Project Summary

United States

Environmental Protection

Agency

Pollution Prevention Opportunity

Assessment United States Naval

Base Norfolk Naval Air Station

Dan Bowman and Jan DeWaters

National Risk Management

Research Laboratory

Cincinnati, OH 45268

Research and Development

This report summarizes work conducted at the U.S. Navy’s Naval Base

Norfolk, Naval Air Station (NAS) located

at Sewells Point in Norfolk, VA under

the U.S. Environmental Protection

Agency’s (EPA’s) Waste Reduction

Evaluations at Federal Sites (WREAFS)

Program, with support provided under

the Strategic Environmental Research

and Development (SERDP) Program.

SERDP is a cooperative effort between

DoD, DOE and EPA to develop environmental solutions that enhance mission

readiness in Defense operations.

Under the Chesapeake Bay Agreement, Naval Base Norfolk is a member

of the Tidewater Interagency Pollution

Prevention Program. At NAS Norfolk,

the Navy and EPA have evaluated techniques and technologies to reduce

waste generation from cooling tower

operations, cooperating on the Pollution Prevention Opportunity Assessment which identified areas for waste

reduction during operation and maintenance of the NAS cooling towers. The

study followed procedures outlined in

EPA’s Facility Pollution Prevention

Guide. Opportunities were identified for

reducing the generation of waste from

cooling tower water treatment operations. The options for changes in operational and treatment processes and

procedures were evaluated for their

potential to achieve pollution prevention objectives, as well as for technical

and economic feasibility.

This Project Summary was developed

by EPA’s National Risk Management

Research Laboratory, Cincinnati, OH,

to announce key findings of the research project that is fully documented

in a separate report of the same title

(see Project Report ordering information at back).

Introduction

The purposes of the WREAFS Program

are to identify new technologies and techniques for reducing wastes from process

operations and other activities at Federal

sites, and to enhance the implementation

of pollution prevention/waste minimization

through technology transfer. New techniques and technologies for reducing waste

generation are identified through waste

minimization opportunity assessments and

may be further evaluated through joint research, development, and demonstration

projects.

A cooling tower is an enclosed device

designed for the evaporative cooling of

water by direct contact with air. Cooling

towers are used in conjunction with air

conditioning and industrial process equipment, acting as the heat sink for these

systems by providing a continuous source

of cool water for process operations. Opensystem recirculating cooling towers are

typically chosen for operation with air conditioning and refrigeration equipment because they are relatively inexpensive and

minimize heat rejection costs while conserving water.

All of the cooling towers at the Norfolk

Naval Air Station identified in this PPOA

are of the recirculating, open-system type.

The Navy and EPA are currently evaluatEPA/600/SR-95/135 September 1995
2

ing techniques and technologies to reduce wastes generated from cooling tower

operations within the Norfolk NAS. Approximately 28 open-system recirculating

cooling towers are currently operated at

18 buildings within the NAS. These units

range in size from 5 to 300 tons, and are

all associated with comfort cooling systems that operate on a seasonal basis

(approximately 6 mo/yr).

General Process Description

Approximately 598 buildings or structures are located at the Norfolk NAS. Of

these, 18 buildings are equipped with air

conditioning systems that operate in conjunction with evaporative recirculating cooling towers for a continuous supply of

process water. The air conditioning systems provide comfort cooling during warm

spring and summer months, largely between April and October. The NAS cooling towers do not operate during the cool

season. Table 1 is a master equipment

list of the 28 cooling towers providing process water for the air conditioners which

service these 18 buildings. As described

in Table 1, these cooling towers are located on building roofs, adjacent to an

exterior wall, or in a courtyard outside of

the building and range in capacity from 5

to 300 tons. One cooling tower ton is

equivalent to the removal of 15,000 BTU/

hr.

Table 1 indicates that only 10 of the 28

towers are currently receiving chemical

treatment for control of scale, corrosion,

and biological fouling. The remaining

18 towers are primarily small units and do

not receive chemical treatment during the

operating season.

The last column in Table 1 lists the

system water volume in gallons for the 10

towers receiving treatment. The volumes

are used to derive some of the alternative

treatment costs. These system volumes,

estimated by Base personnel, depend to

a large extent on unit size, but are also

influenced by the cooling tower locations

and piping systems.

Cooling Tower Discharge

Practices

All cooling towers at the NAS receive

makeup water from the City of Norfolk

public water supply. Each of the cooling

towers is equipped with a discharge valve

which directed the tower blowdown into

floor drains located in the vicinity of the

heat exchanger and condensed water

pump.

