Cost Estimates for GAC Treatment Systems

Cost Estimatesfor GACTreatment Systems Jeffrer Q. Adams and Robert M. Clark Operatorsof severaldrinking water systemsthat are vulnerable to contamination by synthetic and volatile organic chemicalshave shown interest in modifying existing treatment plants to include granular activated carbon (GAC) adsorption. An important consideration in the evaluation of GAC treatment alternatives is the examination of cost factors. This article presentspreliminary cost estimatesfor various applications over a range of systemsizesand carbonbedlives. Costsrelated to postfilter adsorbersusing steel pressureand concretegravity contactorsare examined,as well ascostsassociatedwith fluid-bed, infrared, and multihearth reactivation technologies. Operators of several drinking water systems that are vulnerable to contamination of their raw water supplies by synthetic and volatile organic chemicals

00

0.1

0.2

0.3

0.4

havedemonstrated interest in modifying existing treatment plants to include granular activated carbon (GAC) adsorption. This renewed interest in GAC

0.5

0.6

0.7

sy*tem capacity-nqd

Figure 1. Cost estimates for package-plant GAC adsorbers JANUARY

1989

treatment has been caused by increased regulatory pressure. The 1986 amendments to the Safe Drinking Water Act recognize 83 contaminants for which regulations must be developed.’ Maximum contaminant level goals (MCLGs) must be set by the US Environmental Protection Agency (USEPA) at a level at which no known or anticipated health effects occur, allowing an adequate margin of safety. Maximum contaminant levels (MCLs) must be promulgated simultaneously with MCLGs and be set as close as feasible to the MCLG, In this regard, feasibility is based on the use of best technology, treatment techniques, and other means available, taking cost factors intoconsideration. Insetting the MCLs for synthetic organic chemicals (SOCs), the use of GAC is feasible according to the 1986 amendments. To be the best available for control of SOCs, any other technology, treatment technique, or means must be as effective as GAC for this purpose. An important consideration in the evaluation of choices among various types of technologies is cost. Therefore, the Drinking Water Research Division (DWRD) of USEPA has devoted considerable effort to obtaining and developing preliminary cost estimating data and information that can be used for various applications. This article presents preliminary cost estimating functions and equations for GAC treatment systems and examines various system scenarios. Initial cost studies In response to concerns about the impact of thecost of potential regulations

Copyright © 1989 American Water Works Association

J.Q. ADAMS

& R.M. CLARK

35

Procoss Package pressure CAC contaclnrs

Function*

Co”\c”tlo”al Co”CrCtl’gra\ll> GAC contactors

c

b

n

E’~‘,2ff’f:‘ ‘VAI OL (TSO) Of. (>SO hut 52001

cu It sq ft SC,ft “xd C” ft sq it sq fl

16,lZ 0 0 0 100

256

248.6

766.6

0.00224

1.120 1.0 0.601 0 2104 2.491

cc PE PU.1fl’E

C” it SC,ft wd

100.100 0 0

I’,‘,.6 ii.0

0.997 I.0

BE

sq ft

0

MA1 01‘

sq ft sq fl

1.115 1,460

cc

cu ft

PE

"(1 I1

93.700 0

sq It wd sq fl sq ft

cc PI< + HE Em)

PE + RE (>5Obut 5200)

Con~r”llonal steel pressure’ G.4C contactori

IJnit of Measurement for K4R

HE 1 Pl’Af PE .ztn1 (IL

7.6X.0

0.52’3

2.983.0 203.2

Cl.1289

47.817.6 34.2

-17.817.6

0.712

1.027

>:,.oon

15.150 0 540 1,160

1.0 0.91ti 1.0 0.753 1.068

I.152

400

1.0

cc

Fluld~hcd reactivation

1 102

0.813 1 .o 0.698

G.4C sroragr

ljl:‘ MM 01.

