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\author 109193216 "jem384" 
\author 1000245830 "aguaclara" 
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\begin_body

\begin_layout Title
Foam Filtration Research Final Report
\end_layout

\begin_layout Author
Michelle Gostic, Sarah Levine, Leah Meyerholtz
\end_layout

\begin_layout Date
31 July 2012
\end_layout

\begin_layout Section*
Introduction and Literature Review
\end_layout

\begin_layout Standard
A reticulated polyurethane foam filtration system combined with coagulant
 dosing has proven capable of providing clean, low-turbidity water; however
 the necessary addition of coagulant combined with a non-conventional cleaning
 method makes the foam filtration system inefficient and not ideal to be
 used on a municipal scale.
 For this reason, research on foam filtration methods have been geared towards
 engineering a portable and effective filtration unit to provide clean water
 to devastated areas in emergency situations.
 There is a great demand for such technology as proven by the 1994 Rwanda
 Crisis.
 In this case, 85-90% of deaths in refugee camps were caused by diarrhea
 [Toole and Waldman; Doocy and Burnham].
 Providing a low-cost, sustainable clean water source in emergency situations
 is the best way to prevent waterborne diseases and dehydration.
 The foam filtration team has worked towards designing an apparatus that
 will provide at least 15 liters of water per day per person, based on the
 UNHCR's (United Nations High Commissioner for Refugees) recommendations
 for refugee situations [UNHCR].
 The foam filter is small enough that it can be placed in the back of a
 pick up truck when needed and hooked up to the car's engine to harvest
 electricity needed to power the filtration process.
 
\end_layout

\begin_layout Standard
The current AguaClara foam filtration system utilizes a roughing and finishing
 filter to remove solid particles from influent water.
 Turbid water enters through the linear flow orifice meter (LFOM), which
 maintains a linear relationship between the water level and the flow rate
 of water through the system.
 Coagulant enters the LFOM in regulated doses to ensure consistent mixing
 of coagulant with influent water.
 The water flows through a 30 inch deep roughing filter, consisting of 30
 ppi (pores per inch) foam, and then through a 15 inch deep finishing filter,
 consisting of 90 ppi foam.
 Before effluent water leaves the system, it is dosed with chlorine and
 exits the supercritical flow tube.
 Previous tests showed that head loss from the foam filters was negligible,
 but recent experimentation with an open system has proven otherwise.
 
\end_layout

\begin_layout Standard
Due to the head loss and effluent turbidity standards, the foam filters
 need to be cleaned.
 A 
\begin_inset Quotes eld
\end_inset

plunger
\begin_inset Quotes erd
\end_inset

 method of cleaning has proven to be an efficient and easy way to clean
 the foam filters.
 A long pole with a porous disc attached to one end is used to compress
 the foam and release solid particles trapped in the filters.
 This method is similar to squeezing out a dirty kitchen sponge.
 During the cleaning process, the foam must remain submerged in water to
 prevent the entrainment of air bubbles that would hinder filter performance.
 After plunging, the dirty water and released sediment flow out of exit
 valves located downstream of each filter.
 
\end_layout

\begin_layout Standard
At the 2012 National Sustainable Design Expo in Washington D.C.
 the AguaClara team showed that the foam filter system is effective in removing
 particles from water at relatively high turbidities; however, data from
 these tests does not give concrete evidence of the filter's performance
 in terms of realistic applications.
 At the expo, the turbidimeter was not properly calibrated, thus the data
 collected is not 100% accurate.
 Additionally, the filters were cleaned every 4 hours.
 Although this proved that the filters could return to their initial performance
 level after being cleaned via the plunger method, cleaning every 4 hours
 may be either too frequent or infrequent to maintain a high volume of treated
 water with acceptable effluent turbidity, in an emergency situation it
 is essential to maximize the volume of usable water while still maintaining
 quality standards.
 Effluent at the expo was dosed with clay and recycled so that the effluent
 became the influent.
 There is a possibility that coagulant built up in the filter columns, due
 to the recycle, improved performance beyond what it would have been in
 a more realistic experiment.
\end_layout

\begin_layout Standard
As a new and relatively unexplored technology, there is much research to
 be done in the realm of foam filtration.
 Our current and future research will focus on providing extensive data
 as to the performance of the foam filtration system at different turbidities
 as well as identifying more efficient cleaning cycles.
 