Cooling Tower Maintenance

Activities

Maintenance and operation of the cooling towers and air conditioning units are

performed by the Public Works Command

(PWC), under contract to the NAS. PWC

personnel do not currently have a systematic method for managing the NAS cooling towers. Ten of the 28 NAS cooling

towers are serviced under a chemical treatment contract to PWC by one of two water treatment specialists. Each of these 10

units is maintained by a treatment representative, whose primary responsibility includes cooling tower water testing and

treatment.

The remaining towers, which are not

serviced by a chemical contractor, are the

responsibility of the PWC mechanics.

These units receive no chemical treatment during the operating season aside

from the occasional addition of biocide to

control excessive fouling. General maintenance activities for the cooling towers

not serviced by a water treatment specialist include an annual overhaul of each

unit, which is performed during the winter

months while the unit is not operating.

Following the annual overhaul, PWC

maintenance personnel apply an algicide

to each of the cooling tower units not

serviced by a chemical contractor. A 1-gal

container of algicide is fed by continuous

drip to each unit to control biological growth

in the system. Some of the towers may

occasionally receive additional biocide during the operating season to control excessive biological fouling, although application

rates and schedules vary.

Chemical Addition Program

At the Norfolk NAS, PWC personnel

purchase the chemicals, and a water treatment contractor tests the tower water, adjusts control parameters such as bleed

and makeup water flowrates, and administers chemicals as needed.

Of the 28 towers in operation, 10 are

currently receiving chemical treatment, and

are serviced under contract by one of two

cooling tower water treatment specialists

Table 1. Master Equipment List - Cooling Towers at Norfolk Naval Air Station

Equipment # Building Location Size (Tons) Volume (Gallons)

Cooling Towers Receiving Chemical Treatment*

081275 SP367 East outside 75 127

— SP254** Roof 200 600

— SP256** Roof 200 1,000

028197 V53 Roof 150 1,200

028198 V53 Roof 175 1,400

021087 SP29** West courtyard 300 3,500

024341 U16** East side 300 2,500

081218 SP45 South side 125 1,250

093171 SP91 Behind building 100 1,000

093172 SP91 Behind building 40 400

Cooling Towers Not Receiving Treatment***

022189 LP13 Roof east side 25 N/A

080394 LP13 Roof west side 25 N/A

086933 LP13 Roof west side 25 N/A

080385 LP2 Roof west side 25 N/A

080386 LP2 Roof east side 25 N/A

080387 LP3 Roof west side 25 N/A

080388 LP3 Roof east side 25 N/A

022188 LP4 Roof east side 25 N/A

080389 LP4 Roof west side 25 N/A

052754 S33 Roof 20 N/A

086998 S33 West side 5 N/A

093369 SP238 South end 20 N/A

097454 SP64 Outside building 20 N/A

021751 T26 Roof east side 20 N/A

085676 T26 Roof west side 60 N/A

085677 T26 Roof 60 N/A

050597 U48 West side 7.5 N/A

083286 V82 Roof 45 N/A

* Refers to status of treatment at the time of report preparation, August 1994.

**Chemical treatment has been instituted at these new units since the site visit in June 1994.

***The cooling towers currently not receiving treatment are designed for chemical treatment.

—These two new units have not yet been issued equipment identification numbers.
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who also service other units on base. Four

of these units are equipped with chemical

pumps and metering systems but were

not included in a chemical treatment contract at the time of the site visit in June

1994. Chemical treatment programs have

recently been implemented at these four

units. In the future, all towers at the NAS

would be included in a chemical addition

program.

General Procedure for

Chemical Procurement

The procedure for procurement and administration of water treatment chemicals

involves a cooperative effort between appropriate PWC personnel and the water

treatment or chemical contractor responsible for the unit. Each of the cooling towers under contract to a water treatment

specialist is inspected sporadically to ensure that the tower is operating properly

and is receiving adequate chemical treatment. Operating malfunctions are adjusted

and corrected by the contractor. If the

contractor determines that additional

chemicals must be purchased, PWC is

notified. PWC personnel order the appropriate materials for delivery to the specific

building at the specific zone on base. Once

the chemicals arrive on site, the contractor returns to administer treatment.

PWC personnel who were interviewed

during the site visit stated that under no

circumstances do PWC maintenance personnel administer chemicals to the NAS

cooling towers, regardless of whether or

not the towers are maintained under contract by a water treatment specialist. However, at the time of the site visit, two

towers were observed that were not currently under contract by a water treatment

specialist, but that were connected to a

chemical holding tank and an engaged

metering pump. Thus, the actual chemical

administration procedures as practiced remain somewhat uncertain.

