Animal waste management practices are under scrutiny by the public and by state and federal agencies because of their potential impact on the environment. The public perceive and associate water quality problems of streams and lakes as being caused by irresponsible farming practices. Excessive application of animal manures on crop and pasture lands is generally implicated as a major source of non-point source pollution of streams and lakes. Odors associated with animal manures has hindered expansion and new startups of confined animal operations, especially swine operations. Also, there have been comments associating foodborne disease outbreaks with “insanitary conditions” and improper management and disposal of animal manures on livestock farms. Swine production facilities have been the focus of much criticism in recent years. Odors and the potential for water contamination are cited as problems of such operations. Many swine production facilities employ liquid waste management systems with lagoons as low cost, temporary waste storage structures. The liquid waste must be spread on land periodically to avoid overflow of lagoons, and during land application, manure odors are particularly evident. Alternative liquid animal manure management systems need to be explored which can reduce the impact of the waste on the environment and which permit sustainability of swine and other livestock production enterprises.
Constructed wetlands were first used in Europe and Scandinavia as an affordable alternative to municipal wastewater treatment systems. The technology has been proven to be highly successful for treatment of municipal wastewaters, and this has stimulated interest to apply this technology to the treatment of liquid manures such as liquid swine manure in lagoons. Some of the perceived benefits of using constructed wetlands for the treatment of swine lagoon wastewaters are : (1) low cost of construction, (2) low operation cost, (3) highly efficient process, (4) the process is natural, and low technology, (5) low mechanization, and (6) good potential for controlling odors. It appears that constructed wetlands are well suited for use on livestock farms for the treatment of large volumes of wastewater at a nominal cost. To demonstrate the use of constructed wetlands for the treatment of swine lagoon wastewater, a project was initiated in Alabama with the following project objectives:
1. Develop guidelines for efficient operation of constructed wetlands for bioremediation of swine lagoon wastewater.
2. Determine impact of wetlands treating swine lagoon wastewater on groundwater quality.
3. Demonstrate efficient swine lagoon wastewater treatment by wetlands to regulatory agencies and to area livestock producers.
The wetland system was constructed at the Sand Mountain Agricultural Experiment Station at Crossville, Alabama in the late Fall of 1988. The system was designed according to criteria from the Tennessee Valley Authority for constructed wetlands treating municipal wastewater. A one-acre wetland was built with five, 0.1 acre (26 feet wide X 164 feet long) wetland cells in the upper tier and five cells in the lower tier. The total wetland area is 1 acre which treats all the manure from a 500 market hog/year operation. The wetland cells were planted with emergent aquatic plants in the Spring of 1989 with cattail, soft-stem bulrush and common reed as the predominant aquatic plants. The plants were cultivated for two growing seasons before swine lagoon effluent was treated in the wetland cells. Because animal manure lagoon effluents contain high ammonia levels which can be toxic to plants, the lagoon effluent was first diverted through a shallow 0.25 acre mixing pond to allow dilution of the wastewater, if necessary, before the lagoon effluent entered the wetland. Constructed wetlands work best when animal manures are diluted and some particulate matter is removed prior to the wastewater entering the wetland system. This can be accomplished by water flushing the manure out of livestock production facilities into a two-stage lagoon system where some treatment and settling of particulates occur. Effluent from the secondary lagoon can then be treated in wetlands much more efficiently. This type of wetland treatment system was monitored at two-week intervals for 57 months at a Biochemical/Biological Oxygen Demand (BOD5) loading rate of 4 lbs BOD/acre/day. At this loading rate to the wetland system the wetland effluent had less than 10 ppm total ammonia-nitrogen (NH3+NH4-N), less than 30 ppm of total suspended solids (TSS) and less than 30 ppm of BOD5 as recommended by the USDA/Natural Resource Conservation Service (NRCS). There has been no impact on groundwater quality during the wetland study.
Another study conducted at the Crossville, Alabama demonstration site evaluated three BOD5 loading rates to verify the 4 lbs BOD/acre/day loading rate determined previously was on target or if the wetland loading rate could be increased without impairment of wastewater treatment efficiency. The three BOD5 loading rates (5.2, 7.1, and 11.7 lbs BOD/acre/day) were monitored for 23 months. At the low loading rate (5.2 lbs BOD/acre/day) the wetland outflow had 14.7 ppm of total ammonia-N, 9.5 ppm BOD5, and 25.1 ppm of TSS. Both BOD5 and TSS were within the USDA/NRCS guideline of less than 30 ppm, and total ammonia-N only exceeded the guideline by 4.7 ppm. These results indicate that a wetland loading rate of 4 to 5 lbs BOD5/acre/day will permit sufficient wastewater treatment to achieve USDA/NRCS suggested wetland effluent guidelines for TSS, BOD and total ammonia-N. At this wetland BOD5 loading rate about 7,700 gallons of lagoon effluent can be treated daily with a one acre wetland. Mass loading of TKN and BOD5 into the wetlands was reduced 67.8% and 83.3%, respectively, with 1.8 lbs of TKN and 0.85 lbs of BOD5 exiting the acre wetland daily. This degree of wastewater treatment may be viewed as unnecessary because the treated wastewater cannot be discharged without a regulatory permit. However, water that is treated to meet wetland effluent discharge criteria of government agencies may be interpreted to be safe to be used to flush manure from swine production facilities. Water treatment to achieve water suitable for use in swine production facilities must eliminate odors and practically eliminate potential hazards from enteric pathogenic bacteria.
Studies at the Crossville, Alabama demonstration site with wetland effluent recycled for use as flush water for cleaning swine farrowing and nursery houses, have demonstrated that recycled water had average TKN, total ammonia, and BOD5 concentrations of 7.7, 2.2, and 13.8 ppm, respectively, that meet Georgia Department of Natural Resources guidelines for effluent discharge from constructed wetlands treating municipal wastewater. The Georgia guidelines require the effluent to not exceed a BOD5 of 20 ppm and 5 ppm NH3-N during May to October which is during the Summer and Fall when wetland treatment efficiency is highest. Treatment of swine lagoon wastewater to these final effluent treatment criteria eliminates odors and substantially reduces levels of nutrients and fecal coliform bacteria. The final effluent can be applied to land or recycled for cleaning swine production facilities, thereby reducing the impact of the lagoon wastewater on the environment and also contributing to the sustainability and profitability of swine production enterprises.
In addition to the potential negative impact of animal manure on water and air quality, there is a growing concern that improper manure management might have a major impact on the dissemination of enteric diseases such as E.coli 0157:H7 and Salmonella from infected food-producing animals to humans. Studies have shown that E.coli 0157:H7 and Salmonella, inoculated at over a million bacteria/ml into wastewater collected from various sites in the wetland treatment system, were eliminated in less than 20 days. Lagoons are required to have a minimum of three months storage capacity, wetlands should have at least 12 days detention and the catch basin for the wetland effluent provides additional detention time. The combined water storage time is more than 20 days which has a considerable margin of safety for the elimination of enteric bacterial pathogens. Following treatment of the wastewater through the lagoon/wetland system, the water is safe to apply to land or to use as cleaning water in livestock production facilities.