\end_layout

\begin_layout Standard
The World Health Organization included significantly reducing the number
 of 
\begin_inset Quotes eld
\end_inset

people without sustainable access to safe drinking-water and sanitation
\begin_inset Quotes erd
\end_inset

 in its list of 15 Millennium Development Goals [WHO].
 Refining the foam filtration system has the potential to contribute to
 achieving this goal in addition to providing clean water to those who need
 it the most.
 
\end_layout

\begin_layout Section*
Materials and Methods
\change_inserted 109193216 1343841548

\end_layout

\begin_layout Standard
The foam filtration team has modified the original system prototype, which
 was demonstrated at the EPA National Sustainable Design Expo, in order
 to prepare it for extended testing and data analysis.
 As seen in Figure 
\change_deleted 109193216 1343841546
1
\change_inserted 109193216 1343841546

\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Original-Foam-Filter"

\end_inset


\change_unchanged
, the original apparatus consisted of two reticulated polyurethane foam
 filter columns mounted on an aluminum frame and connected by flexible tubing.
 However, due to high head loss, we could not run tests to breakthrough
 (effluent turbidity greater than 0.3 NTU) because the columns were too short.
 As such, we replaced the shorter columns with taller ones to allow longer
 tests.
 Additionally, ball valves were installed at the base of each column to
 facilitate cleaning.
 The modified apparatus is seen in Figure 
\change_deleted 109193216 1343841530
2
\change_inserted 109193216 1343841530

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LatexCommand ref
reference "fig:Modified-Foam-Filter"

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\change_unchanged
.
 The flow rate to be provided by the apparatus was calculated, as shown
 in Figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Apparatus-Flow-Rate"

\end_inset

, to be just under 3 L/min.
 
\end_layout

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\begin_inset Caption

\begin_layout Plain Layout
Original Foam Filter Apparatus
\change_inserted 109193216 1343841506

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name "fig:Original-Foam-Filter"

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\begin_inset Caption

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Modified Foam Filter Apparatus
\change_inserted 109193216 1343841522

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Apparatus Flow Rate Calculation 
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\end_layout

\begin_layout Standard
For the experiments, clean influent tap water is pumped via submersible
 pump from a bucket to the Linear Flow Orifice Meter (LFOM).
 Water is continuously supplied to the bucket from the sink, and a float
 valve installed in the bucket prevents overflow.
 In the LFOM, the water combines with clay and coagulant, at stock concentration
s of 20 g/L and 3.2 g/L respectively, each pumped into the LFOM from separate
 buckets with a peristaltic pump.
 The influent turbidities are controlled by increasing or decreasing the
 flow rate of the dosing pump.
 The dosing pump is set at a specific rate in order to control the amount
 of clay and coagulant that is added to influent water in order to reach
 a desired turbidity.

\change_inserted 1000245830 1343922248
 
\change_unchanged
The mixture will flow through the 30 ppi roughing filter, the 90 ppi finishing
 filter, and exit through the supercritical flow pipe to a drain.
 To properly test the effectiveness of the system and prevent buildup of
 coagulant in the filters, the effluent water is not recycled.
 
\end_layout

\begin_layout Standard
Three turbidimeters have been connected to the apparatus to monitor the
 turbidity of the water as it flows through the system.
 The first is attached to the tube connecting the LFOM to the roughing filter,
 and measures the turbidity of the influent water.
 The second draws from the tube connecting the roughing and finishing filters
 to measure the intermediate turbidity of the water.
 The third turbidimeter is attached to the tube above the supercritical
 flow pipe, and records the effluent turbidity.
 Water is pumped through these turbidimeters by a peristaltic sampling pump.
 