A chemical exchange program exists

within each zone on base. Most chemicals are stored in the mechanical room of

the building in which they are used. As

more chemicals are needed by a particular building, PWC will first check to see

that excess chemicals do not exist in storage at another building before ordering a

new supply. This procedure avoids stockpiling of surplus chemicals.

Chemical Descriptions and

Usage Data

The chemicals used for cooling tower

water treatment at the Naval Air Station

are presented in Table 2 along with their

primary ingredients, type of control, application rate, and frequency of use. Typical

application rates for each chemical, shown

in Table 2, have been combined with cost

information to estimate annual usage rates

and associated costs. Usage rates are

based on a 6-mo operating season, and

assume that all towers operate with 4

cycles of concentration at 100% capacity

for 12 hr/day. As described above, the

chemicals applied to each of the NAS

cooling towers, which total approximately

814 gal, are ultimately discharged to the

environment through tower bleed. The total annual chemical costs for the NAS

cooling towers currently receiving chemical treatment are estimated at $13,900.

For water usage, Table 3 provides bleed

rates and make up requirements with

monthly costs.

Description of Available

Options

Non-treatment

Although non-treatment alternatives may

eliminate the application and subsequent

discharge of cooling tower water treatment chemicals, these may entail excess

water usage rates to control the accumulation of suspended solids in the system.

In addition, improper treatment and management of cooling tower water may result in excessive buildup of scale deposits

and biological fouling, ultimately resulting

in system failure.

Option 1. No Treatment

Eighteen of the NAS cooling towers currently have no formal chemical treatment

program. One option for pollution prevention is to extend this practice to all 28

NAS cooling towers. Under this scenario,

the towers would receive annual maintenance. During the off-season, the units

would be externally cleaned with wire or

nylon brushes, the heat exchanger end

plates would be removed, and the tubes

roddened with a round wire brush to remove scale deposits as needed. Approximately one gal of algicide would be added

to each unit by means of a drip feed.

Refraining from chemical treatment

would result in the annual consumption of

approximately 28 gal of algicide at a cost

of approximately $15 each, for a total of

$420.00/yr. This represents a savings of

approximately $13,300 annually in chemical costs, and a substantial reduction in

the discharge of cooling tower water treatment chemicals to the environment. However, failure to properly maintain the towers

during the operating season results in the

buildup of scale deposits and significant

algal growth, often leading to operational

down-time for necessary repair work and

mid-season cleaning. This is costly in

terms of employee man-hours. In addition, the operational lifetime of a unit, typically in the range of 15 to 20 yr, is

significantly reduced by improper maintenance and also by failure to provide adequate corrosion protection. Systems

clogged by excessive scale deposits often

require acid dosing to clear blocked passageways; this is an aggressive treatment

procedure and can be harmful to the materials of construction, especially where

corrosion has already exposed oxidized

portions of the metallic surface. Thus, while

a no-treatment option appears to be cost

effective in terms of operating expenses,

ultimately, the expense of new equipment

purchases due to system failure makes

this option less attractive.

Option 2. Continuous Bleed-off or

Blowdown

The purpose in using recirculating cooling systems is to conserve makeup water.

Systems using higher cycles of concentration use less water. Achievable cycles

of concentration depend on the concentration of ions such as calcium and silica

in the makeup water, since these accumulate throughout evaporative losses

which take place in the cooling tower. The

risk of severe scale or corrosion problems

increases dramatically with higher cycles

of concentration. Solids and impurities will

continue to accumulate until the system

water is removed through bleed-off or

blowdown. Dissolved oxygen increases in

a recirculating system because the water

is reaerated during each passage through

the cooling tower. In normal practice, a

portion of the recirculating water will be

removed through system blowdown in order to maintain the concentration of dissolved solids and gases at a required

level, thereby preventing scale deposits

and corrosion.

Maximum concentration factors are recommended for open cooling water systems according to the hardness of the

water and the type of treatment applied.

