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\begin_body

\begin_layout Title
AguaClara POU (Foam Filtration) Challenges
\end_layout

\begin_layout Abstract
Reticulated polyurethane foam with 90 ppi (pores per inch) has been shown
 to be an efficient filter for removal of turbidity from clay.
 The high filtration rate of up to 6 mm/s means that a very small filter
 would be adequate for a Point of Use, POU, application.
 The goal is to design a POU water treatment system that is easy to use,
 reliable, and cost effective.
 This treatment system will be an entire AguaClara facility in miniature.
 It will require alum or PACl to improve particle removal and will include
 flocculation, sedimentation, filtration, and disinfection.
 The AguaClara POU must be easy to use, easy to clean and provide safe drinking
 water even when given high turbidity water.
\end_layout

\begin_layout Abstract
This AguaClara POU could also be a design for a community water kiosk.
 
\end_layout

\begin_layout Labeling
\labelwidthstring 00.00.0000
Students 3 (this team size could be expanded given the broad scope of the
 project)
\end_layout

\begin_layout Labeling
\labelwidthstring 00.00.0000
Skills fluids, AguaClara water treatment processes, process controller,
 fabrication
\end_layout

\begin_layout Section
Introduction
\end_layout

\begin_layout Standard
Porous media depth filtration for POU has been limited to two types of filters,
 
\begin_inset CommandInset href
LatexCommand href
name "intermittent slow sand filters"
target "http://www.cawst.org/en/themes/biosand-filter"

\end_inset

 (ISSF) and 
\begin_inset CommandInset href
LatexCommand href
name "clay pot filters"
target "http://www.filtersfast.com/blog/index.php/2010/07/filterpure-distributes-clay-pot-water-filters-to-developing-nations/"

\end_inset

 (CPF).
 The ISSF are large, heavy, and have poor hydraulic designs that result
 in poor performance.
 The CPF are smaller, are inexpensive, and are prone to breakage.
 Both ISSF and CPF are limited in their ability to treat very turbid waters.
 The 
\begin_inset CommandInset href
LatexCommand href
name "PUR"
target "http://www.purpurifierofwater.com/"

\end_inset

 system of water treatment is essentially a flocculation/sedimentation method.
 The AguaClara POU system is a combination of flocculation/sedimentation
 and porous media filtration.
 The goal is to create a method that requires fewer steps by the user than
 PUR (see the 
\begin_inset CommandInset href
LatexCommand href
name "movie"
target "http://www.purpurifierofwater.com/downloads/pur_water.wmv"

\end_inset

of the PUR process).
 The user should only have to pour the dirty water into the raw water bucket,
 add a tiny scoop of granular PACl, stir briefly, and add a few drops of
 chlorine (liquid bleach) to the treated water bucket.
 The filter system should deliver the clean water to the treated water bucket
 in a reasonable amount of time.
\end_layout

\begin_layout Standard
Previous foam filtration work has focused on showing that foam filtration
 (FF) is an effective filter media.
 Now that we have documented that the foam works well in a controlled laboratory
 setting it is time to begin testing and evaluating prototypes that contain
 all of the unit processes.
 The primary challenges for taking this technology to implementation are
 to create a simple, robust, hydraulic design that controls flow rates,
 prevents filter collapse, prevents air entrapment in the filter, and is
 easy to maintain.
 
\end_layout

\begin_layout Standard
One of the challenges with ISSF, CPF, and FF is to provide a cleaning method
 that minimizes the risk of contaminating the filtered water after cleaning.
 Stacked Rapid Sand Filtration (SRSF) provides a mechanism to automate the
 filter media cleaning process, but it also has the risk of contaminating
 filtered water immediately after cleaning.
 
\end_layout

\begin_layout Standard
It would be useful to consider the foam filtration as a component of a complete
 AguaClara plant in miniature.
 This miniature plant will operate in batch mode to simplify chemical addition
 and eliminate the need for chemical dosers.
 The miniature plant will likely incorporate tube flocculation and a tube
 settler prior to filtration.
 The tube settler will have a sludge trap with a sludge drain.
 
\end_layout

\begin_layout Section
Design Strategy
\end_layout

\begin_layout Standard
Create a detailed Mathcad worksheet with design equations for each unit
 process.
 Create equations for all relevant dimensions.
 