\end_layout

\begin_layout Standard
One hole has been drilled into the side of each filter, just above the fully
 extended height of the foam, where pressure sensors are attached.
 This will allow the increase in head loss to be tracked over the course
 of filtration cycles.
 This data will help determine if head loss is an acceptable indicator of
 when the filters should be cleaned.
 The turbidity and head loss data will be recorded in Process Controller
 for each experiment.
 Figure 
\change_deleted 109193216 1343843033
3
\change_inserted 109193216 1343843033

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 shows a more detailed schematic of how the system is set up.
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	filename Screen shot 2012-07-06 at 12.34.50 PM.png
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Schematic of Apparatus Connections
\change_inserted 109193216 1343843026

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\begin_layout Standard
After about four weeks of testing influent turbidities ranging from 100NTU
 to 450 NTU, the performance level of the 90 ppi foam dropped drastically
 and failed to treat the effluent to below 0.3 NTU.
 For consistency, all three foam parts were replaced.
 Three rectangular foam blocks (two 30 ppi and one 90 ppi) were cut with
 a band saw and smoothed with a razor blade until they were circular.
 Holes for the plastic handles were drilled about an inch from the top of
 each block, then they were reinserted into the filter columns.
 Figure 
\change_deleted 109193216 1343843293
4
\change_inserted 109193216 1343843293

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reference "fig:Foam-Filters-Before"

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\change_unchanged
 shows the foam before and after cutting.
 
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Foam Filters Before & After Cutting
\change_inserted 109193216 1343843287

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\change_unchanged

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\end_inset


\end_layout

\begin_layout Standard
Upon the conclusion of three 450 NTU performance tests, about a week was
 spent studying the cleaning process and evaluating its effectiveness.
 The roughing and finishing filters are cleaned with a 
\begin_inset Quotes eld
\end_inset

plunger,
\begin_inset Quotes erd
\end_inset

 or a long pole with a flat, circular head.
 Holes evenly spaced around the outside of the head enable water flow during
 plunging, allowing the foam to remain completely submerged and thus preventing
 air pockets from forming during the cleaning cycle.
 The plunger is used to compress the filter, forcing clay particles out
 of the foam and through the valves at the bottom of the apparatus.
 Figure 
\change_deleted 109193216 1343843360
5
\change_inserted 109193216 1343843360

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\change_unchanged
 shows a head-on view of the plunger.
 
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	filename Screen shot 2012-07-31 at 11.50.06 AM.png
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\begin_inset Caption

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Topside View of the Plunger Head
\change_inserted 109193216 1343843354

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\end_inset


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\end_inset


\end_layout

\begin_layout Standard
To evaluate the cleaning process, a single test was conducted for three
 days with an influent turbidity of 450 NTU.
 Instead of running the filter to breakthrough, the roughing filter was
 cleaned as soon as the roughing filter effluent reached 5% of the influent
 turbidity, about 22.5 NTU.
 The finishing filter was not cleaned until the conclusion of the test.
 Using this method, the length of a 450 NTU test was extended by essentially
 combining multiple 2 hour 450NTU tests in succession.
 
\end_layout

\begin_layout Section*
Results and Analysis
\end_layout

\begin_layout Subsection*
Filtration Performance
\end_layout

\begin_layout Standard
Thus far, we have completed a series of tests at 100 NTU, 200 NTU, and 450
 NTU, in addition to an extended test at 450 NTU to assess the effectiveness
 of an alternate method of cleaning.
 We recorded data for the influent and effluent turbidities for both the
 roughing filter and finishing filter, pC* values to compare efficiencies,
 and the length of each test.
 The unit pC* serves as an effective measurement of filter performance and
 is calculated by taking the negative log of the effluent turbidity over
 the influent turbidity.
 This information is presented in Table 
\change_deleted 109193216 1343844999
1
\change_inserted 109193216 1343844999

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LatexCommand ref
reference "tab:Comparison-of-Experiments"

\end_inset


\change_unchanged
.
 Time and head loss values in the table are recorded at breakthrough of
 the finish filter, when effluent turbidity exceeds 0.3 NTU.
 After each filter cleaning cycle, the effluent turbidity and head loss
 in both columns appear to return to pre-test levels.
 
