Small-scale Water Desalination Research Articles

Feasibility Assessment of a Small-Scale Agrivoltaics-Based Desalination Plant with Flywheel Energy Storage—Case Study: Namibia

As climate change and population growth threaten rural communities, especially in regions like Sub-Saharan Africa, rural electrification becomes crucial to addressing water and food security within the energy-water-food nexus. This study explores social innovation in microgrid projects, focusing on integrating micro-agrovoltaics (APV) with flywheel energy storage systems (FSSs) and small-scale water desalination and purification plants. Employing a mixed-methods approach to assess the economic viability of FSS and APV-powered desalination, we believe that social innovation could serve as a significant tool for rural development, requiring collaboration between governments, the private sector, and nonprofit organizations. While FSS technology for microgrids has not been entirely developed, it holds promise as an alternative energy storage solution. Our capital budgeting analysis, presented within the context of social innovation, reveals positive Net Present Values (NPV) and a short payback period over the project’s 20-year lifespan.

Natural draft direct dry cooling system performance at various application scales under windless and windy conditions

The natural draft direct dry cooling system (NDDDCS) presents a promising alternative to conventional forced draft air-cooled condensers (ACCs) and indirect natural draft dry cooling systems, overcoming their limitations by efficiently condensing process steam directly and passively. The NDDDCS achieves superior thermal efficiencies while reducing system complexities, operational costs, and auxiliary power consumption. Potential reductions in operational expenses for the system may offset initial capital investments, resulting in lower lifetime costs. While research to date has focused on large-scale NDDDCS performance under varying wind conditions, this work addresses a critical gap by investigating the system’s scalability for various applications, including a large-scale coal-fired power plant (900 MWt, 165 m total height), a medium-scale concentrated solar power plant (CSP) (100 MWt, 65 m total height), and a small-scale water desalination plant (1 MWt, 11.5 m total height) under both windless and windy conditions. To achieve this, a steady-state 3-D computational fluid dynamics (CFD) model is developed, validated and scaled, incorporating innovative features such as an atmospheric pressure gradient and the ability to capture reversed flows through the system’s heat exchangers. Additionally, the model assesses inlet air temperature data at a per-cell resolution, enabling the ability to predict non-uniform temperature distributions in the heat exchangers, including hot-spots caused by airflow recirculation. Analysis of velocity and temperature fields across all scales reveals that recirculation effects negatively impact NDDDCS performance, particularly at the middle circumferential heat exchanger sector. The hyperbolic shape of the tower shell induces internal recirculation zones and reduces the effective flow volume. Under windy conditions, performance losses of 44%, 40%, and 40% are observed at crosswind speeds of 3 m/s, 6 m/s, and 9 m/s for small, medium, and large-scale towers, respectively. Beyond these speeds, the relationship between system performance and draft driving potential becomes non-linear due to crosswind effects dominating. Furthermore, a novel effect is identified at wind speeds of 9 m/s, 15 m/s, and 18 m/s for small, medium, and large-scale systems, respectively, where an inflection point allows for system performance recovery. This study underscores the NDDDCS’s potential as a cooling solution for modern power cycles across various scales, while highlighting the implications of scaling the system for medium- and small-scale thermal applications.

Experimental investigation of a desalination system using porous carbon tube as a humidification media with swirl flow

Humidification-dehumidification (HDH) technology is a technique for small-scale water desalination applications based on carrier gas humidification motivated by thermal energy. The present work introduces an experimental investigation of a desalination unit based on HDH method. The main objective of this study is to evaluate the heat and mass transport properties of porous carbon tubes (PCT) as a humidification medium with swirl flow for HDH unit. Processes for transferring heat and mass are investigated at varied the temperatures of water and air, water-to-air mass ratios (MR), and helical flow channel pitch (HCP). The performance analysis is investigated based on some of performance metrics such as gained output ratio (GOR), humidification efficiency (ηH), exergy efficiency (ηex), sustainability indicator (SI), and water cost (WC). Results indicate that the increase in MR and HCP increases all of performance parameters. High values of MR based on low air flow rate decrease the entropy generation and enhance the exergy efficiency. The humidity efficiency and GOR improve with the rise in the MR based on the water flow rate. The study of sustainability indicator shows that the proposed system has possibilities of doing business. It still has room for energy improvement and losses, though. The system's usability will increase after these modifications are made. When the process temperature associated with heating the feed water or/and input air rises, more freshwater is produced. The proposed system's maximum hourly yield reaches about 0.225 L with cost 0.078 cent. The best value of GOR, exergy efficiency, humidification efficiency and suitability indicator performed by the current system are about 3, 51.67 %, 48.72 % and 2.07 respectively.

