A Sustainable Approach to
Water Desalination
by
Thomas Lisa & Joshua Bumann, NWCTA
Abstract
Current methods of water desalination can cost upwards of $250 million annually to operate,
with energy accounting for 40% of these costs. This research focuses on developing a portable,
hydroelectric-powered desalination system. The goal is to address the global issue of water
inequality at the small scale. The objective of this project is to refine contemporary procedures
by optimizing the cost and energy efficiency of desalination. To aid in understanding and
visualizing the processes of brine treatment, models are being developed with the use of 3D
software. Experts have also been sought out for feedback and assistance as needed. The design
will be validated by experiments and simulations, showcasing its potential for sustainable water
desalination.
1. Introduction
Water inequality is a global issue that affects billions of people across the world. According to
the United Nations, over 2 billion people lack access to safely managed drinking water services,
and over half of the global population lacks safely managed sanitation services. Though many
organizations have helped improve water quality, factors such as global warming and an
ever-growing population are causing many to project that the problem will only continue to get
worse. What’s more, water scarcity has far-reaching impacts, ranging from economic instability
to conflict. Together, these factors have put pressure on the global sphere to implement more
sustainable solutions and increase cooperation.
Water scarcity occurs when there is not enough water to supply the demand. It is often the result
of a physical shortage of water or a lack of adequate infrastructure. The problems often stem
from natural and human causes, but humans are most often the greatest contributors to water
scarcity. In terms of impact, regions in the Middle East and Northern Africa experience the
greatest water scarcity. Some wealthier countries attempt to alleviate this through importing food
and ocean water desalination, but these methods - in their current form - are unsustainable and
expensive.
Ocean water desalination is the process of separating water molecules from seawater. Various
methods exist, but the most common ones utilize reverse osmosis technology. Highly-pressurized
water is pushed through thousands of tightly-wrapped, semipermeable membranes that allow
only smaller water molecules to pass through. As of 2016, desalination provided about 1 percent
of the world’s drinking water, but various investments predict the production capacity to double
by 2030. The main issues with current desalination processes, however, relate to the energy and
cost of the processes. Large-scale desalination units can cost tens to hundreds of millions of
dollars to build. For example, the Carlsbad desalination plant is expected to cost upwards of
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$250 million. These costs are largely a result of energy, as water desalination is heavily
energy-intensive. Figures 1 and 2 below predict that
energy costs can range from 20 to 44 percent of the
entire annual cost to run.
Over the past several decades, ocean water desalination has been heavily invested in, as water
inequality grows and access to resources diminishes. Yet even today, the costs of desalination both literal and figurative - prevail. This paper presents an analysis of an ongoing attempt to
address these concerns, emulated in a small-scale portable system.
Our team has theorized that incorporating a self-sustaining, natural source of power into the
design of a desalination system is most advantageous for improving the overall process.
Accordingly, we are currently prototyping, researching, and developing a hydroelectric power
system to be included at the beginning of the desalination process. The water from a river or
ocean would travel through a funnel and tubes to then come in contact with the hydroelectric
turbine. The natural, highly-energized flow of the water would then convert to mechanical
energy.
As of today, February 14, 2023, the team is in the process of designing and testing a
hydroelectric power system. Furthermore, filtration will be achieved by a multi-step process
involving sieves of finer grain, with a layer of sand at the final step. Once filtration is complete,
the water will be collected into a pressure chamber wherein a pneumatic or mechanical system
will pressurize the water, preparing it for the reverse osmosis (RO) processes in the next step.
Akin to current methods, the reverse osmosis technology will resemble that of RO in domestic
households. Water will travel through semi-permeable membranes, and the purified water will
then be transported into a remineralization process with a calcite or chemical process. The
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highly-salinated water will be disposed of in a safe and efficient manner. Once the purified water
has been remineralized, it will be stored in a container optimized for weight distribution.
2. Methods
The team’s project is still currently in development, and as such, data collection has yet to be
achieved. That said, once an initial prototype is completed, we will conduct further research on
specific dimensions and requirements by utilizing various mathematical principles, formulas, and
digital tests to collect data. The primary areas of focus for the data will be to discern the
efficiency, sustainability, and cost of the proposed innovations.
