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Journal of Mechanical Engineering Research and Developments
ISSN: 1024-1752
Website: www.jmerd.org
Vol. 41, No. 1, 2018, pp. 156-167
DOI: 10.7508/jmerd.2018.01.019
156
Clean Water: Design of an efficient and feasible water treatment
plant for rural South-Bengal
Avijit Mallik*, Md. Arman Arefin
Dept. of Mechanical Engineering, Rajshahi University of Engineering and Technology, Rajshahi, Bangladesh,
*Email: avijitme13@gmail.com
ABSTRACT: Wastewater treatment is an important issue because of lessening water resources. The primary reason for
wastewater treatment process is to expel the different constituents of the polluting load: solids, natural carbon,
supplements, inorganic salts, metals, pathogens and so on. In this paper, the mainly de-centralized method is considered
as a solution. A new rural wastewater treatment process is introduced with proper planning and designing by using
empirical equations. This paper exhibits the wastewater treatment technologies present in Bangladesh, to expel
contaminants from wastewater, for example, halogenated hydrocarbon mixes, overwhelming metals, colors, pesticides,
and herbicides, which speak to the fundamental toxins in the wastewater. This research shows that the proposed
decentralized system is more feasible economically and environmentally (about 75% BOD removal) since the
centralized system needs modern machinery and high initial investment. To design a sustainable wastewater treatment
system for developing an area, further assessment of environmental, health, social and institutional aspects are
recommended.
KEYWORDS: Water; Wastewater; Water treatment plant; Design of treatment plant; South Bengal; Bangladesh.
INTRODUCTION
Municipal wastewater is the conveyed wastes from homes, business offices or modern industries, notwithstanding any
groundwater, surface water, and tempest water that might be available. Untreated wastewater, for the most part,
contains elevated amounts of natural material, various pathogenic micro-organisms, and in addition supplements and
dangerous mixes. It along these lines involves ecological dangers and thus should promptly be passed on far from its
sources and treated properly before definite transfer. An objective of wastewater treatment is the security of the earth
in a way comparable with general wellbeing and financial concerns [1].
Because of increased population, water will end up plainly one of the scarcest assets in the 21st century [2]. In the
year 2015; about 27 megacities were with a population over 10 million each, 17 of which were of developing standard
[3]. Fundamental to the urbanization wonders are the issues related to giving civil administrations and water
segment foundation, including the arrangement of both clear water assets and sanitation administrations. Right now,
giving lodging, medicinal services, social administrations, and access to essential human needs framework, for
example, clean water and the transfer of gushing, presents real difficulties to designers, organizers, and lawmakers [4,
5]. As the population is increasing; more prominent strains will be set on accessible assets and stance considerably
more noteworthy risk to ecological sources. A report by the secretary-general of the united nations commission on
sustainable development reasoned that there is no supportability in the flow employments of new water, and around
the world water use has been developing at more than three times the total increased population, thusly prompting
far-reaching general medical issues, restricting financial and horticultural advancement and unfavorably influencing
an extensive variety of biological communities [4]. A great part of the human used after products enters water bodies
through the release of waste from household, point and non-point sources conveying undesirable and unrecoverable
substances [6]. In spite of the fact that the accumulation of wastewater goes back to old circumstances, its treatment is
a moderately late advancement dating from the late 1800s and mid-1900s [7]. Current learning of the requirement for
sanitation and treatment of wastewater, in any case, began with the often referred to an instance of john snow in 1855,
in which he demonstrated that a cholera episode in London was because of sewage water got from the Thames River
[8]. In developed nations, treatment and release methods can forcefully contrast amongst nations and amongst
provincial and urban clients, as for urban high salary and urban low-pay people [9]. The most well-known wastewater
treatment strategies in created nations are brought together by modern wastewater treatment plants and tidal ponds for
both local and mechanical wastewater.
Bangladesh is one of those developing countries, where water treatment and sanitation are currently facing challenges.
Clean Water: Design of an efficient and feasible water treatment plant for rural South-Bengal
157
Bangladesh has developed in water accessibility and arsenic reduction from potable water although having various
internal problems. Awareness about sanitation and hygiene has been improved considerably in recent times. A number
of local and international organizations are trying to mitigate the water-related issues. Many initiatives have been
taken to install tube wells for safe water sources. But the quality of water from those tube wells has noticed to be
contaminated. Around 11% of death by diarrhea has been associated with the use of untreated groundwater [10].
