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\begin_layout Title
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Foam Filtration
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\begin_layout Date
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December 6, 2012
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\begin_layout Author
\paragraph_spacing single
Carrie Smith and Jianying Guan
\end_layout

\begin_layout Abstract
For large municipal communities, full scale AguaClara plants are necessary
 to treat the large demands.
 For smaller communities made up of 20 families or even fewer, such a treatment
 plant does not make economic sense.
 In such cases, a small scale treatment option such as foam filtration is
 more feasible.
 The foam filtration device that students at Cornell University have developed
 can significantly reduce influent turbidity below even EPA standards.
 This paper outlines additional contributions that we have made to the workings
 of this system.
 These include establishing a way of delivering water to the system without
 the use of electricity, creating a Chemical Dose Controller (CDC) for coagulant
 and chlorine that operators can easily manage, and exploring methods of
 detecting breakthrough from the roughing filter.
 
\end_layout

\begin_layout Section
Introduction 
\end_layout

\begin_layout Paragraph
\noindent

\series medium
For our portion of the AguaClara project, we have been assigned to improve
 on the previous design of the foam filtration system.
 Our tasks build off the previous system.
 We added a CDC for coagulant and chlorine to the system, developed an operator
 friendly method of determining when to clean the filter, and developed
 a way to run the filters without electricity.
 Finally, we designed a Secchi Disk to measure the turbidity of the roughing
 filter so operators can easily determine when to plunge the roughing filter.
 We also wrote an easy-to-use operations manual in Spanish.
 
\end_layout

\begin_layout Section
Literature Review 
\end_layout

\begin_layout Subsection
Previous Filter Experiments
\end_layout

\begin_layout Paragraph

\series medium
Originally, the foam filtration system consisted of a single 90 ppi (pores
 per inch) filter alone, but that caused too much headloss [1].
 As a result, a 30 ppi filter was added so high turbidity water (up to 100
 NTU) could be filtered without overwhelming the 90 ppi filter [2].
 Having the roughing filter before the finishing filter also extended the
 life of the finishing filter and the performance of the filtration system
 [3].
 The roughing filter has the ability to treat turbid influent up to 100
 NTU without overwhelming the finishing filter.
 One design that was tested consisted of two roughing filters in parallel
 so one could be cleaned while water is being filtered through the other
 [3].
 This design was scrapped because the second filter was not necessary since
 the cleaning process is simple and quick.
 
\end_layout

\begin_layout Paragraph

\series medium
Cleaning both filters requires a plunging method that flushes the particles
 through a release valve located towards the bottom of the filter.
 The 
\begin_inset Quotes eld
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plunger
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 consists of a 1.2m PVC pipe with a disk attached to the end.
 Originally, it was proposed that the filters were to be cleaned once every
 eight hours, but was reduced to once every four hours.
 This was found to be the longest period of time that the filter could run
 at varying turbidity without needing to be plunged [3].
 Compressing and decompressing the filter can affect the performance of
 the foam, but plunging at this interval did not appear to have a profound
 effect on the filter’s performance.
 The lifespan of the filter appears to be 1 month with regular use at a
 range of turbidity.
 Water cannot be filtered through the system while it is being cleaned.
 Cleaning the filter uses approximately 3.79 liters of rinse water [3].
\end_layout

\begin_layout Paragraph

\series medium
At this time, headloss is not a viable indicator of when the filter should
 be cleaned as shown in Table 1 [4].
 Terminal headloss depends on both influent turbidity and the condition
 of the foam over the course of its life cycle.
 Even with both the roughing and finishing filter, it has been determined
 that coagulant is needed for the foam filtration unit to be effective [4].
 
\end_layout

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Comparison of Summer 2012 Experiments [4]
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Experiment
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Influent Turbidity
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100NTU
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\series medium
Researchers unaffiliated with AguaClara have also focused their efforts
 on determining optimum filtration.
 Biswas et al.
 determined a relationship between breakthrough time and the degree of media
 compression and pores per linear inch [5].
 They found that the breakthrough time increased as the foam was decompressed,
 with a compression of 0% giving the longest breakthrough time.
 Additionally, they found that the more porous the foam was, the longer
 the breakthrough time.
 Furthermore, Biswas noticed that foam filters have a ripening time leading
 up to optimum filtration.
 Filters require a certain amount of influent to pass through the medium
 before they reach optimum removal efficiency; this is defined as the ripening
 time.
 Past AguaClara students have made similar observations, recommending that
 the filters be left saturated in water until the foam needs to be changed
 [4].
 
