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\begin_body

\begin_layout Title
Demonstration Plant
\end_layout

\begin_layout Abstract
The AguaClara program needs appropriate teaching and publicity aids.
 The team developed a demonstration plant several years ago that illustrated
 the early flow control module, the baffled flocculator, and a sedimentation
 tank with plate settlers.
 In the intervening years we have developed a dose controller that tracks
 the plant flow rate, sedimentation tanks designed to include floc blankets,
 and stacked rapid sand filters.
 The next generation of the AguaClara demonstration unit should illustrate
 as many of these concepts as possible.
 
\end_layout

\begin_layout Abstract
The demonstration plant will be used as a portable demonstration unit to
 advertise the AguaClara technologies.
 The AguaClara POU will be a centerpiece of the EPA P3 competition in April
 of 2012.
\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
The AguaClara POU will be an excellent educational tool and demonstration
 unit as well as a device that can be used in households.
\end_layout

\begin_layout Standard
This team can begin learning the complexities of small scale water treatment
 by setting up a bench scale water treatment plant using the 
\begin_inset CommandInset href
LatexCommand href
name "ENGRI 1131 apparatus"
target "https://confluence.cornell.edu/display/engri1131/WTP+Project"

\end_inset

.
 As the team is setting up the bench scale model they can also begin designing
 components of a new demonstration plant, DP, that incorporates as many
 of the AguaClara concepts as are feasible.
 The DP flow rate should be as low as possible to reduce the need for large
 storage tanks for the raw water.
 The minimum flow rate may be set by the sedimentation tank or by the stacked
 rapid sand filter, SRSF.
\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.
 Some of the equations can be borrowed from the AguaClara design tool files.
 However, care must be taken for flocculator design to account for the laminar
 flow.
 The design tool files assume turbulent flow for the flocculator.
\end_layout

\begin_layout Subsection
Flow measurement and dose control
\end_layout

\begin_layout Standard
Explore the possibility of using a linear flow orifice meter, LFOM, to measure
 the raw water flow into the DP.
 It is possible that the required hole saw for an LFOM would be too small
 to be practical.
 If that is the case, use a long laminar flow tube to generate a linear
 relationship between flow through the DP and elevation of water in the
 DP entrance tank.
 Explore the possibility of using a chemical dose controller for the coagulant
 (Poly aluminum chloride, PACl, or aluminum sulfate, alum).
 It would be excellent if this demonstration plant could fully illustrate
 how a chemical dose controller works.
 The dose controller will require significant elevation.
 Full scale plants use 20 cm of elevation change in the entrance tank.
 Perhaps the elevation change in the entrance tank could be reduced slightly.
 However, if the elevation is reduced too much surface tension will cause
 large errors in dosing.
\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.
 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.
 
\end_layout

\begin_layout Standard
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

.
 The collision potential is a measure of the ability of the flocculator
 to cause flocs to collide.
 
\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 where we would generally use very turbid
 water 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 Subsection
Sedimentation Tank
\end_layout

\begin_layout Standard
The sedimentation tank should include a floc blanket, floc weir, floc hopper,
 and plate settlers.
 The plate settler will likely be replaced with a simple tube settler.
 The floc blanket will require a section of the reactor that has vertical
 walls and an up flow velocity of 1
\begin_inset space \thinspace{}
\end_inset


\begin_inset Formula $\frac{mm}{s}.$
\end_inset

 Previous efforts to create a floc blanket at very small scales have failed.
 It is very possible that the floc blanket failure mode is related to the
 energy dissipation rate of the incoming jet of flocculated water.
 Given the same jet velocity, the energy dissipation rate is higher for
 small diameter jets than for large diameter jets.
 The incoming jet does break up flocs and it is very likely that the high
 energy dissipation rate of a small diameter incoming jet causes the flocs
 to be broken into such small fragments that an excessively high fraction
 of the fragments end up being carried out of the top of the sedimentation
 tank.
 
\end_layout

\begin_layout Standard
The relationship between the jet energy dissipation rate and the diameter
 of the pipe that discharges the flocculator water into the sedimentation
 tank is
\end_layout

\begin_layout Standard
\begin_inset Formula 
\begin{equation}
D_{Pipe}=\left(\frac{Q_{Pipe}}{\epsilon_{Max}^{\frac{1}{3}}}\frac{4\alpha_{Jet}}{\pi}\right)\label{eq:Dpipe}
\end{equation}

\end_inset


\end_layout

\begin_layout Standard
where 
\begin_inset Formula $Q_{Pipe}$
\end_inset

is the volumetric flow rate in the pipe, 
\begin_inset Formula $\epsilon_{Max}$
\end_inset

 is the maximum energy dissipation rate produced by the jet, and 
\begin_inset Formula $\alpha_{Jet}$
\end_inset

 has a value of approximately 0.5.
 The relationship between the energy dissipation rate and G in the tube
 flocculator is 
\end_layout

\begin_layout Standard
\begin_inset Formula 
\begin{equation}
\bar{\epsilon}=\bar{G}^{2}\nu\label{eq:average energy dissipation rate}
\end{equation}

\end_inset


\end_layout

\begin_layout Standard
The relationship between average energy dissipation rate, 
\begin_inset Formula $\bar{\epsilon}$
\end_inset

