Multidisciplinary Senior Design Conference
Kate Gleason College of Engineering
Rochester Institute of Technology
Rochester, New York 14623
Project Number: 13418
Particle and Fluoride Pre-Filter
For B9 Plastics
Dan Charles – Chemical Engineering
Israel Powell – Chemical Engineering
John Markidis – Mechanical Engineering
An Vu – Chemical Engineering
Abstract
The Better Water Maker (BWM), developed by B9 Plastics, is a water filtration system that
utilizes UV-light to kill bacteria and other micro-organisms. However, the effectiveness of the
BWM is hindered by high turbidity and currently does not remove fluoride. The goal of this
project was to develop a pre-filter system to reduce turbidity and the fluoride content of water,
before it enters the BWM filter. The pre-filter system consists of a 5-gallon bucket and filterpress, which is forced down through the water, very similar to the function of a French-press
style coffee filter. Fluoride removal was achieved by adding bone-char to the 5-gallon bucket
and letting the system reach equilibrium, allowing the fluoride ions to adsorb on to the bonechar. In the end, the pre-filter system saw turbidity reductions upwards of 70%, but only small,
erratic reductions in fluoride.
Nomenclature
BWM – Better Water Maker
UV – Ultraviolet
NTU – Nephelometric Turbidity Units
TSS – Total Suspended Solids
Introduction
B9 Plastics is a not-for-profit organization dedicated to social and environmental improvement
through the use of plastics around the world, including Haiti, Africa, South America and the
Middle East. Their BWM filtration system provides clean and safe drinking water where it is
otherwise not available. The BWM uses a hand-crank 12V power source to power a UV-light at
254 nm. The UV-light disrupts the DNA of micro-organisms and the RNA of viruses, making
them unable to reproduce. As previously mentioned, the high turbidity levels in the water of
these regions hinder the effectiveness of the UV light. Turbidity is the cloudiness or haziness of
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water, caused by particles and suspended solids. These particles, which are much larger than
bacteria and viruses, block and absorb the UV-light. The World Health Organization suggests
that one should not drink water with turbidity greater than 5 NTU due to the health concerns
associated with consuming turbid water [4].
Some regions such as Northern Africa have excessively high levels of fluoride in their water
supply. Over long period of time the high fluoride concentrations can lead to skeletal and dental
fluorosis; bones become very brittle and prone to breakage, teeth become discolored and
pitted. Some areas of Africa have Fluoride concentrations greater than 10.0 mg/L
Figure 1 – Effect of prolonged use of drinking water on human health, related to fluoride content [2]
The main objective for this project was to develop a pre-filter device to provide a cost effective
method for people in developing countries to reduce the turbidity and fluoride concentration in
drinking water. In conjunction with the BWM the system will be able to provide safe and clean
drink water in developing countries where clean water sources are nonexistent.
Design Process
Specifications
 The filter is inexpensive ($10 – 20 per device)
 The filter improves UV transmission
 The filter removes particles (reduce 50% -75% of turbidity, particles greater than 5µm
and total suspended solids)
 The filter removes fluoride (reduce 50% - 70% of Fluoride concentration)
 The filter can be used for 6000 hours without replacement
 The filter is easy to clean/recharge
 The filter does not negatively change the taste of the water
 The filter is safe to use (no release of hazardous materials)
 The filter has a flow rate of at least 2 lpm
 The filter is lightweight for transportation (10 – 20 kg)
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In order to accomplish all of the needs, many options were considered. At first traditional
methods for water purification was researched such as distillation, osmosis, slow-sand filtration
and electro dialysis. Given our needs many of these options were quickly ruled out. Simply
filtering the water through some type of mesh was the most efficient way to remove particles
while staying within the resource and budget constraints for the project. Fluoride removal was
more difficult. All traditional methods were impractical due to the need of immense amount of
electricity and resources. Colloidal chemistry was the next step in the design path. The use of
flocculants or adsorption techniques was discovered to have potential benefits.