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\begin_layout Subsection
Chemical Dose Controller Design
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\series medium
AguaClara researchers have developed a constant head dosing system for deliverin
g coagulant or chlorine to a system.
 The doser consists of a float valve that creates a constant elevation of
 fluid at the inlet to the flow control system.
 The chemical flow is varied by varying the elevation of the end of the
 flexible tube coming out of the doser, creating a change in head [6].
 
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\begin_layout Description
Figure 1: Chemical dose controller schematic [6].
 
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\begin_layout Subsection
Secchi Disk
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\begin_layout Paragraph

\series medium
A Secchi disk is a black and white disk mounted on a pole or line and slowly
 lowered down into the water until the pattern on the disk is no longer
 visible.
 The depth at which visibility is lost can be taken as a measure of turbidity
 and is known as the Secchi depth [7].
 Secchi disks are easy to fabricate and to use; thus, they are ideal in
 situations where an expensive or electricity intensive turbidity meter
 cannot be readily installed.
  
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\begin_layout Section
Methods/ Analysis
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\begin_layout Subsection
Coagulant Doser
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\begin_layout Paragraph

\series medium
The system was originally designed for experiments around a computer that
 controls the coagulant dose delivered to the mixing tank.
 One of our tasks for this semester was to create a coagulant doser that
 works without electricity.
 We used the AguaClara design for our system (Figure 2).
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Figure 2 : Constant head tank and coagulant dosing system.
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\series medium
This dosing system has been used by other members of the AguaClara team.
 To set up this system, we used Mathcad to calculate the necessary height
 of the stock tank, coagulant tank, and dosing tubes.
 
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\series medium
To solve for the neccessary height of the dosing tube at various NTUs, we
 first found the empirical ratio of influent turbidity to PAC (Equation
 1).
 
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Equation 1: Empirical ratio of PAC to influent turbidity.
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Equation 2: Range of PAC concentrations given a range of turbidity from
 0-200 NTU and 400 NTU.
 
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\series medium
Using the empirical ratio, we next used a range of NTU values to solve for
 a range of PAC concentrations (Equation 2).
 We chose to use a range of 0 to 200 NTU since these values seemed reasonable
 for normal operating conditions in Honduras.
 We also included an estimate for 400 NTU to demonstrate the scaling of
 the chemical doser.
\end_layout

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\series medium
Finally, we solved for coagulant flow (Equation 3).
 From this, we found a range of coagulant flow rates ranging from 0 to ~30
 mL/min.
 An earlier Foam Filtration team had found that the foam filter could work
 effectively without coagulant at an NTU of <5, so we calibrated the CDC
 to reflect this.
 
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\series medium
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\begin_layout Description
Equation 3: Coagulant flow given filter flow, range of PAC concentrations,
 and the concentration of the PAC stock.
 
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\series medium
Once we obtained the flow of the coagulant, we chose a diameter of 1/16th
 inch for the dosing tube.
 We picked a diameter that we felt was reasonable given the flow of coagulant.
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\series medium
After establishing all of these parameters, we determined the headloss needed
 to get these flows (Equation 4).
 
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Equation 4: Dosing tube heights for varying flow rates.
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\series medium
Since the numbers we found weren't round numbers, we created a range of
 NTUs for a coagulant dose.
 We assumed that when picking the coagulant for this range, it was better
 to pick the dosing height associated with the greater NTU.
 The height of the tube changes very little over a range of NTUs, so for
 example, if the NTU was between 5-30, so we chose the dosing tube height
 associated with 30 NTU.
 The headlosses we determined are shown in Table 1.
 
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NTU Range
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</lyxtabular>

\end_inset


\end_layout

\begin_layout Description
Table 2: Shows the relationship between headloss in centimeters and selected
 NTU ranges.
\end_layout

\end_inset


\end_layout

\begin_layout Paragraph

\series medium
The headloss values correspond to the height the coagulant tube must be
 to get the desired flow rate.
 
