A review of limitations and potentials of desalination as a sustainable source of water

For centuries, desalination, in one way or another, has helped alleviate water scarcity. Over time, desalination has gone through an evolutionary process influenced largely by available contemporary technology. This improvement, for the most part, was reflected in the energy efficiency and, in turn, in terms of the cost-effectiveness of this practice. Thanks to such advancements, by the 1960s, the desalination industry experienced notable exponential growth, becoming a formidable option to supplement conventional water resources with a reliable non-conventional resource. That said, often, there are pressing associated issues, most notably environmental, socioeconomic, health, and relatively recently, agronomic concerns. Such reservations raise the question of whether desalination is indeed a sustainable solution to current water supply problems. This is exceptionally important to understand in light of the looming water and food crises. This paper, thus, tends to review these potential issues from the sustainability perspective. It is concluded that the aforementioned issues are indeed major concerns, but they can be mitigated by actions that consider the local context. These may be either prophylactic, proactive measures that require careful planning to tailor the situation to best fit a given region or reactive measures such as incorporating pre- (e.g., removing particles, debris, microorganisms, suspended solids, and silt from the intake water prior to the desalination process) and post-treatments (e.g., reintroducing calcium and magnesium ions to water to enhance its quality for irrigation purposes) to target specific shortcomings of desalination.

Evaluation of an autonomous smart system for optimal management of fertigation with variable sources of irrigation water

Modern irrigation technologies and tools can help boost fertigation efficiency and sustainability, particularly when using irrigation water of varying quality. In this study, a high-tech irrigation head using a new fertigation optimization tool called NutriBalance, which is designed to manage feed waters of different qualities, has been evaluated from technical and economic perspectives. NutriBalance computes the optimal fertigation dose based on specific data about the equipment, the crop, the irrigation water, and the fertilizers available, in order to enable autonomous and accurate water and fertilizer supply. The system was trialed in a grapefruit orchard irrigated with fresh and desalinated water for several values of crop nutritional requirements and considering different fertilizer price scenarios. The results showed the good interoperability between the tool and the irrigation head and the nearly flawless ability (error below 7% for most ions) of the system to provide the prescribed fertigation with different combinations of irrigation water. Fertilizer savings of up to 40% were achieved, which, for the lifespan of the equipment, were estimated to correspond to around 500 EUR/ha/year. The results of this study can encourage the adoption of novel technologies and tools by farmers.

Recycling drainage effluents using reverse osmosis powered by photovoltaic solar energy in hydroponic tomato production: Environmental footprint analysis

Greenhouse cultivation in the Mediterranean region has undoubtedly enhanced the economic growth and has generated social benefits by making an efficient use of resources. However, these production systems caused undesirable environmental impacts. In order to move towards cleaner production in greenhouse areas, this study has assessed the potential environmental benefits and trade-offs of the integration of an on-farm reverse osmosis system powered by photovoltaic solar energy to recycle the drainage effluents from greenhouses. To that end, we compare the environmental footprint of a greenhouse tomato crop using this technology in a hydroponic system (HS), versus the conventional sanded soil 'enarenado' (CS) with free-drainage to soil. Additionally, for comparison, three independent irrigation sources (desalinated seawater with low electrical conductivity and two different mixes of underground and desalinated water, with moderate and high electrical conductivity, respectively) were evaluated. The use of desalinated seawater can help reduce the overexploitation of aquifers, although if the desalination process is not done with clean energy it also comes with a negative impact on the carbon footprint. Life Cycle Assessment (LCA) was used to analyse and evaluate six environmental impact indicators associated with these production systems and water treatments. In addition, a sensitivity analysis was conducted to explore the potential environmental benefits of increasing the use of renewable energy for desalinated water production, whilst also curbing the common over-fertilisation malpractice reported in the study area. Based on our findings, the HS with leachate treatment technology showed, compared to the CS system, a significant reduction in the eutrophication (72 %), although it did inevitably increase the depletion of fossil fuels (43 %) global warming (37 %) and acidification (32 %) impacts, due to the need for additional infrastructure and equipment. Among the inputs considered for the cultivation systems, the greenhouse structure, and the production of fertilisers and electricity for fertigation represented the highest environmental burdens. When comparing the three irrigation treatments, it was observed that the partial substitution of desalinated seawater by brackish groundwater substantially mitigated (27 %) the global warming footprint. The sensitivity analysis revealed that a significant reduction in the environmental impact is feasible.

Impact of artificial monolayer application on stored water quality at the air-water interface

Evaporation mitigation has the potential to significantly improve water use efficiency, with repeat applications of artificial monolayer formulations the most cost-effective strategy for large water storages. Field investigations of the impact of artificial monolayers on water quality have been limited by wind and wave turbulence, and beaching. Two suspended covers differing in permeability to wind and light were used to attenuate wind turbulence, to favour the maintenance of a condensed monolayer at the air/water interface of a 10 m diameter tank. An octadecanol formulation was applied twice-weekly to one of two covered tanks, while a third clean water tank remained uncovered for the 14-week duration of the trial. Microlayer and subsurface water samples were extracted once a week to distinguish impacts associated with the installation of covers, from the impact of prolonged monolayer application. The monolayer was selectively toxic to some phytoplankton, but the toxicity of hydrocarbons leaching from a replacement liner had a greater impact. Monolayer application did not increase water temperature, humified dissolved organic matter, or the biochemical oxygen demand, and did not reduce dissolved oxygen. The impact of an octadecanol monolayer on water quality and the microlayer may not be as detrimental as previously considered.

Contrasting suspended covers reveal the impact of an artificial monolayer on heat transfer processes at the interfacial boundary layer

The highly variable performance of artificial monolayers in reducing evaporation from water storages has been attributed to wind speed and wave turbulence. Other factors operating at the interfacial boundary layer have seldom been considered. In this paper, two physical shade covers differing in porosity and reflectivity were suspended over 10 m diameter water tanks to attenuate wind and wave turbulence. The monolayer octadecanol was applied to one of the covered tanks, and micrometeorological conditions above and below the covers were monitored to characterise diurnal variation in the energy balance. A high downward (air-to-water) convective heat flux developed under the black cover during the day, whereas diurnal variation in the heat flux under the more reflective, wind-permeable white cover was much less. Hourly air and water temperature profiles under the covers over 3 days when forced convection was minimal (low wind speed) were selected for analysis. Monolayer application reduced temperature gain in surface water under a downward convective heat flux, and conversely reduced temperature loss under an upward convective heat flux. This 'dual property' may explain why repeat application of an artificial monolayer to retard evaporative loss (reducing latent heat loss) does not inevitably increase water temperature.