2= 1

1,000.0 7.32 12.6

Back\vash punrplng

Infrarrd reacllvatio”

4

I’AR Raqe fou

As a result of increased regulatory pyessuye, several opera toys of drinking water systems vulnerable to contamination by organic chemicals have demonstrated an interest in modifying existing treatment plants to include GA C.

energy, kW

h/year; MM-

construction costs were presented as a function of the effective GAC volume (cubic feet) in the contactors, an approach that allows various empty bed contact times (EBCTs) to be examined. This approach provided more information than if the costs were related only to water flow through the treatment plant. Construction costs were determined by aggregating the costs of excavation and site work, manufactured equipment, concrete, steel, labor, cast iron and steel pipes and valves, electrical components and instrumentation, and housing. The construction cost estimates did not include costs for contractor overhead and profit, engineering and legal fees, administration, interest duringconstruction, or special site work. These must be added separately toprovidea total capital cost estimate. Operation and mainte-

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nance (O&M) requirements were developed for unit process energy and fuel, building-related energy, maintenance materials, and labor. Provisions for updating cost values to account for inflation were made using several component indexes or general indexes such as the Engineering News Record (ENR) construction cost index and the producers price index. At the same time that the conceptual design cost data were being developed, DWRD conducted field studies that were designed to collect cost and nerformance data-on full-scale GAC treatment facilities. Granular activated carbon steel pressure contactors used as postfilter adsorbers were studied along with GAC adsorbers converted from conventional sand filters at Cincinnati, Ohio.J On-site carbon reactivation using a fluid-bed furnace was also evaluated. On-site GAC reactivation and regional reactivation were studied at Manchester, N.H.” Studies at Jefferson Parish, La., included the examination of GAC pressure contactors and on-site infrared reactivation.” Using data from these and other studies, cost estimating curves and equations have been developed and can be used for determining preliminary cost effects associated with GAC treatment. Cost estimating equations The functional form of the preliminary cost estimating equations is as follows:

materials, and O&M labor. Table 1 presents the equation parameters applicable to Eq 1 for various components of the unit processes. Also, the units of measure for the design and operating variable (T/AR) used in the equations and the VAR ranges for which z = 1 in the dz factor are specified. Constructioncosts(CC)areexpressed in 1983 dollars. To convert an estimate to present-day dollars, the ENR construction cost index (CCZ) can be used (CC x current CCZ/4114.6). The construction cost estimates do not include

Costs were determined by aggregating the costs of site work, equipment, concrete, steel, labor, cast-iron and steel pipes and valves, electrical components and instrumentation, and housing.

engineering and design fees, contractor profit and overhead, interest during construction and other overhead, and Y = 0 + (b) (I’AKY (d’) (1) costs for special site requirements. These costs must be added separately in order in which Y = the base construction cost to arrive at a final capital costs estimate. or specified O&M requirement; VAR = Annual capital costs are estimated by process design or operating variable; multiplying CC by the capital recovery factor (CRF). CRF = I (1 + I).“/ [ (1 + a,b,c,d = parameters determined from nonlinear regression; and .z = 0 or 1, Z).v- 11,in which Z = interest rate and used to adjust the cost function for a N = payback period. Electrical energy requirements (PE, range of VAR values. BE, PUMPE) are given in terms of This equation form is an improvement over earlier attempts because it does not kilowatt-hours per year. Cost estimates restrict the cost to approximately zero at are determined by multiplying these or near VAR = 0. Also, the d2 factor requirements by the electric rate (dollars per kilowatt-hour). Maintenance mateallows transitions in the cost function that are not smooth by nature of the rial costs (&‘ZkZ)are expressed in terms of 1983 dollars per year. The producers data. As an example, the following equation gives the construction costs of price index for finished goods (PPZ) can a small package-plant steel pressure be used to update an estimate to a present cost base (IV~V X current PPZ/ contactor system: 287.1). Operation and maintenance labor CC = 16,125 + 7.632.0 (CI:F?‘)““2:‘(1.102)’ (2) requirements (OL) are given in terms of work-hours per year. Cost estimates are in which CC = construction cost in 1983 determined by multiplying these requiredollars; CUFT = effective GAC volume ments (hours per year) by the labor rate in cubic feet; and z = 0 if CUFT 5400, (dollars per hour). The OL costs do not includelabor overhead or administrative z = 1 if CUFT ~400. Cost estimating equations have been costs, which must be added separately. developed for several technologies used Naturalgas requirements(NG)aregiven in GAC treatment. For each technology in units of standard cubic feet per year, the overall cost is broken down into which when multiplied by the fuel rate several components. For example, the (dollars per standard cubic foot) provide cost of GAC contactors typically includes an estimate of the annual cost. Where an costs for capital, process energy and alternate fuel such as No. 2 fuel oil is pumping, building energy, maintenance used, an estimate of thegallons per year