Test Methodology
To measure the effectiveness of the prototype three tests were performed. Turbidity, total
suspends solids, and fluoride concentrations were measured before and after use of the
prototype pre-filter. To test turbidity a Hach 2100P turbidity meter was used; the test
procedure was based EPA test method 2130B. Total suspend solids was measured by
evaporating off a 10 mL sample of water and measuring the difference in weight of the sample
container before and evaporating the water off. The difference in weight accounting for the
total suspended solids per 10 mL of the sample. The test for TSS was based on EPA test method
160.2. Fluoride concentration was measured by a
Hach DR2000 spectrophotometer, using method 190
for fluoride concentration and SPADNS 2 reagent.
Procedure for testing fluoride concentration was
based on EPA test method 340.1.
Results and Discussion
Particle Removal
A 5-micron stainless steel Dutch-Weave mesh was
chosen for the particle removal system. The mesh
itself was made up of thousands of 5µm openings,
preventing any particles larger from being decanted
into the BWM after filtration. The makeup of the
filter-press design is shown in Figure 2. The main
filter portion consisted of the mesh in-between two
rubber gaskets and two ABS support rings, as seen in
Figure 2 (the mesh is transparent but would be #8).
The rubber gaskets prevent water from flowing
around the filter and the support rings provide
support for the mesh and allowed the mesh to be
attached to the handles. The two handles were also
constructed out of ABS plastic to allow the operator
Copyright © 2013 Rochester Institute of Technology
Figure 2 – Filter- press assembly drawing
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to apply the force needed to push the filter through the water. This is one of the key
components of the design. In developing countries the gravity filtration systems are slow and
tedious. Achieving the necessary head to flow the water through a fine mesh is extremely
difficult. Using the semi-batch process of pushing the mesh through the water in a 5-gallon
bucket allows the operator to apply the force necessary rather than using the force of gravity.
Everything was sealed with GE kitchen & bath epoxy, and then bolted together with ¼” bolts.
The filter-press was pushed through the five gallon bucket, separating the containments from
the clean water and decanted of into the BWM. Based on equation (1) it was calculated that it
would take approximately 13.353 lbf to be applied to the handles of the filter press to be able
to push the mesh through the water.
128𝑄𝜇𝑡
𝐷 2
(1)
𝐹=(
) (0.05𝜋 ( ) )
𝜋𝐷4
2
F-Force D-Diameter, Q-Volumetric Flow, µ-Viscosity, t-Thickness
Fluoride Removal
Figure 3 – Freundlich isotherm used to model the adsorption of bonechar [1]
(2) Freundlich Adsorption Isotherm
The use of bone-char to remove
fluoride was chosen because of
its effective adsorption of
fluoride and it availability. Bonechar consists of positively
charged calcium molecules; the
fluoride ions in the water are
negatively charged and attracted
to the surface of the bone-char.
The chemical process of Fluoride
ions attaching to the calcium in
the bone-char is referred as to as
adsorption and is modeled using
the Freundlich adsorption
isotherm as shown in figure 3 to
the right.
1
𝑞 = 𝑘𝐶 𝑛
q - mass of fluoride adsorbed per mass of adsorbent, k - is the adsorption capacity, C - concentration of
fluoride at equilibrium, (1/n) - intensity
Bone-char is a material that is available all over the world and can be made locally by charring
animal bones in a low oxygen environment. This activates the calcium and kills all of the living
organic matter in the bone. The bone can then be crushed up using a mortar and pastel to
increase surface area and increase the rate of adsorption. The method for using the bone-char
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with our device required that the bone-char be left to sit in the bucket with water overnight
allowing the adsorption of fluoride to reach equilibrium. This is the most cost effective way to
approach the fluoride removal; it does require that the water be left to sit for twelve hours or
more. The addition of more bone-char and constant mixing could both reduce the amount of
time necessary for the bone-char to remove the desired amount of fluoride from the water.
However the use of more bone-char would costs more and constantly mixing the water
manually for hours at a time is not practical. The bone-char we used to remove fluoride in this
study and create a Freundlich adsorption isotherm was Brimac Carbon BONE CHAR 20x60 (fine
granular bone charcoal).
