In situ denitrification on nitrate rich groundwater in South Africa

The occurrence of high nitrate levels in groundwater is a widespread phenomenon. This is ascribed to both natural and anthropogenic causes. High concentrations of ingested nitrate cause methaemoglobinaemia, which can be fatal for infants and livestock. The maximum permissible level of nitrate in drinking water in South Africa is 20 mg/L (as N). This value has been used as a cut-off for the identification of problem areas for water supply in South Africa. In situ nitrate removal is practised by countries in Europe, the United States and Canada. Nitrate removal methods typically use biological denitrification and sometimes ion-exchange. In the USA and Canada, the permeable reactive barrier is widely used, which promotes biological or chemical denitrification. Other techniques use injection of reagents into the aquifer. Examples for in situ biological denitrification, the Nitredox® method uses a sophisticated arrangement of injection and aeration wells to manipulate oxidation and reduc...

Environmental science and pollution research international, 2015

The paper presents a compilation of various autotrophic and heterotrophic ways of solid-phase denitrification. It covers a complete understanding of various pathways followed during denitrification process. The paper gives a brief review on various governing factors on which the process depends. It focuses mainly on the solid-phase denitrification process, its applicability, efficiency, and disadvantages associated. It presents a critical review on various methodologies associated with denitrification process reported in past years. A comparative study has also been carried out to have a better understanding of advantages and disadvantages of a particular method. We summarize the various organic and inorganic substances and various techniques that have been used for enhancing denitrification process and suggest possible gaps in the research areas whi'ch are worthy of future research.

CATENA, 2015

Evidence for the occurrence of denitrification in shallow groundwater systems in New Zealand (NZ) is poorly documented; however, an observational study of the Toenepi dairying catchment in the Waikato region of NZ revealed a prevalence of reduced groundwater with very low nitrate (NO 3 −) concentrations (predominantly b 0.5 mg L −1 N). Denitrification in the shallow groundwater system could play an important role in catchments with high NO 3 − leaching losses, by reducing the impact of land use and management practices on freshwater bodies. International studies have shown that denitrification below the root zone is often limited by the low availability of carbon (C) or other electron donors. In this laboratory incubation study we investigated three different profiles (to a maximum depth of 4.7 m below ground surface) in the Toenepi catchment (15 km 2). Denitrification capacity was measured following the addition of 15 N-enriched NO 3 − , while glucose was used as a readily available C source when ascertaining the denitrification potentials. The largest total 15 N fluxes (without C amendment) were observed in samples from the Kereone (1.3-2.1 nmol N g −1 h −1) and Topehaehae sites (2.8 nmol N g −1 h −1); however, all sites had samples with fluxes of a similar magnitude (3.3-4.7 nmol N g −1 h −1) 1) with no significant difference between sites (p N 0.05) when glucose was added. The profiles were generally C-limited, as indicated by more than 80% of samples showing an increase (p b 0.01) in total 15 N gas (15 N 2 + 15 N 2 O) production after C addition. The composition of the total 15 N gas flux varied with depth but 15 N 2 was ≥69% of the total 15 N flux and typically N 92%. Extrapolation of denitrification capacity rates to field temperatures (14°C) indicates that much of the material found at depth, particularly at the Kereone and Topehaehae sites could contribute substantially towards attenuating the estimated NO 3 − leaching losses (29-42 kg N ha − 1 year − 1) from the root zone and is likely the cause of the very low NO 3 − concentrations prevalent throughout the catchment.

Denitrification is an important nitrate (NO 3 -) attenuation process in soil-water systems. A sound understanding of this process will aid in the management and mitigation of the impacts of NO 3 -on groundwater and surface water quality. Denitrification in surface soils has been widely studied, but there are relatively few studies of its occurrence and distribution in the subsurface environment, particularly in the Manawatu River catchment, New Zealand. Challenges around the measurement of denitrification in the subsurface environment is one of the reasons that there has been limited research in this important area. Acetylene inhibition (AI) is a commonly employed method to measure denitrification in soil-water systems. However, subsurface denitrification studies using the AI method vary in methodological details, and this variation has implications for the reliability and comparability of results. An experimental site was established at Massey University"s No. 1 Dairy Farm to ...