Contamination is more severe in areas with silt and clay layers. In addition, improper placement of latrines and
discharge of untreated effluent in the surface water are causing more severe contamination.
In Bangladesh, underground water layer depletion is one of the most significant issues. A research of 2011 shows, in
Bangladesh depletion of groundwater, was around 0.01-0.05 m/year. Over the last 50 years, the increment of
extraction of groundwater was 20-260 km3/year [11]. Water extraction for irrigation by deep tube wells are the main
sector of groundwater contamination.
The condition of water contamination is quite different in urban and rural areas. Water scarcity is a serious issue in
urban areas; as on-ground water is contaminated by toxic effluent discharge. In rural areas, relatively more people
have accessibility to water sources. In the past few years, arsenic was a major issue. Somehow, this condition has been
overcome by making significant efforts to minimize this problem. Rural areas still lag in treatment facilities of
wastewater. Village inhabitants discharge wastewater almost untreated to the nearest water bodies although there is a
huge potential of this wastewater to be reused in agricultural fields. Such initiative will not only reduce groundwater
demand but can also serve as a better environment if proper treatment is provided.
Figure 1. Schematic of typical wastewater treatment process.
Wastewater from home has to be treated in an environmentally friendly manner to reuse it. In the system screening is
the very first process where wastewater is cleaned (removal of course particles i.e. sanitary items, cotton buds, face
wipes, glass particles and etc.); though heavy machinery is not used here. Then the primary treatment is applied,
where organic/solid materials are separated. It is done by putting the screened water into settlement tanks for the
solids to sink the bottom of the tank. The rest of the process is termed secondary treatment; high removal of BOD,
COD and toxic materials are done at this stage. Primary treated water is stored in rectangular shaped tanks (Aeration
Lane) and the air is pumped inside to meet the DO. Lastly, sludge is again filtered and scrapped by sand filter bed
resulting in edible water to be reused. Then the clean water is released into nature for reusing. Figure 1 shows the
outline of the proposed system.
In the last few decades, several works have been done for treating wastewater. Chen et al. showed different
electrochemical techniques for treating wastewater. Though all the systems were effective all of them had very high
initial cost and there was a huge chance of chemical exposure [12]. Liu et al. worked on three types of chemical
system to purify industrial wastewater and did a development plant to produce electricity in the meantime of
purification by using a single microbial fuel cell. The researchers mainly focused to produce electricity and systems
had the low effectiveness of treatment process [13]. Crini et al. Reviewed 4 types of the treatment system and
researched on the absorbent based biological treatment process. The system was only applicable for industries and
high scale treatment process; cost is moderate but high risk of contamination via absorbents [14]. Le-Clech et al. did a
research on membrane utilized treatment system via bio-reactor; used osmosis and reverse osmosis process to treat
wastewater. Bio-reactors are very tough to settle and only applicable for the non-tropical region [15].Du et al. did a
compact review on treating water using microbial fuel cells along with electricity generation, showed various
Clean Water: Design of an efficient and feasible water treatment plant for rural South-Bengal
158
drawbacks of this process. It has higher efficiency, but it hampers the normal living of micro-organisms of the pond
[16]. Rozendal et al. did a research on wastewater treatment by using bio-electrochemical systems and implemented a
successful use on treating industrial wastewater along with electricity generation. The method was only applicable for
Industries, can’t be used in natural treatment process [17]. Kampschreur et al. conducted a research project on water
treatment plants and determined the adverse effects of different centralized treatment processes. The system was
effective but a huge amount of NOx was produced while implementing [18]. Fu et al. reviewed various treatment
process and found zero-valence iron to be an effective treatment effluent. Only natural treatment processes can use
zero-valence iron. High risk of iron ion contamination in groundwater was the major deficiency of the plant [19]. Seto
et al. did a case study on centralized treatment process on San Francisco and found that centralized systems the higher
possibility of micro-organism contamination [20]. Yuan et al. did a research on urban areas on Waste Water Treatment
Processes using a decentralized technique. This process is also applicable for urban areas where the underwater level
is good enough [21].
