the wetland is often an add-on, the ow of the water exiting the pond is often known from performance data. The prescription for lagoon operation may be continuous discharge, typical of warm climates, or episodic discharge, typical of cold climates. Lagoon systems often discharge to surface waters, for which the goal is to minimize water quality impacts. Maximum dilution occurs at high ow of the recipi- ent, which in turn occurs during freshets, i.e., the spring thaw and the autumn wet season. Therefore, lagoon discharges are traditionally scheduled for those times of maximum dilu- tion. When a wetland is added to the system, there are more options for scheduling the discharge. For instance, the system may be designed for discharges that avoid ammonia toxicity in the recipient (Kadlec and Pries, 2004). Winter storage may be contemplated, provided capacity is present or designed. Therefore, the designer has an added degree of freedom: the total annual volume may be managed to optimize treatment, perhaps at the expense of more pond volume. This design feature is discussed in more detail subsequently. Me ch anical Plants Pretreatment systems, such as activated sludge plants, are small-retention devices, which do not typically have much capacity to dampen the incoming ow pulses. Hour-to-hour, day-to-day, and month-to-month ow variations are likely to be passed through the pretreatment system, and thus affect what is entering a follow-on treatment wetland. These pulses will then be partially evened out by an add-on wetland. Flows, whether municipal or industrial, are often seasonal in character. It is necessary to anticipate those patterns, because the wetland must function appropriately under these variable hydraulic conditions. Monthly ow estimates will be required for most point-source projects. INFILTRATION AND INFLOW Inltration is dened as groundwater that seeps into a waste- water collection system. It invariably introduces additional ow into the collection network. Inltration is strongly inuenced by groundwater elevation, workmanship of sewer construction, quality of construction materials, and fraction of the overall collection network that relies on gravity ow. Typical sources of inltration include poorly installed service laterals, leaking joints on sewer pipes, cracked sewer pipes, and leaking manholes. Exltration (movement of water out of the collection system) can also occur. Portions of collection systems that are pumped (such as pressure sewers) have posi- tive internal pressures and are often pressure-tested during construction. As a result, pressure sewer collection systems have a much lower potential for inltration. Inow is dened as extraneous water that is directly dis- charged to the wastewater collection system. In combined sewer systems, stormwater is a major source of inow. It is driven by rainfall intensity and amount of impervious sur- face present within the catchment area. In newer collection networks, stormwater is almost always excluded. In these © 2009 by Taylor & Francis Group, LLC Design Basis 599 situations, major sources of inow are generally limited to roof leaders, sump pumps, and foundation drains. Because most inow sources are driven by rainfall, these tend to be high-ow, short-duration events. These “surge” events can have major impacts on treatment systems. The combined effect of inltration and inow depend on a number of fac- tors, including the integrity of the sewer system, size of the collection pipes, the presence of high groundwater, and other factors. Typical allowances for combined inltration/inow range from 0.09 to 0.9 m 3 /d/cm/km (Metcalf and Eddy, 1998). WATER QUALITY The concentrations of the pollutants in the water to be treated are critical to the sizing process, and to the prediction of the wetland performance in the face of