Denitrification woodchip bioreactor two-phase column study: Evaluation of nitrate removal at various hydraulic retention times and effect of temperature on denitrification rates

Denitrification woodchip bioreactor two-phase column study: Evaluation of nitrate removal at various hydraulic retention times and effect of temperature on denitrification rates" (2012). The transport of nitrate to surface waters is an increasing concern in United States and throughout the world. Causal linkages have been established between nutrient loading from the Mississippi River Basin watershed and the formation of the large hypoxic zone in the Gulf of Mexico near the mouth of the Mississippi River (Gulf Hypoxia Action Plan 2008). A quantitative environmental goal of a 30% nitrate load reduction by 2015 was established in 2001(Mississippi River/Gulf of Mexico Watershed Nutrient Task Force 2001); however, implementation of best management practices to meet these goals were based largely on voluntary efforts of stakeholders within the watershed (Rabalais et al. 2002). A landuse model by McIsaac et al. (2001,2002) suggests a reduction of 12–14% in nitrogen load from agricultural lands will be required to meet the overall reduction goal. Surface applications of fertilizers lead to improved production yields, but there is concern that these same chemicals pose a risk to water quality. According to the USDA's 2007 Census of Agriculture, 86% of Iowa's total land area is utilized for agriculture. Commercial fertilizers, which can contribute nitrogen to waterbodies through leaching and runoff into local water systems, are applied to 61.8% of Iowa's 30,747,550 acres of farmland. (USDA, 2009). Reducing nitrogen export from the upper Midwest is a key to maintaining and improving the quality of local, national, and global water resources. Although nitrogen fertilizers provide a measurable benefit to the agricultural industry, the increased nitrate exposure is potentially harmful to human health when consumed in drinking water, and detrimental to the aquatic ecosystems. Several health impairments have been linked to increased nitrate consumption in humans. The Environmental Protection 2 Agency imposed a maximum contaminant level on drinking water of 10 mg L-1 in response to an increased incidence of methemoglobinemia, or " blue baby syndrome " , attributed to formula prepared with well water containing high concentrations of NO 3-N (EPA, 1991). A link to increased methemogloinemia in infants and nitrate intake was further documented in Morooccan study of drinking water with high nitrate concentrations (Sadeq et al., 2008). Additional health risks associated with high nitrate consumption include thyroid dysfunction, colon cancer, and ovarian cancer (Powlson et al., 2008). The transport of nitrate into surface and marine waters also poses a risk …