Year-Round Experimental Analysis of the Productivity of Vapour-Based Multistage Solar Still: A Developmental Study

The standalone vapour-based multistage solar still with stacked stages (MSS-SS) belongs to a pool of widely studied small-scale water desalination devices through solar thermal energy. This work contributes to the body of knowledge by presenting a system with new configurations. There is a need to develop small-scale systems to be reliable devices for freshwater provision, as brackish water is available for processing. The experimental study was conducted in a field under actual weather conditions, with the data logged and analysed to study the systems’ behaviour under varying meteorological conditions. A maximum distillate yield of 7790 ml, corresponded to a maximum daily average solar radiation at high range. There was a 21.8% decrease to 6090 ml at moderate daily average range and a further decline of 80.5% to 1190 ml in the low daily average range, representing a significant drop in the distillate yield caused by the insufficient heat collection at low range. The high, moderate, and low ranges corresponded to summer, spring and autumn, and winter, respectively. The lower values of the moderate range were the most optimum operationally. The impulsive modes were ideal for high rates of the heat inputs, while the continuous were for low rates. The assumption of a continuous mode and a further increase in the rate of thermal energy input caused thermal damage necessitating the augmentation of the thermal energy storage (TES) device due to a larger collector-to-basin area (CBA) ratio. The distillate yield trends from the stages were dynamic and were the inverse of the stage temperature, which was dictated by the mode and rate of the thermal energy input. These trends were such that stage 5 > 3 > 2 > 1 > 4 at moderate to high ranges and changed a low range. The summer season enhanced the cumulative saline water (SW) preheating and heat recovery to 66.8°C. The economic analysis found that at its most productive level, the cost of producing water per litre (CPL) from the vapour-based MSS-SS was R 4.05. The small-scale water purification systems are helpful, especially in remote areas.

Quantitative microbial risk assessment to estimate annual infection risk and disease burden attributable to Escherichia coli O157:H7 in drinking water in the Gaza Strip: a prospective study

BackgroundQuantitative microbial risk assessment (QMRA) with Monte Carlo simulation is the process of estimating the risk of infection through exposure to microorganisms. Worldwide, certain Shiga-toxin-producing types of Escherichia coli, such as E coli O157:H7, have been recognised as pathogens leading to waterborne outbreaks of infection. We attempted to estimate the annual infection risk and the burden of disease posed by E coli O157:H7 in drinking water in the Gaza strip. MethodsIn this prospective study, we applied the typical four steps of the QMRA technique: hazard identification, exposure assessment, dose-response analysis, and risk characterisation. Samples were collected between March, 2018, and January, 2019 from seven reference points in the drinking water supply from catchment to consumers’ taps (water wells, small-scale water desalination plants, tanker trucks, desalinated water at households, municipal water at households, private wells, and private well water at households). Microbiological analysis was performed to identify E coli O157:H7 and log reduction values (LRVs) were calculated using probabilistic modelling for five catchment routes: water wells to household (LRV1), catchment well to desalination plant (LRV2), desalination plant to tanker truck (LRV3), tanker truck to household (LRV4), and private well to household (LRV5). The most probable number (MPN) table was used to obtain the MPN of E coli per 100 mL water sample. The probability of being infected through intake of E coli O157:H7 was estimated with a β-Poisson dose-response model. The estimated magnitude of health risk and burden of disease were determined using a stochastic modelling technique. Values were compared with the health-target-based risk values of the United States Environmental Protection Agency ([EPA] target ≤10−4 infection cases per-person per-year), and the WHO burden of disease values (target ≤10−6 disability adjusted life-years [DALYs] per-person per-year). FindingsAmong 1317 water samples collected, E coli O157:H7 was detected in 91 (6·9%). The mean MPN was 1·97 (SD 9·74)/100 mL and the maximum was 112/100 mL. Negative LRVs were found in tanker trucks (LRV3 –1·465) and private household water wells (LRV5 –1·465), confirming water contamination. The risk model showed that the median of estimated annual risk of infection through consumption of water contaminated with E coli O157:H7 was 3·21 × 10−01 per-person per-year, which was about six logs higher than the EPA acceptable infection risk. The median disease burden was about 3·21 × 10−01 01 DALY per-person per-year, which greatly exceeded the WHO reference level. InterpretationThis study suggests the applicability and effectiveness of QMRA and highlights the necessity for a proactive strategy to incorporate a multibarrier approach to mitigate public health risks posed by contaminated drinking water. FundingNone.

