by Savannah Lloyd (Pre-Veterinary) & Nathan Bush (Natural Resource Studies)

Annoyed with people telling you how to run your farm? Hesitant to lose money in purchasing a new wastewater treatment system?  Many farmers feel the same way.  Negative media forms when a lagoon wastewater treatment system overflows from a hurricane, but you don’t want to spend a chunk of money to change your wastewater system in order to make the media think positively about your farming techniques when you have to lose money in the process. Well, The positive environmental benefits of a constructed wetland outweigh the initial monetary loss, because you can convert an already existing wastewater lagoon system into a vegetative sand bed.

fig. 1 A CAFO with sewage lagoons

Factory farming began at the end of World War II when a rapid increase in the population caused modern farming techniques to fall short in sustaining the population. CAFOs (concentrated animal feeding operations) are large, industrial operations that house thousands of food animals (hogs, cattle, chickens) in confined space. In an article by Constance and Bonanno (1999), they describe in a chart the “estimates of number of hogs produced annually by site, in 1997” (p.16) and clearly show how some farms are containing “15,000 to 400,000” (p. 16) hogs on one farm.  When there are this many animals kept on-site, a lot of waste consisting of  “nitrogen, phosphorus,..and suspended solids” (Marks, 2001, p.43) builds up.  In order to maintain waste, a lagoon system was incorporated. Lagoons are on-site with livestock housing buildings. Livestock waste goes through slits in the floor and flows through pipes outside into the lagoon. In a report, Robbin Marks (2001) states that lagoons “have a size as great as six to seven-and-a-half acres and can contain as much as 20 to 45 million gallons of wastewater” (p.3).  He describes an example “[i]n North Carolina, a facility of 2,500 swine may generate 26 million gallons of lagoon liquid, close to one million gallons of lagoon sludge, and 21 million gallons of slurry” (p.3).  Although these lagoon systems have worked in the past, there are some negatives associated with lagoon system overflow.

fig. 2 Pfiesteria sores on fish from a river in lagoon-flooded river

Most lagoon systems are located near water sources and when it rains, the lagoons overflow into nearby streams, damaging wildlife and water quality.  The three major components in the waste that cause the most harm are nitrogen, phosphorus, and sludge.  “Nutrient pollution fosters the growth of a type of algae known as Pfiesteria piscicida, which has been implicated in the death of more than one billion fish in coastal waters” (Marks, 2001, p.29). Pfiesteria piscicida causes sores on the bodies of fish, which in more cases than not, leads to death in many fish. In his article, David Holt (2008) paints a vivid picture of environmental impact when he states that “North Carolina was devastated by two hurricanes, leading to an environmental catastrophe due to flooding.

Fig. 3 Hog CAFO overflow caused by Hurricane Floyd

[S]cenes of overflowing hog lagoons…had a lasting impact on the public perception of the risks associated with CAFOs” (p.171). It’s for these reasons that the public and others are trying to change the current system, which in turn angers farmers who are constantly being pestered to change.  A constructed wetland can fix these problems and lead to better relations between groups with different opinions whether they are environmentalists, the public, or farmers.

Wetlands are naturally occurring ecosystems where “water covers the soil, or is present either at or near the surface of the soil all year or for varying periods of time during the year, including during the growing season” (Environmental Protection Agency, n.d., p.1). Wetlands include a variety of habitats: from acidic coniferous forests, to sedge and grass dominated wet meadows, from coastal salt marshes to river floodplains. A major similarity is that the soil is wet for most of the year and the vegetation is uniquely different compared to nearby upland habitats. Natural wetlands have many ecological functions, such as improving water quality through nutrient transformation, flood mitigation, acting as groundwater recharge points, and performing processes which are vital for the natural hydrologic regime. Constructed wetlands mimic the biological, chemical, and physical processes of natural wetlands and in some cases provide additional habitat for animals. “[B]ecause constructed wetland systems are designed specifically for wastewater treatment; they work more efficiently than natural wetlands” (Pipeline, 1998, p.1). Unlike natural wetlands where the hydrological regime varies in frequency and timing, constructed wetland’s “water level is usually maintained uniform throughout the year…” (Gopal, 1999, p. 29). Having a regulated flow, Cronk (1996) discusses the ability of chemical processes to be maximized:

In addition, slow water flow causes suspended solids to settle from the water column in wetlands. Biochemical oxygen demand (BOD) is reduced by the settling of organic matter and through the decomposition of BOD causing substances. Besides solids and BOD, the most important constituents in animal wastewater are nitrogen and phosphorous and these can both be reduced in constructed wetlands if conditions are appropriate. (p.98)

Fig. 4 Typical treatment plant via subsurface flow constructed wetland (SFCW) as shown here in a flow diagram

Once suspended solids, excess nutrients, and BOD is reduced within the wetland, a high quality effluent is produced which can be directly deposited into a stream, or, the effluent can be re-circulated through the wetland for further treatment if pathogens exist. Although constructed wetlands are a relatively new technology to wastewater treatment, they “are under study as a best management practice to treat animal wastewater from dairy and swine operations” (Cronk, 1995, p. 97). Constructed wetlands are able to provide an alternative solution to conventional high-energy wastewater systems or environmentally unfriendly settling lagoons. However, like all systems, constructed wetlands have limitations and certain factors must be carefully considered.

Two types of constructed wetlands have been established for wastewater treatment purposes: free water surface flow and subsurface flow. Both systems require much more land than conventional systems. However, in farms, existing lagoons can potentially be converted into wetlands. According to Cronk (1995) “wastewater may receive primary solids separation in a settling basin and then it may flow into a lagoon and/or be land spread. Constructed wetlands could replace or be downstream from a lagoon and they could replace or precede land spreading” (p. 100).

Another limiting factor is the remaining sludge within the settling basin or drying bed. With respect to constructed wetlands, there are two options; according to Baillon-Dhumez, Bernstad, Gill, and Street (n.d.), reed “beds are constructed using a variety of methods depending upon the site conditions, or may even be converted using existing drying beds”(p. 2), or secondly, the sludge can be directly pumped into a newly constructed reed bed from the settling basin. The present method of dewatering sludge is using a filter press, but reed beds provide a much more efficient method of dewatering and will reduce the annual expense of disposal. “Compared to a typical filter press, a reed bed system will produce 1/6th the tonnage of dewatered sludge for disposal” (Baillon-Dhumez, Bernstad, Gill, and Street, n.d., p. 8).

Lastly, plants take time to grow. There is an initial start-up period before vegetation is established and optimal quality effluent is produced. “In some cases, two or more growing seasons may be needed before plants are established enough in the system to realize their full treatment potential” (Pipeline, 1998, p.4). Those being the cons for switching systems, there are more pros in which it’s evident that switching wastewater systems is more beneficial than harmful.

Constructed wetlands provide a relatively low cost, require little energy, look more aesthetically pleasing than current systems, and provide habitat for birds and other small animals. “The integrated constructed wetland approach to the management of livestock wastewater provides…a construction process of low relative cost requiring minimal complex management…” (Harrington, McInnes, 2009, p.5504) compared to conventional systems. To find the exact cost and size of a subsurface flow wetland, certain parameters are taken into consideration. Calculations concerning influent flow rate, detention time for contaminants, and what standards are desired for effluent quality can be found with the following equations:

1.  Q(t)= L2 (h)(f). Q is flow rate, t is detention time, L is length of wetland, h is height of wetland, and f is the porosity of soil (usually 0.35). Variations of this equation will give you the size of the wetland. 2. Ln(Co/Ct) = K(t). Co is the concentration of contaminants desired, Ct is total concentration of contaminants entering, K is a rate constant of bacteria dying and decaying, t is time. Variations of this equation give the rate at which bacteria grow, die, and decay, and the retention time of wastewater to get desired quality. Other monetary considerations include price of plants, soil media, and labor for construction. “For new beds, assuming satisfactory consideration, average costs for the design and installation of a reed bed system will be close to $10.00 to $12.00 per square foot” (Baillon-Dhumez, Bernstad, Gill, and Street, n.d., p. 2).

Compared to other treatment systems “operating costs are low because energy is not required to provide treatment” (Pipeline, 1998, p. 1). Rather than aerators, circulating tanks, and filtering presses, which can cost thousands of dollars to operate, wetlands provide the same functions with near zero energy demand.