required can be determined using a total fuel British thermal unit value equal to that of natural gas (gallons = cubic feet/138.7). Package-plant GAC contactors. The construction cost equation for pressureflow GAC contactor package plants utilizes a design variable (VAR) based on the total effective GAC volume (cubic feet) of all contactors combined. This equation is typically used when estimating costs for systems with carbon volumes of 1,000 cu ft or less. Construction costs include cylindrical steel contactors mounted on a steel skid, piping, valves, instrumentation and control panel, supply and backwash pumps, the initial GAC for thecontactors, and a building to house the system. Costs for a clearwell and finished water pumping are not included. As mentioned previously, construction contractor profit and overhead costs, engineering fees, and special site work costs must be added separately. The VAR variable for process plus building energy and O&M labor is based on the effective GAC filter cross-sectional area (square feet) of all contactors combined. The maintenance material cost is presented as a function of the effective GAC volume (cubic feet) of all contactors combined. The VAR should be adjusted to reflect the percentage utilization of the system. For example, if the system is to operate at 70 percent design capacity and the design GAC volume is 500 cu ft, then the MM cost is determined using a VAR value of 350 cu ft. Process energy requirements are for backwash pumping. Building energy requirements are for heating, lighting, and ventilation of the facilities. The electrical energy cost for pumping water to the contactors (PUMPE) is based on the average production flow rate (millions of gallons per day) of all contactors combined. A pumping head of 25 ft is assumed. Maintenance material requirements were estimated from anticipated costs of replacement parts and for supplies involved in the daily operation of the equipment. The cost of replacement carbon, which is a major operating expense, is not included and must be added separately. Labor requirements were developed assuming that the facilities require little attention. Labor is for backwashing the carbon, performing routine maintenance tasks, and monitoring the performance of the contactors. Overhead, administrative labor, and laboratory labor are not included and must be added separately. Labor for on-site carbon handling and transport is discussed in the section on GAC reactivation. Conventional GAC contactors. The construction cost equations for conventional concrete gravity contactor systems and steel pressurized contactor systems utilize as their design variable (VAR) the J.Q. ADAMS & R.M. CLARK 37

JANUARY 1989


combined effective GAC volume (cubic feet) of all contactors in thegiven system. The VAK value should include planned excess capacitv for the system. Construction costs-include contactor structures, liquid- and carbon-handling piping with headers in a pipe gallery, cylinderoperated butterfly valves, flow measurement and other instrumentation, master operations control panel, a cast-in-place concrete slab, and a building to house the system. Not included in the cost estimate for carbon contactors are backwash pumping, initial GAC for contactors, makeup carbon storage, spent and reactivated carbon handling outside of thecontactor pipegallery, construction overhead, contractor and engineering fees, and GAC reactivation facilities. Separate equations arc given for GAC reactivation, backwash pumps, and additional carbon storage. The construction cost for backwash pumping is based on pump capacity (gallons per minute) and assumes a maximum design rate of 18 gpm/sq ft (43.3 m/h) and a pumping dynamic head of 50 ft (15.2 m). One standby pump was included in the cost estimate. The construction cost for additional carbon storage, other than the spent and regenerated carbon storage tanks for on-site reactivation facilities, can be estimated using the parameters given in Table 1. The VAK is the carbon storage capacity (cubic feet). The O&M cost equations for PE. BE, ilml, and OL utilize a VAR that specifies the total GAC filter area (square feet) of all contactors, adjusted for percentage of plant utilized. A hydraulic loading rate of 5 gpm/sq ft (12 m/h) is assumed. If another rate is contemplated for cost estimating purposes, the effective total filter area must be determined for the given contactor flow rate as if the rate was 5 gpm/sq ft. The electrical energy cost for pumpingwater to the pressurized contactors (PUMPE) is based on the combined average production flow rate (millions of gallons per day) of all the contactors. Process energy requirements are for backwash pumping and carbon slurry pumping. Building energy includes heating, ventilation, and lighting. Maintenance material costs includegenera1 supplies, pump maintenance, instrumentation repairs, and replacement parts. The cost of replacement carbon is not included and must be added separately. Labor requirements are for operating and monitoring the contactors, backwash pumps, and carbon slurry pumps, as well as performing routine maintenance tasks. Labor overhead, administrative labor, and laboratory efforts are not included. Infrared reactivation. Construction and O&M costs for infrared reactivators were developed as a function of furnace capacity in pounds of carbon per day for 38

