Erratum to “Sources of nitrate and ammonium contamination in groundwater under developing Asian megacities”

The status of nitrate (NO₃⁻), nitrite (NO₂⁻) and ammonium (NH₄⁺) contamination in the water systems, and the mechanisms controlling their sources, pathways, and distributions were investigated for the Southeast Asian cities of Metro Manila, Bangkok, and Jakarta. GIS-based monitoring and dual isotope approach (nitrate δ¹⁵N and δ¹⁸O) suggested that human waste via severe sewer leakage was the major source of nutrient contaminants in Metro Manila and Jakarta urban areas. Furthermore, the characteristics of the nutrient contamination differed depending on the agricultural land use pattern in the suburban areas: high nitrate contamination was observed in Jakarta (dry fields), and relatively lower nutrients consisting mainly of ammonium were detected in Bangkok (paddy fields).The exponential increase in NO₃⁻-δ¹⁵N along with the NO₃⁻ reduction and clear δ¹⁸O/δ¹⁵N slopes of NO₃⁻ (∼ 0.5) indicated the occurrence of denitrification. An anoxic subsurface system associated with the natural geological setting (e.g., the old tidal plain at Bangkok) and artificial pavement coverage served to buffer NO₃⁻ contamination via active denitrification and reduced nitrification.Our results showed that NO₃⁻ and NH₄⁺ contamination of the aquifers in Metro Manila, Bangkok, and Jakarta was not excessive, suggesting low risk of drinking groundwater to human health, at present. However, the increased nitrogen load and increased per capita gross domestic product (GDP) in these developing cities may increase this contamination in the very near future. Continuous monitoring and management of the groundwater system is needed to minimize groundwater pollution in these areas, and this information should be shared among adjacent countries with similar geographic and cultural settings.     

Natural denitrification in the Kakamigahara groundwater basin,Gifu prefecture,central Japan

Although nitrate is recognized as the most common groundwater contaminant due to growing anthropogenic sources, such as agriculture in particular, its adverse effects on human and animal health are debatable. The current issue, however, is to control and reduce nitrate contamination with regards to the long residence time of groundwater within aquifers. Denitrification has recently been recognized for its ability to reduce high nitrate concentrations in groundwater. The Kakamigahara groundwater basin, Gifu prefecture, Japan, witnessed rising levels of nitrate (>12 mg/l NO(3)-N) originating from agricultural sources. Chemical analyses for the determination of major constituents of groundwater and delta(15)N of residual nitrate were performed on representative groundwater samples in order to fulfill two main objectives. One is to investigate the current situation of nitrate groundwater pollution. The second objective is to determine whether the denitrification is a potential natural mechanism, which eliminates nitrate pollution in the Kakamigahara aquifer. Agricultural nitrate contamination of groundwater was obvious from characteristically high concentrations of Ca(2+), Mg(2+), NO(3)(-) and SO(4)(2-). High nitrate concentrations were found on the eastern side of the basin in association with vegetable cultivation fields, and decreased gradually towards the west of the basin along the direction of groundwater flow. The decrease of nitrate concentration was conveniently coupled with increase of HCO(3)(-) (the heterotrophic denitrification product), pH and delta(15)N of residual nitrate (due to isotopic fractionation) from east to west. Therefore, denitrification in situ is continuously removing nitrate from the Kakamigahara groundwater system.     

Elevated nitrate levels in the groundwater of the Gaza Strip: distribution and sources

