Using the Plasma for Water Treatment

Introduction

For ages, water treatment has been going on. Plasma methods are an alternative to
conventional water treatment methods where the method effectively combines active chemicals,
ultraviolent radiation as well as the electric fields. However, the knowledge on electric
breakdown of liquids has not been in pace with the increased interest because of the
phenomena’s complexity which is related to the process. This topic of plasma discharge in the
water treatment applications gives engineers and scientists the basic understanding of the
chemical as well as the physical phenomena that is associated with the discharge of plasma in in
liquids specifically in water.
Problem statement
The presence of water that can be used by human beings has been reducing daily. Even
though there has been efforts to improve the quality of water throughout the world, there is more
pollution on daily basis. Barillas states that more than 80 % of sewage in the developing
countries that is untreated is discharged in rivers, coastal areas and in lakes thereby polluting the
waters in those sites. Most of the water from these water bodies is heavily relied on by millions
of people all over the world. Pollution leads to scarcity of water. It is estimated that water

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scarcity affects almost everyone in the world because 2.8 billion people get continuous
availability of water one month in each year while 1.2 billion people cannot access clean water
for drinking (UNESCO).
The scarcity of water involves shortage of clean water for usage, water stress, water crisis
or water deficiency. Some of the main reasons for the scarcity of water include change of
climate, increased human overuse and demand of water and an increased pollution of water
sources. Water crisis is a term that describes a situation where the potable water available and
that which is not polluted in a given region is less than that which is demanded by the population
therein. The phenomena that leads to a shortage of water includes the depletion of freshwater
resources that can be used and the growing use of fresh water. However, the amount of polluted
water is extremely high but it cannot be used in that condition. If such polluted water can be
recovered, the number of people experiencing the scarcity of water would reduce rapidly
Significance and Relation to Physical and Chemical Water and Wastewater Treatment
Without of physical and chemical process for wastewater treatment, most substances
would not be removed from the polluted water. There are different steps involved in the physical
and chemical treatment of wastewaters. The insoluble substances and colloids in water require
sedimentation, filtration or the centrifugal separation so that the wastewater can efficiently be
treated. However, depending on the composition of the wastes in the waters, rakes, strainers and
even membrane technology is required. Methods such as flotation are sometimes used, where the
adhesion forces are used and the finest particles separated when they stick onto the small air
bubbles. In chemical water treatment, the chemical conditions of water are altered to such a
degree where the substances that are harmful dissolve in the water and are then separated in an

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easier manner. The other options that are employed in the removal of harmful substances from
waste water include ionic exchange, UV treatment, precipitation or flocculation (Sabbas et al,).
Basically, physical and chemical treatment of wastewater is commonly done in large
scale water treatment plants. Physical treatment includes filtration and air-stripping while
chemical treatment includes coagulation, chlorination and ozonization. The terms can also
describe the treatment of wastes that are toxic on the surface as well as in the ground waters,
soils and oil spills. Chemical and physical treatment of wastewater are very important in
recovering of clean water for large populations that lack drinking waters.

Literature review

The availability of water for human use and consumption is diminishing daily. Although
there are efforts of improving the quality of water in various regions of the world, pollution of
the clean water sources keeps going on and increasing leading to water crisis and scarcity.
Unfortunately, about eighty percent of the sewage in the countries that are developing is
discharged in water bodies such as rivers, lakes and sea before treatment. Once the large water
bodies are contaminated, the chances of recovering the waters lowers to null. Barillas (2015)
argues that less than 20% of the drainage basins in the world exhibit pristine quality waters.
The problem statement above calls for treatment of the waste waters before they are
disposed from industries especially in the developed countries. The problem calls for a research
on ways in which water can be cleaned and purified for use. Currently worldwide, chemical and
physical treatment of waste water has been ongoing. The rate of water contamination determines
the method that is used in the treatment of water. Contaminated or polluted water has different
particles of different sizes. According to De Sanctis et al (2016), contaminated water has

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particles that are termed as dissolved if they are less than 0.08 µm, they are colloidal if they are
between 0.08 µm and 1 µm, supracolloidal if they are between 100 µm and 100 mm and
settleable if they are greater than 100 µm.
Practically, the type of treatment employed is efficient if it is based on the size of the
contaminants. For instance, the particles that are visible by the eye can successfully be separated
by settling it through floatation or gravity depending on their densities and the densities of
waters. They can also be separated easily by filtration. However, Stratton et al (2015) argues that
particles that are very fine, especially the colloidal ones that have a high stability are important
pollutants. The main reason as to why they are stable is because they have electrostatic surface
charges with the same sign (often negative). The same sign means that they have repulsive forces
that prevent them from aggregating and finally settling. It is for this reason that they cannot be
separated by flotation or settling. However, the particles can be separated using physico-
chemical treatment (Brooks).
Physico-chemical treatment of waste water does not still provide the best and final
solution and therefore this project proposes a different method, plasma usage, of recovering the
waste waters. Physico-chemical treatment focuses on colloidal particles separation which is
achieved by addition of chemicals known as flocculants and coagulants (De Sanctis et al).
However, the use of plasma technology would create a foundation for industrial waste water
plants. According to the higher need of treating the waste waters, plasma purification would
provide increased recovery of the waters. This will also highly reduce the high amount of
wastewater spillage that threatens the other sources of water worldwide (Malik). Water scarcity
can largely affect the development of human beings on the face of the earth. However, this

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project aims at treating water so that it can be consumed by human beings or reused in other
processes.