Science of The Total Environment, 2019

Use of nitrogen and oxygen isotopes of dissolved nitrate to trace field-scale induced denitrification efficiency throughout an in-situ groundwater remediation strategy

Due to human activities like fertilizer production and fossil fuel combustion, reactive nitrogen levels in the biosphere have increased ten-fold in the last 150 years. Once present, reactive nitrogen often cascades through and disrupts multiple ecosystems before being reduced to N 2 gas. As the most mobile of the reactive nitrogen species, nitrate (NO 3 -

Water, Air, and Soil Pollution, 2009

IMWA 2020 “Mine Water Solutions”, 2020

Due to the importance of groundwater in South Africa, the University of the Free State has successfully developed a zero waste bioremediation technology to treat nitrate pollution in water. Groundwater nitrate pollution of a fractured rock aquifer arose due to the storage of fertilizer effluent in unlined quarries. Numerical model simulations indicates that the proposed remediation removes the nitrate from the aquifer in a shorter timescale than the predicted natural attenuation. Treating the polluted water on site with the zero-waste bioremediation technique, and then re-injecting the treated water into the aquifer provides a holistic and sustainable solution to nitrate pollution.

1991

A relatively narrow vertical zone (5-6 m thick) of NO; containing groundwater was identified using multilevel sampling devices in a sand and gravel aquifer on Cape Cod, MA, USA. The aquifer has been chronically contaminated by surface disposal of treated sewage 0.3 km upgradient from the study ama. The NO; zone was anoxic and contained high #n~ntmtions of NzO (16.5 pM), suggesting that it was a zone of active denitrification. Denitrifying activity was confirmed with direct measurement using acetylene block incubations with aquifer core material; the peak rate was 2.4 nmol N reduced (g sed)-' day-'. Concentrations of dissolved inorganic carbon and N2 were close to atmospheric equilibrium in un~n~ina~ groundwater, but were more than 2 times higher within the con~minant plume. Excess CO, and N2 suggested in situ formation with a stoichiometry of C and N mineralized via denitrification of 0.8 (C/N). Denitrification within the aquifer resulted in an increase in the natural 615N of NO; (from + 13.6 to +42.0%-o) and the NZ produced, with an isotopic enrichment factor, 6, of -13.9%. Vertical profiles of NH: and S"N of NH: indicated that ~rn~ato~ reduction of NO; to NH: was also occurring, but mass balance calculations indicated that denitrification was the predominant process. These results demonstrate that a combination approach using field mass balance, stable isotope analysis, and laboratory incubations yields useful insi8ht as to the significance of denittication in aquifer sediments and that closely spaced vertical sampling is necessary to adequately quanti~ the processes controlling C and N transport and transformation within these environments.

The removal of nitrate is essential for water contaminated with nitrate before being utilized, since a large amount of nitrate in drinking water often causes a disease called methemoglobinemia and other health disorders such as hypertension, increased infant mortality, goiter, stomach cancer, thyroid disorder, cytogenetic defects and birth defects. Hence nitrate removal is an important aspect of present day's wastewater treatment process. Physical and chemical processes such as reverse osmosis, ion exchange, electro dialysis and chemical denitrification have been developed for nitrate removal from water. These techniques are effective in removing nitrate from contaminated water; they are very expensive for pilot scale operation with a limited potential application. Owing to these limitations in the removal of nitrate from water and/or wastewater, the most versatile and widely used technology is biological denitrification. Hence in this research work, feasibility study was carried out for removing nitrate from ground water by biological denitrification with optimum amount of carbon source under anoxic condition.