United States Environmental Protection Agency National Risk Management Research Laboratory Cincinnati, OH 45268 Research and Development EPA/600/SR-95/135 September 1995 vvEPA Project Summary Pollution Prevention Opportunity Assessment United States Naval Base Norfolk Naval Air Station Dan Bowman and Jan DeWaters This report summarizes work con- ducted 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 environ- mental solutions that enhance mission readiness in Defense operations. Under the Chesapeake Bay Agree- ment, Naval Base Norfolk is a member of the Tidewater Interagency Pollution Prevention Program. At NAS Norfolk, the Navy and EPA have evaluated tech- niques and technologies to reduce waste generation from cooling tower operations, cooperating on the Pollu- tion Prevention Opportunity Assess- ment which identified areas for waste reduction during operation and mainte- nance 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 opera- tions. The options for changes in op- erational and treatment processes and procedures were evaluated for their potential to achieve pollution preven- tion 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 re- search project that is fully documented in a separate report of the same title (see Project Report ordering informa- tion at back). Introduction The purposes of the WREAFS Program are to identify new technologies and tech- niques 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 tech- niques and technologies for reducing waste generation are identified through waste minimization opportunity assessments and may be further evaluated through joint re- search, 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 equip- ment, acting as the heat sink for these systems by providing a continuous source of cool water for process operations. Open- system recirculating cooling towers are typically chosen for operation with air con- ditioning and refrigeration equipment be- cause they are relatively inexpensive and minimize heat rejection costs while con- serving 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 evaluat- ------- ing techniques and technologies to re- duce wastes generated from cooling tower operations within the Norfolk MAS. Ap- proximately 28 open-system recirculating cooling towers are currently operated at 18 buildings within the MAS. These units range in size from 5 to 300 tons, and are all associated with comfort cooling sys- tems that operate on a seasonal basis (approximately 6 mo/yr). General Process Description Approximately 598 buildings or struc- tures are located at the Norfolk MAS. Of these, 18 buildings are equipped with air conditioning systems that operate in con- junction with evaporative recirculating cool- ing towers for a continuous supply of process water. The air conditioning sys- tems provide comfort cooling during warm spring and summer months, largely be- tween April and October. The MAS cool- ing towers do not operate during the cool season. Table 1 is a master equipment list of the 28 cooling towers providing pro- cess water for the air conditioners which service these 18 buildings. As described in Table 1, these cooling towers are lo- cated 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 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 028197 028198 021087 024341 081218 093171 093172 SP367 SP254* SP256* V53 V53 SP29** U16** SP45 SP91 SP91 East outside Roof Roof Roof Roof West courtyard East side South side Behind building Behind building 75 200 200 150 175 300 300 125 100 40 127 600 1,000 1,200 1,400 3,500 2,500 1,250 1,000 400 Cooling Towers Not Receiving Treatment* 022189 080394 086933 080385 080386 080387 080388 022188 080389 052754 086998 093369 097454 021751 085676 085677 050597 083286 LP13 LP13 LP13 LP2 LP2 LP3 LP3 LP4 LP4 S33 S33 SP238 SP64 T26 T26 T26 U48 V82 Roof east side Roof west side Roof west side Roof west side Roof east side Roof west side Roof east side Roof east side Roof west side Roof West side South end Outside building Roof east side Roof west side Roof West side Roof 25 25 25 25 25 25 25 25 25 20 5 20 20 20 60 60 7.5 45 N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A 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. influenced by the cooling tower locations and piping systems. Cooling Tower Discharge Practices All cooling towers at the MAS 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 cool- ing towers and air conditioning units are performed by the Public Works Command (PWC), under contract to the MAS. PWC personnel do not currently have a system- atic method for managing the MAS cool- ing towers. Ten of the 28 MAS cooling towers are serviced under a chemical treat- ment contract to PWC by one of two wa- ter treatment specialists. Each of these 10 units is maintained by a treatment repre- sentative, whose primary responsibility in- cludes 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 treat- ment during the operating season aside from the occasional addition of biocide to control excessive fouling. General main- tenance activities for the cooling towers not serviced by a water treatment special- ist 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 dur- ing the operating season to control exces- sive biological fouling, although application rates and schedules vary. Chemical Addition Program At the Norfolk MAS, PWC personnel purchase the chemicals, and a water treat- ment contractor tests the tower water, ad- justs control parameters such as bleed and makeup water flowrates, and admin- isters 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 ------- 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 con- tract 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 MAS would be included in a chemical addition program. General Procedure for Chemical Procurement The procedure for procurement and ad- ministration of water treatment chemicals involves a cooperative effort between ap- propriate PWC personnel and the water treatment or chemical contractor respon- sible for the unit. Each of the cooling tow- ers under contract to a water treatment specialist is inspected sporadically to en- sure that the tower is operating properly and is receiving adequate chemical treat- ment. 