All the above electrochemical processes are very much costly and the other processes were invented for industrial and
urban wastewater treatment and a large population. These plants are not very much effective while Bangladesh is a
poor country and most of the people live under the poverty line. For Khulna district of Bangladesh, it is necessary to
find or invent a method which would be efficient and can be implemented at low cost. In the paper, a new technique is
designed and discussed for decentralized wastewater treatment with primary and secondary treatment processes which
has high efficiency and plant initial and running cost is low. This plant is very much effective for a big family or
three-four small families.
QUALITY OF DRINKING WATER IN BANGLADESH
According to Bangladesh national drinking water survey 2009, “22 million people are still drinking water that does
not meet the standard level for arsenic of 0.05 mg/l and 5.6 million are in high risk of having water with more than 0.2
mg/L arsenic” [22].
Table 1 shows the standard values of different elements in water according to Department of Public Health
Engineering and World Health Organization. Some common elements have been selected in this table. In recent few
years, Arsenic was a very big issue of concern for Bangladesh. BOD, COD, Nitrate, Phosphate, and chloride are very
important elements for drinking water. An excessive amount of these elements can cause a health hazard. Drinking
water should contain the following elements according to the standard stated in Table 1 [23].
Table 1. Water quality parameters.
Elements
Bangladesh Standards
(mg/L)
WHO Standards
(mg/L)
BOD5
0.20
0.16
Arsenic
.05
0.01
COD
4.00
4.50
Aluminum
0.01
0.2
Cadmium
0.003
0.002
Iron
0.3-1.0
0.2-0.3
Chloride
150-600
-
Nitrate (NO3-)
10
50
Fluoride
3.5-4.0
1.5
Phosphate
6.0
-
The survey also stated that "98% of the tested samples meet the Bangladesh standard of 600 mg/L for chloride
concentration” [22]. Fluoride concentration was not so high according to this survey. Six samples (1%) exceeded the
Bangladesh standard of 1.1-1.5 mg/L. But, Iron concentration seems to be a little bit concerning in the edible water.
Throughout the country, only 60% of the tested samples meet the national standard of 1 mg/L iron. The other 40% is
below the standard. The amount of phosphorus in almost 93% of the sample meet the standard value 1.96 mg/L, which
is equivalent to 6 mg/L phosphate [22].
In Dhaka city, normally water is pumped from deep aquifers. However, the quality does not remain similar to the
consumers. Along with its transport through the pipe network, a number of sources cause contamination of the water.
The negative pressure of the pump, leakage in the pipes, service installation networks under septic tanks etc. are reasons
behind water contamination in the pipe network [24].
Clean Water: Design of an efficient and feasible water treatment plant for rural South-Bengal
159
Bangladesh government has introduced rules and regulations to protect their water and environment. Different
governmental organizations, as well as NGOs, work for implementing regulations. The Department of Environment
(DoE) is a government organization, it works on that basis. This organization has created a mobile court in order to
implement action against environment conservation violator under the ECA Act, 2010. “Polluters pay principal” is
mentioned in the ECA, 1995 [25].
Table 2 represents guidelines for different parameters in surface water. Surface water used by different activity should
maintain the concentration of various parameters according to the table below [26, 27].
Table 2. Standard for surface water.
Water Use
BOD
(mg/L)
DO
(mg/L)
pH
Total Bacteria
(number per
thousands)
Recreational
5-8
<3
>5
<200
Food Storages
6.5-9
<9
>6
<500
Fisheries Sector
7-8
7-10
>5
-
Agricultural
6.5
<10
<12
<900
The National Environment Management Action Plan (NEMAP), 1995 includes identification of major environmental
issues and action to minimize environmental degradation improving natural environment by conserving biodiversity.
The different international organization also helps financially by providing a fund for implementing environmental
regulations in Bangladesh namely DANIDA, SIDA, USAID, CIDA etc. [25, 27and 28].
PRESENT TREATMENT OF DRINKING WATER OF BANGLADESH
Urban treatment process
In urban areas, DWASA is responsible for treating potable water for the community, in the capital city Dhaka. DWASA
is currently running one large and three small water treatment plants with financial assistance from different funding
organizations.