Systems receiving makeup water of relatively low hardness or those which receive effective scale-inhibiting treatment

may operate at high concentration factors, maximizing the portion of recirculating water and minimizing the makeup water

requirements. Without treatment, concentration values of about 3 to 7 are enough

to cause some salts to precipitate out as

scale. Various water treatment approaches

and devices have historically avoided scale

formation by increasing the bleed and

makeup water rates rather than control-
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Table 2. Treatment Chemicals Currently Used in Norfolk NAS Cooling Towers

Trade Name Principal Ingredients Type of Control Application Rate Usage Rate

Chemicals Used in Cooling Towers for Buildings SP367, SP254, and SP256

Formula 1100* Poly [oxyethylene- (dimethyliminio) ethylene- Biocide 2 qt/wk/300 ton 1/wk

(dimethyliminio) ethylene dichloride] 1/2 qt/wk/100 ton 1/wk

Formula 1109* Disodium ethylene bisdithiocarbamate Biocide 2 qt/wk/300 ton 1/wk

sodium dimethyldithiocarbamate 1/2 qt/wk/100 ton 1/wk

ethylene thiourea

Formula 2055 Sodium hydroxide Scale/corrosion 1 qt/100 ton/day Continuous

methylene phosphonic acid inhibitor

Formula 7200 Potassium hydroxide

1-hydroxyethylidene-1, 1-disphosphonic acid Dispersant/ approximately At start-up and

antifoulant 30 gal/yr shutdown

Chemicals Used in Cooling Towers for Buildings SP45, SP91, V53, SP29 and U16

Dicaton Sodium hydroxide Non-Acid descaler 2.5 gal/1,000 gal system At start-up or

water cleanup

GAX-16* Poly ethylene- ethylene dichloride Biocide 1/4 to 1/2 pt/1,000 gal 1/every other wk

makeup water**

GAX-20* 2,2-dibromo-3 nitrilopropionamide Biocide 1/4 to 1/2 pt/1,000 gal 1/every other wk

makeup water**

GAX-26 5-chlor-2 methyl-4-isothiazolin-3-one Biocide 1/2 gal/1,000 gal system At start-up and

2-methyl-4-isothiazolin-3-one water shutdown

GCO-10-LM Sodium molybdate Scale/corrosion 1/2 to 1 pt/1,000 gal Continuous

polyethylene- ethylene dichloride inhibitor makeup water**

w/ biocide

GCO-10 Poly ethylene- ethylene dichloride Scale/corrosion 1/2 to 1 pt/1,000 gal Continuous

inhibitor makeup water**

w/biocide

Penetrex Not Available*** Dispersant/ antifoulant 1/2 pt/1,000 gal At start-up and

system water shutdown

* Biocides are generally alternated on a weekly basis, to increase the effectiveness of treatment.

** Dosage varies depending on system load.

*** Principal ingredients are listed as proprietary information and are not available.

ling calcium carbonate or silicate formation by chemical or mechanical means.

Minimum dissolved solids and mineral

concentrations could be maintained by

operating the cooling tower with a continuous supply of fresh water and a maximum flow of tower bleed. A once-through

system would avoid the buildup of solids,

gases and impurities in the process water, thereby limiting the potential for scale

deposits and corrosion, and would eliminate the need for administration and discharge of chemicals to the environment

through cooling tower blowdown. However,

the high operating costs of large amounts

of makeup water make this a fairly unattractive option. Makeup water requirements

and associated costs are reduced drastically by operating at higher cycles of concentration.

Although a continuous bleed will avoid

the buildup of dissolved solids and gases,

the potential still exists for algal and bacterial growth. Thus, the system may still

malfunction during the operating season if

the biofouling is allowed to progress. Each

cooling tower unit should still receive an

annual overhaul and application of a 1-gal

biocide drip, which will increase annual

operating costs accordingly.

Additional Options and

Recommendations

In addition to the two pollution prevention options identified above, the PPOA

team noted 6 alternative treatment options

available. Table 4 provides an overview of

all the options. A detailed discussion of

the treatment options is provided in the

full report. Three technologies described,

including the DIAS-AID Tower Treatment

XP-300, the KDF process, and the magnetic treatment application combined with

integrated technologies, are attractive economically as well as for pollution prevention. Recommendations for further research
5

Table 3. Bleed and Makeup Water Requirements and Monthly Costs at Different Cycles of Concentration*

Cycles of Concentration 2 3 4 5 8 10 16

Evaporation (gpm) 3 3 3 3 3 3 3

Total bleed rate (gpm) 3 1.5 1 0.75 0.4 0.33 0.2

Makeup water (gpm) 6 4.5 4 3.75 3.4 3.33 3.2

Water cost ($/mo)** $443.09 $335.07 $297.84 $279.22 $253.16 $247.95 $238.27

*Assumes a 100-ton open-system recirculating cooling tower operating at full capacity for 12 hr/day, with a 10°F temperature drop across the tower.

Pump circulation rate is 300 gal/min.