Figure 3 –left - Filter-press system model; right assembled filterpress prototype
To use the pre-filter, bone-char is added to the bucket or some other reservoir containing
drinking water. The bone-char is left in the water overnight to adsorb the fluoride from the
water. The filter-press and 5-gallon bucket are then be used to remove particulate, including
the bone-char, from the water. After being filtered the clean water is decanted off into the
BWM device to undergo UV treatment.
Turbidity
Table 1
Table 2
Sample 1 (River Water)
Unfiltered
Filtered
Turbidity
Turbidity
Trial
Trial
(NTU)
(NTU)
Sample 2 (Pond Water)
Unfiltered
Filtered
Turbidity
Turbidity
Trial
Trial
(NTU)
(NTU)
1
2
3
31.7
26.9
25.8
1
2
3
4.11
3.48
4.11
1
2
3
20.9
26.3
22.1
1
2
3
6.01
6.17
6.10
Average
28.13
Average
3.90
Average
23.10
Average
6.09
Average Percent Reduction
86.14%
Average Percent Reduction
Copyright © 2013 Rochester Institute of Technology
73.62%
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The prototype was very successful in reducing the turbidity of the samples tested. The
specification set for the project, a 50 - 75 percent reduction, was met and even surpassed in the
river water sample. The reduction of turbidity was one of the major goals for this project.
Turbidity is measure of light scattering, higher values of NTU having more light scattering and
lower values of NTU having less light scattering. This test very closely correlates to the current
drawback of the BWM, that when the water is turbid some of the UV-light is being blocked or
scattered by particles allowing areas to be shaded. This causes some ineffectiveness when
treating the water. Therefore the reduction in turbidity is an exceptional way of measuring the
prototypes effectiveness due to how the test directly correlates to overall project goal. The
device function as it was supposed to, the rubber gaskets prevented the water flowing around
the edges of the filter-press forcing the water to flow through the 5 micron stainless steel
mesh. The water collect and tested was visibly cleaner and reduced the turbidity of the water
to close to acceptable levels for drinking water, 5 NTU, according to the World Health
Organization [4]. The values achieved would be a great improvement compared to current
conditions in developing countries.
Total Suspended Solids
Table 3
Table 4
Sample 1 (River Water)
Unfiltered
Filtered
TSS
TSS
Trial
Trial
(mg/L)
(mg/L)
Sample 2 (Pond Water)
Unfiltered
Filtered
TSS
TSS
Trial
Trial
(mg/L)
(mg/L)
1
2
3
530
570
580
1
2
3
400
410
390
1
2
3
760
800
810
1
2
3
620
570
670
Average
560
Average
400
Average
790
Average
620
Average Percent Reduction
28.57%
Average Percent Reduction
21.52%
The reduction of total suspended solids was not nearly as successful as the reduction of
turbidity. This result did not meet the specification set at the beginning of the project. The test
for total suspended solids is not as good of an indicator for the effectiveness of the filter
compared to turbidity. As mentioned before turbidity is a much better measure for the
effectiveness of the device based on the objective for the project. Larger particles have a
greater effect on light scattering, and therefore turbidity; smaller particles have much less
significant effect on the light scattering. The removal of the large particles with the filter system
caused the turbidity to decline drastically, whereas the total suspended solids to only decrease
mildly in comparison.
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Fluoride Adsorption
Table 5
Bone Char Fluoride Adsorption
Sample
F- Concentration
Initial (mg/L)
Bone Char
(mg)
F- Concentration
Final (mg/L)
F- Removed
(%)
mg F- Removed
Per g of Bone
Char
Mother Solution 1
1
2
3
24
24
24
24
0
267.7
147.0
70.1
24.0
20.2
22.6
21.2
15.83%
5.83%
11.67%
0.852
0.571
2.397
Mother Solution 2
5
6
7
54
54
54
54
0
539.1
271.6
132.2
54.0
47.2
41.2
48.8
12.59%
23.70%
9.63%
0.757
2.828
2.360
Average Sorption
1.627
The addition of bone-char to the fluoridated sample of distilled water caused a reduction in the
concentration of fluoride. However the results were erratic and the desired percent reduction
was not achieved. The use of bone-char to adsorb fluoride ions from water has been widely
studied. Conclusions of the studies vary widely. One of the most common differences between
studies was the bone-char; how the bone-char was prepared (self-made) or different
manufactures (purchased) and how the use of bone-char was implemented. The bone-char
used when testing was not as effective as expected. Due to erratic the results and isotherm was
not constructed for the data collected. More testing could be done to achieve enough data to
accurately model a Freundlich adsorption isotherm.