, and maximum energy dissipation rate in a jet is
\end_layout

\begin_layout Standard
\begin_inset Formula 
\begin{equation}
\epsilon_{Max}=\alpha_{\epsilon}\bar{\epsilon}\label{eq:max energy dissipation rate}
\end{equation}

\end_inset


\end_layout

\begin_layout Standard
where 
\begin_inset Formula $\alpha_{\epsilon}$
\end_inset

is the ratio of maximum to average energy dissipation rate and has a value
 of about 2 for jets.
 The maximum floc size was measured by Ian Tse with a tube flocculator.
\end_layout

\begin_layout Standard
\begin_inset Formula 
\begin{equation}
D_{Floc}=75\mu m\left(\frac{\bar{\epsilon}}{\frac{W}{kg}}\right)^{\frac{-1}{3}}\label{eq:Dfloc}
\end{equation}

\end_inset


\end_layout

\begin_layout Standard
It should be possible to combine equations 
\begin_inset CommandInset ref
LatexCommand ref
reference "eq:Dpipe"

\end_inset

 to 
\begin_inset CommandInset ref
LatexCommand ref
reference "eq:Dfloc"

\end_inset

 to solve for the required pipe diameter given a target floc diameter.
 Ideally the flocs would have a sedimentation velocity that matches the
 up flow velocity in the floc blanket to ensure that they aren't carried
 up and out of the sedimentation tank.
 Or perhaps they only need to have a sedimentation velocity that matches
 the tube settler capture velocity.
 The previous attempts at producing a floc blanket with 2.5 cm diameter sedimenta
tion tanks did not include tube settlers and thus it is possible that this
 floc breakup problem will not occur if tube settlers are in place to return
 flocs that they capture.
 Floc sedimentation velocity is given by
\end_layout

\begin_layout Standard
\begin_inset Formula 
\begin{equation}
V_{t}=\frac{gd_{0}^{2}}{18\Phi\nu_{H_{2}O}}\frac{\rho_{Floc_{0}}-\rho_{H_{2}O}}{\rho_{H_{2}O}}\left(\frac{d}{d_{0}}\right)^{D_{Fractal}-1}\label{eq:Vt of flocs}
\end{equation}

\end_inset


\end_layout

\begin_layout Standard
where 
\begin_inset Formula $d_{0}$
\end_inset

 is the diameter of the primary particles, 
\begin_inset Formula $d$
\end_inset

 is the floc diameter, 
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\begin_inset Formula $\Phi$
\end_inset

is a fluid drag correction factor for the non spherical flocs, 
\begin_inset Formula $\nu_{H_{2}O}$
\end_inset

 is the kinematic viscosity of water, 
\begin_inset Formula $\rho_{Floc_{0}}$
\end_inset

is the density of the primary particles, 
\begin_inset Formula $\rho_{H_{2}O}$
\end_inset

 is the density of water, and 
\begin_inset Formula $D_{Fractal}$
\end_inset

 is the fractal dimension of the flocs.
 The graph of equation 
\begin_inset CommandInset ref
LatexCommand ref
reference "eq:Vt of flocs"

\end_inset

 is shown in Figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Floc-sedimentation-velocity"

\end_inset

.
 The flocs in the floc blanket may grow in size to be several mm in diameter
 and thus have very high sedimentation velocities.
 The up flow velocity in the floc blanket is 1 mm/s and the capture velocity
 in AguaClara plate settlers is set to 0.12 mm/s.
\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename floc velocity.png
	width 10cm

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
\begin_inset CommandInset label
LatexCommand label
name "fig:Floc-sedimentation-velocity"

\end_inset

Floc sedimentation velocity as a function of size.
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Standard
The floc weir will set the maximum level of the floc blanket.
 The floc blanket should probably have a depth between 30 and 60 cm.
 Floc blanket particle capture efficiency improves with depth, but the goal
 for the demonstration plant is to keep the unit processes small and to
 sacrifice performance if necessary.
\end_layout

\begin_layout Subsection
Stacked Rapid Sand Filter
\end_layout

\begin_layout Standard
The stacked rapid sand filter is a hydraulically complex system that would
 be incredibly useful to be able to demonstrate at bench scale.
 A full scale unit has a depth of about 3.7 m based on 6 20
\begin_inset space \space{}
\end_inset

cm filter layers and then the elevation required for the fluidized bed and
 backwash head loss.
 This will require scaling the depth of the filter layers down significantly
 to make a bench top model.
 One possibility will be to reduce the filter layer depth to approximately
 2 cm.
 The plumbing dimensions will also have to be carefully considered.
 The vertical drop tubes on the inlet side of the filter need to be large
 enough to allow counter current flow of air and water.
 That constraint requires a tubing ID of about 9 mm.
 It would also be beneficial if the vertical drop tubes had a small angle
 away from the vertical to making it easier for water to flow down the bottom
 of the tube and air to flow up on the top side of the tube.
\end_layout

\begin_layout Standard
The inlet and outlet manifolds could be custom manufactured stainless steel
 tubes with tiny orifices.
 As many components as possible should be transparent to facilitate direct
 observation of the hydraulics.
 
\end_layout

\end_body
\end_document
