This publication provides guidance to water-sector decision makers and planners on how to deal with the quality dimension of groundwater resources management in the World Bank's client countries. There is growing evidence of increasing pollution threats to groundwater and some well-documented cases of irreversible damage to important aquifers. This guide has been produced in the belief that groundwater pollution hazard assessment must become an essential part of environmental best practice for water supply utilities. The guide is particularly relevant for the World Bank's Latin American and Caribbean Region, where many countries have initiated major changes to modernize their institutional and legal framework for water resources management, but may not yet have considered groundwater at the same level as surface water, because of lack of awareness and knowledge of groundwater issues and policy options.

The use of fluidized-bed bioreactors in waste and drinking water treatment has several advantages, the most significant of which is the specific removal rate, which is an order of magnitude higher than that of equivalent activated sludge processes. In this paper, the usual concept of nitrification-denitrification in separated units is replaced by a new concept in which the two processes are performed together in a single high-performance fluidized-bed. Based on the former nitrifying reactor, new equipment was designed. This reactor contained a fluidized bed with separated aerobic and anoxic sections for nitrification and denitri fication respectively. This was accomplished by the use of different-diameter sand as carrier material and appropriate reactor shape, recirculation, feed and aeration conditions. The reactor (20 L fluidized-bed volume) was operated for 3 months. It was fed with synthetic waste water (50 L/h) containing 25-40 mg NH₄ ⁺-N/L. Propionic acid and ethanol in a 1:4 ratio were used as the carbon source (2.3 g C/L) for deni trification, fed in at different points of the reactor. Ammonium removal reached 50%, while denitrification was 75%. The total nitrogen removal rate was 0.8-1.2 kg N/m ³.d. A new simple hydrostatic pressure method was used to monitor biofilm thickness in the fluidized bed. During the experiments the oxidation-reduc tion potential (ORP) was tested as a tool to monitor reactor performance; its use for the control of the process was found to be limited.

Investigation of surface water and groundwater interaction (SW–GW interaction) provides basic information for regional water-resource protection, management, and development. In this survey of a 10-km-wide area along both sides of the Songhua River, northeast China, the hydrogeochemical responses to different SW–GW interactions were studied. Three types of SW–GW interactions were identified—“recharge”, “discharge”, and “flow-through”—according to the hydraulic connection between the surface water and groundwater. The single factor index, principal component analysis, and hierarchical cluster analysis of the hydrogeochemistry and pollutant data illuminated the hydrogeochemical response to the various SW–GW interactions. Clear SW–GW interactions along the Songhua River were revealed: (1) upstream in the study area, groundwater usually discharges into the surface water, (2) groundwater is recharged by surface water downstream, and (3) discharge and flow-through coexist in between. Statistical analysis indicated that the degree of hydrogeochemical response in different types of hydraulic connection varied, being clear in recharge and flow-through modes, and less obvious in discharge mode. During the interaction process, dilution, adsorption, redox reactions, nitrification, denitrification, and biodegradation contributed to the pollutant concentration and affected hydrogeochemical response in the hyporheic zone.

RESUMEN: Este trabajo tiene como objetivo demostrar la viabilidad de la tecnología de electro-oxidación para el tratamiento y reutilización de agua de mar en el sector acuícola. Una actividad con grandes consumos de agua y en continuo crecimiento que requiere de una calidad óptima del agua de cultivo para poder ofrecer a la población productos sanos, seguros y de calidad. Los resultados de esta tesis muestran la capacidad de la electro-oxidación para la eliminación de compuestos nitrogenados, materia orgánica, bacterias y virus, en aguas de cultivo con peces en el tanque de tratamiento y sin efectos nocivos para las especies acuícolas. Un diseño de una planta de tratamiento móvil en los camiones de transporte de alevines se recoge en este trabajo junto con una evaluación económica. Los resultados recogidos en esta tesis cubren parte del vacío existente en la literatura sobre pruebas de electro-oxidación en preencia de peces en el agua a tratar. | ABSTRACT: This work is aimed to show the viability of the use of electrochemical oxidation in the treatment and reuse of seawater in aquaculture activities. This sector requieres large quantities of water ant it is the fastest growing food-producing sector world. The results of this thesis show the viability of the electrochemical-oxidation on the removal of nitrogen compounds, organic matter, bacteria an viruses in culture seawater with fish in the tank without toxic effects. A design of a water treatment plant for the fingerlings tanks in the trucks has been performed together with an economical evaluation. The results reported in this thesis meet a need of the literature about electro-oxidation treatment in the presence of fish in the water to be treated.

