DAF plant operating cost is the sum of electricity, chemicals, sludge handling and disposal, labour, maintenance and any other costs inside the chosen operating boundary. Calculate these from the site's flow, duty hours, trials and local prices. There is no defensible universal split in which electricity always represents 30–40% or chemicals always represent 40–50%.
Define the boundary and collect the inputs
State whether the estimate covers only the DAF skid or also equalisation, dosing, sludge dewatering, buildings and downstream treatment. Obtain running electrical loads and annual duty hours for each included motor. Use chemical trial results and identify the purchased product concentration. Get a dated disposal quote for the actual wet sludge and destination. Separate estimated assumptions from meter, invoice and laboratory records.
A complete calculation example
All inputs below are invented planning assumptions, not a supplier quotation, field measurement or 2026 market price. Assume feed 20 m³/h, operation 6,000 h/year, annual treated volume 120,000 m³, and currency USD. The assumed doses refer to purchased commercial product, not active ingredient. Sludge mass is an independent hypothetical wet-mass assumption; it has not been derived from a real wastewater test.
| Cost line | Assumption and calculation | Annual USD |
|---|---|---|
| Electricity | 15 kW average running load × 6,000 h × 0.12 USD/kWh | 10,800 |
| Coagulant product | 120,000 m³ × 100 mg/L ÷ 1,000 = 12,000 kg; × 0.50 USD/kg | 6,000 |
| Polymer product | 120,000 m³ × 2 mg/L ÷ 1,000 = 240 kg; × 5 USD/kg | 1,200 |
| Wet-sludge disposal | 0.05 tonne/m³ × 120,000 m³ × 5 USD/tonne | 30,000 |
| Labour | 600 h × 35 USD/h | 21,000 |
| Maintenance and spares allowance | Explicit assumed annual allowance | 6,000 |
| Sampling and laboratory allowance | Explicit assumed annual allowance | 3,900 |
| Total | Sum of the seven included lines | 78,900 |
Specific operating cost = 78,900 ÷ 120,000 = 0.6575 USD/m³. Purchased coagulant consumption is 2 kg/h; polymer consumption is 0.04 kg/h under these assumptions. The example excludes financing, depreciation, tax, civil works, installation and any unlisted treatment stage. It is not a complete project lifecycle estimate.
What changes the answer most?
At the same assumptions, an extra 10 mg/L of coagulant product costs 600 USD/year. An extra 1 kW of average running load costs 720 USD/year. An increase of 5 USD per wet tonne in the assumed disposal tariff adds 30,000 USD/year. These are sensitivities of this example, not predictions for another plant. Changing sludge dryness also changes transported wet mass; do not multiply a dry-solids estimate by a wet-tonne disposal rate without conversion.
Use the estimate to compare equipment
For a proposed DAF system, request a motor duty schedule and test-based dosing range. Include the consumption of the chemical dosing equipment. Evaluate a filter press against measured sludge characteristics, additional power and labour, and an actual disposal quotation. Use the maintenance checklist to identify missing line items, not as evidence of local prices.
Verify the estimate after commissioning with volume, electricity, chemical purchases, sludge tickets and operating hours. Investigate differences in the input assumptions before claiming savings.
DAF cost questions
How should payback be calculated?
Divide incremental investment by verified annual net savings against a defined baseline. If the baseline operating cost is 36,000 USD/year, a hypothetical 30% reduction is 10,800 USD/year, not 40,000 USD/year. Include new costs and compare the same scope.
Are chemical percentages transferable between plants?
No. Calculate consumption and price for each site; the total-cost shares follow from those calculations.
Can a catalogue power rating predict the electricity bill?
Not alone. Use actual running load, duty cycles, hours and tariff, then compare with metered operation.