MANAGEMENT

Figure 2. Cost estimates for conventional steel pressure GAC contactors TABLE

2

Purameters used in cost analysis of GAC systems Value

Parameter

70 percent of capaclt) 75 percent 12 percent 10 percent oxer 20 yrars S0.90/lh for 100.000 Ih $15/h $O.OXikW . h $0.95/gal ,$O.‘Wl 3000’gal For Junr 1988 5 percent 5 perccn I 10 percent 10 percent

GAC contactor system operatmn Reactivator uptlme GAC rractivatmn losses Capital amortization GAC price Labor rate Electric rate Furl oil pr~c Process water price Cost index Conlractor profit factor Special site xork factor Engineering fees factor Construction contingencies factor

TABLE

4

Cost estimate bvenkdown for concrete gmGty GAC contactors

a single reactivator. Conceptual designs for a single reactivator ranged in size from 100 lb/h (45.4 kg/h) to 60,000 lb/d (27,216 kg/d). The construction costs include the premanufactured furnace modules (drying, pyrolysis, and activation), the carbon holding tank, the dewateringfeed screws, thequench tank, the afterburner, the wet scrubber, the exhaust gas blower, all duct work, scrubber water piping and valvingwithin process limits, and process electrical equipment and controls. The equipment is entirely housed in a prefabricated metal building erected on a slab founda

tion. Open sidewall construction facilitates heat removal in the furnace area. Operation and maintenance costs are based on 100 percent utilization of the reactivator. If the reactivator is operated only part of the time, then the cost estimate should be adjusted according to the percentage utilization. Process energy requirements are related to operation of the infrared heating units, thecooling and exhaust blowers, and the scrubbing water system. Building energy is for lighting and ventilation only. Maintenance material costs include replacement of the heating units, replacement of

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Figure 3. Cost estimates for concrete gravity GAC contactors TABLE

3

Cost estimate breakdown for steel pressure GAC contacton COSt--$/Vt?ar Item Capital Power Materials Labor Total

0.5 mgd

1 mgd

10 mgd

47,205 2,603 1,573 13.511 64,892

68,350 5,418 1,903 15,966 91.638

459,222 49,225 8,583 49.401 566,432

I

I

TABLE

I

5

Cost estimate breakdown for on-site reactivation

Cost--$/war Item

700,000

Capital

MakeupGAC Power-fuel Materials Labor Total

lb/year*

158,485 76,129 52,115 23,933 83,935 394,598

5,000,OOO

lb/yea-t

355,639 502,651 150,278 83,647 200,907 1,293,123

10,000,000

lb/yea-t

428,186 977,814 299,986 140,139 276,010 2,122,135

*Assumes infrared reactivator tAssumes fluid-bed reactivator

small moving parts associated with dewatered carbon hauling and the scrubbing system, and general equipment maintenance. Makeup carbon costs are not included and must be added separately. Labor requirements are for O&M of the equipment. Operating attention is required to oversee performance of the equipment and to make occasional process adjustments. Maintenance attention is required on an infrequent basis, principally to service moving parts. Labor overhead and administrative labor are not included and must be added separately. JANUARY

Additional estimated costs not covered by the equations specified in Table 1 are (1) water for the reactivation process21-27 gal/lb GAC (175-225 L/kg GAC), (2) water for on-site carbon transport2-7 gal/lb GAC (17-58 L/kg GAC), and (3) labor for on-site carbon transport0.4 work-hours/l,000 lb GAC (0.88 work-hours/l,000 kg GAC). Fluid-bed reactivation. Construction and O&M costs for fluidized-bed reactivation were developed as a function of the capacity (pounds per day) for a single reactivator. Construction cost estimates include spent and reactivated carbon

