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\begin_layout Title
Low Flow Stacked Rapid Sand Filter Summer 2012 Final Report
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\begin_layout Date
3 August, 2012
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\begin_layout Author
Christian Compton, Alli Hill, Amanda Rodriguez, Samuel Taube
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\begin_layout Section*
Literature Review
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\begin_layout Standard
To begin research on building a stacked rapid sand filter for a low flow
 plant, several design plans from the CEE 4540 capstone design class were
 consulted, as well as previous AguaClara publications.
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\begin_layout Itemize

\series bold
Fabricating Stacked Rapid Sand Filters for Low Flow Rates
\series default
 - this is a power point presentation from the capstone design class by
 Alberto Ferrero Diez, David Gonzalez, Miree Eun Li, Hui Goh.
 This design used four layers of sand, and could potentially be built in
 a garbage can.
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\series bold
SRSF for a Low Flow AguaClara Plant
\series default
 - this is a power point presentation from the capstone design class by
 Bradshaw Irish, Siwei Oon, Weiling Xu, Ruonan Zhang.
 It looked at a potential design similar to the one aforementioned, with
 a square filter and four layers of sand.
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\begin_layout Itemize

\series bold
Stacked Filters: a Novel Approach to Rapid Sand Filtration
\series default
 Michael J.
 Adelman; Monroe L.
 Weber-Shirk; Anderson N.
 Cordero; Sara L.
 Coffey; William J.
 Maher; Dylan Guelig; Jeffrey C.
 Will; Sarah C.
 Stodter; Matthew W.
 Hurst and Leonard W.
 Lion - This paper explained in detail the ideas behind AguaClara's current
 stacked rapid sand filter, and evinced the benefits of using a six layer
 sand filter.
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\begin_layout Itemize

\series bold
A Novel Fluidics Control System for AguaClara Stacked Rapid Sand Filters
\series default
 Michael J.
 Adelman, Monroe L.
 Weber-Shirk, Jeffrey C.
 Will, Anderson N.
 Cordero, William J.
 Maher, and Leonard W.
 Lion - This publication highlighted the virtues of the stacked rapid sand
 filter and also explained the current siphon system which is used during
 the backwash cycle to remove the particles that were trapped in the sand
 during filtration.
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\begin_layout Section*
About the Stacked Rapid Sand Filter
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\begin_layout Standard
The stacked rapid sand filter operates by passing water through layers of
 sand, which removes particles from the water by trapping them in the sand.
 There comes a point in the filtration process in which the sand has trapped
 all of the particles that it can, and the water exiting the filter is no
 longer at its ideal standard.
 In order to remove the particles from the sand, the filter enters a backwash
 mode: the valve at the top of the siphon in manually opened, and due to
 the negative pressure in the siphon the water in the filter is removed
 via the siphon instead of the outlet box; Additionally, the water level
 in the inlet pipes has gone below the riser pipes, and as result, water
 is only going through the lowest manifold in the filter, with the same
 flow as during filtration.

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This fluidizes the sand bed completely so that the particles trapped during
 backwash are released and able to exit with the water via the siphon.
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A diagram indicating the SRSF filter in its two modes of operation
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\begin_layout Section*
Methods
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\begin_layout Standard
The primary objective for this summer was to construct a low flow stacked
 rapid sand filter, for water treatment plants with flows between 0.3 and
 3.0 L/s.
 Using the information obtained from the aforementioned sources, several
 designs were considered.
 Some features of the higher flow stacked rapid sand filter were kept and
 not modified in our potential designs; Specifically, the use of slotted
 pipes, and the idea that the filter would operate in two distinct modes,
 filtration and backwash, were pillars in the design process.
 
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\begin_layout Standard
The geometry of the filter varied with each design.
 The large stacked rapid sand filter in Tamara is a square filter.
 One advantage is that it was easy to build a manifold system which evenly
 distributed water throughout the filter.
 The pilot scale filter that was used for testing in the lab was made from
 translucent four inch PVC pipe, and worked for an ultra low flow filter.
 One advantage with this design was that the pipe was relatively easy to
 obtain, whereas square tanks were far more expensive, and were not available
 in sizes ideal for the needs of this project.
 One disadvantage to the circular design was that a new manifold system
 would need to be developed for a circular filter.
 In the end, it was more economical to purchase a 12 inch PVC pipe and develop
 a new water manifold system than to custom order a rectangular tank and
 use the current manifold system.
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\begin_layout Section*
Analysis
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\begin_layout Subsubsection*
Manifold System
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\begin_layout Standard
The pilot scale model has a geometry similar to that of our design.
 Since the pilot scale is so small, using one slotted pipe works well for
 water distribution, but using this method in a 12 inch pipe filter is an
 inefficient use of space and would generate ineffective flow distribution.
 The manifold system that we will be using consists of a 1 inch trunk line
 which distributes water to six slotted pipes which are capped on the ends.
 Since there is no brace connecting the end of the slotted pipes to the
 wall, the slotted pipes will be free at one end and therefore not as stable.
 To fix this, the strong axis of the slotted pipes will be oriented vertically
 in the filter so that they are rigid in the vertical direction.
 
