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\begin_layout Title

\color black
Low Flow Stacked Rapid Sand Filtration - Final Report
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\begin_layout Author

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Mihir Gupta, Kris LaPan, Rachel Proske, Nadia Shebaro
\end_layout

\begin_layout Date

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May 11, 2013
\end_layout

\begin_layout Abstract

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In January 2013, the Low Flow Stacked Rapid Sand Filter (LFSRSF) was tested
 in Honduras.
 Although the filter worked, it quickly failed due to structural weaknesses.
 The primary tasks this year include improving the durability of the filter
 and increasing the ease of operation.
 New manifold and sand drain designs are in the process of being implemented.
 Additionally, the stacked rapid sand filter (SRSF) went to Washington,
 D.C., in April for the EPA P3 competition.
 A written proposal for the EPA P3 grant was composed and submitted.
 To demonstrate the design and effectivess of the LFSRSF, a fully operational
 unit was designed.
 The prototype underwent hydraulic and performance testing and operated
 well at the competition.
\end_layout

\begin_layout Section*

\color black
Introduction
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\begin_layout Standard

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One of the essential components of human life is accessibility to clean
 drinking water; however, much of the world suffers a deficiency of this
 vital resource.
 In the mean time, the remainder of the countries are able to utilize modern
 technology to treat raw water and enjoy the benefits of pathogen free and
 low turbidity drinking water.
 For example, the United States is able to utilize its wealth and availability
 of electrical power to treat raw water; yet, not all countries are fortunate
 enough to have these resources.
 Therefore, the AguaClara project's aim is to provide an economical and
 electricity-free drinking water solution that can be implemented all over
 the world, especially in regions with economic hardships and power shortages.
 This goal was accomplished through the development of the AguaClara treatment
 facility, which is currently being utilized in several locations in Honduras.
 To further optimize this treatment facility, the conventional filtration
 process was investigated to determine the aspects of the process which
 could be improved.
 The goal of this team's specific research project is to modify the current
 design of the LFSRSF so that it may be implemented by Agua Para el Pueblo
 and other non-governmental organizations (NGO's) and used in any subsequent
 water treatment facilities.
 Previously, a stacked rapid sand filtration system was designed to remove
 the particles remaining after sedimentation in an efficient manner prior
 to chlorination and distribution.
 However, this method is unable to treat flows less than 6 liters per second.
 Smaller communities, who have water treatment plants with less flow, would
 be unable to use this system.
 Thus, a design and prototype low flow filter was created within the last
 year.
 However, the design is not fully complete, and testing and modification
 of the system is necessary before it can be implemented in a plant.
\end_layout

\begin_layout Section

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Literature Review
\end_layout

\begin_layout Subsection

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EPA P3 Phase 2 Project Report for the Foam Filter (2012)
\end_layout

\begin_layout Standard

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The Phase 2 report for the Foam Filter was used as a reference in the process
 of writing the Phase 2 report for the SRSF.
 A large component of the report was focused on the benefits of the filter
 to P3's major topics of people, prosperity, and the planet, and since much
 of this information was relevant to AguaClara in general, it was useful
 as a foundation for the new proposal.
\end_layout

\begin_layout Standard

\color black
The Foam Filter proposal discussed the issue of access to clean water throughout
 the world, citing data from various reports about the scope of this need
 and the degree to which it remains unfulfilled.
 This report also commented on the success, or lack thereof, of the UN's
 Millennium Development Goals and noted the difference between 
\begin_inset Quotes eld
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safe
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 and simply 
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improved
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 water sources.
 The water treated by an AguaClara plant, for example, can be considered
 safe water, because the treated water is expected to meet a standard Nephelomet
ric Turbidity Unit (NTU) and removal of bacteria.
 However, according to some standards, 
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improved
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 access to water can include the piping of untreated water to households.
\end_layout

\begin_layout Standard

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The Foam Filter report also compared the technology to other more traditional
 methods of water filtration.
 Because the foam filter was initially considered for either point of use
 or emergency water treatment, part of this comparison included its viability
 as an emergency response system, and noted the issues with current methods
 in terms of response time and failure rates.
 Citing aspects of the overall AguaClara design philosophy, the report discussed
 how the technology was designed specifically to be sustainable within a
 community and avoid failure, particularly that which would be difficult
 to repair.
 