unknown future varia- tions. A clear denition of the incoming water quality, includ- ing the anticipated temporal distribution of concentrations, is essential. There are often seasonal uctuations for point sources, as well as diurnal uctuations. Incoming patterns of chemical composition propagate through the wetland and undergo modication, resulting in a spectrum of output com- positions. Some of this output variability may be predicted by the design models, namely, those variations that represent responses to moderately slow input changes (those which occur on monthly or less). Faster events involve ecosystem processes that are not included in the design models available at the present time, and therefore will give the appearance of generating stochastic variations. In domestic and municipal wastewater collection sys- tems, the following components contribute to sewage ow: Human excreta (feces and urine) Wastewater generated by personal use, including washing, laundry, food preparation, etc. (graywa- ter), and water used as the carrier media for human bodily wastes (blackwater) Water that inadvertently leaks into the collection system (inltration and inow) Wastewater from commercial or industrial sources • • • • Component concentrations of sewage will depend on the individual circumstances of the community. In communities with hand-carried water supplies or limited water resources, graywater is often looked at as an irrigation resource and is not commingled with excreta. In industrial societies, mixing graywater and blackwater to produce “combined sewage” is the norm (Günther, 2000). As a result of these differences in water usage, and hence composition, wetland designers need to consider how the community is utilizing water. S m allDomesticSystems There is often no composition data to be used for the design of treatment systems for small systems. It is necessary to resort to estimating methods that consider water use and population in the source community. Untreated human urine and fecal material can introduce a variety of pollutants into the environment. Typical per-person generation rates are su mmarized in Table 16.1 (Del Porto and Steinfeld, 2000). Graywater includes spent water from bathtubs, showers, washbasins, washing machines, laundry tubs, kitchen sinks, and dishwashers. In developed countries, graywater accounts for 50 to 82% of household water use and represents about half of the organic waste solids produced in the home. When conventional ush toilets are used in a waterborne sewer sys- tem, graywater is often combined with blackwater. Relative contributions of pollutants by source (for a combined sewer system) are summarized in Table 16.2 (U.S. EPA, 2002c). Typical constituent concentrations for residential septic tank systems are given Table 16.3. Lagoons Another source of treatment wetland inuents arises from pond treatment as the initial component of the treatment train. One or more facultative, anaerobic or aerated ponds or lagoons may be used (Shilton, 2005). Because the wet- land is often an add-on, the quality of the water exiting the pond is often known from performance data. If the entire system is constructed at the same time, the lagoon elements should be designed according to the currently accepted TABLE 16.1 Typical Per-Person Waste Generation Rates Parameter Urine Feces Combined Volume (L per capita·day) 1.2 0.15 1.4 Dry solids (g per capita·day) 60 45 105 Moisture content (g per capita·day) 95% 70% — Organic carbon (g per capita·day) 8.5 22 30 BOD 5 (g per capita·day) 7.5 11 18.5 Nitrogen (g per capita·day) 11 2 13 Phosphorus (g per capita·day) 1 0.6 1.6 Source: From Del Porto and Steinfeld (2000) The Composting Toilet System Book. Center for Ecological Pollution Prevention, Concord, Massachusetts. Reprinted with permission. © 2009 by Taylor & Francis