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.

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

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

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

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)

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

Activated sludge treatment