Development of a procedure for sustainable in situ aquifer denitrification

Abstract

INTRODUCTIONNitrate is the most pervasive contaminant in groundwater in the United States and throughout the world. In Nebraska, more than 85 percent of the population relies on groundwater for drinking water and more than 20 percent of the domestic wells have nitrate concentrations that exceed the drinking water standard (Spalding & Exner, 1993). In drinking water, nitrate is reported to cause methemoglobinemia or blue-baby syndrome (Walton, 1951) in infants and bladder cancer in women (Weyer et al., 2001).Many rural communities have wells that exceed the maximum contaminant level (MCL) of 10 mg NO 3-N l -1 and find available above-ground treatment alternatives economically prohibitive. Above-ground physical/chemical processes such as ion exchange, reverse osmosis, and electrodialysis do not detoxify nitrate, are very expensive, and generate hazardous brine waste that must be disposed off in a secure landfill at additional cost (Rogalla et al., 1991;Bouwer & Crowe, 1982). Biodenitrification is the only process that can specifically target nitrate and convert this anion to innocuous end product. IN SITU DENITRIFICATIONEnhanced in situ biodenitrification (EISBD) is an emerging technology that offers a cost-effective and environmental friendly solution to the nitrate contamination problem (ITRC, 2000). In this study, in situ injection relies on a daisy well system, which constitutes a series of injection wells arranged in a circular pattern around the contaminated well (extraction well) to deliver the needed carbon substrate directly into the nitrate-contaminated zone; whereas the remediated water will be captured by the extraction well. Simultaneous extraction and injection in this configuration creates a pattern of groundwater flow radiating from higher water levels at the injection wells to lower levels created by drawdown at the extraction well. During operation, the water table assumes a configuration that is depicted as being similar to the petals of a daisy flower.When sufficient organic substrate is injected into the groundwater, endemic nitrate degrading microbes (denitrifiers) proliferate in the denitrified zones (DNZ) and enzymatically reduce nitrate to harmless nitrogen gas as follows:Attempts at in situ denitrification have been reported throughout the world with various degrees of success ( McMahon et al., 1998;Nuttall, 1997;Hammon & Fustec, 1991;Kruithof et al., 1985;Janda et al., 1988;Mercado et al., 1988;Braester & Martinell, 1988;Chalupa, 1985). Nitrate removal rates varied from as little as 10 percent to almost complete removal. However, in most cases the performance of the denitrification process was impaired by the excessive and rapid biomass growth in the immediate vicinity of the injection well.This resulted in clogging and rendered the injection well inoperable. Recent researches (Semprini et al., 1988;Shouche et al., 1993;Peyton, 1996;Khan, 2000) suggested that a nutrient pulsing technique minimized biofouling at the injection well. However, these studies were limited to computer simulatio...

Drinking Water: Factors Affecting the Quality of Drinking Water

“…Until recently the use of this technology was limited due to fear of the biofouling of the injection wells [284]. However, detailed research of the given process makes it possible to show that bio-growth may be controlled [284,285].…”

“…However, detailed research of the given process makes it possible to show that bio-growth may be controlled [284,285]. This is achieved by the correct choosing of the carbon source, which produces less biomass than the other sources [276].…”

“…The solution was injected under pressure for four hours [276]. A similar cleaning procedure was described in paper [284].…”

Thermodynamic targeting of microbial perchlorate reduction by selective electron donors

“…This results in an ineffective treatment of the target contaminant, inefficient use of electron donor, plugging of the near-well aquifer matrix, changes in mineral content, hydraulic conductivity, and pH, and a reduction in water quality through direct or indirect release of undesirable end products (Fe(II), HS À , CH 4 sorbed heavy metals, and so on.) (Ponnamperuma, 1972(Ponnamperuma, , 1984Taylor and Jaffe, 1990;Cunningham et al, 1991;Vandevivere and Baveye, 1992;Achenbach, 2001, 2006;Khan and Spalding, 2003).…”

Ethanol Addition for Enhancing Denitrification at the Uranium Mill Tailing Site in Monument Valley, AZ

“…A possible means by which to enhance the rate of denitrification is to inject organic amendments such as ethanol, methanol, and acetate to serve as energy sources for resident microorganisms. This approach has recently been investigated and shown to be successful in laboratory-and fieldscale pilot studies (e.g., ITRC 2000; Smith et al 2001;Tartakovsky et al 2002;Khan and Spalding 2003;Istok et al 2004;Santos et al 2004;Martin et al 2009;Adav et al 2010).…”