What KDDI's Operating Sakai Data Center Changes for Wastewater Design
A data center in Sakai needs a wastewater train that addresses both concentrated evaporative cooling-tower blowdown and residuals from direct liquid-cooling systems, while protecting the reuse or discharge route permitted for the site. KDDI confirms that its Osaka Sakai Data Center began operating on January 22, 2026, combines conventional air cooling with direct liquid cooling, and reuses the former Sharp plant’s cooling infrastructure. However, the announcement does not disclose makeup-water chemistry, blowdown flow, cycles of concentration, cooling-water inventory or discharge limits. Equipment should therefore remain provisional until Sakai source-water testing, a cooling mass balance and confirmation from the competent sewer or environmental authority are complete.
KDDI’s January 22, 2026 announcement establishes that the AI data center reuses the high-capacity power and cooling facilities at the former Sharp Sakai Plant, which KDDI acquired in April 2025. It also confirms the use of direct liquid cooling alongside conventional air-based cooling and reports that the project was built in half a year.
Those facts change the engineering basis. Reusing an industrial cooling system creates compatibility and phased-operation questions, while the coexistence of two cooling approaches means that server-loop residuals must not be assumed to mix with evaporative tower blowdown. A comparison with the data-center cooling-blowdown treatment guide is useful only for process logic; its location-specific assumptions cannot be transferred to Sakai.
The KDDI announcement does not disclose makeup-water chemistry, basin inventory, evaporation or drift rates, blowdown flow, cycles of concentration, chemical products and dosages, server-fluid chemistry, sampling results, permits or reuse targets. This article therefore distinguishes site-confirmed facts from comparative design benchmarks. Sakai flows, limits, recovery rates and prices must come from local testing, the cooling-system mass balance and current authority decisions.
Map the Sakai Wastewater and Cooling Water Mass Balance
Evaporative cooling blowdown is the controlled purge that removes concentrated constituents as pure water evaporates; it is not first-use cooling-water carryover or a direct-liquid-cooling residual. The Sakai mass balance must therefore begin with separate streams and then identify any point at which KDDI permits them to combine.
The core balance is straightforward: municipal or industrial makeup water and recovered permeate enter the cooling system; water leaves through evaporation; drift, sludge, concentrated blowdown and server-loop residuals leave as controllable or separately managed streams. Concentrated blowdown can contain accumulated salts, hardness ions, silica, biocides, corrosion inhibitors, anti-scalants and trace metals, subject to the site’s actual chemical program.
Cycles of concentration, or COC, links the source water to the discharge volume and constituent concentrations. Increasing COC reduces the controlled purge but also concentrates scale-forming species and treatment chemicals. Neither the permissible COC nor the resulting concentration can be assumed from another Japanese data center.
| Design-basis item | Why it is required for Sakai |
|---|---|
| Average and peak makeup flow; operating hours | Sets hydraulic loading and whether treatment must handle a continuous or peak-driven stream. |
| Evaporation, drift and basin inventory | Separates water loss from concentrated discharge and establishes system inventory. |
| Cooling-system COC and blowdown destination | Links discharge volume to dissolved-constituent concentration and reuse demand. |
| Tower and direct-liquid-cooling configurations | Prevents unrelated server-loop residuals from being mixed into the blowdown design. |
| Chemical products, dosages and schedule | Identifies biocide, inhibitor, anti-scalant and dispersant carry-through. |
| Peak-load and phased-operation cases | Tests the train against AI-density changes and staged capacity additions. |
Saltworks’ 2025 brochure presents a 200 MW data-center case in which effective treatment and recycling reduce cooling-system water consumption by up to 40%. That is a comparative benchmark, not an expected saving at Sakai. Sizing should use the proposed RO and UF membrane and filter-element system only after actual water analyses and hydraulic data are available.
Characterize the Wastewater Before Choosing Unit Processes
Sakai wastewater must be characterized by stream, because makeup water, cooling-loop water, concentrated blowdown and direct-liquid-cooling residuals have different treatment objectives. Representative sampling of each stream is required, with seasonal coverage where source-water quality can vary.
For makeup, loop and blowdown waters, the initial analytical panel should cover pH, conductivity or TDS, total hardness, calcium, magnesium, silica, alkalinity, suspended solids and turbidity. Silt density index should be added where filtration or membrane performance is being evaluated. Metals should be assessed against the metallurgy and materials actually installed; the presence or concentration of trace metals cannot be imported from a Kawasaki guide.
