Start With Four Site Inputs That Determine the Treatment Train
A data center in Dortmund generally needs two separate treatment trains: one for cooling-tower blowdown and another for sanitary wastewater. Blowdown control depends on cooling design, evaporative loss, make-up-water chemistry, cycles of concentration and the permitted discharge route. At 4 CoC, blowdown is 25% of intake, while at 6 CoC it is 20%. A typical industrial approach is pretreatment, high-recovery RO for reuse and a controlled concentrate-disposal route, while sanitary sewage is treated with MBR equipment. Final limits must come from Dortmund’s sewer authority and site-specific permits, not a generic German specification.
The preliminary design should begin with four inputs, because none can be inferred safely from IT load alone:
- Cooling architecture and demand: identify evaporative cooling, dry cooling, hybrid systems, liquid-cooling loops, future rack density and seasonal operating conditions. Black & Veatch’s data-center guidance states that blowdown volume depends on the cooling design, climate and make-up-water quality, so the mechanical engineer should establish it rather than apply a generic rule of thumb.
- Water balance: measure or model make-up, evaporation, drift, blowdown, chemical additions, average and peak flow, operating hours and planned cooling-water demand. The 2026 Frankfurt reference guide gives 25% of intake at 4 CoC and 20% at 6 CoC; these are calculation examples, not Dortmund design assumptions.
- Water chemistry: obtain representative results for conductivity, pH, temperature, calcium, bicarbonate, silica, sulfate, chloride, residual oxidant, biocides, phosphonates, dispersants and corrosion-inhibitor residuals.
- Destination and operating objective: decide whether each stream will enter the sewer indirectly, become cooling make-up, have its concentrate disposed of separately, or follow a combined route.
For additional method detail, use the high-TDS RO engineering guide alongside the data center blowdown treatment blueprint. Neither transfers another city’s flow, permit or tariff to Dortmund.
| Required input | Minimum information | Design consequence |
|---|---|---|
| Cooling architecture | Evaporative, dry, hybrid or liquid cooling; future density and operating schedule | Determines whether a continuous blowdown treatment train is needed |
| Water balance | Make-up, evaporation, drift, blowdown, average and peak flows | Sets equalization, pretreatment and RO capacities |
| Influent chemistry | Mineral, scaling and chemical-residual analysis | Defines membrane compatibility, pretreatment and scale control |
| Discharge or reuse route | Sewer, reuse, concentrate disposal and applicable authority | Controls final treatment objectives and permitting |
Separate Blowdown, Condensate and Sanitary Wastewater
Cooling blowdown is recirculating water deliberately drained to control the accumulation of dissolved material as water evaporates; Black & Veatch notes that it is replaced with fresh make-up water. It is not equivalent to sanitary sewage, clean condensate or RO reject. Keeping these streams separate preserves sampling accuracy, avoids unnecessary treatment and prevents cooling chemicals from complicating sanitary treatment.
| Stream | Primary composition and concern | Practical treatment objective |
|---|---|---|
| Cooling-tower blowdown | Concentrated cooling-water salts, scale formers and treatment chemicals | Scale control, membrane pretreatment, recovery or compliant disposal |
| Humidifier or air-handling condensate | Water with site-dependent contamination and corrosion risk | Separate sampling and reuse assessment |
| RO reject | Concentrated dissolved salts and residual pretreatment chemicals | Defined disposal or further concentration |
| Maintenance drain-downs | Variable cooling-water quality and intermittent flow | Segregated collection and controlled return or treatment |
| Sanitary sewage | Organic matter, solids and pathogens | Domestic sewage MBR or another permitted sewer route |
The supplied 2026 Frankfurt guide provides only a reference case: approximately 10–25 m³/day of domestic wastewater for a site with approximately 150–250 on-site staff at any shift. It identifies a packaged MBR range of 1–200 m³/day and cites BOD below 25 mg/L and suspended solids below 35 mg/L under EU Urban Waste Water Treatment Directive 91/271/EEC. These values are Frankfurt figures and must not be presented as Dortmund flow or permit limits.
For sanitary treatment, the specified integrated MBR wastewater treatment system has a stated capacity range of 10–2,000 m³/day and filtration below 1 µm. Equipment capacity is not final process design: Dortmund site flows, wastewater characteristics, operating hours and sewer requirements still need confirmation. The domestic sewage treatment systems guide provides comparative treatment context, not a substitute for local approval.