storage, the carbon dewatering system, the fluid-bed reactor, the fluidizing air blower, thequench tank, the particulate scrubber, interconnecting piping and electrical equipment within process area limits, controls and instrumentation, and a steel building to house the system. Continuous operation is assumed, and O&M costs should be adjusted according to percentage utilization. The PE equation includes both process electrical and building electrical requirements. Maintenance material costs include replacement parts for electrical drive machinery, damaged refractory materials, and other general maintenance items. Makeup carbon costs are not included and must be added separately. Water for the reactivation process and carbon transport must also be added separately as described in the section on infrared reactivation. Labor requirements are for O&M of the equipment and do not include administrative labor or overhead. Labor for on-site carbon transport is estimated at 0.4 work-hours/l,000 lb carbon and must be added separately. Natural gas (NC) was used to provide regenerating steam, but estimates can be adjusted to reflect the use of No. 2 fuel oil. Multihearth reactivation. Construction and O&M costs for multihearth reactivation were developed as a function of the total effective hearth area (square feet) of a single reactivator. The construction costs include the basic furnace, the center shaft drive, furnace and cooling fans, spent carbon storage and dewateringequipment, theauxiliaryfuel system, the exhaust scrubbing system, the reactivated carbon-handling system, the quench tank, the steam boiler, the control panel, instrumentation, and a building to house the system. Operation and maintenance costs assume operation 100 percent of the time and should be adjusted according to percentage utilization. Process electrical energy and natural gas requirements were determined using a hearth carbon loading of 40-50 lb/sq ft/d (195.4-244.3 kg/mz/d). Building energy requirements are for lighting and ventilation. Maintenance material costs were related to repair of the electrical drive machinery, replacement of rabble arms, and damaged refractory materials. Makeup carbon must be added separately, as must water for the reactivation process and carbon transport. Labor requirements are for O&M of the equipment. Labor for on-site carbon transport is estimated at 0.4 work-hours/l,000 lb carbon and must be added separately. Administrative labor and overhead must also be added separately. GAC treatment

costs

The preliminary cost estimating equations can be used to gain a better understanding of the sensitivity of GAC J.Q. ADAMS & R.M. CLARK

1989


39

treatment costs to variations in system characteristics. Costs associated with various GAC postfilter adsorber systems and various types of reactivation systems were examined. Table 2 contains the cost parameters used in this analysis. GAC contactors. For this analysis, the average flow of water through the GAC plant was assumed to be 70 percent of the system’s design capacity. The design hydraulic loading was assumed to be 5 gpm/sq ft (12 m/h). The EBCTs examined in this study were 5,10,15, and 20 minutes, resulting in GAC bed depths of 3.3 ft (1 m), 6.7 ft (2 m), 10 ft (3 m), and 13.4 ft (4 m), respectively. Cost estimates for small package-plant GAC adsorbers are shown in Figure 1. The carbon contactors were assumed to be steel pressure vessels of the downflow type. The overall adsorber cost, which includes both capital and O&M costs, is presented as a function of system capacity, ranging from 0.1 to 1.0 mgd. These estimates do not include the cost of carbon replacement or reactivation. For small systems, the unit cost rises dramatically with decreasing system size. For example, assuming a 15.minute EBCT, the cost rises from $0.36/1,000 gal for a I-mgd plant to $1.27/1,000 gal for a 0.1.mgd plant-an increase of $0.91/1,000 gal. Figure 2 presents GAC adsorption cost estimates related to the use of conventional steel pressure contactors. The unit costs (dollars per thousand gallons) for four EBCTs are plotted as a function of the system’s design capacity, ranging from 1 to 25 mgd. The cost curves exhibit significant economies of scale with respect to system size. Unit cost drops steeply as system size increases from 1 to about 5 mgd and thereafter decreases gradually with increasing size. For example, assuming a 15.minute EBCT, the unit cost drops from $0.36/l ,000 gal at 1 mgd to $0.24/ 1,000 gal at 5 mgd and decreases to $0.20/1,000 gal at 25 mgd. The cost curves associated with the four EBCTs appear to be approximately parallel over the relatively flat portion of the curves from 5 to 25 mgd. In this range, the unit cost appears to increase by about $0.051 1,OOOgalper 5-minute increase in EBCT. An example of an itemized cost breakdown related to GAC adsorbers using steel pressure contactors is presented in Table 3. Costs are given for capital, power, maintenance materials, and labor components for three system sizes: 0.25, 1, and 10 mgd. An EBCT of 15 minutes was assumed. The table shows how the costs (dollars per year) vary with the size of the system. In general, the cost breakdown for steel pressure contactors as a percentage of adsorber cost is capital70-90 percent, power-5-10 percent, materials-l-2 percent, and labor3-20 percent. 40