Seven years of monitoring groundwater in the Gaza Strip has shown that nitrate was and still is a major groundwater pollutant. The objectives of this research were to study the distribution of NO(3)(-) in the groundwater of the Gaza Strip and to identify the sources of NO(3)(-) in the Gaza aquifer system by assessing nitrogen and oxygen isotopes. The most recent samples collected in 2007 showed 90% of the wells having NO(3)(-) concentrations that are several times higher than the WHO standards of 50 mg/L. Potential NO(3)(-) source materials in Gaza are animal manure N, synthetic NH(4) based fertilizers, and wastewater/sludge. The average concentrations of N in the sludge, manure and soil of Gaza were 2.9%, 1% and 0.08%, respectively. The range in delta(15)N of solid manure samples was +7.5 to +11.9 per thousand. The range in delta(15)N of sludge samples was +4.6 to +7.4 per thousand, while four brands of synthetic fertilizers commonly used in Gaza had delta(15)N ranging from +0.2 to +1.0 per thousand. Sludge amended soil had delta(15)N ranging from +2.0 to +7.3 per thousand. For both delta(18)O and delta(15)N, the ranges of groundwater NO(3)(-) were -0.1 to +9.3 per thousand and +3.2 to 12.8 per thousand, respectively. No significant bacterial denitrification is taking place in the Gaza Strip aquifer. Nitrate was predominantly derived from manure and, provided delta(15)N of sludge represents the maximum delta(15)N of human waste, to a lesser extent from septic effluents/sludge. Synthetic fertilizers were a minor source.     

Trends in urbanization and patterns of land use in the Asian mega cities Jakarta,Bangkok, and Metro Manila

Asian mega cities have experienced rapid population growth and continue to grow. Urbanization in those areas is proceeding differently from the patterns of city growth experienced in Western countries. Understanding the characteristics of Asian urbanization will be indispensable for the establishment of a local landscape planning system. In this study, we used the Clark linear exponential model and the Newling quadratic exponential model to compare the spatial distribution of population densities in three Southeast Asian mega cities: Jakarta, Bangkok, and Metro Manila. We analyzed land-use patterns in each of the three cities by examining the mixture of urban and agricultural land use. The Clark and Newling models showed that the three cities were at different stages of urbanization. Jakarta had entered the suburbanization stage, Metro Manila was still at an early stage of urbanization, and Bangkok was at an intermediate stage between Jakarta and Metro Manila. Analysis of spatial patterns revealed areas of mixed land use within and around the city region in the three cities and that these areas of mixed land use would shift outward as urbanization proceeds. These findings indicate that planning concepts need to respect the vernacular landscape of each Asian mega cities as well as its stage of urbanization.     

A dual isotope approach to identify denitrification in groundwater at a river-bank infiltration site

The identification of denitrification in the Torgau sand and gravel aquifer, Germany, was carried out by a dual isotope method of measuring both the delta 15N and delta 18O in NO3-. Samples were prepared by an anion exchange resin method (Silva et al., J. Hydrol. 228 (2000) 22) with a modification to the AgNO3-drying process from a freeze-drying to an oven-drying method. The occurrence of denitrification in the aquifer was confirmed by comparing the reduction of dissolved oxygen, dissolved organic carbon and NO3- concentrations with the dual isotope signatures. High nitrate concentrations were associated with low delta 15N and delta 18O values, and vice versa. The denitrification accords with a Rayleigh equation with calculated enrichment factors of epsilon = -13.62@1000 for delta 15N and epsilon = -9.80@1000 for delta 18O. The slope of the straight-line relationship between the delta 15N and delta 18O data demonstrated that the enrichment of the heavy nitrogen isotope was higher by a factor of 1.3 compared with the heavy oxygen isotope. It is concluded that the identification of this factor is a useful means for confirming denitrification in future groundwater studies.     

Effects of intensive urbanization on the intrusion of shallow groundwater into deep groundwater: examples from Bangkok and Jakarta

