Polyacrylamide preparations for protection of water quality threatened by agricultural runoff contaminants
Introduction
Agriculture is the most wide spread source of water pollution in the United States (USEPA, 1998). For decades, most surface water quality protection from agriculture has focused on soil erosion and related non-point sources that contribute to surface water contamination. The soil erosion control literature is voluminous and links to surface water quality are well documented. In the last decade, there has been an enormus shift in animal rearing towards large scale confined animal feeding operations (CAFOs).
CAFOs are the primary source of agricultural pollution and pose a number of risks to water quality and public health due to the large amount of manure generated. US Environmental Protection Agency (EPA) estimates that animal waste production in 1992 was 13 times greater on a dry weight basis than human production. Sources of water pollution from CAFOs include direct discharges, open feedlots, treatment and storage lagoons, manure stockpiles and land application of manure to fields. Animal waste from CAFOs are a major source of enteric microorganisms (Fraser et al., 1998, Howell et al., 1995, Howell et al., 1996, Mawdsley et al., 1995) and nutrients such as nitrogen (N) and phosphorus (P; Hubbard et al., 1998, Snyder et al., 1998, Jordan et al., 1993) to our nation's water systems.
Dairy and other CAFOs, such as hog production operations are a major agricultural industry in the United States. In 1992, total farm gate revenues across each of the livestock and poultry industries totaled $84.6 billion (USEPA, 1998). However, these operations are also a primary source of pollution and pose a number of risks to water quality and public health due to inability to manage and dispose of the large amount of manure generated. The number and size of animal feeding operations in the United States has been steadily increasing in the last 10 years (USEPA, 1998).
The EPA estimated that in 1992, there were about 510,000 animal production facilities in the United States which produced an estimated 2.07 trillion tons of manure. According to the EPA's 1996 National Water Quality Inventory, agricultural operations, especially animal production facilities, contribute to the impairment of at least 173,629 miles of rivers, 3,183,159 acres of lakes and 2971 square miles of estuaries. Twenty-two states reported on the impacts of specific types of agriculture on rivers and streams, attributing 20% of the agricultural impairment to animal production facilities. These findings, as well as incidents of waste spills, excessive runoff, leaking storage lagoons and odor problems, have heightened the public awareness of environmental impacts from animal production facilities. Clearly a major problem exists which constitutes a number of risks to water quality and public health.
Pollution of surface flow and groundwater from the application of animal waste to soils has been documented (Mallin et al., 1997, Mawdsley et al., 1995, Khaeel et al., 1980). Liquid-waste discharge onto soil initiates solute and microbe movement into the soil that follows natural ground water drainage patterns and contaminates adjoining surface water. These same bodies of water are often sources of drinking water and/or used for recreational activities. Human contact with recreational waters containing intestinal pathogens is an effective method of disease transmission. Therefore, it is critical to employ appropriate treatment strategies in order to maintain the quality of our lakes and streams and keep them free of intestinal pathogens and excess nutrients.
Increased N and P concentrations in water can alter the function and stability of many riparian and aquatic ecosystems. Most aquatic ecosystems develop in conditions limited by N and P. In the past few decades, intensive fertilization has contributed to the accumulation of these elements in aquatic environments (David and Gentry, 2000, Edwards et al., 2000, Sharpley et al., 2000, Vitousek et al., 1997, Koch and Reddy, 1992, Lebo and Sharp, 1993). Changes in flora and fauna have been attributed to increased input of nutrients (Stevenson et al., 1993; Cooper and Brush, 1993, Koch and Reddy, 1992, Davis, 1991). Increased N and P in wetland ecosystems may also cause eutrophication, creating an abnormally high oxygen demand and often resulting in the death of many aquatic organisms (Cooper and Brush, 1993).