According to the department of public health and engineering of Bangladesh, most of the treatment facilities include
filtration, flocculation, sedimentation, and disinfection. Some also include ion exchange and filtration depending on the
quality of collected water. A groundwater rule is developing to specify the appropriate use of disinfection to assure
public health protection.
However, to meet the fastest growing water demand and reduce groundwater extraction, DWASA planned to build four
large surface water treatment plants until 2021. They are "Saidabad Phase II", "Saidabad Phase III", "Padma/Pagla”, and
“Khilkhet”. These plants have been proposed to draw water from less polluted surface water even though they are
distant sources such as rivers. The four plants are expected to have a combined capacity of 1.63 million cubic meters
surface water per day, whereas in 2010 the supply of groundwater was 2.11 million cubic meters per day [28-30].
Rural treatment process
Easy availability and no content of pathogenic microorganisms make groundwater so popular that most of the rural
population is now dependent on low-cost tube wells. Studies stated that Bangladesh achieved a remarkable success
providing 97% of the rural population with bacteriologically safe tube well water. In some regions where tube well
water is not trusted worthy, people usually boil water for purification.
Arsenic contamination is one of the major challenges in the shallow aquifers and many parts of the country have made
shallow tube well water unsafe for drinking. Different strategies have been developed to mitigate the arsenic problem.
Those are classified as chemical and non-chemical treatment. Pond sand filters dug and ring well, chili water purifiers
(CWP) are some nonchemical solution for arsenic contamination. Chulli water purifier is a special type of clay oven
with the metal coil. Water is passing through the coil and gets purified from arsenic by heat [31]. Chemical options
include different types of filters such as SIDKO, SONO, READ F, and AIKAN [26, 30].
MATERIALS AND METHOD
Clean Water: Design of an efficient and feasible water treatment plant for rural South-Bengal
160
The research is mainly focused on wastewater treatment. In this paper, a new economical wastewater treatment for the
urban side of the South-Bengal (Khulna Division) site has been designed and proposed. The process is mainly a
de-centralized one. Decentralized wastewater treatment does not mean one specific plant for the whole population of a
defined area but it rather defines more than one or an assortment of technologies [32]. This system is mainly designed
for a low to moderate population and small-scale treatment [33]. Decentralized wastewater systems are appropriate
especially for semi-urban and rural communities, where population density is comparatively low and scattered. For
treating water septic tank and anaerobic pond can be a better concept. First, a village is selected from the area. Different
parameters for designing the tank and pond are first collected and evaluated. When considering all these parameters a
design calculation for the septic tank and anaerobic pond is done. Only a primary treatment is not enough to make the
effluent in quality of an acceptable level. For secondary treatment, the facilitative pond is chosen. The design method
includes empirical equations. Area requirement for various onsite treatment options has been calculated. Also, nitrogen
and phosphorus removal with these systems have been discussed. For designing this section different parameters were
taken from different experimental values done by different researchers and organization.
Design of a Wastewater Treatment Process
To evaluate the recommended decentralized treatment option in rural areas of Bangladesh, a typical village in the middle
part of the country has been selected as a case to make a design of the proposed treatment process, which is
decentralized wastewater treatment.
Area Selected For Design
The village named “Sundermahal” is situated in Surkhali union, Batiyaghata Upazila, Khulna District, and Khulna
division. The area is mostly flat and the climate is tropical. The average temperature for this area is about 29.9°C and the
total annual precipitation is about 1812 mm. Precipitation/Rainfall is the lowest in December, with an average of 6 mm;
most of the precipitation here falls in July, averaging 357 mm [34]. In 1988, 1992, 1994, 1997, 2005 and 2011 a
number of flood damages were recorded [35].
According to Population Census 2011, the total population of this village is 1233 with 236 households [36]. Agriculture
is the main occupation in this area. Tube wells are the main sources of drinking water. Almost 93% of the population use
tube wells for potable water collection. Also, ponds and other surface water sources are available for collecting water. In
this area, almost 36% of the households use sanitary latrines and 58% has unsanitary latrines. Almost 6% has no latrines
at all [37]. So it indicates that this area has a deficiency in sanitation. No information of wastewater treatment facility
was found for this area. Figure 2 gives an overview of Southern Bangladesh (South-Bengal).