Group, LLC 600 Treatment Wetlands methods (Shilton, 2005). Lagoon systems are typically designed for reduction of BOD and total suspended solids (TSS), and occasionally ammonia. Data and older models exist for pond pathogen reduction, but have not been recently updated and synthesized (Davies-Colley, 2005). Phosphorus data for lagoon systems are not voluminous, because it is not frequently regulated in lagoon discharges. Some approxima- tions of the efuent characteristics of several types of lagoons are shown in Table 16.4. Mechanical Plants Table 16.5 summarizes the typical quality of medium- strength, raw, municipal wastewater in the United States and provides a range of values for commonly observed constitu- ents. Municipal wastewater is composed of a variable array of components characterized by the presence of biodegrad- able organic matter (paper, feces, and food), particulate and dissolved solids, and nutrients. Many municipal wastewaters also receive some component of industrial waste. These ows and residential sources may add trace metals and pesticides to typical municipal wastewater. Table 16.5 also provides a range of estimated treat- ment efciencies for conventional primary and secondary treatment processes, and summarizes the typical quality of secondarily treated municipal wastewaters. These removal efciencies vary widely depending on the types of treatment processes. However, it is generally observed that at least 70% of the BOD and TSS are removed from municipal wastewater during primary and secondary treatment. Treatment require- ments have generally increased over the past decades, and many treatment plants now include at least partial nitrica- tion, perhaps denitrication, and phosphorus removal. These blur the terminology, because they range from “advanced secondary” to “tertiary” and beyond. The follow-on treat- ment wetland may therefore be termed “tertiary” or, as might be supposed, “quaternary.” This summary can be used as a rough estimate of the inu- ent water quality to be applied to a wetland system designed for primary, secondary, or advanced wastewater treatment. TABLE 16.3 Typical Wastewater Component Concentrations Entering and Leaving a Residential Septic Tank Parameter Raw Waste Central Estimate Range Septic Tank Effluent Range Without Kitchen Solids (Central Estimate) With Kitchen Solids (Central Estimate) BOD 5 (mg/L) 450 210–530 180 190 140–200 TSS (mg/L) 500 230–600 80 85 50–90 NH 4 -N (mg/L) 40 7–40 40 45 40–60 TKN (mg/L) 70 50–90 70 75 50–90 NO x -N (mg/L) <1 0–1 <1 <1 0–1 Total phosphorus (mg/L) 17 10–30 16 16 12–20 Fecal coliforms (CFU/mL) —10 6 –10 10 ——10 3 –10 6 Viruses (PFU/mL) — — — — 10 5 –10 7 Source: Data from Metcalf and Eddy Inc. (1991) Wastewater Engineering, Treatment, Disposal, and Reuse. Tchobanoglous and Burton (Eds.), Third Edition, McGraw-Hill, New York; Crites and Tchobanoglous (1998) Small and Decentralized Wastewater Management Systems. McGraw-Hill, New York. TABLE 16.2 Typical Per-Person Combined Sewage Generation Rates Parameter (Mean Values) BOD 5 (g per capita·day) Suspended Solids (g per capita·day) Nitrogen (g per capita·day) Phosphorus (g per capita·day) Garbage disposal 18.0 26.5 0.6 0.1 Toilet 16.7 27.0 8.7 1.6 Bathtubs, sinks, appliances 28.5 17.2 1.9 1.0 Approximate total 63.2 70.7 11.2 2.7 Source: Adapted from U.S. EPA (2002c) Onsite wastewater treatment systems manual. EPA 625/R-00/008. U.S. EPA Ofce of Research and Development: Washington, D.C. © 2009 by Taylor & Francis Group, LLC Design Basis 601 TABLE 16.4 Typical Composition of Lagoon Discharge Water and Percent Removals at Various Levels of Treatment Parameter Primary Anaerobic Secondary Aerobic Facultative Aerated Facultative Aerated Partial Mix BOD Reduction, % 50–85 — 75–95 — Up to 95 Median efuent, mg/L — — — — 25 Efuent range, mg/L — 20–40 