\end_layout

\begin_layout Standard

\color black
The practices of using cheap, locally available materials, and designing
 purely hydraulic systems were cited as components of the technology that
 made it beneficial to the people it would serve, as it is designed to be
 a financially viable system that is intended to improve the quality of
 life of a community.
 Reduction in the needs for electricity and plastic water bottles were both
 given as environmentally beneficial consequences of the technology.
\end_layout

\begin_layout Subsection

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Documentation on the Stack Rapid Sand Filter's Report for EPA P3 Phase 1
\end_layout

\begin_layout Standard

\color black
Last year, the SRSF team won Phase 1 of the competition based on a report
 describing the project's relevance and benefit to communities.
 The report also described the necessary future work and expected expenses.
 The document discussed the innovation, fundamental theory, and flow paths
 associated with the stacked rapid sand filter.
 Additionally, it described the three aspects of sustainability; people,
 prosperity, and planet; and their relevance to the filtration method.
 For social sustainability, the research plan discussed Agua Para el Pueblo
 (APP) as well as the use of an elected water board in each community to
 oversee the management of the AguaClara plant.
 For economic sustainability, the plan discussed the monthly operational
 costs per household and the manner in which chemicals and materials for
 the plant will be acquired.
 For environmental sustainability, the report discussed the reduction in
 backwash water which is required for a SRSF, as opposed to a conventional
 rapid sand filter, and the filter's use of gravitational potential energy
 verses solar or electrical power.
 Laboratory experiments were completed for the SRSF and yielded excellent
 reductions in effluent turbidity and significant reductions in backwash
 time required for contaminant and colloid removal (~ 7 minutes).
\end_layout

\begin_layout Subsection

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Previous AguaClara Filter Teams' Reports
\end_layout

\begin_layout Standard

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In previous years, research mostly focused on features of the SRSF such
 as the flow distribution between the six sand layers, the difference in
 efficiency of turbidity removal by the up-flow and down-flow sand layers,
 and the optimum time required for backwash to achieve ideal sand cleansing.
 This data is relevant to the low flow version of the filter as well; therefore
 included in this report.
 From various experiments run in the lab, it was determined that the flow
 through each sand bed was uniform (
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Flow-Distribution"

\end_inset

) and the upflow and downflow turbidity removal was the same.
 Various switching methods between filtration and backwash mode were also
 studied, and it was decided that a siphon control system would be the ideal
 choice wherein a single valve would be needed to initiate the switch.
\end_layout

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Flow Distribution
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\begin_layout Section

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Methods
\end_layout

\begin_layout Subsection

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Small Scale Filter (for EPA P3 Competition)
\end_layout

\begin_layout Standard

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A small scale prototype was built for the EPA Phase 2 competition.
 The design techniques used were similar to those for the full scale filter
 including the calculation of the required dimensions of the tubes, manifolds,
 and filter column.
 The dimensions were calculated using the backwash constraint for fluidization
 of the sand grains as well as the head loss during both filtration and
 backwash.
 The estimated flow rate required is 0.022 L/s.
 The filter body was constructed out of clear polycarbonate tubing to ensure
 maximum visibility.
 
\end_layout

\begin_layout Standard

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To emulate the manifold construction, a circular wire mesh design was incorporat
ed because the current manifold design for the low flow SRSF could not be
 scaled down to such a size.
 A casing for the mesh was created from 3/8
\begin_inset Quotes erd
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 polycarbonate tubes which are drilled with multiple holes to allow the
 water to enter the main filter column.
 The main column itself was manufactured from polycarbonate tubing with
 an inner diameter of 2 inches and a height of 6 ft.
 The manifolds are drilled through the main column with a distance of 20
 cm separating each inlet and outlet.
 The bottom of the filter is closed off by a polycarbonate plate while the
 top has a detachable grooved cap that is made air tight with an o-ring.
 3/8 inch quick connects are used to connect the manifolds to the external
 piping system.
 The general layout of the setup is similar to the original design; however
 additional ball valves were added to each inlet and outlet to prevent the
 flow from taking shortcuts through the manifolds during backwash, as check
 valves are not applicable at such low flow rates.
 