Comprehensive Risk Assessment of Health-Related Hazardous Events in the Drinking Water Supply System from Source to Tap in Gaza Strip, Palestine.

Background The traditional approach in the management of the quality drinking water, and relying on end-product testing, has proven ineffective in protecting public health. Therefore, the transition to a systematic approach in drinking water supply systems management from the source to the consumer tap was taken as a water safety plan (WSP). Objective The study aims to investigate the health-related hazardous events in order to decide on the best risk-reduction strategies in the supply of drinking water in the Gaza strip. Methods A semiquantitative matrix method for risk assessment was applied. Also, chlorine residual, electrical conductivity, and nitrate concentration further tested in 109 water wells, 109 small-scale water desalination plants, 197 tanker trucks, and 384 households distributed over five governorates of the Gaza strip. Results The mean of the measured chlorine residual values was less than the recommended national and international limits (0.2–1 mg/liter). The mean of electrical conductivity at catchment points and household municipal water taps was 2165.1 μS·cm−1 and 2000 μS·cm−1, respectively. Furthermore, zero percent of water samples met the recommended criteria, indicating that the groundwater in the Gaza strip is nonpotable. Only 12.8% and 8.8% of water samples met the permissible levels at catchment areas and municipal water at household, respectively, indicating sever health impacts on the public. Moreover, the most hazardous events were related to high levels of groundwater salinity, the low level of disinfection, the effect of electricity outages on the efficiency of the desalination process, and leakage of water from the tanker truck tank reservoirs. Therefore, urgent interventions are required to improve the quality of water and to mitigate the possible health effects. Conclusion The prioritization of hazardous events that are proportional to the degree of their attributed risk could help guide in making the right risk-reduction decisions. Urgent interventions are required to improve the quality of water and to mitigate the possible health effects.

Performance evaluation of humidification-dehumidification (HDH) desalination systems with and without heat recovery options: An experimental and theoretical investigation

Humidification dehumidification (HDH) desalination system is a thermal-based desalination technology that is suitable for small-scale water desalination applications. In this paper, we present an experimental and thermodynamic analysis of the energetic performance of two HDH cycles. The HDH cycles considered are the basic open-air open-water (OAOW) cycle and the modified closed-water open-air (CWOA) cycle with the options of brine recirculation. An experimental investigation is performed on the modified cycle to validate the theoretical model that is used to assess the energetic performance of both the basic and modified cycles. The theoretical model is found to be in a good agreement with the experimental data with a maximum percentage deviation of 5% from the experimental data. Furthermore, limiting cases of the system are explored. Within the limiting cases, the modified cycle recorded about 100% improvement in the energy performance over the basic cycle due to heat recovery process associated with the modified cycle. Additionally, a cost analysis was performed to determine the cost of freshwater production by the presented desalination cycles. Results show that the freshwater price varied from 4.10 to 6.55 $/m3 and 0.79 to 2.25 $/m3 for the basic OAOW HDH cycle and the modified CWOA HDH cycle, respectively.

