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.

Little is known of the interactions between groundwater and surface water on deeply weathered landscapes of low relief in the Great Lakes Region of Africa (GLRA). The role of groundwater in sustaining surface-water levels during periods of absent rainfall is disputed and groundwater is commonly excluded from estimations of surface-water balances. Triangulated piezometers installed beside lake gauging stations on Lake Victoria and Lake Kyoga in Uganda provide the first evidence of the dynamic interaction between groundwater and surface water in the GLRA. Stable isotope ratios (2H:1H, 18O:16O) support piezometric evidence that groundwater primarily discharges to lakes but show further that mixing of groundwater and lake water has occurred at one site on Lake Victoria (Jinja). Layered-aquifer heterogeneity, wherein fluvial-lacustrine sands overlie saprolite, gives rise to both rapid and slow groundwater fluxes to lakes which is evident from the recession of borehole hydrographs following recharge events. Darcy throughflow calculations suggest that direct contributions from groundwater to Lake Victoria comprise <1% of the total inflows to the lake. Groundwater/surface-water interactions are strongly influenced by changing drainage base (lake) levels that are controlled, in part, by regional climate variability and dam releases from Lake Victoria (Jinja).

Travel time is one of the important criteria in the design of managed aquifer recharge systems for securing good drinking water quality. Traditionally, groundwater travel time has been modelled without considering the effect of temperature. In this study, a cross-sectional heat transport model was constructed for the Amsterdam dune filtration system (in the Netherlands) to analyse the effect of temperature on groundwater travel times. A groundwater flow model, a chloride transport model, and a heat transport model were iteratively calibrated with measured groundwater levels, chloride concentrations, and temperature series in order to improve model calibration and reduce model uncertainty. The coupled flow and heat transport model with temperature-dependent density and viscosity provided more accurate estimation of travel times. The results show that seasonal temperature fluctuations in the source water in the infiltration pond cause temperature variations in the shallow groundwater. Viscosity is more sensitive to temperature changes and has a larger effect on groundwater travel times. Groundwater travel time in the shallow sand aquifer increases from 60 days when computed with the traditional groundwater flow model to 73 days in the winter season and 95 days in the summer season when computed with the coupled model. Longer travel time is beneficial for water quality improvement. Thus, it is important to consider the effect of temperature variations on groundwater travel times for the design and operation of managed aquifer recharge systems.