\end_layout

\begin_layout Standard

\color black
The frame to support the whole set up was created out of 80/20 steel bars
 with an inverted T cross section.
 The frame has a height of 6 ft, length of 4 ft and a width of 2 ft.
 The frame was assembled in such a way as to enable easy deconstruction
 and reconstruction, to facilitate easy transport of the set up.
 Additionally, it was designed keeping in mind that the set up will rest
 on a standard 2 1/2 ft table.
 It has bench clamps to hold it in place and clamps to attach the filter
 column to the front of the frame.
 To balance the weight of the filter, the bucket containing the water was
 suspended from the back of the frame.
 See Figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Small-scale-filtration"

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 for an illustration of the setup.
\end_layout

\begin_layout Standard

\color black
Design of the small scale filter has illuminated issues with scaling the
 existing LFSRSF design; consequently modifications in the small scale design
 have occurred.
 In an attempt to scale down the full scale filter, the velocity through
 the sand bed layers during the filtration cycle was kept constant, while
 decreasing the flow rate and cross sectional area.
 Thus, the flow rate for the small scale filter was computed to be 0.04 L/s.
 This is greater than the original 0.022 L/s due to changes in the original
 design.
 The rate of 0.04 L/s was deemed necessary because it provided sufficient
 backwash velocity to completely fluidize all the sand layers.
 The constant head tank, a suspended bucket, was used for the small scale
 filter to provide the driving head required for operation.
 To determine the height of water necessary to provide the 0.04 L/s flow
 the following equation was used to solve for h: 
\begin_inset Formula $Q=0.62A\sqrt{2gh}$
\end_inset

.
 In addition, a factor of safety of 1.5 was applied to the required flow
 rate to ensure sufficient head; thus the design rate was 0.06 L/s.
 Using the specified flow rate and diameter of 0.75 inches as the diameter
 of the orifice at the bottom of the constant head tank, a head of 25 cm
 above the orifice was computed to be needed.
 In addition to computing the flow rates needed for the design to be hydraulical
ly functional, the head loss was also computed for both filtration and backwash
 cycles.
 To calculate these two head losses the major and minor head losses were
 computed for each pipe segment over its length, as well as any expansions
 or contactions in the flow due to pipe diameter variability.The head losses
 during filtration and backwash were computed to be 0.65 ft and 4 ft, respectivel
y.
 The equations used to compute the major and minor head losses are as follows:
\series bold

\begin_inset Formula $h_{major}=f\frac{8}{g\pi^{2}}\frac{LQ^{2}}{D^{5}}$
\end_inset

; 
\begin_inset Formula $h_{minor}=K_{e}\frac{V^{2}}{2g}$
\end_inset


\series default
.
 The equation used to compute the major head losses is for the case when
 the flow is turbulent.
 In order to have conservative estimates of the head loss, the flow for
 both filtration and backwash was assumed to be turbulent.
\end_layout

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	scaleBeforeRotation
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	rotateOrigin leftTop

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\begin_layout Plain Layout
Small scale filtration unit at EPA competition.
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name "fig:Small-scale-filtration"