MANAGEMENT

Figure 4. Comparison of costs for steel pressure and concrete gravity contactors

Figure 6. Cost estimates for GAC reactivation and replacement

Cost estimating curves for concrete gravity GAC postfilter adsorbers are presented in Figure 3. The unit cost for the contactors (excluding carbon replacement or reactivation) is given as a function of system capacity, ranging from 1 to 150 mgd. Significant economies of scale exist with respect to system size, especially in the range l-20 mgd. The cost curves are relatively flat in the size range 20-150 mgd. For example, assuming a 15.minute EBCT, the unit cost drops from $0.46/1,000 gal at 1 mgd to about $0.15/1,000 gal at 20 mgd and decreases gradually to $0.10/1,000gal at 150 mgd. In the relatively flat range of

the cost curves, the unit cost . appears to increase by approximately $0.02-0.031 1,OOOgalper 5-minute increase in EBCT. Table 4 presents an itemized cost breakdown related to concrete gravity GAC contactors for three system sizes: 1, 10, and 100 mgd. An EBCT of 15 minutes was assumed. In general, the capital cost represents about 70-90 percent of the total cost of the carbon adsorption system, O&M labor 5-23 percent, power 2-12 percent, and maintenance materials l-2 percent. A cost comparison between systems employing steel pressure contactors and concrete gravity contactors is presented

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AmO”nt 0, GAC--lb x Iovyear

Figure 5. Cost estimates for on-site GAC reactivation

Figure 7. Total cost estimates for GAC systems as a function of system size (1.5min EBCT)

in Figure 4. In this analysis, systems requiring capacities larger than about 5-10 mgd incur lower costs by using concrete gravity postfilter adsorbers rather than steel pressure contactors. It is expected that for big systems, a smaller number of larger concrete contactors would be cheaper than a larger number of smaller steel contactors. For small systems, however, steel pressure contactors appear to be the most costeffective alternative. GAC reactivation and replacement. Onsite reactivation is an important consideration in making GAC treatment cost-effective. Figure 5 shows reactivaJANtJARY

tion cost estimates (dollars per pound) for fluid-bed, infrared, and multihearth technologies as a function of the amount of spent carbon required for reactivation. Reactivators were assumed to have excess capacity to allow for 25 percent operational downtime(75 percent uptime factor). Design capacities for single reactivators ranged from about 100 lb/h (45.4 kg/h) to about 36,500 lb/d (16,556 kg/d). Reactivation unit costs ranged from about $0.70/lb ($1.54/kg) for a very small reactivator to about $0.22/lb ($0,48/kg) for a large reactivator. Significant cost savings are realized by carbon reactivation compared with virgin

carbon replacement as $0.80-$l.OO/lb ($1.76-$2.20/kg). The infrared technology appears to be the most cost-effective alternative for small systems or ones in which reactivation quantities are less than about 3 x 10” lb/year (1.36 X 10” kg/year). Fluid-bed reactivation appears more cost effective for larger systems. Table 5 presents an itemized cost breakdown related to on-site reactivation for three spent carbon requirements. In general, the capital cost represents about 20-40 percent of the total reactivation cost. Makeup carbon needed to replace the assumed 12 percent lost during reactivation and handling represents a significant cost factor, ranging from 20 to 40 percent of the total reactivation cost. The breakdown for other O&M items are labor-15-20 percent, power and fuel-10-20 percent, and maintenance materials-about 5 percent. When projected spent carbon quantities are small, replacement with virgin GAC or use of off-site (regional) reactivation may be more cost effective than on-site reactivation. Figure 6 compares costs for on-site and off-site reactivation and for replacement of spent carbon with new GAC (with and without spent carbon disposal). The on-site reactivation option assumes a 100.lb/h infrared reactivator. Off-site reactivation assumes a commercial operation that includes transport charges for up to 500 mi one way. The “replacement only” option refers to the cost of purchasing virgin GAC, and “disposal and replacement” includes the cost of GAC and the ultimate disposal of spent carbon by incineration (plus transport charges). Total cost. Preliminary total cost estimates for GAC treatment systems have been developed for a range of plant sizes and carbon bed lives. Table 6 presents unit costs (dollars per thousand gallons) for systems with an EBCTof 15 minutes. Contactors were assumed to be in a parallel configuration. Systems of cl0 mgd employed steel pressure contactors; otherwise, concrete gravity contactors were assumed. When spent carbon requirements were ~1,500 lb/d (~680 kg/d), then replacement of spent carbon with virgin GAC was assumed. When carbon requirements were >1,500 lb/d (>680 kg/d) but ~3 X 10” lb/year (cl.36 x 10” kg/year), then on-site infrared reactivation was utilized. When spent carbon requirements were >3 X 10” lb/year (>1.36 X 10” kg/year), on-site fluid-bed reactivation was employed. Single reactivators were limited to a capacity of approximately 50,000 lb/d (22,680 kg/d). Figure 7 shows cost curves for three GAC bed lives-2,6, and 24 months-as a function of system size, ranging from 1 to 200 mgd at a &minute EBCT. As expected, significant economies of scale J.Q. ADAMS

