The International Desalination Association World Congress on Desalination and Water Reuse 2015/San Diego, CA, USA
REF: IDAWC15- InsertFamilyNameHere
EXPANSION OF THE ORANGE COUNTY'S GROUND WATER RECHARGE
SYSTEM - ENERGY AND PERFORMANCE OPTIMIZATION
Authors: Srinivas (Vasu) Veerapaneni, Mehul Patel, Bill Dunivin, Rich ten Bosch, Sunny
Wang, and Jim Clark
Presenter: Srinivas (Vasu) Veerapaneni, Ph.D., P.E.
Desalination Technology Leader & Sr. Process Engineer, Black & Veatch
VeerapaneniS@bv.com
Abstract
The Groundwater Replenishment System (GWRS) treats effluent from the Orange County Sanitation
District’s reclamation facility and uses the treated water to recharge groundwater and for seawater
intrusion barrier. The Advanced Water Purification System (AWPS), that is part of the GWRS consists
of microfiltration, reverse osmosis, advanced oxidation and post-treatment consisting of decarbonation
and lime. The GWRS system currently treats 70 MGD with provisions for expansion to ultimate
capacity of 130 MGD. The first expansion of the facility will be completed in March 2015, increasing
the capacity by an additional 30 MGD.
Expansion of the AWPF provided an opportunity to improve operational flexibility and to enhance the
performance of the RO system. The modifications to the RO system design included the following:
Membrane Elements: Since the commissioning of the first phase of AWPF in 2008, advances in
membrane technology have resulted in the availability of more energy efficient membranes. For the
expansion, newer membranes with higher permeability, and fouling resistance are used. These consume
less energy, while maintaining similar permeate water quality. The performance of these membranes
with the membranes in existing trains (when new) will be compared.
Additional Instrumentation: The existing RO trains have the permeate lines from each column of vessels
connected to permeate header. While this simplifies piping arrangement, it does not allow monitoring of
performance of individual stages within the RO system, with respect to permeability and permeate water
quality. The new trains are piped to allow ability to control flux of each stage and to monitor
performance of each stage online. This data will be used to determine the extent of fouling, if any in
each stage.
Energy Recovery Device: The existing RO trains do not have means of balancing fluxes between
various stages. For the newer RO trains, Energy Recovery Devices have been implemented. These
devices recover energy from the concentrate from 3
rd
stage and boost the pressure of the second stage
feed to balance the fluxes while reducing energy consumption. The energy savings increase as the
membranes age, as there is more energy in the concentrate when older membranes are operated at higher
pressure. The energy consumption of the new RO trains with the older RO trains will be compared.
Further, the performance of the energy recovery device, as tested in the factory will be compared with
the field evaluation. Note that the design information has been presented at an IDA conference 4 years
ago. The plant is going to be commissioned in February 2015, and the actual full scale data obtained
during commissioning will also be included in the final paper and presentation.
The International Desalination Association World Congress on Desalination and Water Reuse 2015/San Diego, CA, USA
REF: IDAWC15-Veerapaneni
Page - 2 - of 8
I. INTRODUCTION
The Groundwater Replenishment System (GWRS) treats effluent from the Orange County Sanitation
District’s reclamation facility and uses the treated water to recharge groundwater and for seawater
intrusion barrier. The Advanced Water Purification System (AWPS), that is part of the GWRS consists
of microfiltration, reverse osmosis, advanced oxidation and post-treatment consisting of decarbonation
and lime. The GWRS system currently treats 70 MGD with provisions for expansion to ultimate
capacity of 130 MGD. The first expansion of the facility will be completed in March 2015, increasing
the capacity by an additional 30 MGD.
Expansion of the AWPF provided an opportunity to improve operational flexibility and to enhance the
performance of the RO system. This paper discusses the performance enhancements of the RO system to
improve performance with respect to fouling and energy consumption.