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The maximum flow rate, 0.04 L/s, through the system was too great during
 the filtration cycle and caused the sand located directly next to the inlets
 to fluidize.
 Therefore, a valve at the entrance of the filter was added to allow the
 flow to be reduced during filtration and increased during backwash as needed.
 Due to limited resources at the competition and the overall goal for preservati
on, water was recycled through the system, which meant that very turbid
 water continuously travelled through the mesh in the manifolds that were
 used for the small scale filter (as mentioned above).
 Since the mesh was a little bit smaller than some of the turbid particles
 in the water, the manifolds would clog with the dirt particles.
 This was especially a problem when a high speed and volume of turbid water
 was passed through the bottom-most manifold during fluidization because
 it would cause the flow out of the pipe to be much lower than what was
 required to reach the necessary fluidization velocity.
 To remedy this problem, certain steps were taken before fluidization.
 The first step was to clean the bottom manifold by allowing the water already
 in filter to travel through the bottom-most manifold in the opposite direction
 that flow normally would pass through the manifold.
 This removed any large particles stuck inside the manifold and transported
 them out of the drain pipe (connected to the bottom manifold and located
 opposite the inlet) and back to the stock tank.
 Next, the filter was filled to the top with water with all of the inlets
 open to prevent the possible reclogging of the bottom manifold.
 During this time, the backwash pipe is kept closed.
 Once the air valve on the backwash pipe began to fill up with water, the
 air valve was closed and the backwash pipe opened.
 All inlets remained opened until any remaining bubbles in the backwash
 pipe were pushed out of the system.
 Finally, all valves except the one at the bottom manifold were closed and
 the bed fluidized.
\end_layout

\begin_layout Subsection

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Manifolds
\end_layout

\begin_layout Standard

\color black
The manifolds for the filter needed to be redesigned due to a low resistance
 to stress.
 When in Honduras, the manifold branches were susceptible to breaking off
 the manifold stem due to the small connection surface area.
 To improve this connection, half inch slotted PVC pipes were connected
 using tee and cross connections in the same configuration as the original
 manifolds.
 Two of the seven manifolds have been constructed, except for the caps that
 close off the six branch pipes.
 The old design is shown below on the left in figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Design-for-old-and-new"

\end_inset

, while the new manifold is shown on the right.
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	scale 50

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	lyxscale 50
	scale 36

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\begin_inset Caption

\begin_layout Plain Layout
Design for old (left) and new (right) slotted manifolds.
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LatexCommand label
name "fig:Design-for-old-and-new"

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\begin_layout Subsection

\color black
Sand Drain
\end_layout

\begin_layout Standard

\color black
One of the main drawbacks of the first and second generation LFSRSFs was
 the removal of sand from the filter column.
 Once the sand was introduced into the filter, it is virtually impossible
 to remove without dismantling the entire unit.
 As a result, it was decided to place a sand drain on the side of the filter
 above the second inlet manifold from the bottom, within the fluidized sand
 layer.
 In order to remove the sand, the prototype will be operated in backwash
 cycle, and the backwash pipe will be closed.
 Prior to installing a sand drain, the only means for flow exiting during
 backwash was through the backwash pipe; however if the backwash pipe is
 closed then it forces the flow path out the sand drain.
 Since the location of the drain is low within the fluidized sand layer,
 nearly all the sand will be able to exit the filter in a sand-water slurry.
 See figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Sand-drain-for"

\end_inset

 for the proposed location of the sand drain on the LFSRSF and the current
 sand drain on the full scale SRSF in Tamara.
 
\end_layout

\begin_layout Standard

\color black
A preliminary model for calculating the sand drain was developed in Microsoft
 Excel which allows the user to change inputs such as height of the drain,
 pipe diameter, angle exiting the column wall, and separation distance between
 the valve and the filter column.This model calculates the height of sand
 removed from the filter as well as the height of sand remaining in the
 filter.
 The equations which were used include trigonometric functions such as sine
 and cosine.
 In addition, it determines whether the input parameters create a drain
 design which is allowable based on the geometric orientation of the drain
 with respect the ground.

\series bold
 
\series default
This is an important result because it needs to be easy for an operator
 to collect the sand slurry as it exits the drain; consequently there needs
 to be sufficient separation.
 Currently this Excel model is available through the shared network, in
 the Low Flow Stacked Rapid Sand Filter, Srping 2013 file.
\end_layout

\begin_layout Standard

\color black
The initial inputs for the sample design were as follows: Height of the
 drain = 30 cm, Pipe diameter = 2 inches, Angle exiting column = 60 degrees,
 and separation distance between the valve and the filter column = 3 inches.
 The model found this design to be acceptable.
 For this design, 102 cm of sand will be removed, and separation distance
 between the ground and drain of 7.3 inches.
 
