A continuous active monitoring approach to identify cross-connections between potable water and effluent distribution systems.

A continuous active monitoring approach was developed for identification of cross-connections between potable water supply systems and treated wastewater effluent reuse distribution systems. The approach is based on monitoring the oxidation reduction potential (ORP) at the potable water system while injecting sulfite (a reducing agent) into the effluent line. A sharp decrease in the ORP of the potable water would indicate a cross-connection event. The approach was tested in batch experiments on treated municipal wastewater effluent of varying degree of treatment, and at dilution ratios of up to 1:100 (effluent/potable). The approach was then examined under continuous flow conditions, which simulated cross-connection events at various dilution ratios (up to 1:100). In the continuous runs, differences between the potable water ORP and the effluent-potable water mixture (containing sulfite as sodium bisulfite (SBS)) ORP were 450-630 mV. This suggests high potential for identifying a cross-connection event. Implementation of the approach includes adding sulfite to effluent used for agricultural irrigation; hence, possible effects on soil and on crops were studied in soil columns and pots planted with basil (Ocimum basilicum) as a model plant. No negative effects of sulfite addition to the irrigation effluent were observed in the irrigated soils and plants, and therefore, it could be safely implemented also in agricultural applications.

Potential impacts of on-site greywater reuse in landscape irrigation.

This study investigated the effects of irrigation with different types of waters on soil, plants, and public health. The test plant was ryegrass grown in 12 planters filled with sandy loam soil and irrigated with three types of waters (4 planters for each type): freshwater, raw domestic light greywater (GW), and treated domestic light GW. The sodium adsorption ratio (SAR), EC, pH and alkalinity of the three types of irrigation waters did not differ significantly, suggesting that raw or treated light GW should not exhibit negative effects. Concentrations of anionic and cationic surfactants in the freshwater and the treated GW were about the same, while their concentrations in the raw GW were higher. Surfactant levels in the three drainage water types were low. Some accumulation of surfactants occurred in planters irrigated with raw and treated GW. The COD of the drainage water of planters irrigated with raw GW was higher than the COD of other two drainage water types. Although raw and treated GW contained faecal coliforms, they were hardly detected in the drainage waters. All plants did not show any signs of stress. This may be due to the fact that the GW originated mainly from showers and washbasins.

Determination of soil nitrate and water content using attenuated total reflectance spectroscopy.

Direct determination of nitrate and soil moisture can significantly improve N-application management and thus reduce N-derived environmental pollution related to agriculture. Several studies have shown that Fourier transform infrared attenuated total reflectance (FT-IR/ATR) spectroscopy could be used to estimate the nitrate content of standardized soil pastes. Paste standardization appeared to be the main obstacle to in situ application of this approach, and the present study shows how FT-IR/ATR can be used to estimate both water content and nitrate concentration of field soil samples. Water content and nitrate concentration are determined sequentially using two subsamples of the initial soil sample. An a priori determined amount of highly concentrated nitrate solution is added to the first subsample and the ATR spectrum of this paste is used to estimate the sample water content. It is then possible to calculate the amount of water that should be added to the second subsample so that the resulting paste is very close to the ideal standard paste. Nitrate concentration, mg [N]/kg [dry soil], is estimated using the FT-IR/ATR spectrum of this second paste. Results are presented for a laboratory experiment with four agricultural soils, as well as for a field trial with a calcareous soil. For water content, the determination errors range from 0.01 to 0.02 g [water]/g [dry soil]. For nitrate concentration, the errors for three of the soils range from 5.9 to 8.4 mg [N]/kg [dry soil], while for the fourth, calcareous clay soil, the determination error is 13.6 mg [N]/kg [dry soil]. The determination errors obtained for the field trial are similar to the ones obtained for a similar soil under laboratory conditions, which shows the potential usefulness of the approach for improving N-application management and reducing environmental pollution.

Modified isotope pairing technique to study N transformations in polluted aquatic systems: theory.