\end_layout

\begin_layout Subsection
Chlorine Doser
\end_layout

\begin_layout Paragraph

\series medium
We developed a system similar to the coagulant doser.
 Thus, the equation for the flow of chlorine is based on the same formula
 for the flow of coagulant (Equations 1-3).
 
\end_layout

\begin_layout Paragraph

\series medium
AguaClara uses a maximum concentration of chlorine of 2 mg/L, so we chose
 the same target value for our system.
 The chlorine doser works the same way the coagulant doser does by using
 gravity and the appropriate headloss to produce the flow desired.
 We chose a dosing tube with the same diameter and length as the dosing
 tube for the coagulant doser.
 The flows produced correspond to a chlorine concentration range from 0-2
 mg/L.
 Ideally, the plant operator should have some leeway in choosing the chlorine
 dose, but as the flow is so low, the spacing between the dosing holes would
 be too close if we were to include a range similar to the coagulant doser.
 
\end_layout

\begin_layout Subsection
Detection Methods
\end_layout

\begin_layout Paragraph

\series medium
To create the Secchi Disk we cut a plastic disk 8.75 cm in diameter and painted
 it in black and white quadrants.
 We attached the disk to a metal pole about 0.45 m long, long enough to lower
 into the finishing tube.
 
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status collapsed

\begin_layout Plain Layout
\begin_inset Graphics
	filename Secchi Disk.jpg
	scale 50

\end_inset


\end_layout

\begin_layout Description
Figure
\series bold
 
\series default
3: A complete view of the Secchi Disk.
 The quadrants were painted in Krylon.
\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Paragraph

\series medium
As we were testing the effectiveness of the Secchi Disk at 5 NTU, we realized
 that this device would not be accurate enough to test low turbidity waters.
 It would only be useful in more turbid waters.
 We noticed in the roughing filter effluent when the disk was lowered until
 it just touched the filter at 20 NTUs, it was difficult to see the Secchi
 Disk.
 Thus, the Secchi Disk would be useful for measuring higher turbidity waters
 and is a good way to measure the finishing filter influent and possibly
 then determine the breakthrough time.
\end_layout

\begin_layout Paragraph

\series medium
At low NTUs the Secchi Disk was ineffective, therefore it is not recommended.
\end_layout

\begin_layout Paragraph

\series medium
We searched for other methods of determining the NTU before the finishing
 filter.
 We found that a previous AguaClara team researched different methods of
 calculating the turbidity.
 The Fall 2011 Turbidimeter Team created a turbidimeter design using a blue
 LED light and a HDPE block that may be able to read values all the way
 down to 7 NTU [8].
 
\end_layout

\begin_layout Subsection
Cleaning the System
\end_layout

\begin_layout Paragraph

\series medium
Cleaning the system is a relatively simple process.
 All of the tubes (1,2, 4, and 6 in Figure 4) are easily detached.
 Clay and coagulant can settle in standing water and precipitate out, causing
 build up in the system.
 We noticed that in the rapid mix pipe (2) and in the roughing filter, when
 water is left in the system, clay can settle out.
 Once the system is run again, the clay is quickly re suspended.
 A similar problem exists with the coagulant in the tube leading to the
 finishing filter (4) and in the effluent tube (6).
 A pink scum forms in the tubes when water is left sitting; it does not
 go away after the system is run.
 This scum does not appear to affect effluent turbidity however.
 
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status collapsed

\begin_layout Description
\begin_inset Graphics
	filename Figure 4 picture.jpg
	scale 50

\end_inset


\end_layout

\begin_layout Description
Figure 4 : Filtration system with elevated tank and CDC dose controllers
 for coagulant and chlorine.
 The different parts of the system are labeled: 1.
 Influent tube, 2.
 Rapid mix pipe, 3.
 CDC for coaguland, 4.
 Finishing filter influent tube, 4.
 CDC for chlorine, 6.
 Effluent pipe.
\end_layout

\end_inset


\end_layout

\begin_layout Paragraph

\series medium
To clean the system, we simply disconnected tubes 1, 2, 4, and 6 and threaded
 wire through a rag, dragging it through the tube.
 We were concerned with removing the residual coagulant as it is not removed
 by water.
 It removed most of the scum.
 After we finished, we returned the same tubes to the system.
 We noticed however, that the fittings were loose following the cleaning.
 This may be because an attachment was added to the existing tubes that
 stretched the tube.
 We fixed this by wrapping the attachments with Teflon tape to prevent leaks.
\end_layout

\begin_layout Subsection
User Manual
\end_layout

\begin_layout Paragraph

\series medium
We created an illustrated user manual in Spanish to concisely guide the
 operator through the task of operating the system.
 Below is the text of the operator's manual in English and Spanish.
 The illustrated version is available in a separate document.
 
