One way to address the cooling water requirements is to use treated effluent. Many people do not realize that effluent, if run through additional stages at the sewage treatment plant, becomes potable water.
How much effluent do you think is generated by a typical city on any given day? If you're still wonder about this:
Yes. Treated sewage effluent can be used for data centre cooling, and it is often a good alternative to drinking water. It is commonly referred to as reclaimed water or recycled wastewater when it is treated and supplied for reuse.
Data centres can consume significant volumes of water, particularly when using evaporative cooling. Reusing treated effluent can reduce demand on municipal drinking-water supplies and freshwater resources.
1.
1. Sewage treatment plant
Secondary-treated effluent is collected for reuse.
2. Additional treatment
Filtration, disinfection, and, where necessary, softening or other processes to control scaling, corrosion, and biological growth.
3. Data centre cooling system
Reclaimed water supplies cooling towers or other suitable heat-rejection equipment.
4. Heat removal
Heat from servers is transferred to a cooling loop and ultimately rejected to the atmosphere or another heat sink.
The key point is that the recycled water normally cools the heat-rejection system, not the servers directly. Servers are typically cooled using a separate water or coolant loop, which may exchange heat with the reclaimed-water system through a heat exchanger.
2.
The water does not usually need to meet drinking-water standards for industrial cooling. Instead, it must meet the requirements of the cooling equipment and applicable regulations. The treatment depends on the effluent quality and the cooling system design.
US EPA
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| Treatment step | Purpose |
|---|
| Fine filtration | Prevent suspended particles from clogging equipment |
| Disinfection | Control bacteria and other microorganisms |
| Softening or scale control | Reduce mineral deposits on heat-transfer surfaces |
| Corrosion control | Protect pipes, heat exchangers and cooling towers |
| Biological growth control | Limit biofilms and manage Legionella risk, particularly in aerosol-generating systems |
| Blowdown management | Remove concentrated salts and contaminants from recirculating water |
Reverse osmosis is not necessarily required. It may be justified where dissolved salts, silica, hardness or other contaminants make the effluent unsuitable for the intended cooling system. Cooling-tower water chemistry must be managed carefully because evaporation concentrates dissolved minerals.
Department of Energy
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3.
Benefits
- Reduces consumption of drinking-quality freshwater.
- Creates a productive use for wastewater that might otherwise be discharged.
- Can improve water security in areas experiencing water stress.
- May reduce costs where reclaimed water is readily available nearby.
Challenges
- Requires suitable treatment, storage and potentially dedicated pipelines.
- Poor water chemistry can cause scaling, corrosion and fouling.
- Cooling towers lose water through evaporation and require controlled blowdown.
- Microbiological hazards and the disposal of concentrated wastewater must be managed.
- Supply must remain reliable during periods of peak cooling demand.
4.
Yes. The US Environmental Protection Agency documents industrial water reuse for data-centre cooling and other industrial applications. One example is Microsoft's partnership with the City of Quincy, Washington, to recycle data-centre cooling wastewater through a dedicated treatment facility.
US EPA
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5.
A practical starting point is to:
- Quantify the data centre's hourly and annual cooling-water demand.
- Assess the sewage treatment plant's effluent quality, available flow and seasonal reliability.
- Test the effluent against cooling-system requirements, including hardness, conductivity, silica, nutrients, suspended solids and microbiological indicators.
- Select the appropriate treatment train and cooling technology.
- Design the cooling-water chemical programme, blowdown treatment and residuals disposal.
- Complete a lifecycle cost assessment covering treatment, pumping, pipelines, energy and water charges.
- Establish continuous monitoring, contingency supplies and regulatory approvals.
Bottom line: Treated sewage effluent is a technically viable and established source of cooling water for data centres. The best solution is usually to treat it to the quality needed for the specific cooling system, rather than to potable-water quality.
