Session C5
Paper #211
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THE INTRODUCTION AND APPLICATION OF TERTIARY WATER
TREATMENT
Chang Chen, [email protected], Sanchez 5:00 PM, Yi Zheng, [email protected], Sanchez 5:00 PM
Abstract— Tertiary treatment is the final cleaning process
that improves wastewater quality before it is reused,
recycled or discharged into the environment. There are two
main reasons of requiring tertiary treatment. First, the lack
of clean water, especially potable water, is one of the
biggest issues worldwide that needs to be solved. Second,
primary and secondary treatments are not able to produce
potable and environmentally friendly water. The
uniqueness, which is also one advantage, of tertiary
treatment is its ability to remove excessive amounts of
harmful compounds from wastewater to produce high
quality water that can pass drinking water standards and
thus support more lives on the earth. In addition, the treated
water from tertiary treatment will not pollute aquatic
environments. Due to the benefits that tertiary treatment
can bring to societies, many countries use this process to
treat water. In the city of Xiamen, China, BIOFOR, a
technology used through tertiary treatment, helps protect
the aquatic environment of this city by treating industrial
wastewater before it is discharged into the environment.
Davco is another technology that aims at removing
nutrients in effluents. Most areas in North America put this
technology into use. In Key West, Florida, people apply
Davco to increase the amounts of water that can be purified
by 350,000 gallons per day. Sustainability is significant to
tertiary treatment since the purpose of this technology is to
“uphold” the balance of natural water system. This paper
is going to specifically talk about the reasons of using
tertiary treatment, its basic work principles, how this
process can benefit the world, some successful examples of
applications of tertiary treatment, and how the word
“sustainability” is significant to tertiary treatment.
inside the Earth, in rivers, oceans, and ice on the surface of
the Earth, and in the air and clouds above the Earth [1].
However, only a small amount of Earth’s water is fresh
enough to drink. Out of all the water on the earth, only 2.5%
of it is considered fresh [1]. Further analyzing the
components of this limited clean water, humans only have
access to 1.2%, which is surface water. The percentage of
ground water is 30.1%, and the rest of drinkable water is
frozen in the form of ice [1]. Even in the surface/other
freshwater, the amount of water found in ground ice and
permafrost is still high, up to 69% [1]. Based on these
percentages, it is apparent that the amount of water that is
easily accessible and potable on the Earth is limited.
Though people know that clean water is precious, there
is still a large number of people taking clean water for
granted and wasting it. Take the U.S. as an example. Nearly
7 billion gallons of water are wasted each day, which is
astonishing [2]. Besides surface and ground water, people
also rely on rain to gain usable water and raise crops to
provide food for themselves. Unluckily, based on the study
of drought under global warming published by Dai in 2011,
the amount of precipitation will decrease greatly in future
years [3]. As a result, there will be a large increase in the
amount of infertile land by the year 2050, which is indicated
by the change of red areas in Figure 1 and Figure 2[3].
Areas that were able to successfully raise crops will not be
able to do so because of the severe water shortage [3]. In
order to improve the severe condition of the lack of water,
tertiary treatment, which can produce clean and also
drinkable water by removing excess phosphorous and
nitrogen, is one way to solve the serious problem of the lack
of clean water to a large extent.
Keywords—advantages, aquatic environment, BIOFOR,
nitrogen, phosphorus, sustainability, tertiary treatment.
THE NECESSITY OF TERTIARY
TREATMENT
THE LACK OF CLEAN WATER
Water is the source of life, but it is not inexhaustible.
On the earth, water seems to be almost everywhere, because
the earth is capable of supporting millions of lives and looks
like a blue ball from outer space. There are several places
where Earth’s water resides: in the top section of the ground
University of Pittsburgh, Swanson School of Engineering
Submission Date: 03.31.2017
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FIGURE 1
A. G. Dai. “Drought under global warming: A review”.
Wiley Interdisciplinary Reviews: Climate Change.