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 appro- priate materials for delivery to the specific building at the specific zone on base. Once the chemicals arrive on site, the contrac- tor returns to administer treatment. PWC personnel who were interviewed during the site visit stated that under no circumstances do PWC maintenance per- sonnel administer chemicals to the MAS cooling towers, regardless of whether or not the towers are maintained under con- tract by a water treatment specialist. How- ever, at the time of the site visit, two towers were observed that were not cur- rently 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 re- main somewhat uncertain. A chemical exchange program exists within each zone on base. Most chemi- cals are stored in the mechanical room of the building in which they are used. As more chemicals are needed by a particu- lar building, PWC will first check to see that excess chemicals do not exist in stor- age at another building before ordering a new supply. This procedure avoids stock- piling 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, appli- cation 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 MAS cooling towers, which total approximately 814 gal, are ultimately discharged to the environment through tower bleed. The to- tal annual chemical costs for the MAS cooling towers currently receiving chemi- cal 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 treat- ment chemicals, these may entail excess water usage rates to control the accumu- lation of suspended solids in the system. In addition, improper treatment and man- agement of cooling tower water may re- sult in excessive buildup of scale deposits and biological fouling, ultimately resulting in system failure. Option 1. No Treatment Eighteen of the MAS cooling towers cur- rently have no formal chemical treatment program. One option for pollution preven- tion is to extend this practice to all 28 MAS cooling towers. Under this scenario, the towers would receive annual mainte- nance. 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 reddened with a round wire brush to re- move scale deposits as needed. Approxi- mately 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 chemi- cal costs, and a substantial reduction in the discharge of cooling tower water treat- ment chemicals to the environment. How- ever, 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 addi- tion, the operational lifetime of a unit, typi- cally in the range of 15 to 20 yr, is significantly reduced by improper mainte- nance and also by failure to provide ad- equate corrosion protection. Systems clogged by excessive scale deposits often require acid dosing to clear blocked pas- sageways; this is an aggressive treatment procedure and can be harmful to the ma- terials 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 cool- ing systems is to conserve makeup water. Systems using higher cycles of concen- tration use less water. Achievable cycles of concentration depend on the concen- tration of ions such as calcium and silica in the makeup water, since these accu- mulate 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 or- der to maintain the concentration of dis- solved solids and gases at a required level, thereby preventing scale deposits and corrosion. Maximum concentration factors are rec- ommended for open cooling water sys- tems according to the hardness of the water and the type of treatment applied. Systems receiving makeup water of rela- tively low hardness or those which re- ceive effective scale-inhibiting treatment may operate at high concentration fac- tors, maximizing the portion of recirculat- ing water and minimizing the makeup water requirements. Without treatment, concen- tration 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- ------- 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- (dimethyliminio) ethylene dichloride] Formula 1109* Disodium ethylene bisdithiocarbamate sodium dimethyldithiocarbamate ethylene thiourea Formula 2055 Sodium hydroxide methylene phosphonic acid Formula 7200 Potassium hydroxide 1-hydroxyethylidene-1, 1-disphosphonic acid Biocide Biocide Scale/corrosion inhibitor Dispersant/ antifoulant Chemicals Used in Cooling Towers for Buildings SP45. SP91. V53. SP29and U16 Dicaton Sodium hydroxide Non-Acid descaler GAX-16* Poly ethylene- ethylene dichloride GAX-20* 2,2-dibromo-3 nitrilopropionamide GAX-26 5-chlor-2 methyl-4-isothiazolin-3-one 2-methyl-4-isothiazolin-3-one GCO-10-LM Sodium molybdate polyethylene- ethylene dichloride GCO-10 Poly ethylene- ethylene dichloride Penetrex Not Available"" Biocide Biocide Biocide Scale/corrosion inhibitor w/biocide Scale/corrosion inhibitor w/biocide Dispersant/ antifoulant 2 qt/wk/300 ton 1/2 qt/wk/100 ton 2 qt/wk/300 ton 1/2 qt/wk/100 ton 1 qt/100 ton/day approximately 30 gal/yr 2.5 gal/1,000 gal system water 1/4 to 1/2pt/1,000gal makeup water" 1/4 to 1/2pt/1,000gal makeup water** 1/2 gal/1,000 gal system water 1/2 to 1 