Proposed solution

Scope of Treatment
Plasma for wastewater treatment is environmentally friendly as well as cost-effective. An
electrical current is applied to produce ions that are reactive and short-lived as well as short-
wave radiations from the atmospheric oxygen and ambient air. The wastewater is then broken
down into its primary constituents. Use of more chemicals as well as their disposal is not
required in this method of treatment because reactive particles are generated at discharge and
they react rapidly with those pollutants that are dissolved because of high reactivity.
Treatment method
The treatment of wastewater consist of three treatments or phases. The treatment begins
with basic treatment where the suspended matter is eliminated using chemical additives and
mechanical operations. The second step is the secondary phase where biological processes take
place. In this phase, the depuration of organic matter that is biodegradable takes place using
microorganisms. In the tertiary treatments, the contaminants that remained after the primary and
secondary phases like the dissolved matter. Tertiary treatments are very expensive and they
include stripping, reverse osmosis, precipitation as well as disinfection using advanced oxidation
processes (AOP) that can use hydrogen peroxide combinations, photocatalysis, ultraviolent
radiation and ozone ().
The ozone for water purification is generated by application of electrical discharge on the
surface of the liquid so that it produces chemical species that are active and capable of

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disinfecting the water. The electric field intensity is lethal for a lot of microorganisms. They
show synergistic lethal effects when combined with disinfectants like and . During this process,
ultraviolet radiation shock waves may be produced and they help in ensuring that pollutants are
destructed (Wright et al).
According to Barillas (2015) there are three types of electrical discharges that are used in
water purification. They include: Dielectric Barrier Discharges, contact glow discharge
electrolysis and pulsed corona discharges. For this project, a Dielectric Barrier Discharges
reactor would be designed because it has various advantages. For instance, it produces non-
thermal plasma which does not increase the temperatures and thus no need for cooling. This
property reduces the costs a great deal.
At this stage of the project, it is considered that the wastewater does not contain colloidal
suspensions or solids because it has already gone through primary treatments. The liquid water is
transformed into plasma so that the pollutants and pathogens would be killed by exposure to
ultraviolet radiations, shock waves and electrical fields.
Testing/evaluation
The success of the projects will be guaranteed by the type of water produced. It is very
important to ensure that the whole project works and really purifies the wastewater. In order to
evaluate the purity of the water, it would first be observed to ensure that it is colorless, without
smell and does not have any taste. Further, the water will be tested for its pH. Pure water has a
pH of 7. This water will be free from toxins and pollutants (Stratton et al).
Cost/time frame

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Since the project requires only an electric current to be passed through the wastewater
liquid, to produce purified water as the end product, the costs of this method will be reduced
greatly. The possible costs for a complete plasma wastewater plant would be about $ 130,000 as
shown below:
Activated sludge polluted water plant that has no primary treatment = $160,000
Prototype reactor = $ 3,500
A plasma plant with primary treatment = $ 130,000
Savings = $ 30,000
Expected results
After the wastewater passes through primary treatment and the large particles are
removed, that is when it would be passed onto this project’s plant for further treatment using
plasma method described in the paper. If the design is well implemented, the project will show
positive results by producing clear, colorless and water without odor. Further tests to the water
will indicate that it has a pH of 7 indicating that the water is completely treated and therefore
pure.
Recommendations and conclusions
This project provides industries with the best alternative of treating wastewaters for
human beings and for purposes of protecting the environment. The currently available methods
may be highly expensive thereby preventing people from treating the used waters. The project
will definitely reduce the cost of water treatment and there will also be no more maintenance
costs as they are being experienced with the traditional treatment methods. Also, in contrast to

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the process that has been established on the advanced oxidation processes, plasma processes of
water treatment does not use any barrier between the medium that is being cleaned and the
plasma itself. This makes the method to be maintenance free thereby increasing its service life.

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Works Cited

Barillas, L. “Design Of A Prototype Of Water Purification By Plasma Technology As The
Foundation For An Industrial Wastewater Plant”. J. Phys.: Conf. Ser. 591 (2015):

12057. Web.
       Brooks, V. A. “Understanding Water Treatment Processes”. Tech Directions, 75(1), 22-25.
       (2015). Print.
       De Sanctis, Marco et al. “Integration Of An Innovative Biological Treatment With Physical Or
       Chemical Disinfection For Wastewater Reuse”. Science of The Total Environment 543
       (2016): 206-213. Web.
       Malik, Muhammad Arif. “Water Purification By Plasmas: Which Reactors Are Most Energy
       Efficient?”. Plasma Chemistry and Plasma Processing 30.1 (2009): 21-31. Web.
       Sabbas, T et al. “Management Of Municipal Solid Waste Incineration Residues”. Waste
       management journal 23 (2003): 61-88. Print.
       Stratton, Gunnar R. et al. “Plasma-Based Water Treatment: Conception And Application Of A
       New General Principle For Reactor Design”. Chemical Engineering Journal 273 (2015):
       543-550. Web.
       UNESCO, and London. The United Nations World Water Development Report 3: Water In A
       Changing World. Paris: N.p., 2009. Print.
       Wright, K.C. et al. “New Fouling Prevention Method Using A Plasma Gliding Arc For Produced
       Water Treatment”. Desalination 345 (2014): 64-71. Web.