Yi Zheng
Chang Chen
This figure shows us the areas those are lacking of water
around in the present.
with excess chemicals is not usable is because too much
phosphorus is harmful to one’s health, and it can negatively
affect water quality and aquatic life. In this case, we need
tertiary treatment to further treat water so that it will be
drinkable and environmentally friendly.
WORKING PRINCIPLE OF TERTIARY
TREATMENT
NITROGEN AND PHOSPHORUS REMOVAL
The main purpose of tertiary treatment is to remove
nitrogen and phosphorus left from primary and secondary
treatment, from the water. Nitrogen, as molecules or ions,
is present in many forms in our daily life. Most nitrogen
exists in human body as organic amino compounds and urea,
which are also the same forms of nitrogen present in
wastewater. The produced water from tertiary treatment is
much cleaner than the water from primary and secondary
treatment, which is clear enough for industrial purpose or
continuing daily life. However, it’s still not potable.
Nitrates can seriously influence one’s health once
consumed [5]. These nitrates always exist in form of
ammonia in the septic tanks after the original organic
nitrogen is broken down by microorganisms in the primary
or secondary treatment. Ammonia, or NH3, should be the
primary form of nitrogen leaving the secondary treatment.
From here, the conversion of ammonia to nitrogen gas
needs two steps to be complete.
The first step is called nitrification. Nitrification is the
process by which ammonium (NH4+) or ammonia (NH3) is
oxidized into nitrite (NO2-) by ammonia-oxidizing bacteria
or AOB, often Nitrosomonas spp, and the NO2- further
oxidized into nitrate (NO3-) by nitrite-oxidizing bacteria or
NOB, often Nitrobacter spp [6]. There are also two steps for
nitrification. The first step is called nitritation. With
addition oxygen or hydroxide, NH3 will be oxidized into
hydroxyl-amine(NH2OH) with help of the enzyme monooxygenase [6]. Then, NH2OH is also oxidized into NO2- by
the oxygen and hydroxides. After NH2OH is oxidized,
electrons, oxygen and free hydrogen ions are converted into
water. This reaction is shown in Equation 1.
FIGURE 2
A. G. Dai. “Drought under global warming: A review”.
Wiley Interdisciplinary Reviews: Climate Change.
This figure shows us the areas those will lack of water in
2050.
THE FLAW OF SECONDARY TREATMENT
Secondary treatment is the second process in the water
purifying system, which mainly uses naturally occurring
biological processes, for example, bacterial decomposition,
to remove remaining solids and organic materials, such as
human waste, food, and soap, which were not removed in
primary treatment [4]. The level of oxygen in wastewater
will be altered at different stages during secondary
treatment, producing aerobic (with sufficient amount of
oxygen) and anaerobic environments (with little amount of
oxygen) so that different bacterial communities can survive
in order to remove different chemical components [4]. In
the tanks of secondary treatment, the small solids and
organic materials that are not screened out in the primary
treatment will settle to the bottom of the tanks, producing a
material called sludge [4]. The sludge will then be pumped
into an oxygen-poor environment, which is called a
fermenter tank [4]. In these tanks, sludge will be broken
down, providing food for bacteria and assisting in removing
phosphorus and nitrogen in later steps in secondary
treatment [4]. After this, what is left in the fermenter tanks
will be moved into anaerobic environments with
wastewater from primary treatment [4]. Due to the fact that
there is no oxygen present in the anaerobic environment to
support bacteria, instead of consuming oxygen, the bacteria
consume other organic materials for nutrition. For example,
bacteria can consume nitrate, which will then be converted
to nitrogen gas, removing nitrate from the wastewater in the
process [4]. In an aerobic environment, bacteria will
remove phosphorus instead of nitrogen [4]. During these
processes, bacteria can successfully clear away certain
amounts of phosphorus and nitrogen, producing water that
is clean enough for people to use for daily activities, such
as washing dishes and doing laundry [4]. Nevertheless,
excessive amounts of nitrogen, phosphorus, and other
chemicals still remain in the water after secondary
treatment, making it impossible for people to drink or to
discharge it into the environment. One reason why water
NH4+ + 2 O2
N03- + 2H+ + H2O (Equation 1)
It is important to note that this process requires and
consumes oxygen. This contributes to the biochemical
oxygen demand (BOD) of the sewage. The process is
mediated by the bacteria Nitrosomonas and Nitrobacter
which require an aerobic environment for growth and
metabolism of nitrogen. Thus, the nitrification process must
proceed under aerobic conditions [5].
