Recover wastewater to supply airport cooling towers

Submitted through the COP31 Sustainable Transformation Awards · SKD Türkiye (WBCSD Global Network Partner)

The company operates İstanbul Airport and employs more than 1,000 people across airport operations (1).

An airport of this size runs a continuous cooling load. The energy centre cooling towers evaporate water to reject heat, and their make-up water requirement was met entirely from the municipal mains supply. That created three exposures at once: dependence on a supply whose production and distribution carry a high indirect carbon intensity, a large consumption of salt to correct the hardness of mains water in the conditioning process, and operational fragility if the regional supply came under stress.

The region carries that risk. The catchment is classified as water-stressed in World Resources Institute analysis, drought risk is rising with climate change, and dense urbanisation is increasing competition for the same supply. For a piece of critical transport infrastructure, water availability is therefore an operational continuity question rather than only an environmental one.

The company started the investment in Q1 2024, before the Ministry of Agriculture and Forestry water efficiency regulation of 27 December 2024 entered into force, so the decision was taken on water risk rather than on compliance.

The stated objective is to reduce mains water dependency and to meet 100 per cent of cooling water demand from treated water by 2030. The year 2025, the first full operating year, is taken as the baseline (2).

Location of the initiative: İstanbul Airport, İstanbul, Türkiye

The initiative closes the water loop inside the airport by treating effluent to a standard high enough for reuse in the cooling system.

An advanced reverse osmosis system with a capacity of 80 m³ per hour was integrated into the existing wastewater treatment plant rather than built as a separate facility, so that the recovered water is produced where the effluent already arrives and the existing treatment stages act as pre-treatment.

The product water is used as make-up water in the energy centre cooling towers. This is a non-potable, continuous and predictable demand, which is what makes it the right first application for recovered water: the volume is large, the quality requirement is defined, and it recurs every day of the year.

Because reverse osmosis produces water of controlled and consistent quality, the conditioning regime of the towers changes as well. Less salt is required to correct hardness than when the towers are fed from the mains.

The loop is instrumented. IoT-based smart water management systems, smart sensors and remote real-time monitoring track quality, consumption and system performance continuously, and the data is optimised and reported into corporate sustainability reporting rather than reviewed at sampling intervals.

The system is planned around a minimum service life of 20 years and is embedded in the airport's financial and operational resource planning as permanent infrastructure, not as a pilot.

Figure 1: Closed-loop water recovery and reuse: treated airport wastewater passes through the wastewater treatment plant and the reverse osmosis system and is reused as make-up water in the Energy Centre cooling towers

Figure 2: Reverse osmosis treatment system at the airport's wastewater treatment plant, showing the membrane units, pressure filters, pumps and associated piping

Sustainability Impact

Climate

The avoided emissions arise upstream of the airport, in the production and distribution of municipal water and in the energy used to deliver it, rather than in the airport's own combustion or purchased electricity. They are therefore accounted as Scope 3 Category 1 – Purchased Goods and Services, and the company states that both the water supply and treatment reductions and the energy-related reductions were calculated in line with DEFRA standards.

Against supply from the municipal network, the initiative avoids 27 tonnes of CO₂ equivalent per year.

The same substitution produces an indirect energy saving of approximately 60,000 kWh per year, calculated on average consumption in mains water production and transmission processes.

The figures cover 2025, one full year of operation, which is the baseline year for the initiative. Data is collected continuously through IoT-based smart water management systems, remote real-time monitoring automation and smart sensors, and is reported to stakeholders in corporate sustainability reporting.

Nature

In 2025 the system produced and used 130,052 m³ of recovered water, which met 37.6 per cent of the total annual water demand of the cooling towers. That volume is water not abstracted from a catchment already classified as water-stressed, and it is also effluent not discharged.

The quality of the recovered water reduced the salt used to soften mains water hardness by 40 per cent, which lowers the chemical load entering the conditioning process and, subsequently, the discharge.

By reducing both abstraction pressure and discharge volume, the initiative lowers the airport's physical footprint on local water ecosystems rather than shifting it from one point to another.

Social

Water security at a major airport is a public resilience question. Reducing mains dependency lowers the airport's claim on a supply shared with surrounding communities and increases the airport's own ability to keep operating if regional supply comes under stress.

Internally, the IoT-based systems reduce operational disruption and improve the working environment for the teams running the water and energy infrastructure, since faults and quality deviations are visible immediately rather than at the next sample.

