Ws with Emergent Macrophytes

These systems typically consist of basins or channels, with some sort of subsurface barrier to prevent seepage, soil or another suitable medium to support the emergent vegeta tion, and water at a relatively shallow depth flowing through the unit (Figure 2a). The shallow water depth, low flow velocity, and presence of the plant stalks and litter regulate water flow and, especially in long, narrow channels, ensure plug flow conditions. The water surface is above the sediment, litter, and soil, but live and stand ing dead plant parts are above the water. In FWS CWs the near surface layer is aerobic, whereas deeper water and substrate are usually anoxic/anaerobic. Typical water depths range from a few centimeters up to a meter. Dense vegetation covers significant fraction of the sur face, usually more than 50%. Besides planted macrophytes natural assemblages of volunteer re growth from native seed banks are also in use. One of their primary design purposes is to contact wastewater with reactive biological surfaces.

In spite of many prejudices among civil engineers about odor nuisance, attraction of flies, and poor perfor mance in cold periods, the IJssel Lake Polder Authority in Flevoland (The Netherlands) constructed its first FWS CW in 1967. A star shaped layout was chosen in order to obtain optimum utilization of the available area, which, however, complicated macrophyte harvesting and main tenance in general. Therefore, longitudinal channels were added to facilitate mechanical biomass harvesting and system maintenance. The new wetland design included channels 3 m wide and 200 m long, separated by parallel stretches of 3 m resulting in an increase in land require ment from 5 to 10 m2 per population equivalent (PE). The system was called planted sewage farm (or Lelystad pro cess). In 1968, an FWS CW was created in Hungary near Keszthely in order to preserve the water quality of Lake Balaton and to treat wastewater of the town. The FWS system in the Nyirbogdany Petrochemical Plant (Hungary) was created in the 1970s and has an area of 15 500 m2.

Contrary to North America where FWS CWs were spread intensively, FWS CWs did not spread throughout Europe significantly. However, FWS CWs are in operation in many European countries, for example, Sweden, Poland, Estonia, the United Kingdom, and Belgium. Recently, FWS CWs have drawn more atten tion in Australia.

In the literature, various relationships have been developed in order to assess the wetland area necessary to produce required water quality. Each regulated para meter gives rise to a wetland area necessary for the reduction of that pollutant to the required level. The required wetland area is the largest of the individual required areas. It has been shown that the order of size necessary for effective removal of various pollutants is in the order SS < BOD < nitrogen < phosphorus.

FWS wetlands with emergent macrophytes are usually designed using the first order area based model:

where Ce is the effluent target concentration (mg l J); Ci is the influent concentration (mgl ); C is the background concentration (mg l 1); k is the first order areal rate con stant (m d 1); q is the hydraulic loading rate (m d 1, q = Q/A, where Q= daily flow in m3 d 1 and A = area of the wetland in m2).

Rearranged, the area required for a particular pollutant is then

Based on large data set from FWS CWs in North America following values of areal rate constant 'k adjusted to 20 °C are: BOD5: 0.093 md 1; TSS: 2.74m d 1; total N (TN): 0.06 md 1; organic N: 0.047 md 1; ammonium N: 0.049 md 1; nitrate N: 0.096 md 1; total P (TP): 0.033 m d 1; and fecal coliforms: 0.205 m d 1.

Wetland ecosystems typically include diverse auto trophic and heterotrophic components. Most wetlands are more autotrophic than heterotrophic, resulting in a net surplus of fixed carbonaceous material that is buried as peat or is exported downstream to the next system. This net production results in an internal release of par ticulate and dissolved biomass to the wetland water column, which is measured as nonzero of BOD, SS, TN, and TP. These wetland background concentrations are denoted by C*. Treatment wetlands background concen trations ranges can be estimated from systems that are loaded at a low enough rate to result in asymptotic con centrations along gradient of increasing distance from the inflow. Wetland systems typically have C* values within these ranges: BOD5: 1-10mgl 1; TSS: 1-6mgl 1; organic and total N: 1-3 mgl 1 ammonium N: <0.5mgl 1 nitrate N: <0.1 mgl 1 total P: <0.1 mgl \ However, many wetlands (and in Europe nearly all treat ment wetlands) have been designed with C* = 0.

The design criteria and recommendations developed for FSW with emergent vegetation can be summarized as follows: pretreatment: to at least the primary level; organic loading: <80 kg BOD5 ha 1 d 1; hydraulic loading: 0.7-5.0 cm d 1 detention time: 5-15 days; aspect ratio (L:W): 2:1 to 10:1; water depth: 0.4m; bottom slope: 0.5%; soils: 20-30 cm to support the growth of emergent macro phytes, no special requirements for high hydraulic conductivity (local soils used in many cases); vegetation: most commonly used species (in North America: Scirpus spp. (bulrushes), Typha spp. (cattails); in Europe: Phragmites australis (common reed)); harvest frequency: 3-5 years but harvest is not required (frequently also difficult).