The chemical inventory is equally important. Record biocide chemistry, including oxidizing and non-oxidizing products, as well as corrosion inhibitors, anti-scalants, dispersants and defoamers. Identify phosphorus-based products because their presence can change both reuse-water treatment needs and the information required from the discharge authority.
| Stream | Minimum characterization | Design decision supported |
|---|---|---|
| Makeup water | Major ions, hardness, silica, alkalinity, conductivity, turbidity, SS, metals where relevant | Source concentration, scaling tendency and pretreatment selection |
| Cooling-loop water | Loop chemistry, product carry-through, suspended solids, biological indicators, corrosion evidence | Filtration, side-stream control and biocide compatibility |
| Concentrated blowdown | Full panel plus TDS, silica, hardness and biocide residuals | Sewer pretreatment, reuse treatment and concentrate handling |
| Direct-liquid-cooling residual | Fluid inventory, manufacturer data, chemistry, residual treatment chemicals and disposal instructions | Whether the residual can be segregated, treated or discharged separately |
Residual-oxidant and TOC testing should precede RO or other membrane reuse. The Kawasaki and Tokyo references identify dechlorination and organics removal as important pretreatment controls, but neither supplies Sakai residual values. Bench or pilot work on actual Sakai water is therefore necessary before a high-recovery membrane train is fixed. The multi-media filtration for RO pretreatment and PVDF ultrafiltration pretreatment for Sakai cooling blowdown should remain alternatives or complementary stages until that testing defines the required pretreatment sequence.
Choose a Sakai-Compliant Discharge and Reuse Route
The Sakai treatment route must begin with the receiving authority, not with a preferred machine. Confirm whether discharge will enter a sewer, surface water or another route; obtain the applicable pretreatment agreement, monitoring requirements and current numerical limits; and establish whether cooling-water reuse is recognized for the intended application.
Controlled sewer discharge is the first scenario to test. It may require equalization, suspended-solids removal, chemical control and monitoring appropriate to the local agreement. Concentrated constituents and the acceptable COC remain unknown until the authority provides them, so this scenario cannot yet be dimensioned.
Cooling-makeup reuse is the second scenario. Filtration and UF can protect an industrial RO system for cooling-water recovery, with recovered permeate returned to the cooling system and concentrate routed to a permitted destination. The decision must compare freshwater savings against membrane energy, chemical demand, membrane cleaning and concentrate handling.
High-recovery reuse is a third option. Controlled silica or hardness removal, or an additional membrane stage, should be added only after pilot testing confirms that the chemistry, recovery rate and concentrate route remain workable. ZLD or minimal liquid discharge is a fourth, site-specific option justified by an unavailable discharge route or a formal water-minimization objective; the supplied evidence does not establish such a requirement for Sakai.
| Route | Indicative process direction | Decision gate |
|---|---|---|
| Controlled sewer discharge | Equalization, solids control, chemical control, monitoring and agreed pretreatment | Authority confirms route, limits and monitoring conditions |
| Partial cooling-makeup reuse | Filtration and UF, then RO where justified; concentrate remains a controlled stream | Water balance, pilot recovery and freshwater-saving assessment are complete |
| High-recovery reuse | Additional hardness or silica control and/or a second membrane stage | Pilot data and concentrate destination demonstrate technical and permit feasibility |
| ZLD or minimal liquid discharge | Advanced separation and solids or salt management | A formal discharge constraint or approved water-minimization objective exists |
The life-cycle trade-off must be presented to decision-makers. In the 2026 study by Cartagena Vaca and colleagues, the wastewater-reuse scenario had about twice the global warming potential of the freshwater scenario; treatment energy explained roughly 80% of that difference. The UF+RO case used more than five times the energy of the freshwater case, while the indirect water penalty was approximately 0.93 L/m³, less than 0.1% of direct displacement. These are study results, not Sakai operating forecasts. The regional data-center wastewater treatment guide can support scenario comparison, but it cannot establish Japanese permit requirements.
Build a Pretreatment-to-Recovery Treatment Train
The treatment train should follow the confirmed water balance and route: protect downstream membranes, recover only the water required by the cooling system, and leave every residual stream with a defined destination. No Sakai flowrate, recovery rate or unit count can be stated until the design basis is complete.
Start with equalization and side-stream solids control where the cooling inventory and operating profile justify them. Filtration and UF can remove suspended solids, colloids and biofilm material before RO, while the return arrangement should limit dead zones and keep the basin clean.
Oxidant control is required where the biocide program leaves a membrane-incompatible residual. The final method and target must follow product compatibility data and actual water testing. Hardness removal should be included only where source analysis and the chosen COC show a scaling constraint; softening alone does not remove silica or all dissolved salts.