Externally, the airport's sustainability summit, site visits with academic partners and workshops brought employees, sector representatives, local authorities, non-governmental organisations and engineering students into the same discussion, and feedback from those events is assessed by the company.

Business Impact

Benefits

The first benefit is the water bill and the risk behind it. Replacing 130,052 m³ of purchased mains water in a single year removes both a cost and an exposure to supply interruption and tariff movement in a water-stressed region.

The second is chemical consumption. A 40 per cent reduction in the salt used for hardness correction is a direct consumable saving, and it also reduces handling, storage and dosing effort.

The third is energy. Approximately 60,000 kWh per year of indirect energy consumption is avoided in the production and transmission of the water no longer purchased.

The fourth is regulatory position. Because the investment was started before the water efficiency regulation entered into force, compliance became a consequence of a decision already taken rather than a cost to be met under time pressure.

Beyond the operating account, the initiative supports the company's disclosure position — a CDP Water Security A score was achieved — and it produced the technical expertise and operating experience that the company treats as the foundation for its larger planned water investments.

Costs

The principal cost is the capital investment in advanced membrane technology, which the company identifies as the main barrier to replication.

Operating costs follow the technology. Membrane fouling has to be managed and the energy consumption of the reverse osmosis stage has to be optimised, both of which are continuing technical requirements rather than commissioning tasks. The monitoring layer — sensors, automation and remote monitoring — adds its own capital and maintenance cost.

The cost is contained in two ways. The reverse osmosis unit was integrated into the existing wastewater treatment plant, so the effluent collection and primary treatment infrastructure did not have to be duplicated. And the system is planned on a minimum 20-year service life and included in the airport's financial and operational resource planning, so it is amortised as permanent infrastructure rather than assessed as a short-payback project.

A structural limitation remains: at 37.6 per cent of cooling tower demand, mains supply is still required, so the connection and its standing costs cannot be removed.

According to the feasibility study, the payback period of the investment was calculated as approximately 3 years.

Impact Beyond Sustainability And Business

Co-benefits

Reduced abstraction leaves more of a stressed regional supply available to surrounding communities and to other users, which is a benefit that accrues outside the company's own boundary.

Demand of this kind pushes suppliers towards better membrane technology, and the company reports that effect across the sector as one of the results of the initiative.

The operating data and technical experience from the first year form the basis for the company's longer-term plans, which include meeting all cooling water demand from treated water and installing seawater reverse osmosis capacity by 2030.

The model is transferable. Any site with its own wastewater treatment plant and a continuous non-potable demand — industrial facilities, organised industrial zones and data centres as well as other airports — can apply the same sequence, and the case is strongest in catchments identified as water-scarce.

Potential side-effects

Reverse osmosis separates a concentrate stream from the product water, and that stream is more saline than the feed. The concentrate is discharged through the existing permitted sea outfall and is monitored as part of the facility’s environmental monitoring programme. Its discharge is therefore included in the environmental assessment of the initiative.

The reported energy result is an indirect saving upstream in the municipal supply chain. Reverse osmosis itself consumes electricity on site. An estimated indirect energy saving of approximately 60,000 kWh per year was achieved in relation to the production and distribution of municipal mains water.

Recovering water increases the number of systems on which cooling depends. A fault in the recovery loop is now a cooling risk as well as a water risk, which is one reason the continuous monitoring layer is not optional.

The salt reduction is a consequence of the higher and more controlled quality of the recovered water; if feed quality varies, the conditioning regime has to be recalculated rather than assumed.

Typical Business Profile

The approach suits single-site operators that already run their own wastewater treatment plant and carry a large, continuous non-potable water demand — airports, industrial facilities, organised industrial zones and data centres with significant cooling loads.

It is most valuable where the site sits in a catchment identified as water-stressed, because the case rests on securing supply as much as on reducing consumption.

Delivery engages an environment and water management function with the authority to set capacity and recovery targets, together with design, planning, procurement, mechanical, electrical, electronic and building maintenance functions, and it requires a monitoring capability that can run continuously.

Approach

1. Locate the largest demand that does not need drinking water quality: Quantify which consumption on site could accept recovered water — here the make-up water of the energy centre cooling towers — and establish how much of it is currently supplied from the mains, because this defines the size of the prize before any technology is selected.

2. Compare the existing effluent quality with what that demand requires: Test the output of the current wastewater treatment plant against the water quality parameters the cooling towers need, so that the treatment gap to be closed is known in advance rather than discovered during commissioning.