Management practices that are currently used to mitigate the input of pollutants from animal waste to surface and groundwater include control of animal numbers (Gary et al., 1985, Jawson et al., 1982), control of animal diet (Diez-Gonzalez et al., 1998), constructed wetlands, and riparian filterstrips (Coyne et al., 1995, Coyne et al., 1998, Walker et al., 1990, Young et al., 1980). However, there are several problems with vegetative systems; (1) vegetation in wetlands or riparian areas can take from months to years to establish, (2) vegetative systems are not effective when vegetation is not growing (winter months) and can become nutrient sources rather than nutrient sinks (Hubbard et al., 1998, Snyder et al., 1998, Jordan et al., 1993), (3) riparian filterstrips or constructed wetlands are effective for only small quantities of runoff (relatively infrequent or low intensity runoff events) because continuous application can quickly overload the vegetative system's ability to withdraw nutrients (Entry et al., 2000a, Entry et al., 2000b, Hubbard et al., 1998, Snyder et al., 1998, Jordan et al., 1993), and (4) vegetative systems can not be transported to the site of a waste spill or runoff area. Therefore, even when best management practices are used, animal production operations can sometimes contribute large amounts of nutrients and enteric microorganisms to watercourses.
Since the early 1990s use of polyacrylamide (PAM) has been shown to be an effective strategy for erosion control and water quality protection (Lentz and Sojka, 1994). The application of anionic polyacrylamide (PAM) to soils and/or vegetative treatments may also provide a cost-effective way to dramatically reduce bacteria and nutrient loads in animal waste effluent and thereby reduce pollution in surface and ground waters receiving these effluents. PAM application can be used alone or in conjunction with vegetative strategies, which may then operate more effectively due to reduced contaminant loads in waste streams entering the system.
Section snippets
Polyacrylamide
Polyacrylamide (PAM) is a generic chemistry term, referring to a broad class of compounds. There are hundreds of specific PAM formulations that vary in polymer chain length and number and kinds of functional group substitutions. In some chain segments PAM amide functional groups are substituted with groups containing sodium ions or protons. They freely dissociate in water, providing negative charge sites (Fig. 1). In PAM formulations used for erosion control, typically one in five chain
Environmental and safety concerns
Environmental and safety considerations of anionic PAMs have been reviewed (Barvenik, 1994, Bologna et al., 1999, Seybold, 1994). The most significant environmental effect of PAM use is its erosion reduction, protecting surface waters from sediment and other contaminants washed from eroding fields. PAM greatly reduces nutrients, pesticides, and biological oxygen demand (BOD) of irrigation return flows (Agassi et al., 1995, Lentz et al., 1998, Lentz et al., in press). In Australian tests of PAM,
Polyacrylamide degradation in soil and water
PAM degradation rates in soil are estimated to be approximately 10% year−1 (Barvenik, 1994). Degradation of the acryamide monomer (AMD) is fairly rapid (Kay-Shoemake et al., 1998a, Shanker et al., 1990, Lande et al., 1979). AMD was completely degraded within 5 days after applying 500 mg PAM kg−1 garden soil (Shanker et al., 1990). Lande et al. (1979) applied 25 mg PAM kg−1 soil and reported that half life of an AMD in agricultural soils was 18–45 h.
There have been mixed, and sometimes
Polyacrylamide use for removal of enteric bacteria and nutrients from wastewater
Sojka and Entry (2000) found that after water traveled 1 m at 7.5 and 15.5 l min−1, PAM-treatment reduced algae, total bacterial and microbial biomass and total fungal biomass relative to the control treatment. After water traveled 40 m at 7.5, 15.5, and 22.5 l min−1, PAM-treatment reduced algae, the numbers of active and total bacteria, active and total fungal length, total bacterial biomass, total fungal and microbial biomass relative to the control treatment. In a study to determine the
Future research
Future research may be directed toward efficacy of PAM-related compounds to remove specific bacterial species from waste water. We have not found reports investigating the ability of PAM compounds to remove specific species of disease causing bacteria or fungi. These tests may require the release of specific bacteria such as Escherichia coli O157H7 or Salmonella typhi in controlled water environments. We have not found reports investigating the efficacy of PAM, PAM+Al(SO4)3, and PAM+CaO to
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