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Constructed wetlands for dairies |
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Component aids dairy wastewater treatment system By Joanne Littlefield
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Keeping cows clean and healthy requires |
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In the mid-1990s Rovey Dairy in Glendale, Arizona (northwest of Phoenix)
began meeting with CALS faculty to determine the suitability of the
site for experiments focused on plants and pond lining systems that
would result in the cleanest water. Dairy owner Paul Rovey says he decided
to participate in the project because it would benefit not only his
operation, but the university and the dairy industry in Arizona as well.
“We liked the idea of having some new avenues for dealing with
wastewater in a different, maybe a proactive kind of a way,” Rovey
says. “It’s truly a dairy constructed project, and we’ve
proven that if the dairy industry in Arizona decides dairies need to
use this kind of system, a dairy can build a constructed wetlands on
their own with the information that’s available.” Conventional on-site treatment for manure has included scraping the
pens and stockpiling the manure for fertilizing adjacent crops. In contrast,
a flush system uses dairy wash water to remove manure from the dairy
cow feeding lanes. This method saves labor, but increases the quantity
and nutrient loading of wastewater, which requires an improved wastewater
treatment system for dairies with flush systems. The Natural Resources Conservation Service (NRCS) and CALS have been
working on guidelines for dairy operators and other confined animal
feeding operations to meet Clean Water Act standards and Arizona Department
of Environmental Quality inspection criteria. Beginning in 1996 an integrated
dairy wastewater treatment system, which includes wetlands, was constructed
at the Rovey Dairy adjacent to the milking parlor and feeding pens to
meet these more stringent clean water regulations. The two-phase project includes research equipment for conducting experiments
on the treatment system. Phase one was completed in 2000; phase two’s
redesign and re-engineering were undertaken in response to phase one
research results, and system modifications were completed in 2001. The Treatment System Over the last few years, municipalities across the nation have been
developing wetlands systems of some kind to treat wastewater for reuse.
The system being investigated for dairies is intended to be less complex
and therefore less expensive for dairy operations to install and maintain. The dairy wetlands component at Rovey Dairy includes a series of treatment cells or ponds to filter and remove contaminants from the water so that it can be recycled and conserved. The system, while man-made, is designed to mimic a natural setting, allowing plants to do the work of complicated pumps and filters. These treatment cells (see chart, right) include solids separators, anaerobic lagoons, and aerobic ponds. |
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The goal of the entire treatment system, including the wetlands, is to enable the dairy to decrease new water consumption. Thus the research team is examining ways to treat dairy wastewater so that the dairy can use it either as blended irrigation water for flushing back into the barn flush lanes, |
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or as the water applied to composting the dairy manure solids. Martin
Karpiscak, an associate research scientist with the CALS Office of Arid
Land Studies and Bob Freitas, an associate in Cooperative Extension
in the Department of Agricultural and Biosystems Engineering are the
principal investigators on a collaborative project that includes researchers
from the UA Department of Animal Sciences; the Department of Soil, Water
and Environmental Science; and Cooperative Extension, Maricopa County.
According to Freitas, the arrangement of the ponds and lagoons is critical.
The team has tried different configurations of the system, and found
during the first phase of the project that insufficient oxygen was available
for transforming nitrogen from the ammonium form to plant-available
nitrate form, which the wetlands plants can use more readily. One of the most significant findings indicates the importance of lining
the ponds. Freitas says a compacted clay liner offers a considerable
degree of sealing capacity. “For protection for groundwater we
suggest that, at the very least, a clay liner be used that meets NRCS
standards,” he says. “Our research shows that over time the
spaces clog between soil particles. As a biofilm is formed, the leakage
rate declines.” Water Quality, Plants Along with structural concerns, the research team needed to develop ways to keep the water clean. Karpiscak says the scientists checked the water for contaminants, including 1) pathogen levels, such as Cryptosporidium and Listeria; 2) indicator organisms such as total and fecal coliform; and 3) various forms of nitrogen such as nitrates and nitrites. They investigated the suitability of different plant species for the wetlands, taking plant measurements and samples to see how quickly the plants were growing. “We also looked at things such as electro-conductivity to determine
water salinity, at water temperature and at dissolved oxygen content,”
Karpiscak says. “One of our graduate students collected data on
water quality of the wetlands cells, and wrote a master’s thesis
on the nitrogen content in the soil profile as well as in the plant
material.” Unfortunately, mosquito breeding can be a problem with open bodies
of water such as wetlands. Karpiscak says Bacillus thuringensis var.
israeliensis (Bti.) is typically used to control mosquito larvae in
clear water. “The problem is that dairy water is not clear water.
Neither Bti. nor Bacillus sphaericus worked very effectively for any
period of time because of the high organic content,” he notes.
Research showed that the application of a larvicide (mineral oil) to
seal the water surface so that the mosquito larvae could not breed worked
the best in this situation. The project is now moving into its second phase, according to Freitas.
“Based upon our initial results, a new design of increased path
length, multiple aerobic and anaerobic cycling, and an improved gravel
based wetlands cell system shows promise in more effective water treatment,”
he says. The gravel-based system will also limit mosquito breeding.
As the researchers fine-tune their recommendations, new guidelines will
be developed and made available to dairy operators throughout the arid
regions of the country. Major funding for this project was provided by the Arizona Department of Water Resources, the Arizona Department of Environmental Quality, and the U.S. Bureau of Reclamation.
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