Denitrification of nitrate in sediments of polluted aquatic systems has the potential to release considerable nitrogen amounts into the atmosphere in the form of dinitrogen (N2) and/or nitrous oxide (N2O). Nitrate may diffuse into the anoxic sediment layer either from the oxic sediment layer (after being produced there by nitrifiers) or directly from the overlying water. Currently, the most common technique that explicitly distinguishes between the two main nitrate sources is the Isotope Pairing Technique (IPT). 15N-labeled nitrate is added to the water column, and formation of 15N labeled N2 molecules is subsequently monitored. The main shortcoming of the IPT is that the formation of N20 is ignored, thus resulting in an underestimation of sediment denitrification. Another limitation is the inability to account for a possible influx of nitrate through the hyporheic zone (e.g., nitrate-polluted groundwater) into the anoxic sediment layer. We have further developed and analyzed the theoretical basis of the original IPT. The two important factors that we took into account are the isotopic composition of N20 and the input of an external source of nitrate. We also examined the option of adding 15N-labeled ammonium to the water column to specifically adjustthe technique to field studies. The presented modified technique allows us to (i) improve the estimation of sediment denitrification capacity, (ii) gain an insight into the N20 formation mechanism(s) and fluxes, and (iii) assess inputs of nitrate-polluted water through the hyporheic zone.

Nitrite formation and nitrous oxide emissions as affected by reclaimed effluent application.

The effect of irrigation with reclaimed effluent (RE) (after secondary treatment) on the mechanisms and rates of nitrite formation, N2O emissions, and N mineralization is not well known. Grumosol (Chromoxerert) soil was incubated for 10 to 14 d with fresh water (FW) and RE treated with 15NO3- and 15NH4+ to provide a better insight on N transformations in RE-irrigated soil. Nitrite levels in RE-irrigated soil were one order of magnitude higher than in FW- irrigated soil and ranged between 15 to 30 mg N kg(-1) soil. Higher levels of NO2- were observed at a moisture content of 60% than at 70% and 40% w/w. Nitrite levels were also higher when RE was applied to a relatively dry Grumosol (20% w/w) than at subsequent applications of RE to soil at 40% w/w. Isotopic labeling indicated that the majority of NO2 was formed via nitrification. The amount of N2O emitted from RE-treated Grumosol was double the amount emitted from FW treatments at 60% w/w. Nitrification was responsible for about 42% of the emissions. The N20 emission from the RE-treated bulk soil (passing a 9.5-mm sieve) was more than double the amount formed in large aggregates (4.76-9.5 mm in diameter). No dinitrogen was detected under the experimental conditions. Results indicate that irrigation with secondary RE stimulates nitrification, which may enhance NO3 leaching losses. This could possibly be a consequence of long-term exposure of the nitrifier population to RE irrigation. Average gross nitrification rate estimates were 11.3 and 15.8 mg N kg(-1) soil d(-1) for FW- and RE-irrigated bulk soils, respectively. Average gross mineralization rate estimates were about 3 mg N kg(-1) soil d(-1) for the two water types.

Gaseous nitrogen emissions and mineral nitrogen transformations as affected by reclaimed effluent application.

Irrigation with reclaimed effluent (RE) is essential in arid and semiarid regions. Reclaimed effluent has the potential to stimulate gaseous N losses and affect other soil N processes. No direct measurements of the N2 and N2O emissions from Mediterranean soils have been conducted so far. We used the 15N gas flux method in a field and a laboratory experiment to study the effect of RE irrigation on gaseous N losses and other N transformations in a Grumosol (Chromoxerert) soil. The fluxes of N2, N2O, and NH3 were measured from six Grumosol lysimeters following application of either fresh water or RE. The N fertilizer was applied either as 15NH4 or 15NO3. Only up to 0.3% from the applied N fertilizer was lost as N2O + NH3. Reclaimed effluent enhanced the losses of NH3, but did not affect those of N2O. Nitrification and denitrification were equally important to N2O production. Laboratory incubations were performed to both confirm the influence of the irrigation water type and to test the effect of moisture content. Significant quantities of N2 and N2O (up to 3.1% of the applied fertilizer) were emitted from saturated soils. Reclaimed effluent application did not induce higher N2O emissions, yet significantly more (approximately 33%) N2 was emitted from RE-irrigated soils. Denitrification contributed up to 75% of the N2O amounts emitted from saturated soils. Reclaimed effluent application inhibited nitrification in the Grumosol by 15 to 25% and induced NO2 accumulation in soils incubated at a field-capacity moisture content.

