S Curre Wast n Rea ents Study en ewate actor y Rep er

381 Pages·2014·15.14 MB·English

HHoward F. Curreen
AAdvannced Wastewateer Treeatmeent Pllant
NNitrificcationn Reaactor Air DDistribbutionn Sysstem
Immproovemeents

PPhasee 1 – SStudyy Repport

#200-084494-12002
MMarch 2014
Table of Contents
Page
Executive Summary………………………………………………………………………………………1
Section 1.0 Introduction…………………………………………………………………...…7
Section 2.0 Air Distribution System Evaluation……………………………………………9
Section 3.0 Wastewater Process Modeling………………………………………………11
Section 4.0 DARs Instrumentation and Controls Conceptual Design…………………13
Section 5.0 Budgetary Cost Opinion for Improvements to DARs Train 1..…………...14
Section 6.0 Construction Phasing Schedule……………………………………………..16
Section 7.0 Summary……………………………………………………………………....17
Appendix A Technical Memorandum No. 1 – Howard F. Curren Advanced
Wastewater Treatment Plant Diffused Aeration System Replacement
Alternatives
Appendix B Technical Memorandum No. 2 – Howard F. Curren Advanced
Wastewater Treatment Plant Diffused Air Reactor Diffuser Replacement
Modeling Report
Execuutive Summaary

Tetra Tecch, Inc. (Tettra Tech) waas authorizedd by the Cityy of Tampa (City) to coonduct a Stuudy of
improvemments to the CCity’s Howard F. Curren Addvanced Wasttewater Treattment Plant NNitrification Reeactor
Air Distribbution Systemm. The work aas part of thiss project incluudes improvinng the air disstribution systtem in
the Nitrificcation Reactoors (also knoown as the DDiffused Air RReactors – DDARs), improving the opeerating
efficiency of the reactoors, and improving the ability of the sysstem to provide other metthods of treattment.
There aree four (4) DARs (Trains 1 through 4) aat the plant. EEach DAR is divided into 6 zones (Zones 1
through 66) and each zzone is currenntly equipped with fine bubbble membraane disc diffussers. This Stuudy is
Phase 1 of the projeect. Phase 22 of the project is the ddesign, permitting, and construction oof the
improvemments to DAR Train 1. Subsequent phasses include thhe design, peermitting and construction of the
DAR Trainns 2, 3, and 44.

The Howaard F. Currenn Advanced WWastewater TTreatment Plaant (HFCAWTTP) has a permitted capaccity of
96 millionn gallons per day (MGD) oon an averagge annual daily flow (AADDF) basis. The current AAADF is
approximaately 56 MGDD and the faacility maintains consistentt compliancee with regulattory agency ppermit
requiremeents related to effluent quality. Figuree ES-1 preseents the overall process schematic foor the
treatment facility whichh in general inncludes prelimminary treatmment followed by primary ssedimentationn, two-
stage actiivated sludgee, denitrificatioon filters, disinfection, solids digestion, and biosolids dewateringg. This
Study foccuses on the second stagee of the two-sstage activateed sludge sysstem, the Difffused Air Reaactors
(DARs).

Fiigure ES-1
Overrall Process Schematic oof HFCAWTPP

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The first stage of the activated sludge system includes 6 high-rate activated sludge reactors that use High
Purity Oxygen (HPO) for removal of carbonaceous biochemical oxygen demand (CBOD). These reactors
are referred to as the HPO reactors throughout this study. Each HPO reactor has four zones, each with a
mechanical aerator to mix the basin and facilitate oxygen transfer. The HPO reactors are followed by 12
rectangular clarifiers. HPO is generated on-site cryogenically using either a 60 ton per day (tpd) or an 80
tpd generating unit. The second stage of the activated sludge uses four (4) Diffused Air Reactors (DARs)
which are mainly used for nitrification. Each DAR is divided into 6 zones (Zones 1 through 6), each
currently equipped with fine bubble membrane disc diffusers. Air is delivered to the diffusers by multi-
stage centrifugal blowers. There is a spike line from the Main Pumping Station (MPS) to the DARs that
allows for a portion of the primary effluent to bypass the HPO reactors. The current AADF at the
HFCAWTP is approximately 56 MGD which means the plant is operating at about 59% of the rated
capacity. While the facility is operated at lower flows and loadings than the design capacity, there is
potential to optimize the operation to minimize operations costs.

The diffusers in the DAR basins have reached the end of their useful life and the design for replacement
of these diffusers will occur in Phase 2 of this project. This Phase 1 Study presents the findings from the
evaluation of the aeration system replacement alternatives, the wastewater process modeling, and the
preliminary opinion of construction costs associated with the improvements to the DARs and associated
electrical and instrumentation and controls.