\end_layout

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\begin_layout Plain Layout

\color black
\begin_inset Caption

\begin_layout Plain Layout
Sand drain for full scale SRSF (right) and proposed sand drain location
 for LFSRSF (left).
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name "fig:Sand-drain-for"

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\begin_layout Section

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Conclusions
\end_layout

\begin_layout Standard

\color black
The primary focus of in this semester was to design and construct a small
 scale filter which could be taken for demonstration purposes to the EPA
 P3 competition in Washington, D.C.
 The main issue faced during this process was the scaling down of the filter
 to an easily transportable device, while still keeping it large enough
 to maintain the underlying physics of the model.
 Fluidization was the determining factor in designing the flow rate required,
 while the cleaning capacity per depth of sand bed decided the height of
 the filter column.
 Another predicament faced due to scaling issues was the large number of
 valves that needed to be operated to switch the flow from filtration to
 backwash.
\end_layout

\begin_layout Standard

\color black
The small scale model at the EPA P3 competition won second place in the
 ASCE sustainable development award.
 The results of the EPA awards from the competition have not been announced.
\end_layout

\begin_layout Standard

\color black
In addition to constructing this model for the EPA, a new design for the
 manifolds for the full scale system was developed.
 The drilled-hole connections were replaced by cross- and T- connections
 to enhance the manifold's structural strength.
 A sand drain was also designed, but has yet to be incorporated into the
 full scale filter.
\end_layout

\begin_layout Section

\color black
Future Work
\end_layout

\begin_layout Subsection

\color black
Manifolds
\end_layout

\begin_layout Standard

\color black
Two newly designed manifolds have been produced, but the last five manifolds
 still need be constructed along with the addition of the end caps to the
 branched slotted pipes.
 Furthermore, the manifolds will be structural and hydraulically tested
 to ensure that the head losses through the manifolds at the given flow
 rate of 0.8 L/s are not so large that they cause the filter to fail.
\end_layout

\begin_layout Subsection

\color black
Sand Drain
\end_layout

\begin_layout Standard

\color black
Now that there is a preliminary design for the sand drain, it will need
 to be tested and potentially modified based on how it functions.
 Implementation and testing of the sand drain will be dependent on the construct
ion of a new lab filter, for which the drain will be incorporated into the
 new overall design.
 Testing will determine if the angle, length, and location of the drain
 are appropriate to achieve the required removal of sand from the filter,
 as well as if the design allows for easy capture of sand once it has been
 removed.
 Additional research on the most efficient and stable valve for use in the
 sand drain is also still required.
\end_layout

\begin_layout Subsection

\color black
Construction Techniques & Ease of Operation
\end_layout

\begin_layout Standard

\color black
The new filter design will need to incorporate improvements to fabrication,
 including the specific techniques and materials used in the process.
 The goal will be to minimize the cost and increase the ease of fabrication
 of the filter.
 One component of fabrication which needs to be improved is the pipe drilling
 method that is used for the filter body.
 In Hondruas, the pipe for the filter body was cut on a drill press, and
 further research will need to be done to determine how this method can
 be replicated and improved.
 In order to minimize the cost of fabrication, possible alternatives for
 the cap design will also be investigated, due to the high expense of the
 current aluminum caps.
 There is potential to develop a cap design based off of the design that
 was used for the small-scale filter, which used a grooved cap made from
 a PVC plate and an o-ring to make it air tight.
\end_layout

\begin_layout Standard

\color black
There will also be further work done to improve the ease of operation of
 the low flow filter.
 Currently, an operator is required to turn three separate valves in order
 to switch the low-flow filter between filtration and backwash modes, as
 opposed to the one valve required for the full-scale.
 As evidenced by the performance of the small-scale (P3) filter, ease of
 operation becomes more difficult to achieve as the size and flow of the
 filter are scaled down, and further design research will need to be done
 to determine how hydraulics can be used to achieve the transition to and
 from backwash more easily at this scale.
\end_layout

\end_body
\end_document
