Download Report

Lessons Learned from Ozone
Contactor Tracer Testing at Little
Falls Water Treatment Plant
2015 AWWA NJ Annual Conference
Wednesday, March 18, 2015
Agenda
Project Background
Tracer Test Overview
─ Protocol Development
─ Protocol Modifications
Tracer Test Results
Findings and Recommendations
Project Background
Little Falls Water Treatment Plant
Source: Passaic River
─ Occasionally Pompton River or Point View Reservoir
Process:
─ Sand-ballasted sedimentation process, ozonation and
granular activated carbon and sand filters, and chlorination
Ozone Contactor
Ozone Contactor Sections
Tracer Test Overview
Purpose of Tracer Tests
New Jersey Administrative Code 7:10-9.5a [7:10-11]:
─ …the tracer study evaluation report prepared as recommended
in the U.S. Environmental Protection Agency's "Guidance
Manual for Compliance with the Filtration and Disinfection
Requirements for Public Water Systems Using Surface Water
Sources" (dated March 1991) as amended and supplemented,
shall be submitted ……
Determine hydraulic baffling factor (T10/HDT)
─ T10 is defined as the detention time at which 90 percent of the
water passing through a contact vessel is retained within the
reservoir
─ T10 is to consider it as the detention time that is equal, or
exceeded by, 90 percent of the fluid passing through the
contactor.
Tracer Test
Step-Dose Method
─ Constant dosage until
steady-state concentration
The results are used
for modifying the ideal
hydraulic detention time
to reflect the nonidealities of the actual
flow patterns for use
when performing
calculations for
determining disinfection
performance.
Effective Contact Time (T) = HDT * (T10/HDT)
Comparison of SWTR Requirements and LFWTP
Tracer Test Plan
U.S. EPA SWTR Guidance Manual Requirement
At least 4 flow rates that span the entire range of flow
rates of the process being tested.
The flow rate should be not less than 91 percent of the
maximum rated flow for the process being tested.
LFWTP Tracer Testing Plan
Two flow rates, ~18 mgd and ~28 mgd, were tested on
each of the four ozone contactors. (flow rates typically vary
from 17 to 28 mgd per contactor).
~28 mgd was selected as one of the two test flow rates. 28
mgd is > 91 percent of the maximum flow, 29.25 mgd.
Tracer testing should be performed at a constant process
flow rate wherever possible.
The water surface in a process being tested should be at
or slightly below the minimum normal operating level for
the process.
Tracer addition and sampling should be continued for a
period of two to three times the theoretical detention
time.
Tracer should be applied at the point of application for
the disinfectant to be used in the CT calculations
whenever possible, or as close as possible to this point.
Tracer testing was performed at a constant process flow
rate.
The water surface was at the normal operating level for
the respective flow rates, and thus would remain relatively
constant during each tracer test period.
Tracer addition and sampling was continued for a period of
three times the theoretical detention time.
Tracer response should be measured at the sampling
point for disinfectant residual whenever possible, or as
close as practical to this point.
The tracer to be used should be conservative (nonreactive) through the unit process being tested, and
added at a concentration of at least 10 times the
background concentration.
Tracer was measured at the end of cells 2, 4, 6, and 8
where online sampling currently measures ozone residual.
Tracer was added at the effluent channel of the clarifiers,
upstream of where ozone will be introduced in Cell 1.
Fluoride in the form of hydrofluosilicic acid (H2SiF6) with a
target feed rate of 2.5 milligrams per liter (mg/L) as
fluoride was used as the tracer.
Fluoride Dosing Location
Dosing Point – Existing
Chlorine Injection Line
Steady-state concentration not met
Fluoride Dosing Location
Dosing Point Revised –
Actiflo Effluent
Tracer Test Results
Tracer Study Plots
Dimensionless time and fractional fluoride concentrations were plotted.
