Turning seawater into Gold: An alternative to Desalination Plants

ABSTRACT

This article explores an innovative and economical greenhouse technique that utilizes solar radiation and wind to simulate an artificial hydrologic cycle for harvesting pure water and minerals from seawater. The method employs simple and sustainable technology to evaporate seawater, condense the vapor into pure water, and collect precipitated minerals for further processing. Compared to conventional desalination plants, this approach offers a cost-effective and environmentally friendly solution for addressing global water and mineral needs. The article outlines the methodology, theoretical foundation, financial analysis, and schematic design of this technique.

INTRODUCTION

The natural hydrologic cycle, driven by solar radiation, evaporates water from the oceans & surfaces into the atmosphere. The water vapour forms clouds and precipitates as rain, which is naturally the purest form of water, Rain, hail, sleet or snows – the various forms of precipitations. However, by the time rainwater reaches the earth, it accumulates contaminants, dust particles, pollutants, gaseous and other substances, necessitating treatment for drinking, industrial, and agricultural purposes.

With erratic monsoons , droughts , and overexploitation of groundwater, the world faces a severe water crisis. Available ground water is diminishing day by day and to cope up the water demand for domestic, agricultural and industrial consumptions, there is no more water left in the ground. Seawater, being an abundant resource, is a viable solution.

Unfortunately, sea water cannot be used directly as it is for drinking, industrial and agricultural purpose. However, it can be make suitable after certain treatment called desalination, which is expensive, both in terms of capital and operational costs. This article introduces a greenhouse-based technique that mimics the hydrologic cycle to produce pure water and harvest minerals, providing a sustainable and cost-effective alternative.

COMPONENTS

Following components are involved in this technique:

• Green House Structure: It consists of hot dip galvanized Steel foundations, columns, trusses, purlins, bracing, gutters & accessories
• Translucent covering materials: Translucent covering materials like polycarbonate sheet allow transferring direct solar radiation as a source of heat energy for speeding up the evaporation rates.
• Axial Blower: High capacity & speed axial blowers allow speeding up the rate evaporation in night as well as day time. Also it allows dehydrating the minerals during harvesting.
• Exhaust cum suction Fan & Duct: High capacity exhaust-cum suction fans are provided at root top to suck and convey the evaporation to condenser via duct.
• Condenser: Cool water is circulated around the evaporation duct to convert vapour to water drops.
• Water collection Tank / Bottling plant: Condense water drops are then collected either collection tank or directly bottling plants.
• Mineral Processing unit: Harvest precipitated minerals.

THEORY

Evaporation is the process by which water (liquid) is changed to vapours (the gaseous state) at the free surface, below the boiling point of water. The amount of energy used by a unit mass of water from the liquid state to vapour state at constant temperature is known as the latent heat of evaporation, which is about 585 calories per gram. Vapour molecules continuously leave the water during evaporation. The motion of these molecules produces a pressure on the water surface, which is known as vapour pressure. The partial pressure exerted by the water vapours at that stage is called the saturation vapour pressure (es). The saturation pressure increases with an increase in temperature. If the vapour pressure in the air above the water surface less than that of the water surface, evaporation continues. As soon as the vapour pressure reaches the saturation vapour pressure, evaporation stops.

The following factors are influencing the rate of evaporation.

• Temperature: Higher temperatures increase evaporation rates.
• Wind Velocity: Enhances vapour transfer.
• Atmospheric Pressure: Lower pressure accelerates evaporation.
• Mineral Concentration: Higher concentrations reduce evaporation.
• Water Body Characteristic: Shallow and expansive surfaces promote evaporation.

DALTON’S LAW

The fundamental principle of evaporation from a free surface was enunciated by Dalton in the year 1882. Dalton states that the evaporation is a function of the difference in the vapour pressure of the water and vapours pressure of the air and is expressed as:

ROHWER’S EQUATION

There are several empirical equations are available which are based on Dalton’s law.

For evaporation to continue, the following three main conditions should be satisfied

1. There should be a constant supply of water.
   1. There should be a constant supply of heat.
   1. There should be a vapour deficit.

ADVANTAGES

1. Overall investment is low as compared to desalination plants.
2. Simple and easy to set up, easy to handle, operate and maintain.
3. Overall electrical consumptions/ charges and maintenance charges are very low.
4. No complicated technology involved.
5. Number value added by products can be harvested from it by using simple technology.
6. Rain water can be simply collected from roofs and re-used for condenser and as raw water so that it can lower the cost of pumping power.
7. It is not just suitable for desalination of sea water but also suitable for waste water treatment.

LIMITATIONS

1. Inconsistent water production during cloudy weather.
2. During cloudy and rain weather, non-consistence flow of water.
3. Under high humidity metal components are susceptible for corrosion so it needs to be painted periodically.
4. To process by product special technology has to be used.

CONCLUSION

This greenhouse-based technique offers an economical and sustainable solution for addressing water scarcity and mineral recovery. By utilizing solar energy and simple technologies, it presents an innovative alternative to costly desalination plants, with potential applications in both water desalination and wastewater treatment. This technique is essential for communities facing acute water scarcity and a lack of economic opportunities. By providing access to clean water through a sustainable and low-cost method, it directly addresses health and hygiene challenges. Additionally, the mineral by-products offer economic benefits by creating new avenues for local industries. The system’s minimal environmental impact ensures responsible resource use, fostering long-term sustainability and resilience against climate change-induced water crises.