Establish the Dortmund Discharge and Reuse Route
The permitted route should be established before treatment equipment is ordered, because indirect sewer discharge and direct surface-water discharge impose different authorization requirements. First identify Dortmund’s receiving sewer authority, hold a pre-application meeting and obtain the current discharge criteria, sewer-capacity position and information on whether the flow needs an industrial discharge permit or enhanced sewer agreement.
The supplied 2026 Frankfurt guide identifies Germany’s Abwasserverordnung and local sewer rules as regulatory starting points for conductivity, temperature, pH, chloride, sulfate and persistent substances. It gives indicative indirect-discharge values of conductivity typically below 2,500 µS/cm, temperature below 35 °C and pH 6.5–10 in its Frankfurt scope. Dortmund’s current requirements may differ and must be confirmed with the competent authority.
| Decision point | Evidence to obtain | Why it affects equipment |
|---|---|---|
| Indirect sewer discharge | Current Dortmund discharge criteria, sewer capacity and permit conditions | Sets pretreatment, equalization and monitoring requirements |
| Cooling make-up reuse | Required permeate quality, reuse fraction and cooling-water compatibility | Determines RO, polishing and disinfection scope |
| Concentrate disposal | Authorized receiver, permitted composition and volume | May require another treatment stage |
| Direct surface-water discharge | Relevant German and European discharge authorization | Creates a separate, potentially more complex consent |
Reuse should be compared with disposal on a whole-system basis. Recovered cooling make-up can reduce incoming water and sewer-discharge volumes, but additional pretreatment, pumping, storage, disinfection and concentrate management may offset those benefits. The Samarkand treatment reference and Mukalla data-center treatment guide can inform the decision structure, but neither establishes Dortmund requirements.
Build a Pretreatment-to-Reuse Treatment Train
A technically defensible recovery train normally follows this sequence:
- Segregate and equalize: keep blowdown, condensate, RO reject and sewage separate; equalize the selected process stream.
- Filter and remove suspended material: protect downstream equipment from solids, colloids and biological fouling.
- Control scale and chemistry: identify incompatible additives and define the chemical program around membrane and discharge constraints.
- Apply industrial reverse osmosis: recover low-conductivity permeate for reuse while producing a controlled concentrate.
- Polish and disinfect where required: apply the quality and hygiene controls required by the cooling loop or reuse specification.
- Manage concentrate: define an authorized outlet rather than treating it as an unresolved by-product.
Where suspended solids, colloids and bacteria must be removed, the supplied ultrafiltration pretreatment specification states operation from 2,000 to 40,000 L/h, use of 0.03 µm PVDF hollow-fiber membranes, automatic backwash and air scour, and acceptance of up to 300 ppm turbidity. Those are equipment capabilities, not guaranteed Dortmund influent values or required operating conditions.
The PLC-controlled automatic chemical dosing specification covers coagulants, flocculants, pH adjusters and specialty chemicals. The bidder should identify each cooling chemical that may interfere with membranes, disinfection or the permit, then define dosing control against measured flow and chemistry.
For reuse, the supplied industrial reverse osmosis system specification states recovery up to 95% and fully automated PLC control. Actual recovery depends on feed chemistry, scaling control, operating conditions and system design. The Frankfurt reference guide lists conductivity below 50 µS/cm, silica at or below 1 mg/L, 80–90% recovery and 99.5% salt rejection as illustrative reuse targets, not universal Dortmund limits.
Recovery must remain compatible with the water chemistry. The 2026 Frankfurt guide states that conventional brackish-water RO commonly plateaus at 60–80% recovery, while controlled precipitation or dynamic RO may be needed at higher recovery. It also reports that full zero-liquid discharge can increase capital cost by 2–3× and power consumption per cubic metre by an order of magnitude, with payback potentially exceeding 10 years at German tariff levels. ZLD should therefore be selected only after route and water-reuse constraints justify it.
