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\begin_body

\begin_layout Title
Questions and challenges for the filter team to answer and surmount
\end_layout

\begin_layout Date
August 31th 2012
\end_layout

\begin_layout Section*
Background
\end_layout

\begin_layout Standard
Filtration is the final step in water treatment before the clean water is
 chlorinated and sent to the distribution system.
 Stacked Rapid Sand Filtration makes used of a sand bed to remove the remaining
 particles at the end of the treatment process in an efficient manner.
 Unlike conventional Rapid Sand Filters, the SRSF uses multiple layers of
 sand and injection points to enable the filter to be backwashed using the
 same driving head that runs it during filtration.
 This eliminates the need for pumps, elevated storage tanks, and reduces
 the number of filters necessary to treat a given flow rate.
 
\end_layout

\begin_layout Standard
The possible flow rates in a given filter are dictated by the necessary
 backwash velocity to fluidize the sand bed and expand it by 15%.
 The dimensions of the filter are then dictated by the area necessary to
 achieve that backwash velocity at a given flow rate.
 Current filter dimensions are constrained by the area necessary in the
 filter bay for a person to move around to install and service the internal
 parts in the filter.
 This limits area of the filter to something on the order of a box 0.75 m
 on a side.
 The filter requires a backwash velocity of approximately 11 mm/s, this
 means that the lowest flow rate the current filter design can treat is
 about 6 l/s (
\begin_inset CommandInset ref
LatexCommand ref
reference "Adelman et. al."

\end_inset

).
 
\end_layout

\begin_layout Section*
Scope of the project
\end_layout

\begin_layout Standard
There is a strong demand for plants with flow rates on the order of 3 l/s.
 Because of the constraints on dimensions, it is not possible to build a
 viable filter for that flow rate using current fabrication techniques.
 The Low Flow Stacked Rapid Sand Filter prototype is built from 12
\begin_inset Quotes erd
\end_inset

 PVC pipe and can handle a maximum flow of 0.8 l/s.
 Several of these filter could be connected in parallel to accommodate a
 range of low flow plants.
 It may also be possible for the filter to operate as a stand alone treatment
 option if high quality influent water is available.
 
\end_layout

\begin_layout Standard
While construction on the filter is mostly complete, the testing apparatus
 still needs to be designed and built and then the filter must be tested
 and refined in time for the January 2013 trip to Honduras.
 The filter needs extensive testing before we can install it in a plant,
 this will include hydraulic testing to ensure that it operates in the way
 we intend it to.
 There will also need to be performance testing to ensure that it is effective
 in treating water and causes better performance in a plant.
 Finally the filter will need to undergo failure testing to find out what
 its limits of operation are and what possible failure modes might be encountere
d in the field.
\end_layout

\begin_layout Standard
The prototype filter was constructed during the summer of 2012 and made
 use of a variety of new techniques and construction methods.
 Many of these methods were developed as needed and were only developed
 as far as the 
\begin_inset Quotes eld
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works-well-enough
\begin_inset Quotes erd
\end_inset

 stage.
 While these techniques might be appropriate for the construction of a prototype
, they deserve more refinement before they are put to use making production
 scale filters.
 Materials, construction techniques, and designs should all be scrutinized
 and evaluated, then improved on if possible.
 
\end_layout

\begin_layout Standard
The filter may also have commercial applications outside of sustainable
 water treatment.
 If time permits, the filters performance should be tested for a variety
 of commercial applications including agriculture, aquaculture, remote water
 treatment, and industrial applications.
\end_layout

\begin_layout Part*
Challenges
\end_layout

\begin_layout Section
Hydraulic Testing
\end_layout

\begin_layout Standard
The filter still requires some work before it is ready for testing.
 The first area is the flow control coming from the hydraulic test facility.
 The flow rates are not currently high enough because there is too much
 headloss in the delivery pipe.
 The flexible tubing should be replaced with 2
\begin_inset Quotes erd
\end_inset

 PVC and hydraulic analysis should be done to see if it is worth switching
 from a 1
\begin_inset Quotes erd
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 ball valve to a 2
\begin_inset Quotes erd
\end_inset

 ball valve as the control device.
 Once a control system has been set up that can reliably provide 0.8 l/s,
 the filter should be filled with sand, then hydraulic testing can begin
 in earnest.
 The following areas should be investigated:
\end_layout

\begin_layout Itemize
Headlosses should be measured during filtration and backwash.
 These headlosses are what determine the placement of inlet boxes, outlet
 boxes, and backwash outlets in the plant.
 These headlosses should be compared to our theoretical understanding of
 the filter to see if it is functioning as we expect.
 If it is not, the inconsistancies in headlosses should be investigated
 and it should be determined whether or not the filter is functioning properly
 or not and whether our theoretical understanding is correct.
\end_layout

\begin_layout Itemize
The relative heights of the backwash outlet and outlet free surface should
 be adjusted relative to the inlet pipe and the impact on the hydraulic
 stability of the filter assessed.
 This will help to determine how a filter might connect to the rest of the
 plant.
 