Asian megacities have severe pollution problems in both coastal and urban areas. In addition, the groundwater potential has decreased and land subsidence has occurred because of intensive groundwater pumping in urban areas. To prevent the adverse effects of urbanization on groundwater quality, it is necessary to confirm the changes in groundwater flow and contaminant transport caused by urbanization. We examined the effects of urbanization on contaminant transport in groundwater. The research areas were located around Bangkok, Thailand, and Jakarta, Indonesia, cities with populations of approximately 8 and 12 million, respectively. Each metropolitan city is located on a river delta and is adjacent to a bay. We measured the water level and collected water samples at boreholes at multiple depths (100 to 200 m) in 2004 and 2006 in Bangkok and Jakarta, respectively. The current hydraulic potential is below sea level in both cities because of prior excess abstraction of groundwater. As a result, the direction of groundwater flow is now downward in the coastal area. The Cl(-) concentration and delta(18)O distributions in groundwater suggest that the decline in hydraulic potential has caused the intrusion of seawater and shallow groundwater into deep groundwater. Concentrations of Mn and NO3(-)-N in groundwater suggest the intrusion of these contaminants from shallow to deep aquifers with downward groundwater flow and implies an accumulation of contaminants in deep aquifers. Therefore, it is important to recognize the possibility of future contaminant transport with the discharge of deep groundwater into the sea after the recovery of groundwater potential in the coastal areas.     

Evaluating the sources and fate of anthropogenic dissolved inorganic nitrogen (DIN) in two contrasting North Sea estuaries

Nitrogen isotope ratios (delta(15)N) were used to help elucidate the sources and fate of ammonium (NH(4)(+)) and nitrate (NO(3)(-)) in two northeastern English estuaries. The dominant feature of NH(4)(+) in the heavily urbanised Tyne estuary was a plume arising from a single point source; a large sewage works. Although NH(4)(+) concentrations (ranging from 30-150 microM) near the sewage outfall varied considerably between surveys, the sewage-derived delta(15)N-NH(4)(+) signature was remarkably constant (+10.6+/-0.5 per thousand) and could be tracked across the estuary. As indirectly supported by (15)N-depleted delta(15)N-NO(3)(-) values observed close to the mouth of the Tyne, this sewage-derived NH(4)(+) was thought to initiate lower estuarine and coastal zone nitrification. In the more rural Tweed, NH(4)(+) concentrations were low (<7 microM) compared to those in the Tyne and delta(15)N-NH(4)(+) values were consistent with mixing between riverine and marine sources. The dominant form of dissolved inorganic nitrogen (DIN) in the Tweed was agricultural soil-derived NO(3)(-). A decrease in riverine NO(3)(-) flux during the summer coinciding with an increase in delta(15)N-NO(3)(-) values was mainly attributed to enhanced watershed nutrient processing. In the Tyne, where agricultural inputs are less important compared to the Tweed, light delta(15)N-NO(3)(-) (ca. 0 per thousand) detected in the estuary during one winter survey pointed to a larger contribution from precipitation-derived NO(3)(-) during high river discharge. Regardless of the dominant sources, in both estuaries most of the variability in DIN concentrations and delta(15)N values was explained by simple end-member mixing models, implying very little estuarine processing.     

Potential nitrate removal in a coastal freshwater sediment (Haringvliet Lake, The Netherlands) and response to salinization

Nitrogen transformations and their response to salinization were studied in bottom sediment of a coastal freshwater lake (Haringvliet Lake, The Netherlands). The lake was formed as the result of a river impoundment along the south-western coast of the Netherlands, and is currently targeted for restoration of estuarine conditions. Nitrate porewater profiles indicate complete removal of NO(3)(-) within the upper few millimeters of sediment. Rapid NO(3)(-) consumption is consistent with the high potential rates of nitrate reduction (up to 200 nmol N cm(-3) h(-1)) measured with flow-through reactors (FTRs) on intact sediment slices. Acetylene-block FTR experiments indicate that complete denitrification accounts for approximately half of the nitrate reducing activity. The remaining NO(3)(-) reduction is due to incomplete denitrification and alternative reaction pathways, most likely dissimilatory nitrate reduction to NH(4)(+) (DNRA). Results of FTR experiments further indicate that increasing bottom water salinity may lead to a transient release of NH(4)(+) and dissolved organic carbon from the sediment, and enhance the rates of nitrate reduction and nitrite production. Increased salinity may thus, at least temporarily, increase the efflux of NH(4)(+) from the sediment to the surface water. This work shows that salinity affects the relative importance of denitrification compared to alternative nitrate reduction pathways, limiting the ability of denitrification to remove bioavailable nitrogen from aquatic ecosystems.     