Humidification-dehumidification desalination system operated by a heat pump

Humidification-dehumidification is a carrier gas based thermal technique that is ideal for small-scale water desalination applications. One advantage of humidification-dehumidification systems is the ability to utilize low grade and renewable energies as heat source to drive the system. This work presents theoretical investigation of humidification-dehumidification desalination system operated by a heat pump. The model is based on the first law of thermodynamics, describing heat and mass transfer in the combined humidification-dehumidification-heat pump cycle. The model predicts the performance of closed-air open-water water-heated, and modified air-heated cycle coupled with a heat pump. To improve the Gain output ratio and energy recovery of the system, a heat pump is used as the source of heating and cooling for the humidification-dehumidification desalination system. Energy rejected in the condenser is used as a source of heat in the humidifier whereas the cooling effect of the evaporator is used to cool incoming seawater for effective condensation of humid air in the dehumidifier. A parametric study is conducted to investigate the influence of system operating parameters, including water and air flowrate, seawater temperature, and refrigerant flow rate on the system performance. Results indicate a maximum Gain output ratio of 8.88 and 7.63 obtained at 80% components effectiveness and mass flow rate ratio of 0.63 and 1.3 for modified air heated and water heated cycle, respectively. A maximum gain output ratio greater than 10 can be achieved for humidifier and dehumidifier effectiveness of 100% leading to more energy efficient systems. The cost of desalinated water production is calculated and the effect of major parameters on its variation is also presented.

The Bubble-Greenhouse: A holistic sustainable approach to small-scale water desalination in remote regions

The Bubble-Greenhouse system combines the well established Seawater Greenhouse concept with a novel humidification–dehumidification (HD) process, based on the large air/water interface generated by bubbling air through a water filled column. Multistage bubble evaporators and multistage bubble condensers allow for effective recovery and reuse of latent heat via a heating/cooling circuit throughout all column stages. The system can operate with salinities of 5000–35,000ppm. Following the HD process, cooled vapour provides the tropical type greenhouse with a humid environment for selected crops. Additional condensation occurs along the greenhouse skin and is gravity-fed to drip line irrigation. Low grade energy options such as solar-thermal, photovoltaic, wind, geo-thermal and salinity-gradient solar ponds provide the energy for the Bubble-Greenhouse. Alternatively, waste heat from diesel power stations nearby can provide cogeneration of electricity and bubble evaporator heat and pressure requirements. Crops grown inside a greenhouse demonstrate a strongly reduced water demand and the closed environment protects crops from insects and diseases. As the technology is conceptually simple to implement, it holds great potential for community participation, empowerment, skills development and capacity building of local people in remote locations.

Performance simulation of integrated water and power systems — software tools IPSEpro and RESYSpro for technical, economic and ecological analysis

Demand for small-scale water desalination and power supply including the utilisation of renewable energy sources at off-grid arid sites is rapidly increasing. Integrated systems for the simultaneous de-centralised supply of water and power at “water and power points” in many cases are the most appropriate solutions for settlements and industrial sites in sun belt regions with limited access to grid power and fuel supply. SimTech and ZSW are developing their software tools, IPSEpro and RESYSpro, for the prediction oftechnical, economic and ecological performance ofwater and power point systems including desalination and water treatment (membrane and thermal processes), renewable energy sources for power (e.g., wind and PV power) and conventional power generator (e.g., Diesel). A good example for a typical application of these tools is the reported design and performance analysis of a demonstration plant for seawater reverse osmosis (RO) desalination powered from renewable energy sources on the African coast of the Mediterranean Sea. The water and power point shall supply 300 m 3/d and 240 kW electricity to a village. For the RO demand of 60 kW, a 200 kW wind turbine is integrated with a 300 kW diesel GenSet. The key results from the systems analysis are the renewable energy fraction, the costs of investment, O&M and replacements, the life-cycle cost and present value of the project, and finally the levelised electricity and water costs.