\end_layout

\begin_layout Itemize
Check and see how much, if any sand is lost during the backwash cycle.
 If there appear to be large sand losses, determine if there is a better
 way to operate the filter to avoid these losses, and if necessary, design
 and fabricate a sand trap to keep the filter from losing sand.
\end_layout

\begin_layout Itemize
investigate the control system for the filter (valves controlling backwash
 and indicators for bed fluidization and various water pressures) and assess
 their efficacy and easy of use.
 Propose changes if deemed necessary.
\end_layout

\begin_layout Itemize
(if time permits after filter performance has been tested) Analyze flow
 patterns through the sand bed using the pressure sensor ports along the
 filter body.
 Attempt to determine if there is an even distribution of flow between each
 layer.
 
\end_layout

\begin_layout Section
Performance Testing
\end_layout

\begin_layout Standard
Before we install the filter in a plant, we would like to know whether or
 not it is effective at improving water quality.
 To do this, a recirculating filter system will need to be constructed that
 can also backwash effectively.
 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Recirculating-filtration-test"

\end_inset

 shows a schematic for a testing apparatus using the existing hydraulic
 testing facility.
\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename test facility.pdf

\end_inset


\begin_inset Caption

\begin_layout Plain Layout
\begin_inset CommandInset label
LatexCommand label
name "fig:Recirculating-filtration-test"

\end_inset

Recirculating filtration test facility 
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset

 In order to backwash for six minutes, the filter will require approximately
 300 l of water.
 This water will be stored in reserve tanks which are connected to the bottom
 of the hydraulic test facility.
 During backwash, these reserve tanks will be emptied.
 The water will flow through the filter and out through the backwash pipe
 which will terminate in another 50-100 l tank.
 This tank will also contain a sump pump which will pump the backwashed
 water up over the bench and into the sink.
 PAC, clay, and Sodium Hydroxide (?) will be metered in at the inlet pipe
 using a peristaltic pump.
 The water will also be sampled at this point using a peristaltic pump and
 turbidimeter which will send data to process controller which will control
 the dosing to the system.
 There will also be a turbidimeter sampling from the outlet pipe to determine
 filter performance.
 Challenges and tasks for this stage of the project include:
\end_layout

\begin_layout Itemize
Construct the testing apparatus based on 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Recirculating-filtration-test"

\end_inset

.
 When building this system be sure to test that the sump pump removing water
 from the backwash tank can pump at least 0.8 l/s and that the sink can drain
 at the same rate.
 If the sink can not drain quickly enough, devise some method of water retention
 so that we do not flood the entire basement.
\end_layout

\begin_layout Itemize
Test the filter at a range of turbidities 
\begin_inset Note Note
status open

\begin_layout Plain Layout
not sure of the specific range, maybe 0.5 to 15 NTU or so?
\end_layout

\end_inset

and determine the length of time between backwash cycles, terminal headloss,
 and filter performance.
 If the flow distribution is not even amongst the sand layers during hydraulic
 testing, see if they even out during filtration.
 
\end_layout

\begin_layout Itemize
Determine whether or not the technology is ready to install in plants and
 if not, propose and test changes to the design that might improve performance.
\end_layout

\begin_layout Section
Improve on Construction Techniques
\end_layout

\begin_layout Itemize
Devise a way to drill the holes for the manifolds in the filter body without
 the use of a mill and potentially without the use of a drill press.
 Test the method on 6
\begin_inset Quotes erd
\end_inset

 pipe.
\end_layout

\begin_layout Itemize
improve on the way the manifolds are constructed.
 The current method (see construction documentation) is slow and labor intensive.
 It is also very difficult to drill the holes in the 1
\begin_inset Quotes erd
\end_inset

 pipe for the 1/2
\begin_inset Quotes erd
\end_inset

 slotted pipe.
 Try and come up with a better way to make that connection that does not
 reduce the total number of slots in each section of slotted pipe.
 
\end_layout

\begin_layout Itemize
The plastic end caps on the filter are likely to fail due to fatigue.
 Evaluate the possibility of using aluminum to make the caps, special care
 will have to be given to how the bed tester connects in this setup.
\end_layout

\begin_layout Itemize
Evaluate the cost and feasibility of constructing the filter out of aluminum
 or stainless steel.
 Does it make sense to move in that direction?
\end_layout

\begin_layout Section
The Mini Plant
\end_layout

\begin_layout Standard
The filter opens the door to another way of treating water.
 Mini plants would consist of a dosing system and a filter.
 Ideally these mini plants could easily be packaged in a crate and delivered
 to a site.
 All a community would need to do with one of these systems is connect the
 inlet to a spring with a low turbidity, connect the outlet to the distribution
 system, and provide some sort of drain for the backwash and they could
 have clean water.
 Coordinate with the doser team (?) to develop the control system for the
 mini plant and test it on the hydraulic test facility.
 Also propose design changes to the filter so that it will be easy to operate
 the mini plant, this might include moving valves and adjusting the position
 of plumbing.
 
\end_layout

\begin_layout Section
Other Applications
\end_layout

\begin_layout Standard
The filter is a novel piece of technology that may be applicable to industries
 outside of sustainable water treatment.
 One area might be the aquaponics industry.
 Brainstorm and research other industries that might need low flow filters.
 Determine what their specific filtration needs might be and evaluate the
 filter in terms of those needs.
 Will the filter fulfill those needs? If not, what design changes might
 allow the filter to be useful for those applications? What might be a selling
 point for the low flow filters if we were to market in those industries?
 
\end_layout

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