Direct monitoring of soil and water nitrate by FTIR based FEWS or membrane systems.

The development of silver halide fibers that transmit with minimal loss into the mid-IR (MIR) paved the way to their successful utilization as effective ATR (Attenuated Total Reflectance) elements, promoting the implementation of Fiberoptic Evanescent Wave Spectroscopy (FEWS) for direct monitoring of nitrate in environmental systems. Samples containing nitrate in water, soil extracts, and pastes were used for the determination of nitrate concentration with a common ATR ZnSe crystal and with silver halide fibers (FEWS). Spectra of soil pastes and suspensions and those of phosphate, carbonate, sulfate, ammonium, and soil organic constituents were collected to study possible interference with nitrate determination. The standard error of estimate (SEE) and R2 values obtained with flat fibers, using the simple single-point correlation method, were superior to those obtained for cylindrical FEWS and ZnSe ATR crystals in pure water. A significant improvement in the SEE and R2 was achieved in most soil pastes by applying the simple mode of the Cross Correlation method. Direct transmission of MIR radiation through ion-exchange membranes, partially loaded with nitrate or carbonate, was found an effective alternative for MIR-FTIR determination of these ions. Further development and modification of the FEWS devices should allow in-situ and online determination of nitrate in soil and environmental systems.

Wetting mechanisms of gel-based controlled-release fertilizers.

The release mechanism of gel-based controlled release fertilizers (CRFs) involves water penetration into dry mixtures of fertilizers and gel forming polymers. Water penetration provides an upper limit to the whole release process. Where wetting prediction is often based on models that describe the flow of the liquid phase, vapor motion may become significant when a sharp wetting front exists. In this study we examine the role of vapor and fluid flows in the wetting process of CRFs consisting of urea or KNO(3) mixed with polyacrylamide (PAM). Vapor adsorption isotherms were obtained for typical fertilizer-PAM mixtures. Wetting and release experiments were conducted by dividing the CRFs into regions alternately filled with a pure fertilizer and mixtures of PAM and fertilizer. The experiments were designed in such a way that when the wetting front reaches a mixtures interface, its motion depends on the gradient imposed by the difference in osmotic potential (OP). The coupled equations of vapor and liquid flow in initially dry conditions were solved numerically to demonstrate the conceptual understanding gained by the experiments. The results show that wetting front motion is affected by transport and adsorption of vapor. It was also shown that the release rate is different when wetting is governed by vapor flow or by liquid flow. The release pattern from a multi-regions device was consistent with the wetting pattern, demonstrating the possibility to tailor the release according to periods of peak demand.

Influence of effluent irrigation on community composition and function of ammonia-oxidizing bacteria in soil.

The effect of effluent irrigation on community composition and function of ammonia-oxidizing bacteria (AOB) in soil was evaluated, using techniques of molecular biology and analytical soil chemistry. Analyses were conducted on soil sampled from lysimeters and from a grapefruit orchard which had been irrigated with wastewater effluent or fertilizer-amended water (FAW). Specifically, comparisons of AOB community composition were conducted using denaturing gradient gel electrophoresis (DGGE) of PCR-amplified fragments of the gene encoding the alpha-subunit of the ammonia monooxygenase gene (amoA) recovered from soil samples and subsequent sequencing of relevant bands. A significant and consistent shift in the population composition of AOB was detected in soil irrigated with effluent. This shift was absent in soils irrigated with FAW, despite the fact that the ammonium concentration in the FAW was similar. At the end of the irrigation period, Nitrosospira-like populations were dominant in soils irrigated with FAW, while Nitrosomonas-like populations were dominant in effluent-irrigated soils. Furthermore, DGGE analysis of the amoA gene proved to be a powerful tool in evaluating the soil AOB community population and population shifts therein.