The second step of nitrification is called nitratation. In
this step, NH3NO2- is oxidized into NO3 - with the help of
the nitric-oxide reductase (NOR) enzyme. A NOR enzyme
is an enzyme that catalyzes the chemical reaction. After this
reaction, the remaining oxygens, electrons, and protons
assembles into water. We call them the first step and second
step of nitrification, but it doesn’t matter which reaction
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occurs first. It is generally accepted that although there is
much more NH4+ than NH3 present in places where
nitrification takes place, it is NH3 that is the substrate for
the bacteria, not NH4+ [6].
The second step of tertiary treatment is called
denitrification. Bacteria also mediate this process like
before. The denitrification process is a microbial facilitated
process involving the stepwise reduction of nitrate to nitrite
(NO2-) nitric oxide (NO), nitrous oxide (N2O), and,
eventually, to nitrogen gas (N2) by the enzymes nitrate
reductase, nitrite reductase, nitric oxide reductase, and
nitrous oxide reductase [7]. Denitrification needs carbon to
start the reduction reaction, so the dissolved oxygen (DO)
level must be low. Carbon is necessary for the bacteria to
thrive. Since the previous step, nitrification, requires low
carbon content, we need to add extra carbon into the system.
If the factory wants to lower the cost of this step, they can
use a small amount of primary effluent, bypassed around
the secondary process and nitrification reactor, as a carbon
supply [7]. This would not affect the denitrification process
because those un-nitrified compounds would appear in
effluent. Since we need to remove all the nitrogen, we need
to have an external source of carbon containing no nitrogen.
The most commonly used one source is methanol.
After nitrogen removal, the next focus is phosphorous
removal phosphorus. Phosphorus is a common component
of people’s daily wastewater and industrial wastewater. The
principal forms are organically bound phosphorus,
polyphosphates, and orthophosphates. Organically bound
phosphorus originates from the body as food waste and,
upon biological decomposition of these solids, is converted
to orthophosphates. Polyphosphates are used in synthetic
detergents, and contribute to, as much as, one-half of the
total phosphates in wastewater [7]. Polyphosphates can be
hydrolyzed to orthophosphates. Thus, the principal form of
phosphorus in wastewater is assumed to be orthophosphates,
although the other forms may exist. Orthophosphates
consist of the negative ions PO43-, HPO42-, and H2PO4 –.
These may form chemical combinations with cations [7].
About ten to thirty percent of phosphorus is removed
by the secondary treatment. Normally, there are three ways
to remove the remaining phosphorus in tertiary treatment.
One is a physical process, which includes filtration for
particulate phosphorus and membrane technologies; one is
a chemical process, including precipitation, the main
process, and physical-chemical adsorption, which is not
necessary; and the last one is biological process, which
includes assimilation and enhanced biological phosphorus
removal.
Chemical precipitation is used to deal with the
inorganic phosphate. Precipitates are formed by adding a
coagulant and wastewater. Metals, such as calcium,
aluminum and iron are used in this process because they are
relatively more active than other elements.
For calcium, people usually use lime, or Ca(OH) 2
power or solid. It reacts with the with wastewater to produce
calcium carbonate, which becomes reactants in a later
reaction to remove phosphate. Because lime is a strong base,
it will bring the pH value up and even goes above ten. Here,
the calcium ions in the calcium carbonate will react with the
phosphate to form the precipitate in hydroxyapatite.