15–35 1–45 15–40 TSS Reduction, % — — — — — Median efuent, mg/L — — — — 40 Efuent range, mg/L 80–160 80–140 10–90 1–90 20–60 NH 4 -N Reduction, % — — 23–97 — — Median efuent, mg/L — — 20 — 4 Efuent range, mg/L — — 0.2–25 0–12 — TP Reduction, % — — 50 — 15–25 Median efuent, mg/L — — — — 5 Efuent range, mg/L — — — 3–4 — FC Reduction (log 10 ) — — 1–5 1–5 — Median efuent, CFU/100 mL — — 200 100 100 Source: Shilton (2005) In Pond Treatment Technology. Shilton (Ed.), IWA Publishing, London; Metcalf and Eddy Inc. (1991) Wastewater Engineering, Treat- ment, Disposal, and Reuse. Tchobanoglous and Burton (Eds.), Third Edition, McGraw-Hill, New York; Crites and Tchobanoglous (1998) Small and Decentral- ized Wastewater Management Systems. McGraw-Hill, New York; Crites et al. (2006) Natural Wastewater Treatment Systems. Meyer (Ed.), CRC Press, Boca Raton, Florida; U.S. EPA (1983a) Design manual: Municipal wastewater stabilization ponds. EPA 625/1-83/015, U.S. EPA Ofce of Water: Cincinnati, Ohio; U.S. EPA (1983c) Wastewater stabilization ponds: Nitrogen removal. U.S. EPA Ofce of Water: Washington, D.C.; Rich (1999) High Performance Aerated Lagoons. American Academy of Environmental Engineers, Annapolis, Maryland. TABLE 16.5 Typical Composition of Municipal Wastewater and Percent Removals at Various Levels of Treatment Constituent Raw Wastewater (mg/L) Percent Removal Secondary Effluent (mg/L) Typical Range Primary Secondary Typical Range BOD 5 220 110–400 0–45 65–95 20 10–45 COD 500 250–1,000 0–40 60–85 75 35–75 TSS 220 100–350 0–65 60–90 30 15–60 VSS 165 80–275 — — — — NH 4 -N 25 12–50 0–20 8–15 10 <1–20 NO x -N 0 0 — — 6 <1–20 Org-N 15 8–35 0–20 15–50 4 2–6 TKN 40 20–85 0–20 20–60 14 10–20 Total N 40 20–85 5–10 10–20 20 10–30 Inorg P 5 4–15 — — 4 2–8 Org P 3 2–5 — — 2 0–4 Total P 8 6–20 0–30 10–20 6 4–8 Arsenic 0.007 0.002–0.02 34 28 0.002 — Cadmium 0.008 <0.005–0.02 38 33–54 0.01 <0.005–6.4 Chromium 0.2 <0.05–3.6 44 58–74 0.09 <0.05–6.8 Copper 0.1 <0.02–0.4 49 28–76 0.05 <0.02–5.9 Iron 0.9 0.10–1.9 43 47–72 0.36 0.10–4.3 Lead 0.1 <0.02–0.2 52 44–69 0.05 <0.02–6.0 Manganese 0.14 0–0.3 20 13–33 0.05 — Mercury 0.001 <0.0001–0.0045 11 13–83 0.001 <0.0001–0.125 Nickel 0.2 — — 33 0.02 <0.02–5.4 Silver 0.022 0.004–0.044 55 79 0.002 — Zinc 1.0 — 36 47–50 0.15 <0.02–20 Source: W PCF (1983) Nutrient Control. Manual of Practice FD-7, Water Pollution Control Federation: Washington, D.C.; Metcalf and Eddy Inc. (1991) Wastewater Engineering, Treatment, Disposal, and Reuse. Tchobanoglous and Burton (Eds.), Third Edition, McGraw-Hill, New York; Richardson and Nichols (1985) In Ecological Considerations in Wetlands Treatment of Municipal Wastewaters. Godfrey (Ed.), Van Nostrand Reinhold Company, New York, pp. 351–391; Krishnan and Smith (1987) In Aquatic Plants for Water Treatment and Resource Recovery. Reddy and Smith (Eds.), Magnolia Publishing, Orlando, Florida, pp. 855–878; Williams (1982) In Water Reuse. Middlebrooks (Ed.), Ann Arbor Science, Ann Arbor, Michigan, pp. 87–136. © 2009 by Taylor & Francis Group, LLC 602 Treatment Wetlands 16.3 CHARACTERIZATION OF OTHER WASTEWATERS I NDUSTRIAL WASTEWATERS Although industrial wastewater quality varies among indus- tries, it has a fairly consistent intrasystem efuent quality. Table 16.6 summarizes the typical quality of raw wastewater from a number of industries that have used wetlands treatment technology. Raw industrial wastewater usually receives some level of pretreatment before discharge to a wetlands treatment system. If total concentrations of BOD, suspended solids, and ammonia nitrogen in untreated industrial wastewater are in the concentration range of hundreds to thousands milligrams per liter, it is generally not acceptable for wetlands discharge without additional pretreatment. LANDFILL LEACHATES Treatment and disposal of liquid leachates is one