Tetra Tech completed two (2) Technical Memorandums (see appendices) as part of this Phase 1 Study,
including:

1. Technical Memorandum No. 1 – Howard F. Curren Advanced Wastewater Treatment Plant
Diffused Aeration System Replacement Alternatives (March 6th, 2013).
2. Technical Memorandum No. 2 – Howard F. Curren Advanced Wastewater Treatment Plant
Diffused Air Reactor Diffuser Replacement Modeling Report (March 7th, 2014)

As presented in Technical Memorandum No. 1 (Tech Memo 1), several different types of aeration floor
covering systems (e.g. disc, panel, tubular) are available for the City’s consideration. To assist in the
evaluation of the different aeration systems, the City and Tetra Tech developed a Request for Information
(RFI) that was transmitted to various aeration system vendors. The RFI included a range of criteria for
sizing of the aeration equipment and development of budgetary costs. The City’s recent Capacity
Analysis Report (CAR) was utilized to estimate the projected wastewater flows within the City’s service
area. The CAR indicates that flows are expected to increase by about 0.9 MGD/year for the next few
years. The flows and average daily DAR oxygen requirements were projected for the next 20 years. In
addition, the manufacturers were advised that the floor cover system for the first three (3) zones of each
DAR should be compatible with submersible mixers sized for an intensity of 25 horsepower (hp)/million
gallons. The manufacturers provided detailed proposals that resulted in a total of eight (8) feasible
options, including the following:

 Aquarius Disc Membranes (standard density)
 Aquarius Disc Membranes (high efficiency)
 SSI Disc Membranes
 Sanitaire Disc Membranes
 Sanitaire Panel & Disc Membrane Combination
 OTT Tubular Membranes
 Ovivo Membrane Panels
 Parkson Membrane Panels

The information from the manufacturers and the budgetary 20-year present worth cost for replacing the
floor cover system in all four DARs (DAR 1 through 4) is detailed in Appendix A (Technical Memorandum
No. 1 – HFCAWTP Diffused Aeration System Replacement Alternatives) and is summarized as follows in
Table ES-1:
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Table ES-1
Diffused Aeration Equipment Budgetary 20-Year Present Worth Costs
Diffused Air Reactors – All 4 Trains

Manufacturer Aquarius Aquarius SSI Sanitaire Sanitaire OTT Aerostrip Parkson
Standard High
Efficiency Efficiency

Type Disc Disc Disc Disc Panel & Tubular Panel Panel
Disc
Capital Cost $775,000 $910,000 $1,289,000 $761,000 $1,257,000 $889,000 $1,362,000 $1,263,000
Present Worth
$4,252,000 $3,929,000 $4,011,000 $4,434,000 $3,477,000 $3,881,000 $3,905,000 $5,076,000
of Power Cost
Present Worth
of Membrane $38,000 $57,000 $33,000 $46,000 $138,000 $76,000 $261,000 $359,000
Replacement
Total 20-Year
Present $5,065,000 $4,896,000 $5,333,000 $5,241,000 $4,872,000 $4,846,000 $5,528,000 $6,698,000
Worth
Notes:
A. Power costs based on performance curves for the existing blowers and a unit cost for energy of $0.08/kWh.
B. Present worth values based on an interest rate of 6.0%.