Because the reaction between the lime and the
alkalinity of the wastewater, the quantity required will be
independent of the amount of phosphate present. It will
depend primarily on the alkalinity of the wastewater. The
lime dose required can be approximated at 1.5 times the
alkalinity as CaCO3. Neutralization may be required to
reduce pH before subsequent treatment or disposal.
Recarbonation with carbon dioxide (CO2) is used to lower
the pH value [2].
The processes for aluminum and iron are about the
same. Aluminum or hydrated aluminum sulfate is usually
used to precipitating phosphates and aluminum phosphates
(AlPO4). The basic reaction is shown in Equation 2.
Al3+ + HnPO43-n ↔ AlPO4 + nH+
(Equation 2)
This seems like a simple equation; however, it has a lot
of requirements on the environment. It must be considered
that there are many competing reactions and their
associated equilibrium constants and the effects of
alkalinity, pH, trace elements found in wastewater. The rate
and efficiency of precipitation decrease as the concentration
of phosphorus decreases. The phosphorus can be removed
completely in ideal case.
Ferric chloride or sulfate and ferrous sulfate also known as
copperas, are all widely used for phosphorous removal [2].
The basic reaction is shown in Equation 3.
Fe3+ + HnPO43-n ↔ FePO4 + nH+ (Equation 3)
Ferric ions combine to form ferric phosphate. They
react slowly because of the natural alkalinity, so a coagulant
aid, such as lime, is normally add to raise the pH to enhance
the coagulation [5].
UVC RADIATION AND H2O2/UVC PROCESS
Secondary treatment, such as Conventional municipal
wastewater treatment plants (MWWTPs), are not able to
entirely remove micro-pollutants, such as pharmaceuticals,
personal care products, pesticides, detergents and various
industrial additives. This kind of pollutions needs higher
level treatment to be removed. Tertiary treatment is used for
the final step wastewater treatment. Tertiary treatment
removes pharmaceuticals in the product water from
secondary treatment with advanced oxidation processes
(AOPs) and electrochemical AOPs (EAOPs) like UVC,
H2O2/UVC, anodic oxidation (AO), AO with
electrogenerated H2O2 (AO-H2O2), AO-H2O2/UVC and
photoelectro-Fenton (PEF) using either UVC radiation
(PEF-UVC) or UVA radiation (PEF-UVA) [1].
We are focusing on UVC in this paper. UVC refers to
ultraviolet light with wavelengths between 200 – 280
nanometers (nm). Light in the UVC wavelength can be used
for disinfecting water, sterilizing surfaces, destroying
harmful micro-organisms in food products and in air [6].
However, the H2O2/UVC process can make a higher ability
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to remove TMP because H2O2 is separated and makes
hydroxyl radicals. The electrogeneration of H2O2 can make
oxidants directly without any problem or danger of
transportation, operation, and storage of these oxidants. To
filter out soluble iron ions or compounds, people add iron
at neutral pH into the wastewater and that causes the
precipitation of iron oxides, which can filter the light in the
process of PEF-UVC. For the iron remained dissolved,
people use Fenton’s reaction and increasing the organic
removal [5]. However, H2O2 electrogeneration also is able
to remove active chlorine species, this could make the
whole process less efficient since active chlorine can
remove impurities. UVC radiation can dissolve
micropollutants. Some of the micropollutants don’t have
stable structure, so they directly photolyase when they meet
the light. In this case, the light from radiation excites the
pollutant and causes the transfer of an electron from the
excited state to ground state of oxygen molecule. Also, the
light can cause homolysis to which forms organic radicals
to react with the oxygens to reach the same result [7].
once consumed, the purified water after tertiary treatment is
drinkable for humans. As a result of tertiary treatment, the
amount of potable water will increase, supporting more
humans around the world with enough clean water to
consume every day throughout their lives. As we all know,
the lack of fresh water is one of the most significant issues
worldwide, resulting in water and food poverty, and
prevalence of diseases in the areas that do not have
sufficient water to maintain the lives of people living there.
