COST ESTIMATING

One of the most challenging elements in your design will be estimating the cost to build and operate the wastewater treatment facility that you design. Cost estimation is also an important element when selecting between alternative designs. This discussion contains some tips that you should find helpful when developing your cost estimates.

One good place to start when looking for cost information is the EPA website. There are a variety of cost estimation documents that have been written by the U.S. EPA. For example: Construction Costs for Municipal Wastewater Treatment Plants, Cost Estimating Manual for Combined Sewer Overflow Storage and Treatment, Estimating Water Treatment Costs. Most of the EPA guides have so-called "cost curves". These cost curves were developed by looking at a large number of treatment plants constructed across the United States. For example, the Construction Costs for Municipal Wastewater Treatment Plants (EPA 40980003) were developed from 737 plants. In a cost curve, the cost of a particular unit process is given versus the design flowrate of the process or the size of the process. This is therefore a simple way to determine an approximate cost for a given treatment process. Some cautions: these are average costs for the entire U.S., and adjustments may be needed to account for differences in the local construction market. These so-called "location factors" are published yearly by R.S. Means, EPA, and others. Further, due to inflation costs are not constant over time. It is important to know the TIME for which any costs data was valid and adjust for inflation. The Construction Costs for Municipal Wastewater Treatment Plants (EPA 40980003) were data collected from 1973 to 1978, but then adjusted to report in equivalent 1979 dollars. Adjustments for the time value of money can be made using inflation equations from you Engineering Economy class or "time factors".

1995 $ = cost curve data (1978) * (1995 index / 1978 index) * 1995 location factor
1995 $ = cost curve data (1978) * (107.6/46.9) * 1.1
1995 $ = 2.52 * 1978 $

Note that in the above example, if you neglected to correct for inflation and location, your cost estimate would be low by a factor of 2.5!!

Keep in mind that over the operational lifetime of the wastewater plant that operation and maintenance costs are as important (and may be even MORE important) that construction costs. Operation and maintenance costs include energy to run equipment, man-power time to maintain equipment, replacement parts, and consumables (such as added chemicals). Also, carefully evaluate the cost curves to determine what is included -- do capital costs of an activated sludge system include excavation, concrete work, mechanical devices, etc.? When calculating costs, carefully reference the sources of all of your information to justify your values.

The required accuracy of your cost estimates will vary depending on the stage of your project. Somewhat less accuracy is needed for the alternatives comparison (this avoids detailed calculations on each unit process that would be needed to derive the most accurate cost estimates). With the preliminary design of the selected alternative you should be able to get closer to the true project cost. Calculate the "20-year lifetime" present worth of the project (which will include both capital and O&M); also translate costs into a consumer price ($/1000 gal). The consumer cost is important for residents since it is what they will see on their water bill.

I have some examples of cost estimates that were provided by a consulting company to a client during the alternatives assessment phase…and how they changed after they "narrowed" the alternatives to a shorter list and conducted more detailed analysis. See me….

A SUMMARY OF SOME COST INFORMATION...

SOURCE: SEDLAK, R., Editor. Phosphorus and Nitrogen Removal from Municipal Wastewater. Principles and Practice. 2nd Edition. 1991.

Capital Costs

Basins: concrete 0.5-2 MG
18’ deep with top at grade $0.75/gal for 0.5MG tank, $0.50/gal for 2 MG tank
(costs include metal work, finishes, mobilization, overhead, admin)

Baffle walls: $7.50/ft2 for 8" thick reinforced concrete, $11/ft2 for 12" reinforced concrete

Installed cost of mechanical aeration equipment:
$1900/hp for 25 hp aerator, $750/hp for 100 hp aerator
~$20-$53 / lb O2 / d capacity

Installed cost for diffused aeration systems:
blower $250-$550 / hp for 500-1000 hp aerator
14-20 $/lb O2/hp-hr
diffuser system $7.70 - $11.30 / lb O2 / d
if 3500 lb O2/day capacity total cost of diffusers will be $27K-$40K, blower $48K-$70K

Installed cost for mixers in anoxic or anaerobic zones:
$2300 / hp for 5 hp mixer to $1000 / hp for 40 hp mixer
if require 50 hp / MG => $65,000 / MG w/ 20 hp mixer

Installed cost for recycle pumping for WAS or RAS:
$9 - $10 / gpm capacity; $6250 - $7000 / MGD capacity (if pump >2000 gpm capacity)
if recycle ratio 4:1: $25 - $30K / MGD plant capacity with large pumps