\end_layout

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Comparison of Experiments to Date
\change_inserted 109193216 1343844992

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<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
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23.37
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\begin_layout Plain Layout
4.01
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7
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<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
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450NTU
\end_layout

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1h 23m
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25.60
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11.13
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\begin_layout Plain Layout
4.02
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8
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450NTU
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1h 25m
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27.15
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10.46
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\begin_layout Plain Layout
4.02
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9
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1000NTU
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50m
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20.74
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10.90
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4.05
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</lyxtabular>

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Subsection*
Head Loss and Cycle Timing 
\end_layout

\begin_layout Standard
To a large extent, the tests performed this summer have determined how often
 the components will require cleaning independent of a turbidity test, but
 further testing will be required to refine these boundaries.
 With unreliable electricity and less precise handheld turbidity meters
 in the field, it would be useful for an operator to be able to rely on
 visual cues like color of the filter columns or head loss as flocs build
 up in the filter bed to know when the filter media needs cleaning.
 As more particles accumulate in the reticulated polyurethane foam, the
 effluent will eventually have a higher turbidity.
 The columns will appear muddier and there will be additional head loss
 as pores in the foam become clogged.
 The goal was for one of these cues to be obvious and predictable enough
 that an operator would not need a turbidity meter to know when a column
 needs cleaning.
 However, based on the difference in head loss between the 450 NTU, 200
 NTU, and the 100 NTU tests that have been performed so far, head loss may
 not be a viable indicator.
 
\end_layout

\begin_layout Standard
Figure 
\change_deleted 109193216 1343846668
6
\change_inserted 109193216 1343846668

\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Influent,-Roughing,-and"

\end_inset


\change_unchanged
 shows the influent, roughing filter, and finishing filter turbidities throughou
t one test, including during the cleaning process at the end.
 For an influent of 200 NTU, the roughing filter functioned for about 45
 minutes, until it became too clogged with clay.
 After the roughing filter effectively stopped working, the finishing filter
 continued to provide an effluent below the US EPA potable water standard
 of 0.3 NTU for another 45 minutes, for a total of roughly 1.5 hours of effective
 filtering.
 Figure 
\change_deleted 109193216 1343846824
7
\change_inserted 109193216 1343846824

\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Roughing-and-Finishing-1"

\end_inset


\change_unchanged
 shows the head loss data captured by our pressure sensors for the same
 test.
 Head loss in the roughing filter was about 15 cm and increased linearly
 during the entire test.
 Head loss in the finishing filter was minimal until the roughing filter
 was no longer functioning, then built up quickly and at the end of the
 test was approximately 20 cm.
 After cleaning the filters, which occurred at just under 2 hours into the
 test, the water heights in both filter columns returned to the level consistent
 with clean bed head loss.
 This means that the plunger cleaning method is effective and is capable
 of returning the foam to its original filtration capacity after each test.
 