India is one victim of water shortage. The population of
India is more than 1.2 billion [8]. However, 77 million of
India’s population is not able to access fresh water [8]. Even
worse, the usage of unclean water in India causes a great
number of diseases there. According to the estimation
provided by The World Bank, 21% of communicable
diseases are related to unclear water [8]. Once the amount
of fresh water is increased due to the use of tertiary
treatment, the predominant issue of a lack of clean water is
solved to a large extent, and more people will be healthier
and happier because they have a sufficient amount of clean
water.
Another way for UVC radiation to dissolve
micropollutants is that it can form different kinds of reactive
species like hydroxyl radicals (OH), peroxyl radicals
(ROO), singlet oxygen (1O2), carbon-centered radicals and
excited triplet states by reactions involving the irradiation
of recalcitrant dissolved organic matter (DOM) available in
the effluent [5]. Different from UVC radiation, H 2O2/UVC
process produce hydroxide ions by direct homolytic
cleavage of the peroxide by putting peroxide under the
UVC light. Since H2O2 is very unstable, it dissociates into
water, hydroxide ions and oxygen by the light. The
hydroxide ions would increase the UVC radiation oxidation
power. As discussed in the previous paragraphs, the process
of nitrification needs hydroxides to react. However,
hydroxides are unstable and they are basic, so it’s hard to
store and transports them. In this case, H2O2/UVC process
can solve these two questions because H2O2 itself is neutral
and harmless, and all the processes can react in one place.
H2O2/UVC can be a technology to improve the whole
tertiary treatment process. It’s still a new technology and
factories or companies seldom use it because it also has a
setback: it’s expensive since H2O2 is not cheap.
PROTECT THE ENVIRONMENT
Being environmentally friendly is the second
advantage of using tertiary treatment. Nitrogen and
phosphorus are necessary nutrients needed by organisms
living in aquatic environments. However, too much
nitrogen and phosphorus will have negative effects on
animals and fish, and the quality of the water will decrease.
Excess nutrients can cause water in the environment to be
so nutrient-rich that algae can grow rapidly, and people are
not always able to remove it as fast as it grows [9]. The
quick growth of algae can then reduce the amount of
oxygen in the water to a large extent, causing organisms to
die, and resulting in polluted water environment [9]. Since
tertiary treatment can remove excessive amounts of
phosphorus and nitrogen from water, the water is safe for
organisms, and usable by people. Purified water can be used
to irrigate farmland without polluting the soil and ground
water. Along with fertile soil, more crops can be raised to
feed an increased number of people around the world.
THE SETBACKES OF TERTIARY
TREATMENT
BENEFITS TO THE WORLD
Although tertiary treatment can increase the amounts
of potable water provided for people and produce
environmentally friendly water that can be safely
discharged into the aquatic environment, it does have some
setbacks. One disadvantage of this process is that it can be
affected by temperature.
One benefit that tertiary treatment will bring to society
is increasing amounts of clean water that is both safe to
drink by individuals and safe to discharge into the
environment. The main purpose of this process of water
treatment is to produce cleaner water with smaller amounts
of phosphorus and nitrogen, which has two other major
benefits to the world.