Lastly, wetlands are aesthetically appealing to the public. Harrington and McInnes (2009) say that constructed wetlands are “landscape-fit to improve aesthetic site values and enhanced [the] biodiversity” (p. 5498). Rather than huge aerator tanks which have a potential for odors, wetlands conceal the odor within the soil media, especially in subsurface flow designs. Urban sprawl and unsustainable livestock management threaten biodiversity. “The restorations and enhancement of biodiversity is an essential component of intergraded constructed wetlands. This is achieved through intrinsic design, which aims to maximize the inherent species richness associated with freshwater wetlands” (Harrington, McInnes, 2009, p. 5501). Constructed wetlands are not only a great idea in theory, but also in practice.

Constructed wetlands have been put into effect to make lagoon systems more updated and efficient.  Marks (2001) states that “constructed wetlands have been used successfully…to further reduce concentration of nitrogen, phosphorus, biochemical oxygen demand, and suspended solids” (p.43).  This is further proof that constructed wetlands have been used and have worked. Wetland systems decrease contaminants and can accept high amounts of rainfall to account for flooding. This alternative is easy to associate into a farm, saves the farm more money in the long run, and can dissolve negative effects by pleasing not only the farmer, but nearby residents as well.

References

Baillon-Dhumez, A., Bernstad, A., Gill, N., & Street, S.I. (2010, October 12). Constructed Wetlands For Wastewater Treatment. Retrieved from http://www.chemeng.lth.se/vvan01/Arkiv/Wetlands%5B1%5D.pdf

Constance, D. H., & Bonanno, A. (1999). CAFO controversy in the Texas panhandle region: The environmental crisis of hog production. Culture & Agriculture, 21(1), 14–26. doi: 10.1525/cag.1999.21.1.14

Cronk, J. K. (1996).  Constructed wetlands to treat wastewater from dairy and swine operations: A review.  Agriculture, Ecosystems & Environment, 58(2-3), 97-114. doi: 10.1016/0167-8809(96)01024-9

Environmental Protection Agency (n.d.). America’s Wetlands: Our Link Between Land and Water. Office of Wetlands, Oceans and Watersheds. Retrieved November 2, 2010 from http://water.epa.gov/type/wetlands/toc.cfm

Gopal, B. (1999). Natural and constructed wetlands for wastewater treatment: Potentials and problems. Water Science and Technology, 40(3), 27-35. Harrington, R., & McInnes, R. (2009). Integrated constructed wetlands (ICW) for livestock wastewater management.  Bioresource Technology, 100(22), 5498-5505. doi: 10.1016/j.biortech.2009.06.007

Holt, D. M. (2008).  Unlikely allies against factory farms: animal rights advocates and environmentalists.  Agriculture and Human Values, 25(2), 169-171. doi: 10.1007/s10460-008-9122-4

Marks, R. (2001). Cesspools of shame: How factory farm lagoons threaten environmental and public health.  National Resource Defense Council and the Clean Water Act, 1-60.  Retrieved from http://www.nrdc.org/water/pollution/cesspools/cessinx.asp

Pipeline (1998, Summer). Constructed Wetlands: A Natural Treatment Alternative, 9(3).

Volland, C., Zupancic J., Chapelle J. (2003). Cost of remediation of nitrogen-contaminated soils under CAFO impoundments. Journal of Hazardous Substance Research, 4, 1-18.

Figure 1. Lighthawk. (2010). A CAFO with sewage lagoons. Retrieved from http://sierraclub.typepad.com/scrapbook/2010/09/family-farmer-kos-cafos.html?cid=6a00d83451b96069e20133f4908c1f970b

Figure 2. Marks, R. (2001). Pfiesteria sores on fish from a river in lagoon-flooded river. Retrieved from Cesspools of Shame report.

Figure 3. Marks, R. (2001). Hog CAFO overflow caused by Hurricane Floyd.  Retrieved from Cesspools of Shame report.

Figure 4. MedLibrary.org. (n.d.) Typical treatment plant via subsurface flow constructed wetland (SFCW) as shown here in a flow diagram. Retrieved November 29, 2010 From http://medlibrary.org/medwiki/Sewage_treatment