Proyecto de Graduación (Licenciatura en Ingeniería Ambiental) Instituto Tecnológico de Costa Rica, Escuela de Química, 2021. | Esta tesis cumple con el Objetivo ODS 12: Garantizar modalidades de consumo y producción sostenibles. Meta 5 Disminuir considerablemente la generación de desechos mediante actividades de prevención, reducción, reciclado y reutilización. | Este trabajo pretende presentar posibles soluciones para la gestión de residuos sólidos y mitigar el déficit hídrico en sitios que no cuentan con una red de suministro, como en la Isla Caballo, Puntarenas. Para ello se estudiaron arenas hidrofóbicas, las cuales tienen poca área superficial, por lo que pueden ser fácilmente recubiertas por materiales hidrofóbicos. Esto provoca una disminución en su capacidad de infiltración y una menor retención de humedad haciéndolos materiales con potencial para la construcción de barreras capilares hidrofóbicas como alternativa para geotextiles. Por lo anterior, se fabricaron arenas hidrofóbicas con un enfoque en el uso de materias primas locales disponibles, de bajo costo y que actualmente no se aprovechan. Se utilizó cristalería dañada de laboratorio como fuente de vidrio borosilicato y se molió para obtener una arena sintética con un diámetro entre 106 µm y 210 µm. Asimismo, se realizó una extracción líquido sólido del lodo residual de la producción de palma aceitera como fuente de grasa (GLAP). Se recubrió la arena producida con GLAP, utilizando dos metodologías distintas: mediante mezclado (LP-M) y mediante disolvente (LP-D). Se realizaron pruebas de ángulo de contacto a concentraciones de 0,1 g/kg, 0,3 g/kg, 0,6 g/kg, 1 g/kg, 1,3 g/kg y 1,6 g/kg; a grados de compactación de 1,2 g/cm3 y 1,3 g/cm3 ; en arenas secas al aire y secas a 105°C; comparando los resultados obtenidos de arenas recubiertas de ácido esteárico (AE) como referencia. Posteriormente, se realizaron pruebas hidráulicas en las arenas hidrofóbicas y en muestras empacadas con suelo de Isla Caballo. Se obtuvieron ángulos de contacto máximos de 119,73°, 118,83° y 107,48° para LP-M, LP-D y AE, respectivamente. Los resultados de las pruebas hidráulicas de las arenas mostraron una reducción en la conductividad hidráulica saturada, donde la arena sin recubrimiento obtuvo un valor de 170,5 cm/h mientras que LP-D y AE, de 4,5 cm/h y 3,4 cm/h, respectivamente. Adicionalmente, se realizó un estudio de las condiciones climáticas de la isla utilizando datos de los últimos 5 años provenientes de estaciones meteorológicas cercanas, del IMN. A partir de los datos se encontraron dos fechas con precipitaciones efectivas aptas para recolectar agua de lluvia: mayo y junio; y setiembre y octubre. Mediante un balance simulado con Hydrus 1D, se determinó que la cantidad de lluvia que podría ser interceptada en un año se encuentra entre 764 L/m2 y 767 L/m2 . Los resultados obtenidos son prometedores para el manejo de residuos sólidos y el aprovechamiento de agua de lluvia en Isla Caballo mediante arenas hidrofóbicas en barreras capilares hidrofóbicas. | This study aims to present possible solutions for waste management and mitigation of water deficit in areas with no water distribution, for example, Isla Caballo, Puntarenas. Hydrophobic sands have low surface area, therefore can be easily coated by hydrophobic materials. This causes a reduction in its infiltration rate as well as a lower water retention capacity, making these potential materials for building hydrophobic capillary barriers, as an alternative to geotextiles. Moreover, this study manufactured hydrophobic sands using locally available, low-cost materials, which are currently discarded. Laboratory glass waste was used as a source of borosilicate glass, which was later crushed in order to produce synthetic sands with diameter range between 106 µm and 210 µm. Furthermore, a liquid-solid extraction was applied to residual sludge from the production of palm oil as a source of fat (GLAP). The sand was coated with GLAP through two methods: mixing (LP-M) and solvent-aided (LP-D). Contact angle measurements were performed at coating concentrations of 0,1 g/kg, 0,3 g/kg, 0,6 g/kg, 1 g/kg, 1,3 g/kg and 1,6 g/kg; at 1,2 g/cm3 y 1,3 g/cm3 compaction levels; on air-dry sand and sand dried at 105 °C. Its results were compared to stearic acid coating (AE) as a reference. Subsequently, hydraulic properties of the sands and packed soil from Isla Caballo were measured. Maximum contact angles for LP-M, LP-D and AE were 119,73°, 118,83° and 107,48°, respectively. The results of the hydraulic measurements revealed a reduction in saturated hydraulic conductivity: sands with no coating were at 170,5 cm/h, whereas LP-D and AE were at 4,5 cm/h and 3,4 cm/h, respectively. In addition, the meteorological conditions of the island were studied using data from the last 5 years, from nearby IMN meteorological stations. The data showed there are two periods with apt effective precipitation to harvest water: May to June and September to October. Through a simulated water balance using Hydrus 1D, a total amount of rainwater that could be intercepted was calculated to be around 764 L/m2 y 767 L/m2 . The results indicate that the use of these hydrophobic sands in hydrophobic capillary barriers are a promising for waste management and water harnessing in Isla Caballo.

To investigate the effect of recharge water temperature on bioclogging processes and mechanisms during seasonal managed aquifer recharge (MAR), two groups of laboratory percolation experiments were conducted: a winter test and a summer test. The temperatures were controlled at ~5±2 and ~15±3 °C, and the tests involved bacterial inoculums acquired from well water during March 2014 and August 2015, for the winter and summer tests, respectively. The results indicated that the sand columns clogged ~10 times faster in the summer test due to a 10-fold larger bacterial growth rate. The maximum concentrations of total extracellular polymeric substances (EPS) in the winter test were approximately twice those in the summer test, primarily caused by a ~200 μg/g sand increase of both loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS). In the first half of the experimental period, the accumulation of bacteria cells and EPS production induced rapid bioclogging in both the winter and summer tests. Afterward, increasing bacterial growth dominated the bioclogging in the summer test, while the accumulation of LB-EPS led to further bioclogging in the winter test. The biological analysis determined that the dominant bacteria in experiments for both seasons were different and the bacterial community diversity was ~50% higher in the winter test than that for summer. The seasonal inoculums could lead to differences in the bacterial community structure and diversity, while recharge water temperature was considered to be a major factor influencing the bacterial growth rate and metabolism behavior during the seasonal bioclogging process.