pt/1,000gal makeup water" 1/2 to 1 pt/1,000gal makeup water" 1/2 pt/'1,000 gal system water 1/wk 1/wk 1/wk 1/wk Continuous At start-up and shutdown At start-up or cleanup 1/every other wk 1/every other wk At start-up and shutdown Continuous Continuous At start-up and 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 forma- tion by chemical or mechanical means. Minimum dissolved solids and mineral concentrations could be maintained by operating the cooling tower with a con- tinuous supply of fresh water and a maxi- mum flow of tower bleed. A once-through system would avoid the buildup of solids, gases and impurities in the process wa- ter, thereby limiting the potential for scale deposits and corrosion, and would elimi- nate the need for administration and dis- charge of chemicals to the environment through cooling tower blowdown. However, the high operating costs of large amounts of makeup water make this a fairly unat- tractive option. Makeup water requirements and associated costs are reduced drasti- cally by operating at higher cycles of con- centration. Although a continuous bleed will avoid the buildup of dissolved solids and gases, the potential still exists for algal and bac- terial 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 preven- tion 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 mag- netic treatment application combined with integrated technologies, are attractive eco- nomically as well as for pollution preven- tion. Recommendations for further research ------- Table 3. Bleed and Makeup Water Requirements and Monthly Costs at Different Cycles of Concentration* Cycles of Concentration 10 16 Evaporation (gpm) Total bleed rate (gpm) Makeup water (gpm) Water cost ($/mo)** 3 3 6 $443.09 3 1.5 4.5 $335.07 3 1 4 $297.84 3 0.75 3.75 $279.22 3 0.4 3.4 $253.16 3 0.33 3.33 $247.95 3 0.2 3.2 $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 2. Continuous bleed 3. Conventional chemical addition 4. DIAS-aid tower treatment XP-300 5. pH adjustment 6. Base exchange and ion exchange processes 7. KDF process 8. Magnetic applications •Minimal chemical costs •Minimal discharge of chemicals to environment •Minimal chemical costs •Minimal discharge of chemicals to environment •Fairly reliable method •Several chemical options available for customized treatment •Recently developed product which has demonstrated effective treatment •Operates with little or no system bleed •Cost effective, in terms of chemical and water use •Minimal chemical costs; sulfuric acid an economical choice •Minimal discharge of chemical to environment •Minimal chemical costs •Minimal discharge of chemical to environment •Produces soft, non-scaling water •Minimal chemical costs •Minimal discharge of chemical to environment •Waste product consists of recyclable metallic alloy •System is self-regulating by responding to changes in pH •Minimal chemical costs •Minimal discharge of chemical to environment •Lifetime warranty •Minimizes maintenance demands •Effective against scale and corrosion •High maintenance demands •Poor system operation •Reduced operating lifetime of equipment •Excessive water consumption and associated costs •Treatment can be costly in terms of chemicals purchased, required testing and maintenance •Chemicals may be limited in discharges •Limited operating experience on which to base a level of confidence •Additional intermittent treatment may be needed for control of biological growth •Difficult to maintain adequate control •Undesirable dissolved solids may still accumulate in system •Softened water may be corrosive •Generally quite expensive •Provide scale control only •Limited operating experience on which to base a level of confidence •Additional filter unit necessary for solids removal •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 •Limited operating experience on which to base a level of confidence •Additional sidestream treatment usually necessary for solids removal •Additional control may be required for microbial growth ------- Table 4. (continued) Treatment Option Advantages Disadvantages 9. Ozonation, U. V. light treatment 10. Sidestream treatment •Minimal chemical costs •Minimal discharge of chemical to environment •Effective Sterilization Techniques •Effective treatment for solids removal and control of fouling •Minimal chemical costs •Minimal discharge of chemical to environment •Several options are available •Generally quite expensive •U. V. limited to small size; ozone limited to larger size units •Not effective against scale or corrosion •Generally used in conjunction with another treatment method to reduce solids and the potential for microbial growth; not an effective stand-alone treatment methodology include site visits to facilities which em- ploy each of these three types of treat- ment technologies, in order to gather operating data and to observe the sys- tems in operation. Additional information gained through site visits would be used to select an appropriate technology option to be used in a demonstration project de- signed to evaluate the potential for effec- tively treating the MAS cooling tower water. The full report was submitted in fulfill- ment of Contract No. 68-D2-0181, Work Assignment No. 1-011 by TRC Environ- mental Corp. under the sponsorship of the U.S. Environmental Protection Agency. ------- 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 United States Environmental Protection Agency National Risk Management Research Laboratory Cincinnati, OH 45268 Official Business Penalty for Private Use $300 BULK RATE POSTAGE & FEES PAID EPA PERMIT No. G-35 EPA/600/SR-95/135 ------- |