Figure 2. Location of the selected area (Collected from: Maps of Bangladesh).
Clean Water: Design of an efficient and feasible water treatment plant for rural South-Bengal
161
In the data source used, 30 km2 areas were given for the total area of the Upazila including 15 other villages [36, 37]. To
make the calculation simple, it has been assumed that all the villages are similar in size. Then the area of the selected
village has been found about 2 km2.The condition presented is a typical condition for most of the villages in Bangladesh.
There is a significant improvement potential in latrine use and reduction of open defecation but still, people are at risk
without any proper wastewater management. The only use of latrines cannot be a single solution, also appropriate
wastewater treatment is needed to complete the process and make a healthy environment.
Estimation of Water Flow and BOD5
Before designing the process, some basic parameters have been collected from various sources. Among them, average
water consumption in rural areas of Bangladesh was found to be 83.17 liters /person/ day [38]. It is a bit lower than the
urban water consumption. This could be due to less water availability or poor economic condition.
Average daily water consumption Q = 83.17 liters/person/day = 0.083 m3 /person/day (Appendix-1) will result in an
average daily wastewater flow QD = 87.17 m3/day, where, wastewater flow is assumed to be 85% of daily water
consumption.
Table 3 includes BOD, TN, N as NH4+ and TP in the daily wastewater flow. It also includes required an amount of BOD,
N, and P in the effluent for water use in irrigation. Average BOD5 in the influent is calculated in Appendix. The required
BOD value in the effluent is found from Table 2. The required values for Nitrogen and Phosphorus in the effluent are
found from a report named Water Quality for Agriculture. The average amount of TN, N, and TP in the influent is
estimated as typical content in municipal wastewater with a minor industrial contribution. Calculations are found in
Appendix-1. Table 3 shows concentration in effluents and influents [20-39].
Table 3. Concentration of various parameters in influent and effluent.
Parameter
Concentration (Influent)
mg/L
Concentration
(Effluent)
mg/L
NO3- component
28
10
NH4+ component
20
<5
Phosphates
6-10
<2
BOD5
<500
15
BOD in the influent is calculated from an empirical equation (Appendix-1), for influent BOD, C0 =1000 B/QD, BOD
contribution per day (B) is assumed to 40 g/capita/day for medium-sized communities [39].
Pre-treatment Facility
A primary treatment is needed to make the whole treatment process more efficient and to reduce the organic load in the
secondary treatment. A septic tank is one of a common type of primary treatment. Also, anaerobic ponds can also act as
a primary treatment tool. Septic tank can be installed in each household or one anaerobic pond can be used for the whole
community.
RESULTS AND DISCUSSION
Design of septic tank
An Indian standard code will be used for the design of the septic tank in ‘Sundermahal’ village.
Figure 3 represents recommended the size of septic tanks according to the number of users (Bureau of Indian standards,
1993).
If 5 persons in each house are assumed for the selected village, then from Figure 3 the size of a septic tank can be found
to be of 1.5 m long and 0.75 m wide. The depth is assumed 1.3 m including 1 m depth from the outlet pipe to the bottom
of the tank and 0.3 m distance from roof to liquid. So a 1.13 m2 septic tank is recommended for each household in this
village.
V (volume of septic tank) = (1.5*0.75*1.3) = 1.46 m3 (approximately)
This septic tank can store 1460 L liquid and each of the houses will need a septic tank of approximately 1.46 m3.
Several requirements are stated for installing a septic tank. It should be 60 m away from any community well, 9 m away
Clean Water: Design of an efficient and feasible water treatment plant for rural South-Bengal
162
from any buried water storage tank and 15 m from any source of potable water or natural water body [40-42].
A septic tank can remove BOD, TSS, oil, and grease. Typically a septic tank can remove 30 to 50% BOD and 60 to 80%
TSS [43].
Figure 3. Length and width of septic tank according to the number of users.