Simultaneous carbon and nitrogen removal from high strength domestic wastewater in an aerobic RBC biofilm

High strength domestic wastewater discharges after no/partial treatment through sewage treatment plants or septic tank seepage field systems have resulted in a large build-up of groundwater nitrates in Rajasthan, India. The groundwater table is very deep and nitrate concentrations of 500-750 mg/l (113-169 as NO3(-)-N) are commonly found. A novel biofilm in a 3-stage lab-scale rotating biological contactor (RBC) was developed by the incorporation of a sulphur oxidising bacterium Thiosphaera pantotropha which exhibited high simultaneous removal of carbon and nitrogen in fully aerobic conditions. T. pantotropha has been shown to be capable of simultaneous heterotrophic nitrification and aerobic denitrification thereby helping the steps of carbon oxidation, nitrification and denitrification to be carried out concurrently. The first stage having T. pantotropha dominated biofilm showed high carbon and NH4(+)-N removal rates of 8.7-25.9 g COD/m2 d and 0.81-1.85 g N/m2 d for the corresponding loadings of 10.0-32.0 g COD/m2 d and 1.0-3.35 g N/m2 d. The ratio of carbon removed to nitrogen removed was close to 12.0. The nitrification rate increased from 0.81 to 1.8 g N/m2 d with the increasing nitrogen loading rates despite a high simultaneous organic loading rate. However, it fell to 1.53 g N/m2 d at a high load of 3.35 g N/m2 d and 32 g COD/m2 d showing a possible inhibition of the process. A simultaneous 44-63% removal of nitrogen was also achieved without any significant NO2(-)-N or NO3(-)-N build-up. The second and third stages, almost devoid of any organic carbon, acted only as autotrophic nitrification units, converting the NH4(+)-N from stage 1 to nitrite and nitrate. Such a system would not need a separate carbon oxidation step to increase nitrification rates and no external carbon source for denitrification. The alkalinity compensation during denitrification for that destroyed in nitrification may also result in a high economy.     

Mass balance and isotope effects during nitrogen transport through septic tank systems with packed-bed (sand) filters

Septic tank systems are an important source of NO3(-) to many aquifers, yet characterization of N mass balance and isotope systematics following septic tank effluent discharge into unsaturated sediments has received limited attention. In this study, samples of septic tank effluent before and after transport through single-pass packed-bed filters (sand filters) were evaluated to elucidate mass balance and isotope effects associated with septic tank effluent discharge to unsaturated sediments. Chemical and isotopic data from five newly installed pairs and ten established pairs of septic tanks and packed-bed filters serving single homes in Oregon indicate that aqueous solute concentrations are affected by variations in recharge (precipitation, evapotranspiration), NH4+ sorption (primarily in immature systems), nitrification, and gaseous N loss via NH3 volatilization and(or) N2 or N2O release during nitrification/denitrification. Substantial NH4+ sorption capacity was also observed in laboratory columns with synthetic effluent. Septic tank effluent delta15N-NH4+ values were almost constant and averaged +4.9 per thousand+/-0.4 per thousand (1 sigma). In contrast, delta15N values of NO3(-) leaving mature packed-bed filters were variable (+0.8 to +14.4 per thousand) and averaged +7.2 per thousand+/-2.6 per thousand. Net N loss in the two networks of packed-bed filters was indicated by average 10-30% decreases in Cl(-)-normalized N concentrations and 2-3 per thousand increases in delta15N, consistent with fractionation accompanying gaseous N losses and corroborating established links between septic tank effluent and NO3(-) in a local, shallow aquifer. Values of delta18O-NO3(-) leaving mature packed-bed filters ranged from -10.2 to -2.3 per thousand (mean -6.4 per thousand+/-1.8 per thousand), and were intermediate between a 2/3 H2O-O+1/3 O2-O conceptualization and a 100% H2O-O conceptualization of delta18O-NO3(-) generation during nitrification.     