Tracer Testing Summary Table
Test Date
Average Flow
Contactor Rate (mgd)
Max Fluoride
Concentration in Plant
Effluent (mg/L)
4/26/13
1
17.8
0.24
3/13/13
1
27.8
0.37
4/11/13
2
18.1
0.35
4/10/13
2
28.0
0.35
4/26/13
3
18.2
0.24
4/17/13
3
27.7
0.36
4/17/13
4
18.1
0.36
4/22/13
4
27.9
0.35
Lag Time
Adjustment
(min)
5.3
3.4
3.4
2.2
2.3
1.5
1.8
1.2
T50/HDT Ratios
T50/HDT ratios for ~18 mgd Tests
Cell
2
4
6
8
Contactor 1
0.94
1.10
1.00
1.05
Contactor 2
1.04
1.03
1.02
1.00
Contactor 3
1.00
0.98
1.00
1.02
T50/HDT ratios for ~28 mgd Tests
Cell
2
4
6
8
Contactor 1
1.17
1.25
1.08
1.12
Contactor 2
1.20
1.13
1.12
1.03
Contactor 3
1.12
1.13
1.08
1.02
Contactor 4
1.00
1.00
0.97
0.99
Contactor 4
0.98
1.10
1.00
1.03
T50/HDT Ratios Results
In an ideal plug flow reactor, fractional concentrations of 0.5
(T50/HDT) should occur at dimensionless time of 1.0.
Ozone contactors should be considered rectangular tubular
reactors with axial dispersion in an open system – non-ideal
plug flow.
The further away the T50/HDT ratio is from 1.0 indicates
more mixing in the flow pattern entering the ozone contactors.
T10/HDT Ratios
T10/HDT ratios for ~18 mgd Tests
Cell
2
4
6
8
Contactor 1
0.30
0.50
0.54
0.57
Contactor 2
0.44
0.50
0.58
0.53
Contactor 3
0.43
0.58
0.54
0.60
T10/HDT ratios for ~28 mgd Tests
Cell
2
4
6
8
Contactor 1
0.40
0.63
0.67
0.63
Contactor 2
0.55
0.61
0.60
0.58
Contactor 3
0.53
0.61
0.64
0.61
Contactor 4
0.45
0.58
0.53
0.54
Contactor 4
0.50
0.58
0.58
0.59
T10/HDT Ratios Results
More uniform flow through the system at higher flow rates.
Contactors 2, 3, and 4 behave similarly because their
T10/HDT ratios for cells 2, 4, 6 and 8 are similar.
The T10/HDT ratio for Cell 2 of Contactor 1 is significantly
lower than that for Cell 2 in the other contactors. This is
attributed to short-circuiting in Cell 2 caused by the north
tunnel.
The longer distance of conduit and channels leading to
Contactor 1, combined with the abruptly changing geometry
of the influent channels, exacerbated these differences in
Contactor 1.
Findings and Recommendations
Recommendations
It is standard industry practice to use only one value for the
T10/HDT ratio.
USEPA’s Long Term 2 Enhanced Surface Water Treatment
Rule (LT2ESWTR) Guidance Manual (USEPA 2010)
recommends the following:
─ a minimum of two tracer tests be conducted (the tracer tests
used two different flow rates).
─ data be used from the test that demonstrates the greatest
“spread” (i.e., dispersion or variance) in the tracer.
─ data from one contactor may to be applied to all contactors, but
it does not rule out using data from more than one contactor.
Final Recommendation
AT10/HDT ratio of 0.56 is recommended for used for the LFWTP
ozone contactors based on the following:
─ 0.56 is the average value for Cells 4, 6, and 8 as determined in the low
flow (~18 mgd) tests, which showed the greatest spread in the tracer
─ The 0.56 value is for Cell 6 in the low flow tests (~18 mgd), which is the
end of the contactor for practical purposes for ozone since that is the
location of the last ozone monitor used for disinfection credit
─ The average is used because data may be used from more than one
contactor, and the Cell 6 minimum value (0.54) was very close to the
average (0.56)
A T10/HDT ratio of 0.60 has historically been used for the LFWTP
ozone contactors per USEPA guidance.
Questions