II. EXISTING PHASE I FACILITY
The GWR System consists of three major components: (1) the Advanced Water Purification Facility
(AWPF) and pumping stations; (2) a major pipeline connecting the treatment facilities to existing
groundwater recharge basins; and (3) an existing seawater intrusion barrier. The expansion will add 30
million US gallons per day (mgd) to the current 70 mgd production capacity of the AWPF. A major
portion of the Expansion Project is to review existing design and operations of the RO system at the
AWPF, evaluate applicability of energy recovery device (ERD) for the new RO units, and evaluate
adequacy of instrumentation and controls of the existing RO unit design. Based on this evaluation,
preliminary design criteria for the 30 mgd expansion were developed to enhance the energy efficiency
and operability of the new RO units.
RO System Facilities
The existing RO system at the AWPF consists of RO transfer pumps, cartridge filters, RO feed pumps,
the RO units, RO Flush System, and RO Clean-In-Place (CIP) system. A summary of the design criteria
for the existing RO system is provided in Table 1.
Table 1: Design Criteria of Existing RO System
Parameter
Value
RO Transfer Pumps
No. of Pumps
4 duty, 1 standby
Design Capacity, each
23,000 gpm
Total Pumping Capacity (Duty)
92,000 gpm (132 mgd)
Rated Head
176 ft
Power, each
1250 hp
Cartridge Filters
No. of Cartridge Filters
10 duty
Max capacity, each
11.75 mgd
Max Differential Pressure
15 pounds per square inch
The International Desalination Association World Congress on Desalination and Water Reuse 2015/San Diego, CA, USA
REF: IDAWC15-Veerapaneni
Page - 3 - of 8
(psi)
RO Feed Pumps
No. of Pumps
15
Design Capacity, each
4,340 gpm
Rated Head
681 ft
Power, each
1000 horsepower (hp)
RO Units
No. of RO Units
14 duty + 1 standby
No. of RO Trains
5
No. of RO Units per Train
3
Design Production Capacity, each
unit
5 mgd
Design Production Capacity, total
70 mgd
Number of Stages per RO Unit
3
RO System Recovery
85 percent
RO System Permeate Flux
12 gfd
RO Flush System
Flush Rate
1,000 gpm
Flush Duration
20 minutes
No. of RO Flush Pumps
3 duty
Pump Capacity, each
1,000 gpm
Rated Head
120 ft
Power, each
50 hp
III. MODIFICATIONS TO THE EXISTING PLANT
As part of the AWPF expansion, operating data from the existing RO system was reviewed to evaluate
its performance and identify areas that could be enhanced, taking advantage of the opportunity to modify
design during expansion. After careful review of the existing RO system design and operating data,
guidelines to improve overall RO performance were developed:
 Provide additional online instrumentation to improve performance monitoring
capabilities of each individual RO stage within each RO unit.
 Provide flux balancing capabilities between RO stages to improve overall membrane
performance and life.
 Minimize effects of concentrate polarization by maintaining a beta factor of less than
1.13 and maintain adequate concentrate flow (~18 gallons per minute [gpm] per pressure
vessel).
 Install membranes that have higher energy efficiency and fouling resistance that are
currently available.
Energy Recovery Devices
The International Desalination Association World Congress on Desalination and Water Reuse 2015/San Diego, CA, USA
REF: IDAWC15-Veerapaneni
Page - 4 - of 8
RO systems consume significantly more energy than other treatment processes at the AWPF. RO
membranes have a higher energy requirement in order to overcome the osmotic pressure of feed water
that is concentrated by a factor of approximately 6.7 within the RO system, when it is operating at the
typical recovery of 85%. Further, fouling of the membranes by organic, inorganic, and biological
constituents is inevitable for wastewater applications and contributes to increased energy consumption
over time. This results in high amount of energy that is wasted on the concentrate stream that can be
recovered and used beneficially within the system.
As part of the project, a review of currently available ERDs was conducted. These included centrifugal
force based (Pelton Turbine, Turbo Energy, and Hydraulic Pressure Boosters) and positive displacement
(work exchanger and pressure exchanger). Of all these devises, the centrifugal devices were considered
appropriate for this application.