Electrocatalytic reduction of nitrate in water

Nitrate (NO(3)(-)) contamination of groundwater is a common problem throughout intensive agricultural areas (nonpoint source pollution). Current processes (e.g., ion exchange, membrane separation) for NO(3)(-) removal have various disadvantages. The objective of this study was to evaluate an electrocatalytic reduction process to selectively remove NO(3)(-) from groundwater associated with small agricultural communities. A commercially available ELAT (E-Tek Inc., Natick, MA) carbon cloth with a 30% surface coated Rh (rhodium) (1microg x cm(-1)) was tested at an applied potential of -1.5 V versus standard calomel electrode (SCE) with a Pt auxiliary electrode. Electrocatalytic reduction process (electrolysis) of NO(3)(-) was tested with cyclic voltammetry (CV) in samples containing NO(3)(-) and 0.1M NaClO(4)(-). Nitrate and NO(2)(-) concentrations in test solutions and groundwater samples were analyzed by ion chromatography (IC). The presence of Rh on the carbon cloth surface resulted in current increase of 36% over uncoated carbon cloths. The electrocatalysis experiments using Rh coated carbon cloth resulted in reduction of NO(3)(-) and NO(2)(-) on a timescale of minutes. Nitrite is produced as a product, but is rapidly consumed upon further electrolysis. Field groundwater samples subjected to electrocatalysis experiments, without the addition of NaClO(4)(-) electrolyte, also exhibited removal of NO(3)(-) on a timescale of minutes. Overall, results suggest that at an applied potential of -1.5 V with respect to SCE, Rh coated carbon cloth can reduce NO(3)(-) concentrations in field groundwater samples from 73 to 39 mg/L (16.58 to 8.82 mg/L as N) on a timescale range of 40-60 min. The electrocatalytic reduction process described in this study may prove useful for removing NO(3)(-) and NO(2)(-) from groundwater associated with nonpoint source pollution.     

Erratum to “Effects of intensive urbanization on the intrusion of shallow groundwater into deep groundwater: Examples from Bangkok and Jakarta”

Asian megacities have severe pollution problems in both coastal and urban areas. In addition, the groundwater potential has decreased and land subsidence has occurred because of intensive groundwater pumping in urban areas. To prevent the adverse effects of urbanization on groundwater quality, it is necessary to confirm the changes in groundwater flow and contaminant transport caused by urbanization. We examined the effects of urbanization on contaminant transport in groundwater. The research areas were located around Bangkok, Thailand, and akarta, Indonesia, cities with populations of approximately 8 and 12 million, respectively. Each metropolitan city is located on a river delta and is adjacent to a bay. We measured the water level and collected water samples at boreholes at multiple depths (100 to 200 m) in 2004 and 2006 in Bangkok and Jakarta, respectively. The current hydraulic potential is below sea level in both cities because of prior excess abstraction of groundwater. As a result, the direction of groundwater flow is now downward in the coastal area. The Cl⁻ concentration and δ¹⁸O distributions in groundwater suggest that the decline in hydraulic potential has caused the intrusion of seawater and shallow groundwater into deep groundwater. Concentrations of Mn and NO3⁻-N in groundwater suggest the intrusion of these contaminants from shallow to deep aquifers with downward groundwater flow and implies an accumulation of contaminants in deep aquifers. Therefore, it is important to recognize the possibility of future contaminant transport with the discharge of deep groundwater into the sea after the recovery of groundwater potential in the coastal areas.     