1989


& R.M. CLARK

41

TABLE 6 GAC treatment cost estimates as a function of system size and bed life* GAC Bed Life days

30 45 z 90 105 122 150 182 225 273 365 545 730

system 0.1

mgd 2.590 2.165 1.950 1.820 1.732 1.669 1.619 1.554 1.507 1.464 1.431 1.393 1.355 1.335

0.25 mgd 1.985 1.576 1.368 1.242 1.158 1.097 1.046 0.986 0.940 0.899 0.868 0.831 0.794 0.775

0.5 wd 1.742 1.344 1.142 1.019 0.937 0.878 0.828 0.770 0.726 0.686 0.655 0.619 0.583 0.565

Cost-$/1,000ga1~

10

15

mgd 0.994 0.900 0.889 0.774 0.697 0.641 0.595 0.540

5 mgd 0.783 0.661 0.598 0.559 0.541 0.541 0.541 0.488

mgd 0.630 0.550 0.491 0.455 0.430 0.412 0.397 0.379

0.365 0.347

0.318 0.301

0.291 0.275

mgd 0.519 0.438 0.404 0.369 0.345 0.328 0.313 0.296 0.283 0.271 0.264 0.264 0.233 0.217

1.0

2.5

mgd 1.562 1.175 0.978 0.859 0.779 0.722 0.673 0.617

0.435 0.417

25 mgd 0.450 0.373 0.333 0.309 0.300 0.283 0.269 0.253 0.240 0.229 0.220 0.209 0.209 0.195

35 mgd 0.440 0.341 0.303 0.279 0.263 0.251 0.241 0.231 0.219 0.208 0.199 0.189 0.186 0.183

50 mgd 0.424 0.313 0.276 0.253 0.238 0.226 0.217 0.205 0.200 0.189 0.181 0.171 0.161 0.156

75 mgd 0.386 0.313 0.251 0.229 0.214 0.203 0.194 0.183 0.175 0.167 0.164 0.154 0.144 0.139

100

150

mgd 0.385 0.293 0.257 0.220 0.201 0.190 0.181 0.171 0.163 0.155 0.149 0.144 0.135 0.130

mgd 0.368 0.283 0.235 0.213 0.198 0.187 0.167 0.156 0.148 0.141 0.136 0.129 0.123 0.119

200 mgd 0.367 0.277 0.232 0.210 0.186 0.176 0.167 0.157 0.140 0.133 0.127 0.121 0.114 0.112

*Nov. 7,1988; assumer infrared and hid-bed reactivation; EBCT-15 min t$/l.OOO L = $/l,OOOgal x 0.2642 L