Bernoulli’s Equation will be frequently measured and calculated to understand the speed and
pressure of the water at various points within the system. The intention is to build a pressure
chamber, either with pneumatics or mechanics, to pressurize the water before entering RO.
Bernoulli’s Equation will be essential to adequately design and construct the chamber. It is
important to note that Bernoulli’s Equation is applicable since it will be a closed system. The
desalination unit will have a valve between the sand filter and the pressure chamber to enable the
pressurization of the water. Furthermore, due to the portability of the entire system, adequate
pipes must be utilized, with the correct inner and outer diameters and thickness. To aid in
determining these values, Barlow’s Formula will also be integrated.
2.1 Apparatus and Equipment
Components and processes within the desalination unit separate the team’s design from other
commercial desalination methods. Key features within the unit are in the following series: a
funnel intake, a hydroelectric generator, a series of sieves and silica sand filtration, a pressure
chamber, a reverse osmosis system, a remineralization process, and an outtake.
The funnel directs flowing water into the desalination unit. It can also be used vertically and rely
on the force of gravity in bodies of water without a sufficient flow rate (i.e. ponds and lakes).
Exterior pipes connecting the funnel to the main body of the unit will be able to rotate to
accomplish this clever use of gravity and existing components.
Generating power with a hydroelectric turbine allows for the unit to be fully autonomous and
sustainable. The team did not want to rely on batteries or outside energy forms so utilizing
existing energy from the water itself simply makes sense. The turbine is made up of five concave
fins to capture the most energy from the water. Using a turbine design that has vertical fins
allows for water to be captured and utilized even when at low volume.
Sieves and silica sand are used to capture all non-dissolved particles within the water. The design
of the sieves themselves is very unique as they are conical to catch more leaves before needing to
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be emptied compared to a flat sieve. Sieves on the unit are detachable to allow users to empty
them periodically to clear blockades of impurities. The grain of the sieves starts with a ½”
spacing and becomes half as small with 1/16” spacing being the smallest. Following the sieves is
a layer of silica sand.
The pressure chamber pressurizes the filtered water enough to pass through the reverse osmosis
system, 60 psi is recommended. Between the silica sand and the pressure chamber is a valve to
isolate and close the system when pressurizing. This enables the use of Bernoulli's equation as
well as the practical applications of sealing off the chamber when increasing the pressure of the
water within. A secondary valve will open once 60 psi is released and the water will flow into
the next component, the reverse osmosis system.
Reverse osmosis is a process in which pressurized water flows through semi-permeable
membranes to remove dissolved impurities from water. Two byproducts are created, highly
salinated brine and pure water. These two liquids are separated and brine is typically disposed of
back into the original source of water and the pure water is sent to remineralization.
Introducing minerals back into the water is essential for the well-being of those who consume the
water. Without minerals, pure water would have dehydrating effects and lack taste. The
remineralization process reintroduces elements such as micronized calcium carbonate and carbon
dioxide into the purified water. Then, the pH levels of the water are rebalanced, with the final
output being safe for human consumption.
One of the design’s greatest strengths is its flexibility. As the design is purely digital,
specifications can be adjusted and re-designed with ease. Furthermore, a focal point for the team
is designing a product that can be easily adjusted by the user. The outtake can be exchanged
depending on the user’s needs. Attachments such as storage within the unit and foldable storage
containers can be utilized. Onboard storage is essential for an autonomous unit as the water
needs a place to go once ready for consumption. With future updates and improvements, even
more portions of the design may be interchangeable and modifiable as well.
The team will use 3D printers provided by the school to create physical representative models.
Printing out the desalination unit in a simplified state is the closest the team can get to physically
modeling the project due to budget and time constraints.
2.2 Procedures to Collect Data
A multitude of equations have been used to guide the team and assist in creating a model that
would be functional if made with adequate materials. Without the use of calculations, the team
can only speculate that the designs would function as intended.