RO is appropriate where permeate-quality reuse and lower blowdown justify the energy and maintenance burden. Recovery must come from pilot results and the concentrate disposal route, not a generic maximum. If high recovery requires removal of scale-forming constituents that filtration and RO cannot manage safely, precipitation and solids separation may be added before further membrane recovery.
| Process function | Equipment role | Design basis to close |
|---|---|---|
| Solids control and equalization | Side-stream filtration, equalization and monitored pumping | Basin inventory, return profile, peak flows and operating schedule |
| Membrane protection | Multi-media filtration and UF, with oxidant control where required | Turbidity, SS, SDI, residual oxidant, TOC and biocide chemistry |
| Permeate recovery | Industrial RO for cooling-makeup reuse | Pilot recovery, permeate quality, energy use and concentrate route |
| Controlled chemistry | PLC-controlled pretreatment and antiscalant dosing | Product compatibility, dose control, interlocks and chemical storage requirements |
| Residual-solids management | Plate-and-frame filtration for dewaterable solids | Solids generation, dewatering performance and final disposal route |
The final package must also define membrane cleaning, backwash, cartridge replacement, concentrate disposal, alarms, bypasses and operator access. Automatic dosing should be interlocked with flow and water chemistry rather than operate as an unrestricted setpoint. This sequencing keeps the design testable without presenting a provisional train as the confirmed Sakai installation.
Specify, Pilot and Commission the Treatment System
A testable equipment enquiry requires daily and peak flows, operating hours, redundancy, source-water analyses, cooling-program chemistry, recovery target, concentrate route and reuse demand. Missing inputs should remain explicitly open rather than replaced with generic design values.
Request a process guarantee tied to Sakai site-water performance, not nameplate throughput alone. It should define permeate quality, recovery, chemical consumption, cleaning frequency and availability. Require a membrane-compatibility review covering the actual biocide, anti-scalant, corrosion inhibitor and cleaning chemicals.
Specify PLC controls, online conductivity and pH monitoring, permeate and concentrate flow measurement, leak detection, high-pressure protection and accessible maintenance clearances. These controls are necessary because both feed chemistry and concentrate destination can change with operating load and permit conditions.
Require factory and site acceptance-test plans, membrane-cleaning procedures, operator training, spare-parts recommendations and a 12-month performance review after commissioning. Membrane-fouling controls should be included in the enquiry, using the supplied membrane-fouling prevention for the Sakai treatment train as a technical reference rather than as a substitute for pilot testing.
A modular, factory-tested approach can fit phased Sakai operation, but neither module count nor delivery time is supported by the research. The enquiry should list utilities, foundations, access, chemical storage, drainage and future expansion envelopes. Components and replacement strategies should be checked through the treatment parts, valves and filter-media package, with quotations tied to the same design basis.
Frequently Asked Questions
What wastewater and cooling blowdown treatment does a data center in Sakai, Japan need?
It needs a permit-aligned train matched to the actual cooling configuration: treatment of evaporative cooling-tower blowdown, separately assessed management of direct-liquid-cooling residuals, and a defined route for the resulting concentrate. The required flow, recovery and equipment capacity cannot be set from KDDI’s public announcement; they require Sakai source-water testing, a cooling mass balance and current authority confirmation.
How much will wastewater treatment cost for the Osaka Sakai Data Center?
No defensible Sakai price can be given without daily and peak flows, pretreatment depth, RO recovery, concentrate management, controls, redundancy and site-specific construction. A supplier should quote each route separately and state chemical consumption, energy demand, membrane replacement and concentrate costs. Sakai water analysis, the authority’s limits and the cooling design basis are the inputs needed for a comparable budget.
How should a supplier be selected for Sakai cooling-blowdown treatment?
Require evidence from comparable cooling-water applications, a site-water-based recovery guarantee, membrane-compatibility confirmation, FAT and SAT documentation, service capability and a complete concentrate plan. The supplier should identify how [membrane-fouling prevention for the Sakai treatment train](https://newsroom.kddi.com/english/news/detail/kddi_nr-916_4323.html) will be verified. The final process should be selected from pilot data rather than equipment claims alone.
Should KDDI direct liquid-cooling residuals be combined with evaporative cooling blowdown?
Do not combine them without evidence. First obtain the server-loop fluid inventory, chemistry, chemical carry-through and manufacturer disposal instructions, then compare those conditions with the evaporative blowdown. Separation may be necessary where the fluid is incompatible with the cooling chemistry, membrane system or permitted discharge route.