Installed cost of chemical storage facilities: $3000 / 3000 gal tank, $7800 / 12,000 gal tank
PVC piping 1" dia $9/LF, 2" dia $15/LF, 4" dia $24/LF
Valves ~$140 - $260 each
Safety equipment where chemicals used : safety shower & eyewash $470 each
chemical pumps for FeCl3 addition about $6000-$8000
Electrical and instrumentation costs ~15% construction cost

Operation and Maintenance Costs:

power for aeration: O2 for carbon removal, lb/d = Q, MGD * So, mg/L * 8.34
O2 for nitrogen removal, lb/d = Q * 4.57 * No * 8.34

typical oxygen transfer efficiency 2 lb O2/hr/hp
motor efficiency ~90%
hp for O2 trans * 0.746 kw/hp * 24 * 365 / 0.9 = kwh/yr
power cost approx. $0.07 / kwh

mixing for anoxic tank: min detention time 2 hrs
reactor size = Q * 2 hr / 24 = X MG
energy: 50 hp / MG
Y hp * 0.746 kw/hp * 24 * 365 * 0.07 $/kwh = $/yr

recycle pumps:
if 3:1 recycle ratio, 10’ head, efficiency 0.75
pump brake hp = Qr * 694 gpm/MGD * head in ft / 3960 / efficiency = hp
power = hp * 0.746 * 24 * 365 / motor effic = kwh / yr
approx. $0.07 / kwh

alkalinity:
$250-$350 / dry ton NaOH; lb NaOH/d = 40/50 * alk as CaCO3 lb/d
nitrification consumes 7.2 lb CaCO3 / lb N
denitrification produces 3.6 lb CaCO3 / lb N

30% FeCl3 solution $0.95 / gal, operators $24/hr, maintenance ~2% of initial capital cost/yr

Lime use for Phostrip = 300 mg/L * Q MGD * 0.25*0.75*8.34*365 = lb/yr
lime cost $40-$60 / ton, shipping of lime $10-$40 / ton

Odor gas collection & tmt Options:

place covers on unit processes such as primary & secondary clarifiers, trickling filters,...
Cover costs generally range from $12-$80 per ft2 surface area depending on type
fixed roof cover for primary clarifiers $12/ft2 in Orange County, CA
fixed cover costs generally 12-26/ft2
rigid floating covers $42-$56/ft2
flexible floating cover $3-$7/ft2
air supported structure $54-65/m3 to install; operating costs about 250000 kWH/yr

carbon adsorption gas tmt costs (73 GAC suppliers in US, about 6 sell complete systems):
10,000 scfm flow and 100 ppmv inlet conc, capital cost $475K, O&M $250K/yr
250-cfm flow capital $20K and O&M $148K/yr

wet scrubbers with oxidants (hydrogen peroxide, chlorine, ozone, potassium permanganate)

spray chambers (usu. 50-75’ tall, 200 cfm air/ft2) or packed towers (17’ packing, 30’ total height, ~300 cfm air/ft2)
high chemical cost, difficult maintenance & frequent attention needed, safety hazards
cost about $0.70 / 10,000 cfm

catalytic oxidation - waste gas contacts catalyst bed to allow rapid reactions at 700-900°F.
S compounds deactivate certain types of catalyst materials; life of catalyst 2-5 yrs;
not common in WWTPs; capital cost for 250 cfm system of $55K and O&M of $20K/yr

Biofilters: packed bed of media on which the biomass grows

low energy costs compared to other methods; only enough power to overcome 2-3" head loss
cost: 10,000 cfm, H2S 20 ppm in & <1 ppm out; $97.3K capital, $7.9K/yr O&M (1990)
cost: $0.10 / 10,000 cfm ; capital for 250-cfm system $34K, $7200 /yr O&M
cost: capital $17-$69 / cfm for a 25K-cfm system, $10-$40 / cfm for a 75K-cfm system

Activated sludge treatment

use the odorous air as the inlet air fed into the activated sludge tanks
should probably use non-ferrous piping and diffusers to prevent corrosion & fouling
perhaps should use stainless steel dry filter fittings & flowmeters; have observed corrosion problems with aluminum & steel guide vanes on the blower
general aeration rate of 0.25 to 0.5 m2/1000 m3/d; aeration rate 3.5K cfm for a 5-MGD plant;
longest experience at the Hyperion WWTP in Los Angeles, which installed odor treatment from headworks, primary clarifiers, DAF thickeners, and effluent pump station in their activated sludge basins in 1959. Since then, they have cleaned the blower twice, reported no corrosion of fine bubble diffusers, and estimate odor removal at 96-99%
lab studies found removal of odor compounds to below detection limits of 0.1 ppm in an activated sludge reactor of 2 to 4.2 ft depth; nitrification occurred in the reactor
if need activated sludge tanks for ww tmt, no additional capital costs other than selection of proper materials to resist potential corrosion

References:

Ando, S. 1980. Odor Control of Wastewater Treatment Plants. Journal WPCF. 52(5): 906-13.
Bowker & Assoc. 1996. Odor Control by Diffusion into Activated Sludge Basins. NEWEA J. 30(2):137-46.
Environmental Technology. 1988. 8(5): 18-19. Morris & Lecky. Controlling Wastewater Treatment Plant Odors in a Resort Community. Environmental Protection. Feb. 1998.
Romain, M. 1996. "Biotreatment of Odor-Containing Gases from Municipal Wastewater Treatment Plants." Masters Thesis, University of Washington.
Bishop, Witherspoon, Card, Chang, Corsi. 1990. VOC Vapor Phase Control Technology. WPCF Res. Found.
Torres, Devinny, et al. Biofiltration: Controlling Air Emissions through Innovative Technology. 1997. WERF.
vanLith, C., Leson, Michelsen. 1997. Evaluating Design Options for Biofilters. J. Air&Waste Mgmt. 47: 37-48.
Williams, T. & F. Miller. 1992. Odor Control Using Biofilters. Biocycle. 33 (Oct/Nov):72-7, 75-9.

from: Estimating Water Treatment Costs Vol 1 - Summary from EPA (1979)

40mgd conventional water treatment plant:

rectangular clarifiers 1000 gpd/ft2; 40,000 ft3, construction $2,247330; energy 70,560 kwh/yr, maintenance 4,770 $/yr, labor 4,344 hr/yr
basket centrifuge 115,000 gpd, construction cost $334,810; energy 476,760 kwh/yr, maintenance $3000/yr, labor 8,300 hr/yr
dewatered sludge hauling 20 miles, 20,000 yd3/yr; construction cost $81,510; diesel fuel 7820 gal/yr; maintenance $5250/yr; labor 914 hr/yr

5 mgd conventional water treatment plant

rectangular clarifiers 1000 gpd/ft2; 5000 ft2, construction cost $380,570; energy 10,380 kwh/yr; maintenance $1250/yr; labor 689 hr/yr

from: Design manual for fine pore aeration systems (EPA, 1989)

due to diffuser fouling, cleaning is needed at approximately $1/diffuser every 12 months
DO sensor maintenance at Monroe, WI requires 35 labor hr/yr & $100 for materials
2 150 hp & 5 125 hp blowers in San Mateo, CA require about 200 labor hr/yr for routine maintenance and $20,000/yr in material costs
capital cost of 2 new 2590 scfm centrifugal blowers in 1985 was $22,000 or $4.25/scfm capacity
estimates of annual maintenance requirements of 3% of uninstalled mechanical equipment cost for centrifugal blowers and 5% for positive displacement blowers recommended

from: EPA Process Design Manual: Land Application of Sewage Sludge & Domestic Septage; EPA/625/K-95/001 Sept 1995

truck hauling of liquid sewage sludge

liquid sludge hauled in tanker trucks with capacities of 1600, 2500, 4000 or 6000 gal ; capital cost of trucks in 1994 $ of 79K, 106K, 132K, and 158K, respectively; fuel consumption of trucks in miles per gallon of 8, 7, 6, and 5, respectively.

truck loading time ~0.4 hr; unloading time ~1 hr; travel time ~25 mph for urban travel, ~35 mph for rural travel and ~45 mph for highway travel; usually haul 7 hr/d, 120 d/yr

number of roundtrips per year = 365 * daily sludge volume / capacity of tanker trucks

cost of diesel fuel in 1994 $1.09/gal; cost of opeation labor for driver $23/hr in 1994; additional labor needed at loading facility

cost to build truck loading facility in 1994$: 100,000-500,000 gal sludge/yr = $27K

1-2M gal sludge/yr = $54K; 4-8M gal sludge/yr = $82K; >20M gal sludge/yr $136K

vehicle maintenace costs per mile traveled for 1600, 2500, 4000, and 6000 gal trucks are 0.37, 0.42, 0.47, and 0.53 $/mile traveled, respectively

truck hauling of dewatered sludge (all costs in 1994 $)

Truck capacity, yd3

truck cost, $

fuel use, miles/gal

maintenance, $/mile

7

86,000

9

0.34

10

129,000

8

0.42

15

172,000

7

0.49

25

226,000

6

0.59

36

282,000

5

0.70

* other costs similar to above; conversion ~202 gal / cu yd

Other EPA references:
EPA 430980003 Construction Costs for Municipal Wastewater Treatment Plants: 1973-1978
EPA 600/2-76-286 Cost Estimating Manual - Combined Sewer Overflow Storage and Treatment, 1976
Accessing EPA document:
www.epa.gov/ncepihom/nepishom then search