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The square filter and manifold system in the Tamara Plant
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The manifold system that will be used in the low flow SRSF
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\begin_layout Subsubsection*
Pilot Scale Experiment
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\begin_layout Standard
The pilot scale was modified to see if the design of a pressure filter was
 feasible.
 There were some initial problems with the first few trials, and these failure
 modes were documented below.
 In order to make the previous pilot scale filter into a pressure filter,
 the top segments of the filter were removed, along with the siphon piece,
 and an airtight cap and a backwash pipe with a valve were added.
 Below is a picture of the stacked rapid sand filter before it was modified
 and after.
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Photos of the pilot scale model before and after being modified as a pressure
 filter
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\begin_layout Subsubsection*
Failure Modes
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\begin_layout Itemize
When the inlet box is too low, there is not enough water velocity to completely
 fluidize the sand bed during the backwash cycle.
 Also, if it is too low, the riser pipes for the top three inlet manifolds
 take in water during the backwash cycle, when water should only be going
 through the lowest manifold.
 See Fig.
 1).
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If the inlet box is too high, the water level plummets so quickly during
 the backwash cycle that the filter takes in air through the inlet box resulting
 in bubbles in the sand bed.
 This causes the sand to be released via the backwash outlet.
 Over time, this will cause the top layers of the sand bed to deplete.
 This is due to a large amount of negative pressure, and was solved by implement
ing plumbing traps where the water goes from the inlet pipes to the filter.
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One problem that arose during the testing of the pilot scale model was that
 there was supercritical flow, a flow which contains both significant amounts
 of water and air, through the backwash outlet.
 This issue was resolved by placing the end of the back wash outlet in a
 pitcher which when filled with water prevented the water from free falling
 in the backwash pipe.
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The end of the pilot scale backwash outlet resting in a pitcher of water
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\begin_layout Itemize
Using a pressure filter requires that it be perfectly sealed.
 One problem that arose was that the seal in the pilot scale model was not
 as tight as it needed to be, and as result, it released water during filtration
 and took in air during backwash.
 Therefore it is crucial to avoid this mechanical failure which leads to
 supercritical flow.
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\begin_layout Section*
Conclusion
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\begin_layout Standard
The final design for the low flow stacked rapid sand filter will comprise
 of large buckets for inlet and outlet boxes, which are connected to the
 filter by 2 inch PVC pipelines to each manifold, four connecting to the
 inlet box, three connecting the the outlet box.
 The inlet PVC pipes will have the plumbing traps before entering the filter.
 In the final prototype, the backwash outlet will come out of the top of
 the filter as opposed to the pilot scale model, in which it came out of
 the side.
 The manifold system will consist of a 1 inch PVC trunk line, with six total
 1/2 inch PVC slotted pipes, three on each side, oriented with the strong
 axis parallel to the long axis of the filter, and capped on each end.
 The end of the backwash outlet will need to rest in a container of water
 to prevent the free fall of water in the backwash outlet and therefore
 supercritical flow.
 Below is a photo of the partially finished design.
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The partially finished filter prototype
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\begin_layout Section*
Future Work
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\begin_layout Standard
The next step in the process of creating the stacked rapid sand filter will
 involve constructing the full size model.
 The fabrication team has recently drilled the holes in the 12 inch PVC
 pipe for the inlet and outlet pipes, and has also created a prototype of
 the manifold system.
 The exact geometry of the inlet pipes with the plumbing traps needs to
 be finished on the AutoCAD drawing.
 Once completed, the filter and its inlet and outlet boxes will be joined
 with the hydraulic testing facility, which is capable of generating the
 flow needed to test this filter.
 Depending on the actual flow produced by the hydraulic testing pumps, devices
 like values, flow gauges, and orifice plates may be necessary to regulate
 the flow to 0.8 L/s, the flow rate for which the 12 inch filter was designed.
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