\end_layout

\begin_layout Subsection
Flow Rate and Hydraulic Design
\end_layout

\begin_layout Standard
Determine a target flow rate (perhaps 20 L in 30 minutes for the POU device)
 so that 1 hour later the finished water has all had at least 30 minutes
 of contact time with the chlorine.
 The target flow rate for the demonstration unit could be approximately
 1 mL/s.
 Create a preliminary hydraulic design and estimate the flow rate variability
 due to the decreasing water level in the raw water bucket.
 Note that this flow variability can be reduced by increasing the head loss
 through the POU device.
 The tradeoff is that increased head loss will require increased elevation
 of the raw water bucket.
 Evaluate hydraulic designs that will minimize flow variation through the
 filter.
 Explore methods to eliminate spilling of treated water when the treated
 water container fills.
\end_layout

\begin_layout Subsection
Tube Flocculator
\end_layout

\begin_layout Standard
Design a tube flocculator to be as short as possible given the maximum flow
 rate predicted above.The velocity gradient, G, will likely be in the range
 of 30 to 100/s.
 We can explore the relationship between G and maximum floc size to determine
 the optimal value for G.
 
\end_layout

\begin_layout Standard
\begin_inset Formula 
\begin{equation}
\overline{G}=\frac{64Q}{3\pi D^{3}}\label{eq:G}
\end{equation}

\end_inset


\end_layout

\begin_layout Standard
The equation for G (equation 
\begin_inset CommandInset ref
LatexCommand ref
reference "eq:G"

\end_inset

) can be used to determine the optimal diameter of the flocculator.
 The collision potential for a laminar flow flocculator is proportional
 to the product of the velocity gradient and the residence time, 
\begin_inset Formula $\theta$
\end_inset

.
\end_layout

\begin_layout Standard
\begin_inset Formula 
\begin{equation}
G\theta=\frac{16L}{3D}\label{eq:Gt}
\end{equation}

\end_inset


\end_layout

\begin_layout Standard
The fractal flocculation model predicts that for 50 NTU water that 
\begin_inset Formula $G\theta$
\end_inset

 of 1400 would be adequate to produce 70 μm flocs and those flocs should
 be able to settle out with a capture velocity of 0.12 mm/s.
 Thus for demonstration purposes it may be adequate to use a relatively
 short residence time.
 Equation 
\begin_inset CommandInset ref
LatexCommand ref
reference "eq:Gt"

\end_inset

 can be solved for the length of the flocculator.
\end_layout

\begin_layout Section
Sedimentation tank
\end_layout

\begin_layout Standard
The sedimentation tank should be designed to to take advantage of a tube
 settler to reduce the size (and residence time) of the tank.
 The sedimentation tank should concentrate the flocs and have a method to
 drain the sludge.
\end_layout

\begin_layout Section
Preliminary Design
\end_layout

\begin_layout Standard
Create a preliminary design for an entire prototype POU unit including materials
, a realistic sketch, and reflection on how a homeowner would use the device.
\end_layout

\begin_layout Standard
Build the prototype and as you build the prototype evaluate methods to improve
 the design.
 Test the prototype under simulated real conditions.
 Evaluate for ease of use, ease of fabrication, release of unwanted air
 during start up, and cost.
 
\end_layout

\begin_layout Standard
Evaluate the tradeoff of flocculator length.
 Longer flocculators will make it possible to remove more particles with
 the sedimentation tank rather than with the filter.
\end_layout

\begin_layout Standard
Make sure to calculate flow rate through the filter as a function of time
 based on the imperfect flow control system and ensure that the filter is
 sized appropriately to handle the maximum flow rate.
\end_layout

\begin_layout Standard
Develop a method to add alum or PACl to the raw water bucket.
 
\end_layout

\begin_layout Standard
Find a source of foam.
 
\end_layout

\begin_layout Standard
Run a series of experiments with the prototype.
 This will show how well the unit actually works and if we can get the same
 performance achieved with the foam column experiments.
 These experiments will also help refine the design of the filter making
 it more user-friendly.
 These experiments should include a study regarding the long term structure
 and re-usability of the foam
\end_layout

\begin_layout Standard
Further investigate the possibility of using an alum or PACl pretreatment
 of the foam.
 This would eliminate the need for an alum doser in the POU unit.
 This research was begun in the fall of 2010 by Sarah Stodter, though more
 research needs to be done in order to make any conclusions.
\end_layout

\begin_layout Standard
Investigate the effect of natural organic matter (humic acid) on filter
 performance.
 
\end_layout

\end_body
\end_document