Design of anaerobic pond
Design of an anaerobic pond below has been done using Waste stabilization pond and Constructed Wetland Design
Manual,
Volume of anaerobic pond, VA = C0QD/ (1) [41]
Hydraulic retention time, tAN = 𝑉A/𝑄D (2)
From equation (1), VA = 141 m3 (Appendix 2); for temperature > 250C; = 350 g/m3/day [9]. The depth of the
anaerobic pond is considered to be 3 m and the area would then be almost 37 m2.
Hydraulic retention time, tAN = 1.6 days (approx.) (Appendix 2)
The minimum value of retention time is recommended to be one day. With the designed anaerobic pond almost 70%
BOD removal is possible at the temperature above 25oC [42, 42].
Secondary treatment
Only a primary treatment is not enough to make the effluent in quality of an acceptable level. With the above design
of septic tank and anaerobic pond, 30 to 70% of BOD removal is expected. For secondary treatment different options
can be chosen, such as wetland, facultative pond or sand filters. Depending on the geography, landscape and weather
condition various options can be adopted.
Design of Facultative pond
Area of facultative pond, AF = 10C0QD/λ (3)
In Bangladesh, the average temperature is assumed to be more than 25°C. Here in the calculation 28oC have been used.
In this design, a primary treatment has already been suggested. In primary treatment, for septic tank almost 30% BOD
is removed. So in further secondary treatment design, a reduced BOD in the secondary influent is assumed.
From equation (3), AF = 784.692 m2 (Appendix 3)
Retention time,
𝑇F = 𝐴FD / 𝑄M (4)
Where D is the depth of the pond (1.5 m usually) and QM is mean flow, QI is influent flow, QE is effluent flow and ‘e’
is evaporation rate.
Evaporation rate for Bangladesh is found from a historical data study and the values vary with temperature during the
year. An average monthly evaporation value of 120 mm for 28°C is considered in this calculation [44]. From this, a
daily evaporation rate can be calculated.
Average daily evaporation rate (e) = 120 /30 = 4 mm/day
Clean Water: Design of an efficient and feasible water treatment plant for rural South-Bengal
163
𝑄M = (QI + QE)/2 (5)
𝑄E = 𝑄I– 0.001 𝐴F.e (6)
From equation (6) and (5),
QE = 84 m3/day
QM = 85.67 m3/ day = 86 m3/day
Then, putting values of QM and QE in equation (4),
TF = 14 days (approx.) (Appendix 3)
Again, if an anaerobic pond is considered as a primary treatment, from the above equation the area for facultative
pond becomes 260 m2 and the retention time found 6 days. This variation is because of the high BOD removal in the
anaerobic pond, with almost 70% BOD removal in an anaerobic pond.
Design of wetland
Area of reed bed of wetland,
AW = K.QD (ln𝐶0− ln𝐶t) (7)
K is a rate constant, the value found for BOD removal K20 = 180 m /year = 0.5 m/day for subsurface wetland and θ is
constant and the value is 1.1 [6-9].
KT = K20 (8)
K28 = (0.5) = 1.08 m/day (for 28o C)
Using values of K in equation (7),
AW = 346.386 m2 (approx.) (Appendix-4)
This area for subsurface wetland is calculated with 30% BOD reduction from the septic tank. The value varies if an
anaerobic pond is used as a pretreatment. Then the area needed will be 209 m2. The depth of the wetland designed
above is considered to be 0.6 m. Equation 7 and 8 have been collected from reference no [41] and [42, 46].
Design of sand filter
Using a guideline from Washington State Department of Health (2012) an intermitted sand filter is designed below.
The surface area of filter bed
𝐴S = 𝑄D/ Loading rate (9)
The maximum loading rate is 2 to 5 gal/day/square feet recommended in the EPA design manual; the depth of media
is 46-91 cm [45, 46]. Design loading rate is considered 4 gal/day/square feet.
AS = 534.785 m2 (approx.) (Appendix 5)
420 m2sand filters are found to be suitable for loading rate 4 gal/day/square feet.
DESIGN SUMMARY
The above design shows an overview of the total decentralized system for a typical village. The area of the village is
about 2 km2 (assumed). Primary treatment facilities show, occupying a small area of about 37 m2 for the anaerobic pond.