**Costs are based on a combined water and sewer cost of $3.40/1000 gal. Norfolk City water prices are currently $1.34/1000 gal, and sewer prices are

$2.06/1000 gal. Since cooling towers at the Norfolk NAS are generally not provided separate metering systems for drainage, combined rates are

charged for makeup water. It is obvious from the above table that as the operating cycles of concentration increase, the volume of bleed discharged to

the drain is substantially reduced. Separate metering systems would allow calculation of a credit for makeup water which is not discharged to the drain

(e.g., evaporative losses), and would result in substantial savings.

Table 4. Summary of Treatment Options: Advantages and Disadvantages

Treatment Option Advantages Disadvantages

1. No Treatment •Minimal chemical costs •High maintenance demands

•Minimal discharge of chemicals to environment •Poor system operation

•Reduced operating lifetime of equipment

2. Continuous bleed •Minimal chemical costs •Excessive water consumption and associated

•Minimal discharge of chemicals to environment costs

3. Conventional •Fairly reliable method •Treatment can be costly in terms of chemicals

chemical addition •Several chemical options available for customized purchased, required testing and maintenance

 treatment •Chemicals may be limited in discharges

4. DIAS-aid tower •Recently developed product which has demonstrated •Limited operating experience on which to base a

treatment XP-300 effective treatment level of confidence

•Operates with little or no system bleed •Additional intermittent treatment may be needed for

•Cost effective, in terms of chemical and water use control of biological growth

5. pH adjustment •Minimal chemical costs; sulfuric acid an economical choice •Difficult to maintain adequate control

•Minimal discharge of chemical to environment •Undesirable dissolved solids may still accumulate in

 system

6. Base exchange and •Minimal chemical costs •Softened water may be corrosive

ion exchange •Minimal discharge of chemical to environment •Generally quite expensive

processes •Produces soft, non-scaling water •Provide scale control only

7. KDF process •Minimal chemical costs •Limited operating experience on which to base a

•Minimal discharge of chemical to environment level of confidence

•Waste product consists of recyclable metallic alloy •Additional filter unit necessary for solids removal

•System is self-regulating by responding to changes in pH •May cost slightly more than conventional chemical

 treatment

•Operating experience shows inadequate control

 over microbial growth; dosing with biocide or acid

 may be necessary to maintain a clean system

8. Magnetic applications •Minimal chemical costs •Limited operating experience on which to base a

•Minimal discharge of chemical to environment level of confidence

•Lifetime warranty •Additional sidestream treatment usually necessary

•Minimizes maintenance demands for solids removal

•Effective against scale and corrosion •Additional control may be required for microbial

 growth
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Table 4. (continued)

Treatment Option Advantages Disadvantages

9. Ozonation, U.V. light •Minimal chemical costs •Generally quite expensive

treatment •Minimal discharge of chemical to environment •U.V. limited to small size; ozone limited to larger size

•Effective Sterilization Techniques units

•Not effective against scale or corrosion

10. Sidestream treatment •Effective treatment for solids removal and control of •Generally used in conjunction with another treatment

 fouling method to reduce solids and the potential for

•Minimal chemical costs microbial growth; not an effective stand-alone

•Minimal discharge of chemical to environment treatment methodology

•Several options are available

include site visits to facilities which employ each of these three types of treatment technologies, in order to gather

operating data and to observe the systems in operation. Additional information

gained through site visits would be used

to select an appropriate technology option

to be used in a demonstration project designed to evaluate the potential for effectively treating the NAS cooling tower water.

The full report was submitted in fulfillment of Contract No. 68-D2-0181, Work

Assignment No. 1-011by TRC Environmental Corp. under the sponsorship of

the U.S. Environmental Protection Agency.
7

Dan Bowman and Jan DeWaters are with TRC Environmental Corp., Chapel

Hill, NC 27514.

Kenneth R. Stone is the EPA Project Officer (see below).

The complete report, entitled "Pollution Prevention Opportunity Assessment

United States Naval Base Norfolk Naval Air Station," (Order No. PB95-

264040; Cost: $27.00, subject to change) will be available only from:

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22161

Telephone: 703-487-4650

The EPA Project Officer can be contacted at:

National Risk Management Research Laboratory

U.S. Environmental Protection Agency

Cincinnati, OH 45268

BULK RATE

POSTAGE & FEES PAID

EPA

PERMIT No. G-35

United States

Environmental Protection Agency

National Risk Management Research Laboratory

Cincinnati, OH 45268

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Penalty for Private Use

$300

EPA/600/SR-95/135