Conclusion and Recommendations
In the end, the pre-filter did not meet all the desired specifications, but still performed well. It
reduced turbidity levels over 70%, and reduced fluoride concentrations and TSS, but not the
desired amount. The particle filtration system was a success. The reduction of turbidity to the
levels seen would greatly improve the efficiency of the UV-light in the BWM system. The
reduction of fluoride concentration was not as successful but bone-char as an adsorbent should
not be abandoned for a method of removing fluoride in developing countries. A study was
conducted of Tanzania households using a bone-char based bucket system for the removal of
fluoride. This different implementation of bone-char as an adsorbent removed 83% of fluoride
after being in operation in the field for two months and processing 32.5 L/day. The unit was
also cost effective at dollars per unit [3].
Copyright © 2013 Rochester Institute of Technology
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The mechanical performance of the system could be improved by some modifications on a
second generation system. First, using a straight-sided bucket; the filter-press was designed for
use in a bucket with a constant diameter. The bucket that was used is a regular tapered bucket;
the bottom diameter is smaller than the top opening diameter. This prevented the filter-press
from travelling all the way down through the bucket. Straight-sided buckets are difficult to find
in-store locally, and could only be purchased from online-retailers who had minimum order
requirements that did not work with our given budget. Second, adding more support for the
handles would be beneficial. The handles loosened after only a few uses; this was partially due
to high force needed to pull the filter-press out of the tapered bucket. Adding cross beam
supports between the handles, or including the modified bucket-lid. Also, usability could be
improved with some type of pressure or suction relief valve to aid in pulling the press up out of
the bucket. Testing was performed for extreme cases of turbidity; extremely turbid and
contaminated water was tested in the bucket and ended up clogging up the mesh. Pre-filter
through a t-shirt is recommended in extreme cases of turbidity to prevent clogging of the mesh.
According to B9 t-shirts is already being used in many regions to filter water.
A very basic and crude cost analysis was performed to find that in mass production, each
prefilter device would cost $22 (excluding any bone-char). A key aspect in calculating this was
buying the 5 micron mesh from an international supplier located in China, which is sold at a
fraction the cost of the one used in the prototype. This price also does not take into account the
fact that B9 Plastics themselves are a plastics company. Their production costs for the plastic
components would most likely be much lower.
References
[1] Nahum A. Medellin-Castillo,† Roberto Leyva-Ramos,*,†,‡ Raul Ocampo-Perez,† Ramon F. Garcia de
la Cruz,† Antonio Aragon-Pin˜a,† Jose M. Martinez-Rosales,§ Rosa M. Guerrero-Coronado,† and
Laura Fuentes-Rubio†, Adsorption of Fluoride from Water Solution on Bone Char. Ind. Eng. Chem.
Res. 2007, 46, 9205-9212
[2] M. Mohapatraa,*, S. Ananda, B.K. Mishraa, Dion E. Giles b, P. Singhb. Review of fluoride removal
from drinking water. Journal of Environmental Management 91 (2009) 67–77.
[3] P Jacobsen*, E Dahi*. BONE CHAR BASED BUCKET DEFLUORIDATOR IN TANZANIAN HOUSEHOLDS
2nd International Workshop on Fluorosis Prevention and Defluoridation of Water
[4] World Health Organization. Guidelines for Drinking-Water Quality. 4th ed. Geneva: World Health
Organization, 2011.
Acknowledgment
The team would like to thank B9 Plastics, Bob Bechtold and Kate Chamberlain for the opportunity to
work on this project. The team would also like to Sarah Brownell and Scott Wolcott for their help and
guidance along the way.
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