exist with respect to system size up to about 30 mgd, and thereafter only gradual decreases in unit cost occur with increasing size. The curves also demonstrate that there is only a small gradual increase in cost between a twoyear and a six-month reactivation frequency. Many of the SOCs being considered for regulatory control would probably fall within the two-month to two-year bed life range at a 15-minute EBCT.8 Cost estimates for GAC systems having bed lives in the range of six months to two years are about $0.57$0.41/1,000 gal for a 1-mgd system, $0.37-$0.27/1,000 gal for a lo-mgd system, and $0.16-$0.13/1,000 gal for a lOOmgd system. Cost estimates increase by 30-70 percent for systems having GAC bed lives that fall in the range of six to two months. Summary and conclusions An important consideration in the evaluation of GAC treatment alternatives is cost. The USEPA DWRD developed preliminary cost estimates for various applications over a range of system sizes and GAC bed lives. This article compares the costs of postfilter adsorbers using steel pressure contactors and concrete gravity contactors. Also, the costs associated with fluid-bed, infrared, and multihearth reactivation technologies are examined. Several variables and parameters are important in affecting costs: size of system, carbon exhaustion frequency, EBCT, choice of adsorption and reactivation technologies, interest rate and life of facility, carbon loss rate, and GAC purchase cost. The sensitivity of GAC treatment costs to variations in these factors can be studied by using the cost estimating equations and graphs presented in this article. Steel pressure GAC contactors appear to be more cost effective than concrete 42

gravity contactors for small systems (~10 mgd in this analysis). Concrete gravity contactors exhibit significant economies of scale with respect to system size up to 30 mgd and appear to be cost effective for large treatment systems. Infrared reactivation appears to be cost effective for small systems, and fluidbed reactivation appears to be cheaper when spent carbon is >3 X 106lb/year. Multihearth reactivation appears to be slightly more expensive than fluid-bed and infrared systems. The evaluation of choices among on-site and off-site reactivation and virgin GAC replacement is important because the reactivation or replacement cost may represent up to more than 50 percent of the total cost of the GAC treatment system. The GAC bed lives for many of the SOCs being considered for regulatory control will probably be greater than two months with systems using an EBCT of 15 minutes or more. In these cases, total cost estimates for GAC systems range from about $l.OO/l,OOO gal ($0.26/1,000 L) for small (1 mgd) systems to about $O.lO/l,OOO gal ($0.026/1,000 L) for very large systems. Unit costs are highest for small systems with short GAC bed lives and show a steep drop with increasing system size up to about 30 mgd and with increasing bed life up to about six months. Thereafter, unit cost decreasesgradually with increases in system size and bed life. Acknowledgment The authors thank Benjamin W. Lykins Jr. for providing valuable cost data used in developing the cost estimatingfunctions for GAC treatment systems and Sandra Dryer for assistance in preparing the manuscript. References 1. US Environmental Protection Agency. Safe Drinking Water Act 1986 Amend-

ments. EPA-570/g-86-002. Ofce.of Drinking Water (1986). 2. GUMERMAN,R.C.; CULP,R.L.; & HANSEN,

S.P. Estimating Water Treatment Cost, Vol. II, Cost CurvesApplicableto 1to200 mgd Treatment Plants. EPA-600/2-79162b(1979). 3. GUMERMAN, R.C.; BURRIS,B.E.; & HANSEN,

S.P. Estimation of Small System Water Treatment Costs. EPA-600/S2-84-184 (Mar. 1985). 4. MILLER, R. ET AL. Feasibility Study of Granular Activated Carbon and On-Site Regeneration. EPA-600/2-82.087A (1982). 5. KITTREDGE,D. ET AL. Granular Activated Carbon Adsorption and Fluid-Bed Reactivation at Manchester, New Hampshire. EPA-600/2-83-104 (1982). 6. KOFFSKEY, W. & LYKINS, B. JR. Expe-

riences with Granular Activated Carbon Filtration and On-Site Reactivation at Jefferson Parish, Louisiana. AWWA 1987 Ann. Conf., Kansas City, MO., June 14-18. 7. ADAMS,J.Q. & CLARK, R.M. Development

of Cost Equations for GAC Treatment Systems. Jour. Envir. Engrg:ASCE, 114:3 (June 1988). 8. MILTNER, R. ET AL. Final Internal

Report

on Carbon UseRateData. Drinking Water Res. Div., USEPA Uune 1987). About the authors: For the past 10 years, Jeffrey Q. Adams has been an environmental engineer with the Systems and Field Evaluation Branch qf the Drinking Water Research Division, US Environmental Protection Agency, 26 W. Martin Luther King Dr., Cincinnati, OH 45268, where he has worked primarily on projects involving the cost of water treatment technologies. He is a member of A WWA and holds bachelor’s and master’s degrees from the University of Cincinnati. Robert M. Clark is director of USEPA? Drinking Water Research Division.

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