\end_layout

\begin_layout Enumerate
Put new filters in system.
 
\shape italic
Poner filtros nuevos en el sistema.
\end_layout

\begin_layout Enumerate
Turn on hose.
 Allow tank to fill; adjust flow control valve on tank tube until water
 level in Linear Flow Orifice Meter (LFOM) is at the marked level.
 
\shape italic
Encender la manguera.
 Permitiar que el tanque se llene; ajustar valvula de control de flujo en
 el tanque de tubo hasta que el nivel de agua en el medidor de orificio
 de flujo lineal llegue al nivel indicado.
 
\end_layout

\begin_layout Enumerate
After the water level in the tubes have reached the marked water height,
 compress the filter to remove air bubbles.
 
\shape italic
Despues de que el nivel de agua en los tubos llegue al nivel indicado, comprimir
 el filtro para remover en burbujas de aire.
 
\end_layout

\begin_layout Enumerate
Check the influent turbidity and accordingly adjust the CDC for the needed
 coagulant dose.
 
\shape italic
Revisar turbidez influente y ajustar el dosificador quimico para dosificar
 el coagulante requerido.
\end_layout

\begin_layout Enumerate
Run system until break through at finishing filter exceeds 5 NTU.
 At that point, open the waste valve and compress filter to clean.
 Repeat from step 3.
 
\shape italic
Correr el sistema hasta que la turbidez en el filtro finalizador exceda
 5 NTU.
 En ese punto, abra la valvula de desperdicio y limpie el filtro comprimiendolo.
 Repetir de acuerdo a paso numero tres.
\end_layout

\begin_layout Enumerate
After roughly a month of running the system (based on 4 hours a day), change
 the filters.
 If after plunging, the finishing filter doesn't experience a decrease in
 turbidity, change the filter.
 
\shape italic
Cambiar los filtros despues de correr el sistema por aproximadamente un
 mes.
 Cambiar el filtro finalizador si despues de comprimir el filtro, el filtro
 no reduce la turbidez.
\end_layout

\begin_layout Section
\noindent
Conclusions
\end_layout

\begin_layout Paragraph

\series medium
The addition of the CDC for coagulant and chlorine give the operator the
 ability to regulate the amount of chemicals added to the system.
 We expect the operator to have knowledge of the influent turbidity so that
 he or she can dose the system appropriately.
 With the addition of the Secchi Disk, the operator will be able to determine
 the breakthrough point of the roughing filter, and clean the system accordingly.
 The point at which the operator should change the roughing filter is about
 1 month; we have not yet determined if the finishing filter should be changed
 at the same time or at a later date.
 The user manual we compiled will simplify the process of maintaining the
 system.
\end_layout

\begin_layout Section
Future Work
\end_layout

\begin_layout Paragraph

\series medium
As tests were being run, we noticed that we could visually track the flocs
 getting trapped in the roughing filter.
 A continuous line on the outside of the first roughing filter forms as
 the system runs, but upon reaching the second roughing filter, this no
 longer happens.
 Based on this, we feel that stacking two foam pieces on top of one another
 may not be the most efficient method of filtration.
 Future experiments need to be designed and run to determine if stacking
 two foam pieces is ineffective and what makes this method ineffective.
 
\end_layout

\begin_layout Paragraph

\series medium
Further experiments need to be done using the Secchi Disk.
 As they are ineffective in low turbidity waters, they could only be employed
 in waters with a higher turbidity.
 It is still not clear just what NTU the water would have to be.
 Additionally, it would be useful to know the best location to take readings
 from the Secchi Disk.
 One method would be to place the Secchi Disk just above the foam during
 operation.
 A consistent depth would also promote consistency among readings.
 