\end_layout

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

\begin_layout Plain Layout
\align center
\begin_inset Graphics
	filename Screen shot 2012-07-06 at 12.35.54 PM.png
	lyxscale 80
	scale 50

\end_inset


\begin_inset Caption

\begin_layout Plain Layout
Influent, Roughing, and Finishing Turbidities for a 200 NTU Test
\change_inserted 109193216 1343846645

\begin_inset CommandInset label
LatexCommand label
name "fig:Influent,-Roughing,-and"

\end_inset


\change_unchanged

\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout
\align center
\begin_inset Graphics
	filename Screen shot 2012-07-06 at 12.36.01 PM.png
	lyxscale 80
	scale 50

\end_inset


\begin_inset Caption

\begin_layout Plain Layout
Roughing and Finishing Head Loss for a 200 NTU Test
\change_inserted 109193216 1343846813

\begin_inset CommandInset label
LatexCommand label
name "fig:Roughing-and-Finishing"

\end_inset


\change_unchanged

\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
The tests with an influent turbidity of 100 NTU lasted about 7-8 hours,
 which is 4 times the length of a 200 NTU test.
 Breakthrough in the roughing filter did not occur for between 4 and 8.5
 hours.
 Additionally, some tests had to be stopped before breakthrough because
 the roughing filter column was not tall enough to accommodate terminal
 head loss.
 Head loss in the finishing filter ranged from 11 to 20 cm at the end of
 the tests.
 Figure 
\change_deleted 109193216 1343849770
8
\change_inserted 109193216 1343849770

\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Influent,-Roughing-Filter,-1"

\end_inset


\change_unchanged
 shows the influent and effluent turbidities for the 100 NTU tests and Figure
 
\change_deleted 109193216 1343849819
9
\change_inserted 109193216 1343849819

\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Roughing-and-Finishing-1"

\end_inset


\change_unchanged
 shows the head loss traces.
 These results differ significantly from the results of the 200 NTU tests,
 although the effluent turbidity from the roughing filter is similar and
 the head loss is linear, which is consistent with depth filtration theory
 and the 200 NTU test results.
 Additionally, particles had visibly penetrated the roughing and finishing
 filters more deeply (causing the foam to appear muddier to a greater depth)
 during the 100 NTU test than during the 200 NTU test.
 
\end_layout

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

\begin_layout Plain Layout
\align center
\begin_inset Graphics
	filename 100ntu graphs.bmp
	lyxscale 60
	scale 45

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Influent, Roughing Filter, and Finishing Filter Turbidities for Three 100
 NTU Tests
\change_inserted 109193216 1343849764

\begin_inset CommandInset label
LatexCommand label
name "fig:Influent,-Roughing-Filter,"

\end_inset


\change_unchanged

\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout
\align center
\begin_inset Graphics
	filename 100ntu graph2.bmp
	lyxscale 50
	scale 55

\end_inset


\begin_inset Caption

\begin_layout Plain Layout
Roughing and Finishing Filter Head Loss for Three 100 NTU Tests
\change_inserted 109193216 1343849804

\begin_inset CommandInset label
LatexCommand label
name "fig:Roughing-and-Finishing-1"

\end_inset


\change_unchanged

\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
It is interesting to note that the 450 NTU tests each lasted a little less
 than two hours, longer than the 200 NTU tests although it was predicted
 that because of the heavier particle loading the tests would be much shorter.
 Breakthrough in the roughing filter occurred around 45 minutes into the
 test again, while the finishing filter continued to maintain 0.3 NTU effluent
 for about an hour after that.
 With each test, finishing filter head loss was an average of 15 cm and
 returned to clean bed head loss after plunging.
 Roughing filter head loss also returned to clean bed head loss after each
 cleaning cycle, but increased from 15 cm in the first test to 25 cm in
 the last test, potentially indicating a buildup of particles in the foam
 that increased the collision potential of particles in later tests.
 As expected, penetration of particles was more concentrated towards the
 top of each column of foam than in the 100 NTU and 200 NTU tests.
 Figure 
\change_deleted 109193216 1343850580
10
\change_inserted 109193216 1343850580

\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Influent,-Roughing-Filter,-1"

\end_inset


\change_unchanged
 shows the influent and effluent turbidities for the roughing and finishing
 filters and Figure 
\change_deleted 109193216 1343850588
11
\change_inserted 109193216 1343850588

\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Roughing-and-Finishing-2"