Technical Memorandum No. 2 (Tech Memo 2) presents the results from the GPS-X® modeling. Tetra
Tech’s modeling effort included:
1. Calibration of the GPS-X model (model provided by the City).
2. Performing modeling using 24-hour composite data provided by the City:
a. Conducted modeling focused on optimization of DARs operation.
b. Conducted modeling focused on combined optimization of HPO (high purity oxygen)
reactors and DARs.
3. Performing modeling of DARs operation using updated grab samples and ChemScan® data.
Tetra Tech originally modeled denitrification performance and oxygen demand at the DARs based in part
on 24-hour composite data provided by the City that indicated a significant quantity of nitrification at the
HPO reactors. Plant staff later indicated that the HPO effluent NOx-N concentrations are not as high or
corresponding NH -N and TKN concentrations as low as reported by the daily composite lab data. This is
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supported by recent grab samples collected at the same location as the composite sampler and by
ChemScan® data from just downstream of the composite sample point. The results of the original Tetra
Tech process modeling and the updated process modeling are included in Technical Memorandum No. 2
(attached).
Based on these modeling results, City staff have indicated a desire to install new equipment in DAR Train
1, including new diffusers, air flow control equipment, automated process control sampling/monitoring
points, internal recycle, and mixing components. This will allow DAR Train 1 to be operated in a variety of
modes to demonstrate the denitrification potential before converting DARs Trains 2, 3, and 4. In order to
properly size the aeration equipment for the demonstration basin upgrade of DAR Train 1, the process
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model was recalibrated to better agree with the grab sample data that City staff support as the more
reliable data to utilize in the modeling.
The City has established the following goals for the design of the diffuser replacement for the DARs:
1. The diffusers should use a tapered design to more closely match the oxygen demand profile
through the reactors and to maximize oxygen transfer efficiency.
2. The diffuser design should be capable of providing sufficient aeration to meet the air demand at
the DARs without denitrification in the DARs.
3. The diffusers should not be negatively affected by periods of non-aeration such that anoxic
conditions can be created to allow denitrification at the DARs.
4. DAR aeration system sizing should consider the full range of potential aeration demands for
each zone, including from 57 MGD with denitrification to 96 MGD without denitrification.
5. The effluent ammonia and TKN from the DARs shall not exceed 0.8 and 2.0 mg/L, respectively.
Table ES-2 shows the recommended oxygen demands for use in the diffused aeration system design in
DAR Train 1. In order to ensure that the current rated capacity of the plant is maintained, diffusers should
be installed in Zones 1 and 2 to meet the maximum actual oxygen required (AOR) shown below. These
numbers are based on the steady state 96 MGD case at worst case month conditions with all DAR zones
fully aerated. The maximum design oxygen demands for Zones 3 through 6 are based on Zones 1 and 2
being operated as anoxic at 67 MGD AADF under the worst case conditions. At higher flows it may be
necessary to aerate either one or two of the first two DAR zones under high loadings and cooler
temperatures. The minimum oxygen demand case is based on the current flow, with average loading and
high temperatures and only DAR 1 in denitrification mode. The average oxygen demand is based on
annual average loading conditions at 67 MGD and warm water temperatures. The total AOR is taken from
the diurnal modeling for the minimum and average cases and from the steady state modeling for the
maximum case.
Table ES-2
Air Demands Recommended for Basis of Design of DAR Train 1
Design  Total AOR  AOR by Zone, lbs/day
Basis  lbs/day  1  2 3 4 5  6
Minimum 54,499 0 0 6,691 2,769 1,379 1,183
Average 79,533 0 0 8,749 5,873 3,352 1,910
Maximum 132,961 12,091 10,602 9,877 8,721 7,596 5,410

Phase 2 of this project includes the following elements:
1. The design of the complete diffuser replacement system for DAR Train 1. The design will include
the following components:
a. Diffusers
b. Mixers
c. Piping
d. Automated Sampling/Process Control Points
e. Internal Recycle
f. Programming
2. Permitting and construction of the DAR Train 1 improvements.
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3. Optimization of DAR Train 1 nitrification/denitrification process.
4. The evaluation of future upgrades to DARs Trains 2, 3, and 4.

The budgetary cost opinion for completing the improvements to DAR Train 1 are as follows:
Table ES-3
DARs Train 1 Diffused Aeration Equipment Replacement/Process Optimization
Budgetary Cost Opinion

Aquarius Aquarius
Manufacturer Standard High SSI Sanitaire Sanitaire OTT Aerostrip Parkson
Efficiency Efficiency
Panel &
Type Disc Disc Disc Disc Tubular Panel Panel
Disc
Train 1 Floor
$260,000 $310,000 $430,000 $260,000 $420,000 $300,000 $460,000 $425,000
Covering Capital Cost
Electrical/I&C
$90,000 $90,000 $90,000 $90,000 $90,000 $90,000 $90,000 $90,000
Equipment
Engineering,
Permitting, $215,000 $215,000 $215,000 $215,000 $215,000 $215,000 $215,000 $215,000
Construction Admin
Subtotal $565,000 $615,000 $735,000 $565,000 $725,000 $605,000 $765,000 $730,000
Contingency (20%) $113,000 $123,000 $147,000 $113,000 $145,000 $121,000 $153,000 $146,000
Budgetary Cost $678,000 $738,000 $882,000 $678,000 $870,000 $726,000 $918,000 $876,000