TEMPERATURE EFFECTS
SUPPORT LIVES
When people put tertiary treatment into use at different
places, the water treated by this process will not always
meet drinking and dischargeable water standards because of
the difference in temperature. For example, in wetlands, the
removal of nutrients from wastewater can be negatively
First, unlike water produced from secondary treatment,
which contains excessive amounts of phosphorus and
nitrates that will have negative effects on human health
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impacted by temperature [10]. As temperature increases,
many reactions tend to be more efficient. However, there is
a range of temperature in order to achieve the highest
efficiency. If temperature of surrounding environment is
above or below this range, the reactions will not be optimal
and thus reduce the amounts of chemicals that need to be
removed from wastewater [10]. More specifically,
temperature not only has bad influence on organic
decomposition, but also on al nitrogen cycling reactions,
such as nitrification and denitrificaiton [10]. Based on the
study of the effects of temperature in treating wetlands
conducted by Robert H. Kadlec and K. R. Reddy, there is a
seasonal correlation between temperature and the reduction
of nitrogen: from 1.04 to 1.11 for removing ammonium
nitrogen, and from 1.04 to 1.16 for eliminating nitrate
nitrogen [10]. In addition, for nitrogen cycling processes,
the temperature coefficient fluctuates from 1.05 to 1.37
during isolated conditions [10]. For nitrogen removal, the
temperature coefficient is between 0.988 and 1.16 [10].
Even more, when in colder environments, the cold weather
may cause a seasonal decline of treatment, leading to an
overall decrease in efficiency of tertiary treatment and
passive implications of water quality [10].
pollution was further intensified because of the rapid
increase of nutrients in the water, especially phosphorus and
nitrogen, [12]. Even worse, companies always discharged
industrial wastewater into aquatic environments without
purifying it first [12]. All the reasons above lead to the
serious water pollution in Xiamen.
Degremont, a company that focuses on water
purification, works with Xiamen to help it solve the serious
issue of polluted water [13]. During the collaboration, they
succeeded in constructing a conventional treatment line,
which was then followed by the erection of another 100,000
m3/d treatment line [13]. In addition to these achievements,
by using BIOFOR technology, the plant in Xiamen can
discharge 300,000 m3 of environmentally friendly water
into the environment everyday [13].
DAVCO
DAVCO, another application of tertiary treatment, is
used by Key West, Florida to remove an even greater
amount of nutrients in wastewater to protect its fragile
marine environment [14].
DAVCO has several stages for removing nutrients. As
the index of stage increases, the amount of nutrients that can
be removed also rises. Since the ability of eliminating
nutrients is different, how the tanks are constructed is not
same.
In the second stage of nutrients removal tanks, each of
them is divided into five parts: Inf EQ, anoxic zone, aerobic
zone, aerobic digester, and clarifier at the center of the tanks.
The effluent will first enter the Inf EQ, passes through
anoxic zone, and finally enter aerobic zone. After the
wastewater is purified in aerobic zone, it will then go to
clarifier to be further treated. In clarifier, the water is
separated into three streams. One stream is clean enough
and will get out of the tank. The second stream will go to
aerobic digester. The third stream will enter anoxic zone to
go through the whole process again in order to be further
treated. The produced water from this stage has total
nitrogen that is less than 8 mg/L [15].
In the fourth stage of nutrient removal tanks, the anoxic
zone is divided into a primary zone and secondary zone. In
addition, it also includes a reaeration zone after the
secondary anoxic zone. The effluent still enters Inf EQ first.
After this, the wastewater will flow through the tank
following the order of primary anoxic zone, aerobic zone,
secondary anoxic zone, and a reaeration zone. The
wastewater will move into the clarifier from reaeration zone.
The treated water from forth stage will have total nitrogen
less than 3 mg/L. The only difference between the forth
stage and fifth stage is the use of anaerobic zone before
primary anoxic zone in fifth stage. The total nitrogen
present in the treated water will still be less than 3 mg/L.
However, the total phosphorus existed in the water will be
less than 1 mg/L [15].
Because of its capability of removing nutrients from
wastewater and producing potable and dischargeable water,
DAVCO is used widely and has many achievements. Every
part of North America applies DAVCO to treat effluent
since it can meet the standards of the amounts of nutrients
SUCCESSFUL EXAMPLE OF TERTIARY
TREATMENT
Tertiary treatment is successful in removing
phosphorus and nitrogen to further improve the quality of
water so that the produced water can be safe enough to drink
or discharged into the aquatic environment without
polluting it.