3. Add the polishing stage to the existing plant rather than building a new one: Integrate a reverse osmosis unit sized to the demand, 80 m³ per hour in this case, into the wastewater treatment plant, so that collection and primary treatment infrastructure is reused and the recovered water is produced where the effluent already arrives.

4. Take the investment decision on water risk, not on the regulatory calendar: Assess the exposure of the site to regional water stress and act on it, so that later regulatory requirements are met by an asset that is already operating and paid for.

5. Instrument the loop before it goes into service: Install IoT-based smart water management, smart sensors and remote real-time monitoring so that quality, consumption and system performance are visible continuously, since recovered water feeding a critical cooling system cannot be verified by periodic sampling alone.

6. Recalculate the chemical dosing once recovered water enters the towers: Review the water conditioning regime after changeover, because water of controlled and consistent quality needs less salt for hardness correction than mains water, and that saving is only captured if the dosing is actually reset.

7. Fix a baseline year and a short indicator set: Take the first full operating year as the baseline and track recovered volume, share of demand met, avoided emissions, indirect energy saved and chemical reduction, so that the water, energy and carbon effects are measured together rather than claimed separately.

8. Scope the next capacity step from the operating data: Use the first year's results and the operating experience to plan the longer-term targets — meeting all cooling water demand from treated water and adding further recovery capacity — so that expansion is based on measured performance rather than on design assumptions.

Stakeholders Involved

• Project leads: The initiative is owned at Board and senior management level, where water management is treated as a component of operational continuity and corporate resilience rather than as an environmental project. The Environment and Water Management team developed the idea and set the capacity and recovery targets, and is the main executing group.

• Company functions: Technical and operational delivery is managed by a coordinated committee structure in which the design, planning, procurement, electronics, electrical, mechanical systems and building maintenance departments participate directly. This structure keeps the recovery loop inside normal asset management once construction is complete, since the same departments operate it. The monitoring layer — IoT systems, smart sensors and indicator tracking automation — is what allows a cross-functional committee to manage the system without a dedicated permanent project team.

• Main providers: Specialist suppliers and engineering consultants contributed to the technical design of the recovery system alongside the internal departments, working as contributors to the design rather than only as equipment vendors. Independent third-party assurance covers the reported environmental data.

• Other: Universities take part through site visits and workshops, non-governmental organisations and local authorities through the airport's sustainability events, and sector representatives and employees through the airport sustainability summit, where feedback is collected and assessed. The company reports its water performance through CDP, where a Water Security A score was achieved, and its disclosure practice also covers alignment with SBTi-approved targets, ISSB (IFRS S1–S2) and TCFD, TNFD-aligned reporting and independent third-party assurance.

Key Parameters To Consider

The reverse osmosis system has a capacity of 80 m³ per hour and a minimum design life of 20 years, and it is integrated into the existing wastewater treatment plant.

The investment started in Q1 2024 and 2025 is the baseline year, covering one full year of operation. Impact is measured in four areas: water saving, energy efficiency, chemical consumption and greenhouse gas emissions, tracked through five indicators — recovered water volume, share of cooling tower demand met, avoided greenhouse gas emissions, indirect energy saving and the reduction in salt consumption.

The technical risks are the capital cost of advanced membrane technology and, in operation, membrane fouling and the energy optimisation of the reverse osmosis stage.

The regulatory reference is the water efficiency regulation of the Ministry of Agriculture and Forestry, published on 27 December 2024, which the investment preceded.

The longer-term targets are to meet 100 per cent of cooling water demand from treated water and to install seawater reverse osmosis capacity by 2030.

Implementation And Operations Tips

Start from the demand, not from the technology. The reason this loop works is that cooling tower make-up water is continuous, large and non-potable; a site without such a demand will struggle to absorb recovered water at a useful rate.

Measure the chemical effect as well as the water. The 40 per cent reduction in salt consumption was not the objective of the project, but it is a recurring saving that would have been missed if only volume had been tracked.

Build the monitoring in from the start. Continuous instrumentation is what allows recovered water to feed a system on which operations depend, and retrofitting it after commissioning is more expensive and less trusted.

Act ahead of the regulation where the physical risk already exists. Starting the investment before the water efficiency rules entered into force meant the asset was operating and delivering results by the time compliance became a requirement.

Treat the first installation as a capability, not a project. The operating experience and technical expertise built in the first year are what make the larger next step — full substitution of cooling water and seawater desalination capacity — a planning question rather than a research question.

External Links

• Sustainability

• CDP

Source List

(1) İGA Sustainability Green Library

(2) İGA CDP Disclosure