The recovered energy is intended to be used for boosting the pressure of the 2
nd
stage fed to allow for
balancing the fluxes between the first and second stages. For instance, at the existing plant, with no
means of controlling permeate flow from the first stage, the permeate flow from first stage is
considerably higher than the other stages, resulting in higher energy consumption. By using the energy
in the concentrate to boost the feed pressure of the 2
nd
stage, the fluxes can be balanced. This is sown in
Figures 1 & 2, where the permeate flows with and without energy recovery devices are shown.
A schematic of RO operation with and without ERD is provided on Figures 1 and 2, respectively.
Further reduction in energy consumption per RO unit is possible by incorporating an ERD with a
booster pump. Preliminary RO membrane projections indicate that the inter-stage booster pump motor
will be operated initially (approximately first two years of operation) with external power supplementing
the ERD. It may not be necessary toward the end of the membrane life as concentrate pressure increases
as the membranes are fouled, and thus increasing amount of energy recovered from the concentrate at
higher pressures. Since the rate of fouling to be expected in the future is not clear, having an ERD with
a motor would provide a high degree of flexibility for system operation.
Figure 1. Schematic of Existing RO Units Without ERD
FM
Permeate (12 psi)
Feed
Concentrate
5.88 mgd
FM
FM
C
C
C
FM
FM
CC
CC
CC
5 mgd
0.88 mgd
2.16 mgd
1 mgd
140 psi
112 psi
95 psi
3.76 mgd
1.16 mgd
0.11 mgd
73 psi
2.16 mgd
1 mgd
140 psi
112 psi
95 psi
3.76 mgd
1.16 mgd
0.11 mgd
73 psi
17.6 gfd 8.3 gfd 1.2 gfd17.6 gfd 8.3 gfd 1.2 gfd
Fluxes
The International Desalination Association World Congress on Desalination and Water Reuse 2015/San Diego, CA, USA
REF: IDAWC15-Veerapaneni
Page - 5 - of 8
Figure 2. Schematic of New RO Units with ERD (Existing Values are Shown in Grey)
Energy Recovery Cost Analysis
The average energy consumption over the 5 year period for the existing RO system, based on feed
pressure increase from 183 psi to 224 psi, is approximately 481 kW. Given that the feed pressure is only
increasing by approximately 20%, use of linear average is reasonable. The estimated energy
consumption of the existing RO system with an ERD integrated with a motor is estimated to range from
415 kW to 504 kW. The average energy consumption is approximately 459.5 kW. The average energy
consumption of the RO system with ERD is approximately 21.5 kW less than an RO without an ERD.
The difference of 21.5 kW amounts to savings of approximately $17,000 per year at an energy cost of
$0.10/kWh and assuming that the RO units operate only 90 percent of the time. A cost/payback period
analysis for incorporating ERD for the RO units was developed, showing a simple payback period of
five to nine years depending on operating conditions (nine years being worst-case). Incorporation of an
ERD with a motor was recommended for the new RO units as it would reduce energy consumption,
while also allowing means of balancing the fluxes within the RO system to provide process benefits.
Similar benefits would also apply if ERD is added to the existing RO system, but available space for an
ERD needs to be evaluated.
The ERDs are currently being installed in the plant and the results will be available my March 2015, at
which point additional data will be available. The following figure shows shop testing of the ERDs.