The exchange rate between seawater and groundwater in a tidal flat was investigated at Laizhou Bay, China, where there are large-scale seepage faces with horizontal extension of several hundred meters developed during low tides. Taking into account the effects of seepage face and density, a simple and efficient method for estimating seawater–groundwater exchange rate is proposed, based on field measurements of groundwater hydraulic head, temperature and salinity. First, the exchange rate at each well was obtained using the generalized Darcy’s law, then the results were interpolated and integrated along the whole transect. The total submarine groundwater discharge (SGD) and inflow were estimated to be 8.8 and 15.3 m³d⁻¹ m⁻¹, respectively. The spatial distributions of SGD and inflow were different from those of sandy or gravel beaches possibly owing to the low-permeability sediment (silty sand with mud), very gentle slope, and the large-scale seepage faces. A freshwater discharge tube was identified near the low-tide line, as evidenced by significant increase in outflow and low salinity of groundwater observed there. The SGD from the seepage faces accounted for ∼21 % of the total SGD. The outflow rate that occurred from the seepage faces, and the ratio of the outflow from the seepage faces to the total outflow, decreased seaward significantly and monotonically.

Fissures and paleosols are important factors affecting the slope stability of loess. However, the mechanism of water and air migration in the unsaturated zone of loess induced by fissures and paleosols remains unclear. In this study, discontinuous irrigation experiments were conducted using a sand tank and Marriott bottle. The soil- water content (SWC) patterns and pressure differences, under the influence of fissures and paleosols, were observed using the EC-5 moisture sensor and MPXV5010DP differential pressure sensor. The results showed that the fissures are the dominant channels of water infiltration and air exchange, while paleosols and closed soil boundary conditions can significantly impede the downward transport of water and air. During irrigation, SWC near the fissure and paleosol increased rapidly from less than 10–30%, reaching a maximum value of 35% above the paleosol. On the other hand, the maximum pressure difference in the upper part of the paleosol exceeded 1,000 Pa, which is significantly higher than that observed in the lower part. The stability of soil around fissures and paleosols decreased sharply due to high SWC and pressure differences, which may induce landslides after long-term irrigation. This study provides a theoretical basis for revealing the formation mechanism of landslides in loess irrigation areas and preventing landslide disasters.

Beijing is a major metropolis in China, which shows characteristics of significant land subsidence because of long-term overexploitation of groundwater. Since the South-to-North Water Diversion Project Central Route was first operated in December 2014, it has provided Beijing with a new source of water. In this study, a variety of monitoring data has been used to analyze the changes in the groundwater flow field and land subsidence when comparing the conditions before and after the Water Diversion Project started, and to study the stress-strain characteristics of the soil layers at different depths under different water-level-change modes. Meanwhile, causes of the large residual deformation and hysteresis deformation of the cohesive soils are discussed. The study reveals that after the operation of the Water Diversion Project, the area of the groundwater depression cone and the rate of land subsidence in the Beijing Plain showed an overall decreasing trend. The deformation characteristics of different lithological soil layers under different water-level-change modes can be summarized into four categories. The sand layer is mainly characteristic of elastic deformation. The cohesive soil layers of different depths have elastic, plastic and creep deformation, and the viscoelastic-plastic characteristics are obvious. The large residual deformation and hysteresis deformation of the cohesive soil layer are mainly caused by two factors: firstly, the inelastic water storage rate is greater than the elastic water storage rate, and secondly, the cohesive soil has weak permeability.

The groundwater abstracted at a well field near the Yamuna River in Central Delhi, India, has elevated ammonium (NH₄ ⁺) concentrations up to 35 mg/L and arsenic (As) concentrations up to 0.146 mg/L, constituting a problem with the provision of safe drinking and irrigation water. Infiltrating sewage-contaminated river water is the primary source of the NH₄ ⁺ contamination in the aquifer, leading to reducing conditions which probably trigger the release of geogenic As. These conclusions are based on the evaluation of six 8–27-m deep drillings, and 13 surface-water and 69 groundwater samples collected during seven field campaigns (2012–2013). Results indicate that losing stream conditions prevail and the river water infiltrates into the shallow floodplain aquifer (up to 16 m thickness), which consists of a 1–2-m thick layer of calcareous nodules (locally known as kankar) overlain by medium sand. Because of its higher hydraulic conductivity (3.7 × 10⁻³ m/s, as opposed to 3.5 × 10⁻⁴ m/s in the sand), the kankar layer serves as the main pathway for the infiltrating water. However, the NH₄ ⁺ plume front advances more rapidly in the sand layer because of its significantly lower cation exchange capacity. Elevated As concentrations were only observed within the NH₄ ⁺ plume indicating a causal connection with the infiltrating reducing river water.