Stimulating hydrogenotrophic denitrification in simulated groundwater containing high dissolved oxygen and nitrate concentrations

In agricultural areas, nitrate (NO3-) is a common groundwater pollutant as a result of extensive fertilizer application. At elevated concentrations, NO3- consumption causes methemoglobinemia in infants and has been linked to several cancers; therefore, its removal from groundwater is important. The addition of hydrogen gas (H2) via gas-permeable membranes has been shown to stimulate denitrification in a laboratory-scale reactor. This research, using large columns packed with aquifer material to which a simulated groundwater was fed, was conducted to further identify the conditions required for the use of membrane-delivered H2 in situ. In this study, we show that this novel technology was capable of treating highly contaminated (25 mg/L NO3- -N) and oxygenated (5.5mg/L dissolved oxygen) water, but that nutrient addition and gas pressure adjustment was required. Complete NO3- reduction was possible without the accumulation of either NO2- or N2O when the H2 lumen pressure was increased to 17 psi and phosphate was added to the groundwater. The total organic carbon content of the effluent, 110 cm downgradient of H2 addition, did not increase. The results from these experiments demonstrate that this technology can be optimized to provide effective NO3- removal in even challenging field applications.     

Urban warming trends in several large Asian cities over the last 100 years

In this paper, the long-term trends in surface temperature in several large Asian cities (Seoul, Tokyo, Osaka, Taipei, Manila, Bangkok, and Jakarta) have been analyzed for estimating the effects of urban warming. A new index, E-HII, is proposed: it is the value obtained by subtracting the temperature data of the four grids around the city from the observational temperature data in the city. Osaka shows the largest E-HII, increasing from approximately 2.4 °C in 1901 to almost 3 °C after 1981. The E-HIIs of Seoul, Tokyo, and Taipei, have increased by 1 °C to 2 °C. Jakarta and Bangkok exhibited a lower E-HII. E-HIIs of Manila and Bangkok have been increasing rapidly after 1961.     

Nitrate concentration in wetlands: assessing the contribution of deeper groundwater from anions

Denitrification in wetlands is useful for removing nitrate from the surface water, although it can be difficult to assess wetland functioning particularly where it overlies a hard-rock aquifer whose fractures and joints form pathways that mix waters with different chemical composition. The variability of NO3 concentrations in such waters, which partly transit through wetlands, can obscure the effect of denitrification. To address this question, we monitored groundwater chemistry at different depths on three pilot sites overlying (mica)schist aquifers with almost no NO3 contamination at depth, probably due to denitrification. The spatial variability of NO3 concentrations, both along the flowpath and with depth, is related in each site to at least one of the following factors: (1) upward flux of deeper NO3-free groundwater; (2) in situ heterotrophic denitrification; (3) application of different types of fertilizer and other amendments. These factors are efficiently discriminated by the monitoring of just three, easily affordable, parameters: NO3, SO4 and Cl.     

Hydrological controls on nutrient concentrations and fluxes in agricultural catchments

Like many streams draining intensively farmed parts of lowland Scotland, water quality in the Newmills burn, Aberdeenshire, is characterized by relatively high nutrient levels; mean concentrations of NO3-N and NH3-N are 6.09 mg l(-1) and 0.28 mg l(-1), respectively, whilst average PO4-P concentrations reach 0.06 mg l(-1). Nutrient concentrations vary spatially and temporally with levels being highest under arable farming during the autumn and winter. Annual fluxes from the 14.5 km2 catchment are estimated at 25.67 and 1.26 kg ha(-1) a(-1) for NO3-N and NH3-N, respectively, and 0.26 kg ha(-1) a(-1) for PO4-P. Hydrological controls exert a strong influence on both nutrient concentrations and fluxes. Over short timescales nutrient concentrations and fluxes are greatest during storm events when P04-P and NH3-N are mobilized by overland flow in riparian areas, particularly where the soils have been compacted by livestock or farm machinery. Delivery of deeper soil water in subsurface storm flow, facilitated by agricultural under-drainage, provide large contributions of NO3-N on the recession limb of hydrological events. In contrast, groundwater inputs generally have lower NO3 concentrations implying that denitrification may be a pathway of N loss in the saturated zone. Approximately 75% of the N loss for the catchment occurs during the autumn and early winter when high flows dominate the hydrological regime. The close coupling of hydrological pathways and biogeochemical processes has major implications for catchment management strategies such as Nitrate Vulnerable Zones (NVZs) as it is likely that significant groundwater stores with long residence times will continue to cause N losses before water quality improvements become apparent.     