BIOFOR
One application of tertiary treatment that is used by
several countries is BIOFOR [14]. BIOFOR is a technology
which aims at clearing away pollutants, such as ammonia,
through tertiary treatment so that the treated water can meet
the standards for drinking and dischargeable water [14].
The working principle of BIOFOR is simple. The
wastewater that needs to be purified will be pumped from
the bottom of the tank to the filter surface area [14]. After
this, the water will flow through a filter media, in which
nitrogenous pollutants will be removed because of the high
concentration of fix-film biomass [14].
China is one country that uses BIOFOR to treat
wastewater in order to safely discharge it into the aquatic
environment. The condition of water in Xiamen was
worrying before BIOFOR was put into use. Since
aquiculture is one significant way to earn money, and the
government was less restrictive on the amount of aquatic
organisms each person could raise. People raised too many
aquatic organisms within the limited amount of water [12].
As a result, the hydrodynamic was decreased to a large
extent, and the ability of water to self-purify was also
reduced, leading to the pollution of the water [12]. Because
of the feces from growing aquatic organisms, and the food
put into the water for feeding those living things, the
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allowed to be present in the water, especially municipal and
industrial companies [15]. In addition, DAVCO also
manages to save millions of maintenance and operating
costs for cities, which can then be used to develop the
economy and society [15]. DAVCO is also expected to
expand the capacity of treating water in Key West, Florida
from 500,000 gallons per day to 850,000 gallons per day,
providing more water for citizens [14].
companies. Manufacturing development can earn countries
a lot of money, making them rich, and promote the
development of new technologies. However, industrial
countries have a big setback: industrial waste pollution. Due
to the fact that wastewater treatment system can cost certain
amount of money and cause companies have less profits,
some factories, especially small and medium sized one, are
not willing to build a wastewater treatment system and
directly pour wastewater into rivers or lakes. Since
excessive amounts of chemicals exist in wastewater, the
usage of such water could cause diseases for humans and
pollute the environment. If industries can use tertiary
treatment as the last step of treating water, over eighty
percent of harmful components would be removed,
producing more potable and environmentally friendly water.
Tertiary treatment mainly removes nitrogen and
phosphorus from the water left from primary and secondary
treatment. To remove nitrogen, there are two steps to be
used. The first one is called nitrification. Nitrification is the
process by which ammonium (NH4+) or ammonia (NH3) is
oxidized into nitrite (NO2-) by ammonia-oxidizing bacteria
or AOB, often Nitrosomonas spp, and the NO2- further
oxidized into nitrate (NO3-) by nitrite-oxidizing bacteria or
NOB, often Nitrobacter spp [6]. The second step of the
whole process is called denitrification. The denitrification
process is a microbial facilitated process involving the
stepwise reduction of nitrate to nitrite (NO2-) nitric oxide
(NO), nitrous oxide (N2O), and eventually, to dinitrogen
(N2) by the enzymes nitrate reductase, nitrite reductase,
nitric oxide reductase, and nitrous oxide reductase [7]. In
experiment, nitrogen can be completely removed from
wastewater after being treated by these two steps; in actual
cases, they can remove over eighty percent of the nitrogen
due to loss of reactants and process variability.
Sustainability requires technologies to be “green”,
which means that a sustainable technology should have
positive effects to the environment. As one part of
wastewater treatment, tertiary treatment can certainly be a
great example of a sustainable technology. It cleans
wastewater and makes it drinkable. It saves water by
reducing the amounts of wastewater and keeping producing
fresh water. If the majority of factories could use this
technology to treat their wastewater, the problem of water
pollution and lack of drinkable water could be solved to a
large extent. It’s an advantage to use treatment to save water
and making it drinkable.