FWS CWs have been built to treat domestic and municipal wastewater, mine drainage, urban and agricul tural drainage, landfill leachate, and variety of industrial and agricultural wastewaters. The most common use is that for tertiary treatment of municipal sewage (Figure 3) with major attention to removal of organics BOD5, chemical oxygen demand (COD), total suspended solids, and nutrients. Removal of organics and suspended solids is very high while removal of nutrients is only moderate (Table 1). FWS CWs provide limited contact with soil, so adsorption and precipitation processes are very limited and therefore phosphorus removal mostly proceeds via soil accretion. FWS surface provides both aerobic and anaerobic zones but neither nitrification or denitrification processes are complete. FWS CWs also provide high removal of enteric bacteria (e.g., fecal coliforms, fecal streptococci, Clostridium perfringens), usually in the range of 1-2 orders of magnitude.

Another common use of FWS CWs is for the treat ment of acid mine drainage waters rich in iron, manganese, and heavy metals (Figures 4 and 5). In CWs, as in all wetland systems, there are aerobic, anoxic,

Figure 3 CWs for tertiary treatment of municipal wastewater at Nynashamn, Sweden. Photo courtesy J. Andersson, Water Revival Systems, Uppsala AB, Sweden.

Table 1 Removal of pollutants in FWS CWs with emergent vegetation

Average concentration Average loading

Table 1 Removal of pollutants in FWS CWs with emergent vegetation

Average concentration Average loading

IN

OUT

EFF

n

IN

OUT

REM

n

BOD5

39

10.5

73.1

104

12

4.3

7.7

96

TSS

58

16.4

71.7

101

16.2

4.7

11.5

91

TN

14.3

8.4

41.2

85

466

219

247

85

nh4-n

12.9

5.8

55.1

64

137

71

66

72

NO3-N

5.6

2.2

60.7

57

34

18

16

47

TP

4.2

2.15

48.8

85

138

68

70

85

aAverage loading for BOD5 and TSS given in units of kg ha 1 d 1.

IN, inflow; OUT, outflow; REM, removed load; n, number of systems; removal efficiency (EFF) in %. Data from Australia, Canada, China, New Zealand, Poland, Sweden, USA, the Netherlands. Most CWs are designed as tertiary treatment.

Adapted from Vymazal J (2001) Types of constructed wetlands for wastewater treatment: Their potential for nutrient removal. In: Vymazal J (ed.) Transformations of Nutrients in Natural and Constructed Wetlands, pp. 1 93. Leiden, The Netherlands: Backhuys Publishers; and Vymazal J (2005) Constructed wetlands for wastewater treatment in Europe. In: Dunne EJ, Reddy KR, and Carton OT (eds.) Nutrient Management in Agricultural Watershed: A Wetland Solution, pp. 230 244. Wageningen, The Netherlands: Wageningen Academic Publishers.

aAverage loading for BOD5 and TSS given in units of kg ha 1 d 1.

IN, inflow; OUT, outflow; REM, removed load; n, number of systems; removal efficiency (EFF) in %. Data from Australia, Canada, China, New Zealand, Poland, Sweden, USA, the Netherlands. Most CWs are designed as tertiary treatment.

Adapted from Vymazal J (2001) Types of constructed wetlands for wastewater treatment: Their potential for nutrient removal. In: Vymazal J (ed.) Transformations of Nutrients in Natural and Constructed Wetlands, pp. 1 93. Leiden, The Netherlands: Backhuys Publishers; and Vymazal J (2005) Constructed wetlands for wastewater treatment in Europe. In: Dunne EJ, Reddy KR, and Carton OT (eds.) Nutrient Management in Agricultural Watershed: A Wetland Solution, pp. 230 244. Wageningen, The Netherlands: Wageningen Academic Publishers.

Figure 4 CW for treatment of mine drainage waters at Monastery Run, PA. Photo by J. Vymazal.
Figure 5 Deposits of oxidized iron in the CWs at Monastery Run, PA. Photo by J. Vymazal.

and anaerobic zones. In aerobic zones, dissolved iron (Fe2+) and manganese (Mn2+) are oxidized and conse quently precipitated as oxyhydroxides:

The precipitation ofiron and manganese oxides, caused by microbially mediated oxidation, is thought to be the dominant process in metal removal in aerobic zones of FWS CWs. The precipitated oxyhydroxides of iron and manganese strongly adsorb other heavy metals such as Cu, Pb, Ni, Co, and Cr. These metals could also simultaneously co precipitate on oxyhydroxides. Manganese is also retained under aerobic conditions through the microbial oxidation ofthe bivalent form to the tetravalent state. The Mn4+ is then precipitated mainly as MnO2. Manganese oxidation occurs more slowly than iron oxidation and is inhibited by the presence of Fe2+. Consequently, Fe and Mn precipitate sequentially rather than simultaneously. The mine drainage waters are very often very acidic with pH as low as 2.0 and therefore not many plants can survive under such conditions. It seems that for acid mine drainage waters the most suitable plant is cattail (Typha sp.) which can tolerate very low pH values.