As shown in Table ES-3, the improvements included in the Train 1 upgrades are at a minimum:
 New aeration system floor covering (including piping) in all 6 zones of Train 1
 New electrical/I&C associated with the Train 1 aeration system upgrades and process
optimization (including automation of air delivery valves)
 Engineering, permitting, and construction administration for the Train 1 upgrades
Currently, there are ongoing discussions with the City’s staff regarding the replacement or addition of the
following equipment to improve operation and denitrification ability of the DARs:
 Mixers – (replacement)
 Internal Recycle Pumps/Piping – (addition)
 Jockey Air Blower(s) – (addition)
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The details of this equipment, as well as the associated costs, will be presented in the Preliminary Design
Report developed in Phase 2 of this project. Currently, replacement of any of the four (4) existing multi-
stage, 700 HP centrifugal air blowers is not included in this project.
During Phase 2 of this project, the engineer’s opinion of construction cost will be developed during the
preliminary and final design process and will include costs for all of the equipment identified in the
Preliminary Design Report.
In summary, the following key points have been identified as part of this Phase 1 – Study Report effort:
1. The GPS-X modeling results presented in Technical Memorandum No. 2 indicate that at
HFCAWTP’s current average flow, the cost savings in reduced methanol use will exceed
$500,000 per year.
2. The City is currently achieving denitrification within the existing DARs with on-off aeration
operation and has calculated a realized cost savings greater than $500,000 per year due to the
reduction in methanol use in the denitrification filters.
3. As wastewater flows to the HFCAWTP approach the rated plant capacity, less denitrification will
occur in the DARs.
4. The panel-type diffuser is an efficient aeration delivery system with potential for less ragging and
less intensive maintenance requirements. The City is moving forward with installing this diffuser
type in DAR Train 1, monitoring the performance of these panel diffusers, and then confirming the
diffuser type that will be selected to replace the diffusers in DARs Trains 2, 3, and 4.
5. The City will monitor the performance of the existing four (4) existing multi-stage, 700 HP
centrifugal air blowers and determine when these blowers should be replaced.
The City’s proactive approach to optimizing the HFCAWTP’s treatment process will continue to afford the
City overall process and energy cost savings in the operation of this facility.
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Section 1.0 Introduction

The City’s Howard F. Curren Advanced Wastewater Treatment Plant (HFCAWTP) has a permitted design
capacity of 96 million gallons per day (MGD) on an average annual daily flow (AADF) basis. The current
AADF is approximately 56 MGD and the facility maintains consistent compliance with regulatory agency
permit requirements related to effluent quality. Figure 1-1 presents an overall process schematic of the
HFCAWTP.

As shown in Figure 1-1, the facility features a two-stage aerobic treatment process. The first stage of
treatment involves mainly removal of carbonaceous biochemical oxygen demand (CBOD ) although the
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operating data indicates a smaller but significant amount of nitrification. The second stage of treatment
provides nitrification within Diffused Air Reactors (DARs) via a suspended growth activated sludge
process that includes a conventional fine pore diffused aeration system. The DAR structure includes four
(4) parallel process trains that are divided into six (6) zones per train. The diffused aeration system has
been in service for approximately 20 years and is approaching the end of its useful life. Tetra Tech
evaluated various types of diffused aeration technologies that could be considered for replacing the
existing system. The results from the evaluation of eight (8) diffused aeration systems are presented in
Appendix A as Technical Memorandum No. 1 – Howard F. Curren Advanced Wastewater Treatment
Plant Diffused Aeration System Replacement Alternatives.

Additionally, Tetra Tech conducted wastewater process modeling using the City’s GPS-X® model to
evaluate the two-stage activated sludge process. The City established the following goals for the design
of the diffuser replacement for the DARs:

1. The diffusers should use a tapered design to more closely match the oxygen demand profile
through the reactors and to maximize oxygen transfer efficiency.

2. The diffuser design should be capable of providing sufficient aeration to meet the air demand at
the DARs without any denitrification in the DARs and without any nitrification in the HPO basins.
3. The diffusers should not be negatively affected by periods of non-aeration so that anoxic
conditions can be created to allow denitrification at the DARs.

4. The DAR diffuser system is to maintain efficient operation in the event operational changes are
made at the HPO reactors.

5. The effluent ammonia and TKN from the DARs should not exceed 0.8 and 2.0 mg/L respectively.

6. Operation of the DARs will be optimized to achieve more denitrification within the DARs basins,
allowing for reduced methanol use in the denitrification filters and a methanol cost savings.

Tetra Tech formulated and modeled different operational scenarios that vary the oxygen demand
distribution and the degree of denitrification. The diffuser design will be based on information from all of
these scenarios to provide the flexibility necessary to maintain efficient operation over a range of
operational strategies. The results from the wastewater process modeling are presented in Appendix B as
Technical Memorandum No. 2 – Howard F. Curren Advanced Wastewater Treatment Plant Diffused Air
Reactor Diffuser Replacement Modeling Report.

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