of the most difcult problems associated with the use of sanitary land- lls for disposal of solid waste. Leachates are produced when rainfall and percolated groundwater combine with inorganic and organic degraded waste. In unlined landlls, leachates TABLE 16.6 Typical Pollutant Concentrations in a Variety of Untreated Industrial Wastewaters Constituent Units Pulp and Paper a Landfill Leachate b Coal Mine Drainage d Petroleum Refinery e Electroplating f Breweries g BOD 5 mg/L 100–500 42–10,900 — 10–800 — 1,500–3,000 COD mg/L 600–1,000 40–90,000 — 50–600 — 800–1,400 TSS mg/L 500–1,200 100–700 — 10–300 4–600 100–500 VSS mg/L 100–250 60–280 — — 30–100 50–500 TDS mg/L — — — 1,500–3,000 800–5,800 50–350 NH 4 -N mg/L — 0.01–1,000 — 0.05–300 — — TN mg/L — 70–1,900 — — 10–120 25–45 TP mg/L — <0.01–2.7 — 1–10 20–50 – pH S.U. 6–8 3–7.9 3–5.5 8.5–9.5 4–10.5 5–7 Sulfate mg/L — 10–260 20–2,000 ND–400 30–120 — Conductance µS — 1,200–16,000 — — — — TOC mg/L — 11–8,700 — 10–500 — — Aluminum mg/L — 0.5 50 — — — Arsenic mg/L — 0.011–10,000 — — — — Barium mg/L — 0.1–2,000 — — — — Cadmium µg/L — 5–8,200 — — 10,000–50,000 — Chromium mg/L — 0.001–208 — ND–3 10–120 — Iron mg/L — 0.09–678 50–300 — 2–20 — Lead µg/L — 1–19,000 — — — — Manganese mg/L — 0.01–550 20–300 — — — Selenium µg/L — 3–590 — — — — Oil and Grease mg/L — — — 10–700 — — Phenols mg/L — <0.003–17 — 0.5–100 — — Cyanide mg/L — — — — 1–50 — Note: ND  not detected. a From Jorgensen (1979) Studies in Environmental Science 5. Elsevier, New York. b From Staubitz et al. (1989) Constructed Wetlands for Wastewater Treatment: Municipal, Industrial, and Agricultural. Hammer (Ed.), Lewis Publishers, Chelsea, Michigan, pp. 735–742; Lema et al. (1988) Water, Air, and Soil Pollution 40: 223–250; Bolton and Evans (1991) Water, Air, and Soil Pollution 60: 43–53. c From Wildeman and Laudon (1989) In Constructed Wetlands for Wastewater Treatment: Municipal, Industrial, and Agricul- tural. Hammer (Ed.), Lewis Publishers, Chelsea, Michigan. d From Girts and Kleinmann (1986) National Symposium on Mining, Hydrology, Sedimentology, and Reclamation. University of Kentucky Press, Louisville, Kentucky, pp. 165–171. e From Adams et al. (1981) Development of Design and Operational Criteria for Wastewater Treatment. Enviro Press, Nash- ville, Tennessee; ANL (1990) Environmental consequences of, and control processes for, energy technologies. Argonne National Laboratory (ANL) and Noyes Data Corporation: Park Ridge, New Jersey. f From OECD (1983) Emission Control Costs in the Metal Plating Industry. Organization for Economic Cooperation and Development (OECD). g From Cooper (1978) The textile industry. Environmental control and energy conservation. Noyes Data Corporation. Park Ridge, New Jersey; Wildeman et al. (1993a) Wetland Design for Mining Operations. Bitech Publishers, Vancouver, British Columbia. © 2009 by Taylor & Francis Group, LLC [...]... River 612 Treatment Wetlands 1 7 13 10 3 14 13 12 4 1 8 14 11 2 5 1 2 6 1 14 12 3 15 2 18 12 6 16 16 1 10 14 14 15 14 17 3 1 14 3 1 4 9 17 6 18 16 2 1 16 18 1 FIGURE 16. 7 Reference evapotranspiration for the state of California See Table 16. 10 for the annual pattern for each zone (Adapted from California Irrigation Management Information System; http://www.cimis.water.ca.gov/cimis/info.jsp.) wetlands. .. land-economical way The techniques presented in this treatise are applicable to wetlands used as pieces of integrated natural systems Various combinations of treatment wetlands of different types, as well as other unit ecosystems, are considered in Chapter 24 Here, the designs of the three common types of wetlands are considered as individual elements of the integrated treatment system 16. 7 PRE- AND... Francis Group, LLC FIGURE 16. 