\end_inset


\change_unchanged
 shows the head loss for the 450 NTU test.
\end_layout

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

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout
\align center
\begin_inset Graphics
	filename Screen shot 2012-07-31 at 3.33.38 PM.png
	lyxscale 50
	scale 60

\end_inset


\begin_inset Caption

\begin_layout Plain Layout
Influent, Roughing Filter, and Finishing Filter Turbidities for Three 450
 NTU Tests
\change_inserted 109193216 1343850559

\begin_inset CommandInset label
LatexCommand label
name "fig:Influent,-Roughing-Filter,-1"

\end_inset


\change_unchanged

\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout
\align center
\begin_inset Graphics
	filename All 450NTU Head Loss.bmp
	lyxscale 50
	scale 60

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Roughing and Finishing Filter Head Loss for Three 450 NTU Tests
\change_inserted 109193216 1343850566

\begin_inset CommandInset label
LatexCommand label
name "fig:Roughing-and-Finishing-2"

\end_inset


\change_unchanged

\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
In order to assess the lifecycle of the foam in the context of continuous
 use and to take advantage of the two-step filtration process, a test was
 run with an influent turbidity of 450 NTU in which the roughing filter
 was cleaned when effluent turbidity reached 5% of influent turbidity (22
 NTU).
 Instead of requiring clean water to flush the system after cleaning, the
 influent turbidity was maintained at 450 NTU.
 As such, no clean water was necessary for flushing the foam, which increases
 the volume of water the filter can produce.
 Additionally, the filter was only offline for the time it took the finishing
 effluent turbidity to descend below 0.3 NTU, which may be a consistent enough
 time that turbidity measurements in the field will not be required.
 Figure 
\change_deleted 109193216 1343850846
12
\change_inserted 109193216 1343850846

\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Influent,-Roughing-Filter,-2"

\end_inset


\change_unchanged
 shows the influent and effluent turbidity for both the roughing and finishing
 filter during this test.
 It was not necessary to clean the finishing filter at all during the time
 the test was conducted.
 After each cleaning cycle, clean bed head loss was nearly achieved as shown
 in Figure 
\change_deleted 109193216 1343851052
13
\change_inserted 109193216 1343851052

\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Roughing-and-Finishing-3"

\end_inset


\change_unchanged
.
 pC* remained consistent and consistently high for the entirety of the test.
 While these results are not conclusive, they provide a basis for further
 and longer testing of cleaning the columns one at a time before breakthrough
 is achieved.
 Doing so will provide insight into the actual life of the foam in continuous
 use and the feasibility of using head loss as an indicator of breakthrough
 before it occurs.
 It will also provide an environment conducive to testing the effectiveness
 of an external cleaning cycle to dislodge particles that build up in the
 foam that cannot be removed simply by plunging in the event that the foam
 could be reused.
\end_layout

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

\begin_layout Plain Layout
\align center
\begin_inset Graphics
	filename Cleaning Cycle Turbidity.bmp
	lyxscale 50
	scale 70

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Influent, Roughing Filter, and Finishing Filter Turbidities for the Alternative
 Cleaning Cycle Test
\change_inserted 109193216 1343850836

\begin_inset CommandInset label
LatexCommand label
name "fig:Influent,-Roughing-Filter,-2"

\end_inset


\change_unchanged

\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout
\align center
\begin_inset Graphics
	filename Cleaning Cycle Head Loss.bmp
	lyxscale 50
	scale 70

\end_inset


\begin_inset Caption

\begin_layout Plain Layout
Roughing and Finishing Filter Head Loss for the Alternative Cleaning Cycle
 Test
\change_inserted 109193216 1343851037

\begin_inset CommandInset label
LatexCommand label
name "fig:Roughing-and-Finishing-3"

\end_inset


\change_unchanged

\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Subsection*
Durability of Filter Media 
\end_layout