The efficacy of different proportions of silt-loam/bentonite mixtures overlying a vadose zone in controlling solute leaching to groundwater was quantified. Laboratory experiments were carried out using three large soil columns, each packed with 200-cm-thick riverbed soil covered by a 2-cm-thick bentonite/silt-loam mixture as the low-permeability layer (with bentonite mass accounting for 12, 16 and 19 % of the total mass of the mixture). Reclaimed water containing ammonium (NH₄⁺), nitrate (NO₃⁻), organic matter (OM), various types of phosphorus and other inorganic salts was applied as inflow. A one-dimensional mobile–immobile multi-species reactive transport model was used to predict the preferential flow and transport of typical pollutants through the soil columns. The simulated results show that the model is able to predict the solute transport in such conditions. Increasing the amount of bentonite in the low-permeability layer improves the removal of NH₄⁺and total phosphorous (TP) because of the longer contact time and increased adsorption capacity. The removal of NH₄⁺and OM is mainly attributed to adsorption and biodegradation. The increase of TP and NO₃⁻concentration mainly results from discharge and nitrification in riverbed soils, respectively. This study underscores the role of low-permeability layers as barriers in groundwater protection. Neglect of fingers or preferential flow may cause underestimation of pollution risk.

This study investigates the occurrence of greenhouse gases (GHGs) and the role of groundwater as an indirect pathway of GHG emissions into surface waters in a gaining stretch of the Triffoy River agricultural catchment (Belgium). To this end, nitrous oxide (N₂O), methane (CH₄) and carbon dioxide (CO₂) concentrations, the stable isotopes of nitrate, and major ions were monitored in river and groundwater over 8 months. Results indicated that groundwater was strongly oversaturated in N₂O and CO₂ with respect to atmospheric equilibrium (50.1 vs. 0.55 μg L⁻¹ for N₂O and 14,569 vs. 400 ppm for CO₂), but only marginally for CH₄ (0.45 vs. 0.056 μg L⁻¹), suggesting that groundwater can be a source of these GHGs to the atmosphere. Nitrification seemed to be the main process for the accumulation of N₂O in groundwater. Oxic conditions prevailing in the aquifer were not prone for the accumulation of CH₄. In fact, the emissions of CH₄ from the river were one to two orders of magnitude higher than the inputs from groundwater, meaning that CH₄ emissions from the river were due to CH₄ in-situ production in riverbed or riparian zone sediments. For CO₂ and N₂O, average emissions from groundwater were 1.5 × 10⁵ kg CO₂ ha⁻¹ year⁻¹ and 207 kg N₂O ha⁻¹ year⁻¹, respectively. Groundwater is probably an important source of N₂O and CO₂ in gaining streams but when the measures are scaled at catchment scale, these fluxes are probably relatively modest. Nevertheless, their quantification would better constrain nitrogen and carbon budgets in natural systems.

Excess nitrate (NO₃⁻) is a critical problem in agricultural land-use areas, causing eutrophication and hypoxia in surface waters. Diversion of agricultural runoff into saturated buffer zones reduces NO₃⁻ loading. This study seeks to understand nitrate concentration, [NO₃⁻], and environmental factor variability in a saturated buffer zone (~0.007 km²) at a site in the USA on a diurnal scale within and among seasons. Between September 2016 and August 2017, groundwater samples were collected hourly for 24 h from an unconfined aquifer 1.5 m below the surface in the saturated buffer zone. Mean daily [NO₃⁻-N] ranged from 2.18 mg/L in the fall to 4.63 mg/L in the summer and varied by a statistically significant difference from spring to fall and from summer to fall. Differences between 24-h maximum and minimum [NO₃⁻-N] were statistically significant within spring, summer, fall, and winter. The occurrence of a sinusoidal [NO₃⁻-N] trend where the timing of maximum and minimum [NO₃⁻-N] coincide with photoperiod indicates that vegetation uptake is a controlling process. NO₃⁻ leaching, evapotranspiration, and nitrification were identified as processes controlling [NO₃⁻-N] increases over the 24-h period. The magnitude of difference between daily maximum and minimum [NO₃⁻-N] displayed no correlation with daily average air temperature, solar intensity, or mean daily water temperature. This study demonstrated that variation in [NO₃⁻] exists on seasonal and diurnal time scales; the fluctuations are driven by multiple processes consistent over the 24-h period.