16 The Hardin, Kentucky, HSSF Phragmites and Schoenoplectus (Scirpus) wetlands received periodic sludge overflows from the pretreatment device (Imhoff tank) As a result, the inlet to the bed became a sludge bed with no live plants 622 Treatment Wetlands FIGURE 16. 17 The Listowel, Ontario, FWS Typha wetlands received episodic sludge overflows from the pretreatment device (primary... nuisance conditions related to mosquitoes or other wildlife Type A wetlands are typically constructed FWS marshes, relatively low-tech HSSF wetlands, and natural treatment wetlands They are always less costly to operate than Type B treatment wetlands, and may be less costly to construct, depending on the local situation The Type B treatment wetland design and management strategy is preferred when one... poor treatment efficiencies Treatment wetlands are a compatible component of on-farm, total waste management Their land intensiveness is not a serious limitation in most instances Farmers typically have the equipment and skills necessary to build their own wetlands and operate them successfully Table 16. 7 summarizes the composition of wastes from animal operations, both entering and leaving treatment wetlands. .. 47 47 24 47 16 31 55 24 39 31 31 39 31 39 47 63 36 43 57 57 43 57 36 43 71 43 57 50 50 57 57 64 71 85 63 79 94 87 71 87 63 87 102 79 79 87 79 94 94 102 118 134 84 99 122 114 107 122 99 122 130 114 114 130 122 130 145 221 152 175 102 118 134 134 142 142 134 157 150 150 150 173 165 173 189 197 205 220 114 130 145 145 160 160 160 175 168 183 183 198 198 198 206 221 229 244 118 126 142 150 165 165 189 189... constructed HSSF wetlands for improvement of nitrification • Addition of VF components to HSSF constructed wetlands to improve nitrification (potentially with flow recirculation) • FWS or HSSF wetlands and aquatic plant treatment systems with plant harvesting • High solids treatment wetlands with frequently cleaned forebays, or frequent refurbishment and restarting, as for sludge reed beds Type B wetlands. .. the NH4-N, and 70 to 100% of the sulfide (ANL, 1990) As described in Chapter 13, constructed wetlands are providing advanced secondary and tertiary treatment of process water and stormwater at a large number of refineries (Knight et al., 1999; API, 1999) Constructed wetlands typically will reduce remaining concentrations of BOD5, COD, TSS, NH4-N, oils and grease, phenols, and metals to advanced treatment. .. Stormwater wetlands typically embody such elements For HSSF wetlands, there is an increasing body of knowledge that indicates the cross-sectional loading is a critical design parameter (see Chapter 21) For VF wetlands, it is apparent that resting intervals between loading periods are necessary to control solids accumulation and associated bed clogging problems (see Chapter 21) Upsets in pretreatment... Specific examples of Type B treatment wetlands include: Design Basis 615 FIGURE 16. 10 Type A constructed wetlands may be built by berming off a plot of ground and allowing natural regrowth to vegetate the system This wetland at Onaway, Michigan, is used for ultra-polishing of a lagoon effluent that has had post-sand filtration and phosphorus removal by chemical precipitation • HSSF wetlands augmented with . activated sludge plants, are small-retention devices, which do not typically have much capacity to dampen the incoming ow pulses. Hour-to-hour, day-to-day, and month-to-month ow variations are likely. monthly mean water tem- perature (see Chapter 4), which allows the interpretation of thermal effects on some microbial components of treatment. 1 1 1 2 2 2 8 4 2 1 4 6 9 16 16 16 16 6 6 12 17 17 18 18 18 15 14 14 14 13 5 10 15 12 12 11 14 14 14 14 1 1 1 1 1 3 13 10 7 3 3 3 FIGURE. treatment systems must be designed with rea- sonable organic loadings to prevent plant mortality, odors, and poor treatment efciencies. Treatment wetlands are a compatible component of on-farm,