\begin_layout Standard
While previous semesters' research and the few weeks of tests performed
 this summer have shown that filter performance returns to the high initial
 levels of performance after cleaning, wear on the reticulated polyurethane
 foam in long-term performance must be accounted for.
 Not all particles will necessarily be washed out during cleaning, and removal
 of particles may decline over the filter's life as cleaning and particle
 bombardment compromise the foam structure.
 Additionally, cleaning may fail to remove enough particles to return the
 filter to initial performance as an increasing number of particles remain
 trapped in the foam cells.
 Mechanical breakdown will determine how often the components need to be
 replaced, which is important for maintaining filters in working order.
 This occurred after the 200 NTU, one 450 NTU, and three 100 NTU tests.
 A 450 NTU test was run followed by a 100 NTU test, after which the effluent
 turbidity was unacceptably high even after extensive cleaning.
 This may have been caused by the high particle loading from the 450 NTU
 test in addition to the deep particle penetration of the 100 NTU test.
 Effluent turbidity of the beginning and end of the third 100 NTU test is
 visibly higher than previous tests (see Figure 
\change_deleted 109193216 1343851383
8
\change_inserted 109193216 1343851383

\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Influent,-Roughing-Filter,"

\end_inset


\change_unchanged
).
 The foam was replaced and another 100 NTU test was run, which lasted much
 longer and exhibited slightly better performance.
 Afterwards, we ran two more 450 NTU tests and a 1000 NTU test followed
 by another 100 NTU test.
 Performance appeared consistent, with a return to clean bed head loss and
 no noticeable impact on cycle time.
 
\end_layout

\begin_layout Standard
In addition to the mechanical considerations, it must be determined if reticulat
ed polyurethane foam is a safe filter medium - i.e.
 whether it resists chemical breakdown that will lead to unsafe compounds
 in the clean effluent.
 However, reticulated polyurethane foam (like PVC pipe) is known to be a
 stable and durable material.
 Thus, the performance of the filter is not expected to mechanically or
 chemically decline noticeably over the course of these tests or during
 the type of short-term, intense use the filter would be subjected to in
 the field.
 It may be of note that in previous tests the effluent water has had clay
 added to it and has been recycled as the influent so that coagulant may
 have built up in the filter columns and improved performance by facilitating
 the formation of flocs.
 But longer tests with multiple cleanings that avoid recycle of water have
 have shown that with respect to pC* the mechanical durability of the foam
 filtration unit is not affected after ripening by a lower dose of influent
 coagulant on this scale.
\end_layout

\begin_layout Section*
Conclusions
\end_layout

\begin_layout Standard
Reticulated polyurethane foam has shown to be an effective filter medium
 for the range of turbidities that have been tested this summer.
 We expect that any future tests will support this conclusion.
 The lifespan of the filter appears to be about 1 month at a range of turbiditie
s with regular use, and the plunger method appears to be effective at cleaning
 the foam for the entirety of this lifecycle.
 
\end_layout

\begin_layout Standard
Filter runtimes can be extended if the roughing filter is cleaned whenever
 the roughing filter turbidity reaches 1-5% of the influent turbidity instead
 of when it breaks through into the finishing filter.
 Water cannot be filtered by the finishing filter while the roughing filter
 is cleaned, since all water passing through the roughing filter is drained;
 however this method is still beneficial as it reduces how frequently the
 finishing filter requires cleaning.
 
\end_layout

\begin_layout Standard
We do not believe at this time that head loss is a viable indicator of when
 the filter should be cleaned.
 As seen above in Table 1, the terminal head loss depends on both the influent
 turbidity and the condition of the foam over the course of its lifecycle.
 
\end_layout

\begin_layout Section*
Future Work
\end_layout

\begin_layout Standard
Although substantial data has been acquired pertaining to the foam filter's
 performance and the effectiveness of the plunger cleaning method, there
 are still many unanswered questions.
 Future foam filtration teams should run additional experiments using the
 alternative cleaning method in which the roughing filter is plunged as
 soon as it reaches 5% of the influent turbidity, rather than plunging both
 filters when the finishing filter reaches breakthrough (0.3 NTU).
 Comparing data regarding the alternative cleaning method to that regarding
 the original cleaning method may reveal which method is most effective
 and efficient, and whether the alternative cleaning cycle extends the foam's
 lifespan.
 