FM
Permeate (13.5 psi)
Feed
Concentrate
Energy recovery device w/motorEnergy recovery device w/motor
5.88 mgd
1.58 mgd
FM
FM
CC
CC
CC
5 mgd
0.88 mgd
2.16 mgd
1 mgd
140 psi
112 psi
95 psi
3.76 mgd
1.16 mgd
0.11 mgd
73 psi
2.16 mgd
1 mgd
140 psi
112 psi
95 psi
3.76 mgd
1.16 mgd
0.11 mgd
73 psi
124 psi
2.7 mgd
1.12 mgd
3.23 mgd
0.23 mgd
149 psi
102 psi
82 psi
124 psi
2.7 mgd
1.12 mgd
3.23 mgd
0.23 mgd
149 psi
102 psi
82 psi
17.6 gfd 8.3 gfd 1.7 gfd17.6 gfd 8.3 gfd 1.7 gfd
14.4 gfd 12.2 gfd 3.8 gfd14.4 gfd 12.2 gfd 3.8 gfd
Fluxes
The International Desalination Association World Congress on Desalination and Water Reuse 2015/San Diego, CA, USA
REF: IDAWC15-Veerapaneni
Page - 6 - of 8
Shop testing of the ERD
In review of the existing RO unit design, the RO units were designed with additional instrumentation to
provide an accurate assessment of its performance. Specifically, the additional instrumentation was
incorporated to monitor the performance of individual stages and to enable tracking inter-stage
performance. The additional instruction for the new RO units includes: online flow for 2
nd
and 3
rd
stages
and total permeate of each RO units. Permeate flow from the 1
st
stage is calculated by subtracting 2
nd
and 3
rd
stage permeate flows from the total permeate. Permeate conductivity monitoring is provided for
each RO stage of each RO unit. Sample taps are provided on the permeate and feed lines of each stage.
Results
The new RO trains at the GWRS are undergoing commissioning currently and some preliminary data is
currently available.
The International Desalination Association World Congress on Desalination and Water Reuse 2015/San Diego, CA, USA
REF: IDAWC15-Veerapaneni
Page - 7 - of 8
The specific flux of each of three stages in one representative train show stable performance during the
initial period of operation. For comparison, the specific flux of entire trains in Phase 1 were
approximately 0.1 gfd/psi, indicating significant improvements in membrane performance over time.
The normalized differential pressure across each stage is shown in Figure above, again exhibiting no
change, as expected when no fouling is occurring. The total differential pressure loss for entire train is
less than 40 psi. The differential pressure for older trains ranged from 60 to 80 psi, again attributable to
better membrane construction, primarily with respect to rolling and spacer geometry.
0.00
0.05
0.10
0.15
0.20
0.25
04-01-15 04-11-15 04-21-15 05-01-15 05-11-15 05-21-15
Specific Flux (gfd/psi)
Stage 1 SF Stage 2 SF Stage 3 SF
0
5
10
15
20
25
04-01-15 04-11-15 04-21-15 05-01-15 05-11-15 05-21-15
Normalized DP
Stage 1 NdeltaP Stage 2 NdeltaP Stage 3 NdeltaP
The International Desalination Association World Congress on Desalination and Water Reuse 2015/San Diego, CA, USA
REF: IDAWC15-Veerapaneni
Page - 8 - of 8
The normalized salt rejection for each stage is shown in Figure above. The salt rejection is a function of
various parameters, including flux. The flux of the first two stages in the new trains are balanced and the
salt rejection, when normalized, is similar. The third stage has lower flux and hence the rejection is also
lower. The overall rejection is 98.5%, compared with 97% for older trains. This is also attributable to
newer membranes.
Energy reduction
The energy consumption of new RO trains is approximately 1.1 kWh/kgal, compared to that of older
trains, which had 1.6 kWh/kgal when commissioned. Approximatley 60% of this reduction is
attributable to the improved membrane properties and 30 to 40% attributable to use of energy recovery
devices. With flux balancing, the fouling rate of the RO trains is expected to be less for the new trains
compared to the older trains. This will be evident after first one or two years of operations and updated
results will be presented then.
V. CONCLUSIONS OR RESULTS
Expansion of the AWPF provided OCWD with an opportunity to optimize and enhance the existing RO
system, as well as incorporate design features to provide a more efficient and easy to operate RO
system. A major addition to the new RO units provided for the AWPF expansion will be the inclusion
of ERDs that will reduce overall energy requirements of the RO system. It will also potentially prolong
membrane life by balancing the flux between the three RO stages.
95.0%
95.5%
96.0%
96.5%
97.0%
97.5%
98.0%
98.5%
99.0%
99.5%
100.0%
04-01-15 04-11-15 04-21-15 05-01-15 05-11-15 05-21-15
Normalized rejection (%)
Stage 1 Norm Removal Stage 2 Norm Removal Stage 3 Norm Removal