Use of stable nitrogen isotope fractionation to estimate denitrification in small constructed wetlands treating agricultural runoff

Constructed wetlands (CWs) in the agricultural landscape reduce non-point source pollution through removal of nutrients and particles. The objective of this study was to evaluate if measurements of natural abundance of (15)NO(3)(-) can be used to determine the fate of NO(3)(-) in different types of small CWs treating agricultural runoff. Nitrogen removal was studied in wetland trenches filled with different filter materials (T1--sand and gravel; T3--mixture of peat, shell sand and light-weight aggregates; T8--barley straw) and a trench formed as a shallow pond (T4). The removal was highest during summer and lowest during autumn and winter. Trench T8 had the highest N removal during summer. Measurements of the natural abundance of (15)N in NO(3)(-) showed that denitrification was not significant during autumn/winter, while it was present in all trenches during summer, but only important for nitrogen removal in trench T8. The (15)N enrichment factors of NO(3)(-) in this study ranged from -2.5 to -5.9 per thousand (T3 and T8, summer), thus smaller than enrichment factors found in laboratory tests of isotope discrimination in denitrification, but similar to factors found for denitrification in groundwater and a large CW. The low enrichment factors compared to laboratory studies was attributed to assimilation in plants/microbes as well as diffusion effect. Based on a modified version of the method presented by Lund et al. [Lund LJ, Horne AJ, Williams AE, Estimating denitrification in a large constructed wetland using stable nitrogen isotope ratios. Ecol Engineer 2000; 14: 67-76], denitrification and assimilation were estimated to account for 53 to 99 and 1 to 47%, respectively, of the total N removal during summer. This method is, however, based on a number of assumptions, and there is thus a need for a better knowledge of the effect of plant uptake, microbial assimilation as well as nitrification on N isotopic fractionation before this method can be used to evaluate the contribution of dinitrification in CWs.     

Evidence of anoxic methane oxidation coupled to denitrification

Denitrification using methane as sole electron donor under anoxic condition was investigated. Sludge produced by a denitrifying reactor using acetate as electron donor was put in contact with methane at partial pressures from 1.8 to 35.7kPa. Nitrate depletion and gaseous nitrogen production were measured. The denitrification rate was independent of the methane partial pressure when superior or equal to 8.8kPa. The nitrate depletion was asymptotic. A denitrification rate of 0.25g NO(3)(-)-Ng(-1) VSSd(-1) was observed at the onset of culturing, followed by a slower and lineal denitrification rate of 4.9x10(-3)g NO(3)(-)-Ng(-1) VSSd(-1). Abiotic nitrate removal or the availability of another carbon source were discarded from control experiments made in the absence of methane or using sterilized inoculum.     

Application of the 15N technique to determine the contributions of nitrification and denitrification to the flux of nitrous oxide from aerated pig slurry.

In order to elucidate and quantify nitrogen transformations occurring during aerobic treatment of pig slurry, two laboratory experiments were carried out with contrasting levels of aeration, high level (experiment 1) and low level (experiment 2) of aeration. During these experiments, after reaching steady-state conditions, a single pulse of NO3(-)-15N tracer was added directly to the reactor. When nitrification conditions were prevailing (experiment 1), no transformation of added NO3(-)-15N occurred (98.7% 15N-recovery as nitrates in the liquid slurry). Moreover, the unlabelled nitrous oxide (N2O) measured (7.4% of the total nitrogen content of the raw slurry) strongly demonstrated that the source of N2O emitted was nitrification. During simultaneous nitrification and denitrification conditions (experiment 2), the added NO3(-)-15N was found in gaseous nitrogen forms (N2O-15N: 27%; N2-15N: 18%) and in the liquid (TN-15N: 54%). From this result, it was evident that N2O was mainly emitted by denitrification process. Using the decrease of the isotopic excess of the NO3(-)-15N we calculated that 92% of NO2(-)-N was directly denitrified (as gaseous forms) without any previous oxidation to nitrate.