\end_layout

\begin_layout Standard
Future generations of foam filtration teams should make observations that
 may shed light on the long-term durability of the foam filters.
 The Summer 2012 team replaced the foam after approximately four weeks of
 testing influent water at varying turbidities.
 Future teams should continue to monitor the long-term life span of the
 foam to assess how long a foam column would last in the field.
 Further work will also be required to determine how many hours of continual
 use our life cycle tests are equivalent to and whether this number will
 be consistent for use in the field, which will be possible with the new
 type of cleaning test that began at the end of the summer.
 In addition to knowing how long the foam will last in the column, future
 teams should look into the usefulness of an external cleaning cycle for
 the foam in the event that it can be more thoroughly washed than with the
 plunger in the column in order to dislodge more particles so that foam
 can be reused.
\end_layout

\begin_layout Standard
Another focus of future teams should be identifying a physical indicator
 of the end of a filter cycle so operators will know when the columns need
 to be plunged.
 We originally thought that head loss depth or color might serve as indicators
 of breakthrough in a filter column; however, we found that color is too
 subjective and head loss appears to vary significantly with each influent
 turbidity tested.
 Without adequate turbidimeters in the field, we do not believe that head
 loss or color serve as viable indicators if the filters are to be operated
 in the way we have run our tests.
 
\end_layout

\begin_layout Standard
To ensure that the foam filter provides clean, safe drinking water, future
 work should be done to assess whether the mechanical and chemical breakdown
 of the foam releases harmful chemicals into effluent water.
 Although reticulated polyurethane foam is know to be stable and safe (like
 PVC), the blowing agent used in manufacturing the foam may be retained
 in the cells of the foam and wash out during a certain time at the beginning
 of the foam's life cycle.
 Work should be done to determine which compounds and at what concentration
 are coming out of the filter columns.
 This can be done by assessing water samples from the foam columns we replaced
 and the foam currently in the apparatus with a gas chromatograph.
 The company that manufactures the foam, New England Foam Inc.
 will have to be contacted to determine what blowing agent is used and whether
 it will present concerns.
\end_layout

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

\end_inset

 Howard, G.
 (2003).
 Domestic water quantity, service level and health.
 World Health Organization, , 1-39.
\end_layout

\begin_layout Bibliography
\labelwidthstring References
\begin_inset CommandInset bibitem
LatexCommand bibitem
label "Toole and Waldman"
key "key-5"

\end_inset

Toole M, Waldman R.
 THE PUBLIC HEALTH ASPECTS OF COMPLEX EMERGENCIES AND REFUGEE SITUATIONS.
 Annual Review Of Public Health [serial online].
 April 1997;18(1):283.
 Available from: Academic Search Alumni Edition, Ipswich, MA.
 Accessed February 23, 2012.
\end_layout

\begin_layout Bibliography
\labelwidthstring References
\begin_inset CommandInset bibitem
LatexCommand bibitem
label "Doocy and Burnham"
key "key-7"

\end_inset

Doocy S, Burnham G.
 Point-of-use water treatment and diarrhoea reduction in the emergency context:
 an effectiveness trial in Liberia.
 Tropical Medicine & International Health [serial online].
 October 2006;11(10):1542-1552.
 Available from: Academic Search Alumni Edition, Ipswich, MA.
 Accessed February 23, 2012.
\end_layout

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

\end_inset

 Stafford, D.M.
 (1992).
 Water manual for refugee situations.
 Program and Technical Support, United Nations High Commissioner for Refugees
 (UNHCR), , 1-84.
\end_layout

\end_body
\end_document