For secondary treatment, the area of a wetland found was almost half of the facultative pond. To implement a facultative
pond of 784.926 m2 in this small area will not be suitable.
In the above design, several systems are discussed with an example size of the treatment facility. Also, a comparison
between options has been done to evaluate suitable options according to the situation.
To make the effluent reusable, required BOD value has been calculated according to the requirements given by the
government in Table 3. As nutrient concentration is important for reusing the effluent water in irrigation, nitrogen and
phosphorus removal has been discussed. With a facultative pond, the effluent fulfills requirement given in Table 2. But
for the other two systems, N and P concentration was higher than the requirement.
DESIGN ADVANTAGES AND LIMITATION
The new wastewater treatment plant is discussed and designed in this paper which is very much cost effective. The plant
Clean Water: Design of an efficient and feasible water treatment plant for rural South-Bengal
164
is easy to make and it treats the water by removing waste from it especially BOD, Nitrogen, and phosphorus. It can be
implemented in not only rural areas but also in semi-urban areas. It does not need any modern machinery rather it can be
build using very low initial investment comparing to other centralized and de-centralized methods. Any big family or
small two to four families can easily use one plant for water treatment. In the above design, some assumptions have been
done for various parameters for calculation. In some cases, assumptions may not be similar to reality. Also, the
temperature has been considered as 28° C, which may be a bit lower than the real situation. This is considered to make
the calculation simple. Chosen area is considered as a typical village, but there are areas with different topography than
the designed one. So this design may not be appropriate for hilly or coastal regions in the southern and southwest part of
Bangladesh. Nitrogen and phosphorus removal for the designed system has been calculated with a rough estimation.
The efficiency could be different in the practical case. This design is an example and a model of the recommended
solution. When implementing this solution, in reality, some changes according to necessity could be done. Such as for
places with a high groundwater table, depth of anaerobic pond or septic tank could be adjusted. In addition, some
specific value of the area of this village has not been found. Therefore, an estimation and assumption have been done.
CONCLUSION
Water pollution is one of the major concerns of Bangladesh, especially in rural areas. Many people die every year due
to polluted drinking water. The proposed plant is very much efficient and feasible for implementing in the southern
site of Bangladesh. If some modification in the plant is done considering weather, size and pollution rate, then this
plant can also be used in other locations of Bangladesh, which may be a future research consideration. Finally, this
paper would help researchers for further development of the system and be finding more feasible and efficient
treatment plant for Bangladesh.
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NOMENCLATURE
APPENDIXES
Sign
Meaning
BOD
Biochemical Oxygen Demand
COD
Chemical Oxygen Demand
WHO
World Health Organization
BOD5
5-day Biochemical Oxygen Demand
ECA
Environment Conservation Amendment
DO
Demand for Oxygen
DWASA
Dhaka Water Supply & Sewerage Authority
TSS
Toxic Shock Syndrome
AS
Surface Area
N
Nitrogen
P
Phosphorus
EPA
Environmental Protection Agency
Appendix
Parameter
Unit
Equation
Result
1- Water flow
and BOD
Q
QD
B
C0
m3/person/day
m3/person/day
g/capita
g/m3
N/A
% of wastewater flow.Q
N/A
B/QD
0.083
87.17
40
565.8
2- Anaerobic
Pond
VA
tAN
g/m3/day
m3
day
N/A
C0QD/
𝑉A/𝑄D
350
141
1.6
Clean Water: Design of an efficient and feasible water treatment plant for rural South-Bengal
167
3- Facultative
Pond (30%
BOD removal)
(T=280C)
AF
D
QE
QM
TF
kg/ha.day
m2
m
m3/day
m3/day
day
20T-120
10C0QD/
N/A
QI – 0.001AF.e [As, QD = QI]
(QI+QE)/2
AFD/QM
440
784.926
1.5
84
86
14
4-Wetland
K20
KT [T=280C]
C0
CT
AW
constant
m/day
m/day
constant
constant
m2
N/A
N/A
K20.
N/A
N/A
KQD (ln C0 – ln CT)
1.1
0.5
1.08
396.2
10
345.386
5-Sand Filter
Load Rating
AS
L/day/m2
m2
N/A
QD/Loading Rate
163
534.785