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Bernoulli’s Equation is relevant to the pressure chamber since the team needs to know what
pressure the water inside needs to be to pass through the reverse osmosis system at 60 psi. As of
now, the pressure within the tank needs to be approximately 62.5 psi but this is subject to change
as the design continues to develop.
Barlow’s Equation will be used to determine and validate the “infrastructure” of the pipes. The
ultimate purpose of the equation is to ensure that the pipes used can withstand the maximum
potential pressure of each process, particularly within the pressure chamber before RO.
Measurements will be taken from the 3D model created, and specifications will be further
drafted in future updates.
The hydroelectric generator’s possible power generation has been based on the following
formula where η is mechanical efficiency, g is the gravitational constant, Q is the flow rate in
m^3/s, and H is the head.
Power (P) = η × g × Q × H (kW)
Given that the team estimates our unit will process between 0.0000027778 m^3/s and 0.005938
m^3/s, we can assume that the potential power the hydroelectric can generate is approximately
between 0.02 watts per second and 49.5 watts per second with a head of one meter. If the head
were five meters, the hydroelectric generator could produce from 0.1 watts per second to 247.6
watts per second.
It has been vital to the project to have proper equations and formulas to guide the team along this
journey. Otherwise, all of these numbers would be guesses and we could not say for certain if the
physical model made with proper components would function.
2.3 Project Timeline
The 2022-23 Capstone project began in September of 2022 through Engineering Design and
Development. In the months since various deadlines have been established by the instructors, the
team has established its own timeline to guide the project focus. As seen in Figure 3, the team’s
primary focus is on the physical model. Due to financial and time constraints, a complex
working model is not feasible or possible. However, a vast majority of the project has been spent
on research, so the team strives to create a prototype to visualize and test the model.
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Portions of the initial 3D draft have been completed thus far. All components of the design have
been modeled, but have not been designed or melded together. Remedying this fact will be the
team’s primary concern moving forward. That said, when designing the initial draft, the team
attempted to design each part relative to one another to augment future models.
March will be spent preparing for the Capstone presentation day. During this month, the team
will focus on developing the visual aids and presentation, along with finalizing any calculations
or modeling. The capstone presentation day will be open to any and all visitors, so the team must
be prepared to present our idea to peers, school faculty, and business leaders.
Results and Discussion
The project is currently ongoing, and definitive results have yet to be fully ascertained. However,
the team is confident that, based on months of research, designing, and calculations, the overall
design will positively impact local communities. The cost of desalination is immense, and many
third-world countries are incapable of affording large-scale operations. Instead, innovating a
small-scale model utilizing many of the same concepts holds the potential to dramatically
improve water inequality. Communities living near oceans, lakes, or rivers would be capable of
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converting the water into a safe, drinkable source. Not only would desalinated water save time,
but it would also improve the health and safety of those living in these communities.
Introducing a hydroelectric power generation system works as a solution to multiple problems
related to water desalination. First, as the power is being generated by the water entering the
system, it is a self-sustaining operation that does not require external sources of energy. Because
the system is self-sustaining, the cost of energy is dramatically reduced. Furthermore, once
constructed, there is little additional cost to maintain the system, thus enabling it to operate much
more efficiently and inexpensively. Finally, a major concern for many opponents of water
desalination is the source of energy. While desalination might improve the environment in one
matter, if it is powered by fossil fuels, it could be creating greater harm than benefit. By utilizing
hydroelectric power, these concerns are mitigated.
Conclusion
The sustainable approach to portable desalination is still an ongoing project, and many variables
have yet to be fully determined. In the coming months, it is planned for the team to continue
pursuing validation of the design’s legitimacy while also developing a complex and clear visual
model. The end goal of the project is the development of a physical, working prototype that
intakes seawater and produces drinking water. However, the feasibility of this end goal is
uncertain with the time and financial constraints, along with barriers in knowledge and resources.
Regardless, this project has been an outlet for the team to imbue our passions in STEM and
engineering with a real-world problem that affects billions. Upon entry to college, the team plans
to continue pursuing this and related research with the hope of achieving the ambitious goal
established by the 2022-23 engineering Capstone team.
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