Thermal desalination is yet a reliable technology in the treatment of brackish water and seawater; however, its demanding high energy requirements have lagged it compared to other non-thermal technologies such as reverse osmosis. This review provides an outline of the development and trends of the three most commercially used thermal or phase change technologies worldwide: Multi Effect Distillation (MED), Multi Stage Flash (MSF), and Vapor Compression Distillation (VCD). First, state of water stress suffered by regions with little fresh water availability and existing desalination technologies that could become an alternative solution are shown. The most recent studies published for each commercial thermal technology are presented, focusing on optimizing the desalination process, improving efficiencies, and reducing energy demands. Then, an overview of the use of renewable energy and its potential for integration into both commercial and non-commercial desalination systems is shown. Finally, research trends and their orientation towards hybridization of technologies and use of renewable energies as a relevant alternative to the current problems of brackish water desalination are discussed. This reflective and updated review will help researchers to have a detailed state of the art of the subject and to have a starting point for their research, since current advances and trends on thermal desalination are shown.
Reverse osmosis is the leading technology for desalination of brackish water and seawater, important for solving the growing problems of fresh water supply. Thermal technologies such as multi-effect distillation and multi-stage flash distillation still comprise an important portion of the world’s desalination capacity. They consume substantial amounts of energy, generally obtained from fossil fuels, due to their low efficiency. Hybridization is a strategy that seeks to reduce the weaknesses and enhance the advantages of each element that makes it up. This paper introduces a review of the most recent publications on hybridizations between reverse osmosis and thermal desalination technologies, as well as their integration with renewable energies as a requirement to decarbonize desalination processes. Different configurations provide improvements in key elements of the system to reduce energy consumption, brine production, and contamination, while improving product quality and production rate. A combination of renewable sources and use of energy and water storage systems allow for improving the reliability of hybrid systems.
Natural coagulants were evaluated in saline Hylocereus cf. trigonus stems, gum exudate of Albizia saman, bark and seeds of Moringa oleifera and bark of Guazuma ulmifolia in raw water samples from the Sinú river with 56, 104, 200 and 301 Nephelometric Turbidity Units, and Jar tests were conducted to determine the performance removal turbidity of each coagulant, with doses between 5 mg/L to 60 mg/L. pH, color and alkalinity of the water samples were measured before and after treatment to verify the incidence of the coagulant in the purification process. For H. trigons, A. saman, G. ulmifolia and bark of M. oleifera, removal percentages ranged between 50% and 70% and up to 95% for M. oleifera seed. Greater coagulant activity was recorded for applied doses between 20 mg/L to 30 mg/L, independent of raw water turbidity. The pH and total alkalinity had no significant changes for the entire dose range, while the true color slightly increased with extracts of H. trigons, A. saman, G. ulmifolia and bark of M. oleifera, and decreased significantly with M. oleifera seeds to values lower than 5 CU, which was the extract with the highest in removing turbidity and color. RESUMEN:Se evaluaron coagulantes naturales en solución salina de tallos de Hylocereus cf. trigonus, exudado gomoso de Albizia saman, corteza y semilla de Moringa oleífera y corteza de Guazuma ulmifolia, en muestras de agua cruda del río Sinú, con turbidez de 56, 104, 200 y 301 UNT y se realizaron ensayos de jarras para determinar la remoción de turbidez de cada coagulante, con dosis de 5 mg/L a 60 mg/L. Se midió el pH, la alcalinidad y el color de las muestras de agua, antes y después del tratamiento, para verificar la incidencia de los coagulantes en el proceso de potabilización. Los porcentajes de remoción variaron entre el 50% y 70% para H. trigons, A. saman, G. ulmifolia y corteza de M. oleífera y hasta del 95% con semilla de M. oleífera. Para las dosis aplicadas entre 20 mg/L a 30 mg/L se registró mayor actividad coagulante, independiente de la turbidez del agua cruda. El pH y la alcalinidad total no tuvieron variaciones significativas para todo el rango de dosis, mientras que el color verdadero aumentó levemente con los extractos de H. trigons, A. saman, G. ulmifolia y corteza de M. oleífera y disminuyó significativamente con la semilla de M. oleífera hasta valores menores a 5 UC, siendo este el extracto de mayor eficiencia en la remoción de turbidez y color.
Coagulation-flocculation is a physical-chemical process responsible for producing the largest amount of sludge in the purification of natural raw water. Conventionally, aluminum sulfate or alum has been used as a coagulant. However, disposal of the sludge produced has been problematic for the environment due to excess aluminum. Currently, the convenience of using natural coagulants such as seed extracts from Moringa oleifera (MO) is being studied, although, the properties of sewage sludge produced and its possible reuse are unknown. In this paper the physical-chemical, nutritional and dangerous characteristics from MO sludge were evaluated by using standard methods to verify its potential use in agricultural soils. Results indicated that pH, electrical conductivity, ion exchange capacity, organic matter and micronutrients from sludge were suitable for application to soils with agricultural potential; but deficiency of macronutrients and presence of fecal coliforms limits it to be used as soil improver and not as fertilizer. Sludge stabilization with hydrated lime at doses greater than or equal to 3 % was effective to ensure the elimination of pathogenic microorganisms and to obtain a Class A sludge, unrestricted for agricultural use and suitable for acid soils.
En este trabajo se usó información de los registros mercantiles para caracterizar la evolución del sector agrario colombiano sobre los efectos sectoriales y de localización ejercidos en la rentabilidad de sus empresas en el periodo 2014 a 2017. Se halló una mayor rentabilidad en función de la ubicación de las empresas que entre los diferentes tipos de actividades agrarias, lo que amerita políticas estructurales y estrategias comerciales diferenciales para acotar la brecha tecnológica y socioeconómica en los territorios dispares.
Access to freshwater for rural populations is increasingly difficult worldwide. Even in coastal regions with abundantly available seawater, this is not suitable to meet the population’s basic needs. Desalination with solar stills represents a simple, inexpensive, and accessible alternative to obtaining freshwater. This research shows the results obtained with a mathematical model of a single slope solar still proposed by Dunkle, compared with experimental data. Field experiments were carried out in the coastal zone of the Gulf of Mexico to validate the mathematical model. Different operating parameters of the solar still and their performance depending on climatic variations of the study site were studied. The average yield of distilled water was 1.57 L/m2 d.
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