\end_layout

\begin_layout Bibliography
\begin_inset CommandInset bibitem
LatexCommand bibitem
label "1"
key "key-1"

\end_inset

Hurst, M; Weber-Shirk, M; Philipson, R; Stodter, S; Wong, K; Hanna, Cl Merboth,
 A; Shinbein, M; Zheng, L; Lin, PH; Lion, L.
 
\begin_inset Quotes eld
\end_inset

Characterization of Polyurethane foam as Depth Filtration Media,
\begin_inset Quotes erd
\end_inset

 Spring 2011.
 Accessed November 12, 2012, https://confluence.cornell.edu/display/AGUACLARA/Foam
+Filtration (from Spring '11).
\end_layout

\begin_layout Bibliography
\begin_inset CommandInset bibitem
LatexCommand bibitem
label "2"
key "key-2"

\end_inset

Irish, B; Lee, A; Philipson, R.
 
\begin_inset Quotes eld
\end_inset

Foam Filtration AguaClara Research Team,
\begin_inset Quotes erd
\end_inset

 12 December 2011.
 Accessed November 20, 2012, https://confluence.cornell.edu/download/attachments/1
17762950/FoamFiltrationFinalReportFall2011.pdf?version=1&modificationDate=1323725
594000 .
\end_layout

\begin_layout Bibliography
\begin_inset CommandInset bibitem
LatexCommand bibitem
label "3"
key "key-3"

\end_inset

Edwards, K; Grimshaw, W; Irish, B; McBride, K; Shebaro, N.
 
\begin_inset Quotes eld
\end_inset

Foam Filtration AguaClara Research Team,
\begin_inset Quotes erd
\end_inset

 30 March 2012.
 Accessed November 20, 2012, https://confluence.cornell.edu/download/attachments/1
17762950/FoamFiltrationFinalReportSpring2012.pdf?version=1&modificationDate=13367
50185000 .
\end_layout

\begin_layout Bibliography
\begin_inset CommandInset bibitem
LatexCommand bibitem
label "4"
key "key-4"

\end_inset

Gostic, M; Levine, S; Meyerholtz, L.
 
\begin_inset Quotes eld
\end_inset

Foam Filtration Research Final Report,
\begin_inset Quotes erd
\end_inset

 31 July 2012.
 Accessed September 20, 2012, https://confluence.cornell.edu/download/attachments/
117762950/FoamFiltrationFinalReportSummer2012.pdf?version=1&modificationDate=1345
048836000 .
\end_layout

\begin_layout Bibliography
\begin_inset CommandInset bibitem
LatexCommand bibitem
label "5"
key "key-5"

\end_inset

Biswas, Neepa et.
 al, 
\begin_inset Quotes eld
\end_inset

Polyurethane foam filter/PAC absorber,
\begin_inset Quotes erd
\end_inset

 American Water Works Association, 95 (2003): accessed September 21, 2012,
 http://search.proquest.com/docview/221644350?accounted=10267.
\end_layout

\begin_layout Bibliography
\begin_inset CommandInset bibitem
LatexCommand bibitem
label "6"
key "key-6"

\end_inset

Weber-Shirk, Monroe, 
\begin_inset Quotes eld
\end_inset

Flow Control and Measurement,
\begin_inset Quotes erd
\end_inset

 accessed October 26, 2012, http://courses.cit.cornell.edu/cee4540/Flow%20Control%2
0and%20Measurement.pptx .
\end_layout

\begin_layout Bibliography
\begin_inset CommandInset bibitem
LatexCommand bibitem
label "7"
key "key-7"

\end_inset

 EPA.
 “Using a Secchi Disk or Transparency Tube,” last modified March 06, 2012,
 http://water.epa.gov/type/rsl/monitoring/155.cfm .
\end_layout

\begin_layout Bibliography
\begin_inset CommandInset bibitem
LatexCommand bibitem
label "8"
key "key-8"

\end_inset

Morris, J; Forodetsky, A; Rausch, H, 
\begin_inset Quotes eld
\end_inset

AguaClara Turbidimeter Team,
\begin_inset Quotes erd
\end_inset

 accessed December 5, 2012, https://confluence.cornell.edu/download/attachments/13
7953862/Report_Turbidimeter_Fall2011_2.pdf?version=1&modificationDate=13232728310
00 .
\end_layout

\end_body
\end_document