The main idea of sustainability is reducing resource use,
especially for natural resources. Natural resources, such as
water, can slowly regenerate by itself. However, using
resources without controlling them would destroy this
natural balance. People should reduce the use of resources
and keep the natural balance. As mentioned at the beginning,
sustainability is defined as:” The ability to be sustained,
supported, upheld, or confirmed.” To “upheld” is our goal.
These sustainable technologies are making a better future
for human beings. People cannot live without water, and
that is why tertiary treatment and wastewater treatment is
necessary. They are not only saving water and reducing cost,
but also saving water for the future. In this case,
sustainability is significant to tertiary treatment since the
WHAT’S NEXT
Tertiary treatment has contributed a lot to making our
lives better. It produces more potable for people to drink,
which support more humans around the world. In addition,
the treated water from tertiary treatment is also friendly to
the environment so that when it is discharged into the
aquatic environment, individuals do not have to worry
about polluting the environment or being harmful for plants
and animals. However, everything is not perfect. The
technologies that people use through tertiary treatment can
be affected by the change of temperature. As a result, the
amount of removal nutrients may be reduced, which will
not meet people’s expectations. So when companies and
citizens are satisfied by the amount of clean water that the
technologies used in tertiary treatment can produce,
engineers and scientists should still improve the process of
tertiary treatment so that it can be used in many different
areas without being affected by the environments. After all,
the object of engineers is solving problem existed in the
world and make the planet we live in a better place.
SUSTAINABILITY OF TERTIARY
TREATMENT
Sustainability is defined as:” The ability to be sustained,
supported, upheld, or confirmed” in dictionary. We are in a
highly developed period. Everything is advancing quickly
and new technologies are invented every day. However, the
life span of most of the new technologies is not long,
resulting in waste of energies and materials. Since the
environmental protection becomes one of the most famous
topics around the world, engineers are now paying more
attention to the sustainability of technologies. In this case,
tertiary treatment is a great example of the technology
which has sustainability. Sustainability, in the case of
tertiary treatment, means that fresh water can be
continuously produced, assuring all the living things the
enough amounts of water to live long and prosper.
The lack of water is a serious issue worldwide. It seems
that water is everywhere on the earth, especially in the sea,
which covers seventy three percent of the surface area of
the earth. However, only about 2.5 percent of the whole
water is drinkable or useable and only 1.2 percent of total
global water can be accessed by humans. Based on these
percentages, it is apparent that the amount of water that is
easily accessible and potable on the Earth is extremely
limited.
Most countries in the world are developing countries
and a quick way to develop a country is to develop economy,
which relies on the advancements of industries and
6
Yi Zheng
Chang Chen
purpose of this technology is to “uphold” the balance of
natural water system.
http://www.businesswire.com/news/home/2016112800500
6/en/Evoqua-Supply-Field-Erected-WastewaterTreatment-Plant-Key
[15] “Davco Field-Erected Wastewater Treatment
Systems”. Accessed 03.01.2017
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mjJUvs0fhM6ShpBNJl4Q/31031511.pdf
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[1] “The World’s Water”. USGS. 12.2.2016. Accessed
02.27.2017
https://water.usgs.gov/edu/earthwherewater.html
[2] “The U.S. Wastes 7 Billion Gallons of Drinking Water
a Day: Can Innovation Help Solve the Problem?”
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[3] A. G. Dai. “Drought under global warming: A review”.
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[4] “Waste water treatment plant virtual tour”. Sydney
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[6] "Water Treatment Solutions." Lenntech . Web. 03 Mar.
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[7] “Tertiary wastewater treatment”. NPTE IIT Kharagpur
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ACKNOWLEDGEMENTS
We would like to thank our writing instructors for
helping us develop ideas before the start of outline, which
laid the foundation for our complete paper. We also have
many thanks for people in writing center for assisting us on
grammars and sentence structures to help us clearly express
our ideas and change our contents to make the paper better.
In addition, we appreciate the assistance from librarians
when we had troubles finding sources to explain the
working principles of tertiary treatment in the paper.
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