FWS CWs are also very often used to treat waste waters derived from livestock (cattle, dairy, swine, poultry, aquaculture, or any other farm reared animals) operations. CWs for livestock wastewater treatment have been utilized throughout the world but the majority ofthe systems are in North America (Figure 6). However, many fine examples from other parts of the world exist, for example in Ireland (Figure 7). The concentrated waste waters from livestock operations are usually very strong and, therefore, some form ofpretreatment (settling basin, anaerobic lagoon) is usually applied. In some cases, further dilution is necessary in order to achieve pollutant concentrations that could be treated in CWs (Table 2).

FWS CWs are also commonly used to treat runoff waters from various facilities including highways, parking lots, air ports, golfcourses, or agricultural runoff (Figures 8-10). In this case, CWs could be categorized as systems that are designed to store and treat received stormwater prior to

Figure 6 CWs for poultry/meat abattoir (slaughter house) at Pouiliot near Quebec, Canada. Photo by J. Vymazal.
Figure 7 CW for farmyard dirty waters in Ireland. Photo by J. Vymazal.
Figure 8 Highway stormwater runoff CWs in Boucherville near Montreal, Canada. Runoff water is collected in the outside channel and then it flows over the middle section planted with Phragmites australis to the central collection channel. Photo by J. Vymazal.
Figure 9 CWs for parking lot stormwater runoff in Charleston, SC, USA. Photo by J. Vymazal.

Table 2 Examples of FWS CWs with emergent vegetation treatment efficiency for various wastewaters

Wastewater BOD5 COD TSS TP NH4-N TN FC

Swine lagoon (Alabama, USA)a 77/7.9 320/64 136/15.5 28.4/6.8 55.6/8.6 74/12d

Dairy (Connecticut, USA)b 2683/611 1284/130 25.7/14.1 199/21.6 103/74d 5.8/4.1

Poultry (Alabama, USA)c 198/100 350/180 120/43 26/17.1 95/62 118/68d 4.2/2.9

Concentrations of inflow/outflow in mg l 1. Fecal coliforms (FC) in log 10 units.

aMcCaskey TA and Hannah TC (1997) Performance of a full scale constructed wetland treating swine lagoon effluent in northwest Alabama. In: Payne VWE and Knight RL (eds.) Constructed Wetlands for Animal Waste Treatment: A Manual of Performance, Design, and Operation with Case Histories, pp. 5 8. Stennis Space Center, MS: Gulf of Mexico Program.

bMajer Newman J, Clausen JC, and Neafsey JA (2000) Seasonal performance of a wetland constructed to process dairy milkhouse wastewater in Connecticut. Ecological Engineering 14:181 198.

cHill DT and Rogers JW (1997) Auburn University constructed wetlands for the treatment of poultry lagoon effluent A case study. In: Payne VWE and Knight RL (eds.) Constructed Wetlands for Animal Waste Treatment. A Manual of Performance, Design, and Operation with Case Histories, pp. 34 40. Stennis Space Center, MS: Gulf of Mexico Program. dTKN, total Kjeldahl nitrogen.

Figure 10 Stormwater runoff CW for a Rivertowne Country Club golfcourse near Charleston, SC, USA. Photo by J. Vymazal.

releasing it at an appropriate rate once the peak flow has passed. The stormwater wetlands are very effective in reten tion of suspended solids and heavy metals that are often in particulate forms. During the winter, airport stormwater runoff waters also contain aircraft de icing waters (usually glycol based) and urea which is used to defrost the runways. Both BOD and nitrogen are removed successfully in this case. Agricultural runoff CWs very often target herbicides (e.g., atrazine, simazine, metolachlor) and it has been found that CWs are quite effective in eliminating these herbicides.

Recently, FWS CWs have been used to treat all kinds of industrial wastewaters including those from agroindustry. In the United States, China, Germany, Canada, or Hungary, CWs are successfully used to treat refinery effluents, with suspended solids, oil and grease, alkanes, BTEX (benzene, toluene, ethyl ben zene, and xylenes), and phenols being the major target of treatment. FWS CWs have also been successfully tested in treating residuals from production of explo sives, namely TNT (2,4,6 trinitrotoluene) and RDX (hexahydro 1,3,5 trinitro 1,3,5 triazine) contamination. Wastewaters from agroindustry treated in FWS CWs include sugar , potato , milk (Figure 11), meat , wine , beer , spirits , and vegetables processing wastewaters or aquacultures.

CWs with FWS have also been used to treat landfill leachates. These systems usually include aerated lagoons as pretreatment and then combinations of various types of CWs. FWS CWs are very common in this combination (Figure 12). Landfill leachates contain very high concen trations of COD, BOD, suspended solids, ammonia, heavy metals, and volatile organic compounds; however, results from operating systems from North America, Norway, Slovenia, or the United Kingdom indicate that CWs are a suitable technology for the treatment of landfill leachates.

Figure 11 Nine hectares of CWs at Kilmeaden, Ireland, for treatment of cheese factory wastewaters. Photo by J. Vymazal.
Figure 12 CWs for landfill leachate treatment at Pensacola, FL, USA. Photo by J. Vymazal.
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