Where hygiene control is required, the supplied chlorine dioxide generator specification covers industrial cooling loops and process wastewater and states compliance with EU Drinking Water Directive 98/83/EC and WHO Guidelines for Drinking-water Quality. The required dose and residual still depend on the reuse specification and site conditions.
| Process stage | Design basis | Key question for the bid |
|---|---|---|
| Segregation and equalization | Measured stream flows, peaks and operating schedule | What storage and pumping duty cover the actual operation? |
| Filtration and pretreatment | Solids, colloids, turbidity and membrane chemistry | Which unit sizes are required and how are they cleaned? |
| Chemical control | Cooling program, pH and scaling indicators | How are incompatible chemicals managed automatically? |
| RO and optional polishing | Required recovery, reuse quality and feed salinity | What recovery is guaranteed at representative feed chemistry? |
| Disinfection | Cooling-loop hygiene and reuse criteria | What residual and monitoring strategy apply? |
| Concentrate management | Permitted receiver and final composition | Where does every concentrate stream go? |
Size the Plant from Water Balance and Demand
Equipment sizing should start with the site water balance: make-up water, evaporation, drift, blowdown and recovered reuse. IT load is only one demand input, and a cooling system’s seasonal profile may govern peak treatment capacity. The supplied Frankfurt reference case—30 MW IT load, approximately 1.3 L/kWh WUE and 4 CoC—corresponds to approximately 8,000–10,000 m³/month of blowdown, with the referenced treatment train at roughly 9,000 m³/month. These figures are a labeled Frankfurt cross-check, not Dortmund estimates.
The blowdown fraction follows the supplied relation:
Blowdown fraction of make-up water = 1 ÷ (cycles of concentration − 1)
Apply the equation only with the same assumptions used to establish evaporation and drift. A different cooling configuration, make-up source or operating schedule changes the result. Size pretreatment and RO for the required daily treatment window, peak blowdown event and future make-up demand. Define the redundancy strategy, membrane replacement inventory and controls response separately rather than embedding them in nominal flow.
The missing Dortmund inputs are explicit: cooling configuration, local climate and summer peak, make-up-water analysis, operating schedule, reuse target, permitted route and concentrate destination. Pilot testing or vendor-side modeling is warranted where scaling, high silica, chemical carryover or unusually variable blowdown makes desktop calculations unreliable. The high-TDS RO engineering guide and high-salinity RO guide provide relevant method references, not site measurements.
Compare Disposal, Recovery and Zero-Liquid-Discharge Options
Direct disposal is the simplest option when the sewer has adequate capacity, the chemistry is compliant and no reuse target applies. Partial recovery reduces water demand and discharge volume but leaves a concentrate stream. High-recovery reuse adds pretreatment, polishing, controls and concentrate management, while full ZLD adds further energy and capital requirements.
The supplied 2026 Frankfurt economics are reference values only. A 60% recovery rate on approximately 9,000 m³/month is described as avoiding roughly €25,000–€35,000/month in combined water and discharge cost, using an indicative €4–6/m³ Frankfurt tariff band. Neither the tariff nor the saving applies to Dortmund without current local data. The same source reports that full ZLD may raise capital cost by 2–3× and power consumption per cubic metre by an order of magnitude, with payback potentially beyond 10 years at German tariff levels.
| Option | Permit and operating burden | Recovery and concentrate | Best fit |
|---|---|---|---|
| Direct compliant disposal | Industrial discharge requirements, monitoring and sewer-capacity confirmation | No intended water recovery; discharge flow remains | Simple operation, available sewer capacity and compliant chemistry |
| Partial recovery with sewer discharge | Two destinations to manage: permeate and concentrate | Reduces incoming water and discharged volume; concentrate remains | Moderate reuse benefit with a feasible concentrate outlet |
| High-recovery reuse | Greater pretreatment, controls, polishing and verification burden | More permeate returned to cooling; smaller discharge volume | Water conservation targets, high water cost or sewer constraints |
| Full ZLD | Highest equipment, energy and operational complexity | Minimal liquid discharge; creates concentrated solid or residual streams | Only where disposal access or site objectives justify the burden |
Reuse becomes more defensible where sustainability targets apply, water costs are high, sewer capacity is constrained or discharge load must be reduced—but only if the concentrate route is feasible. The Gulf data-center disposal comparison and RO-capacity reference case can support comparison work; neither changes Dortmund costs or rules.
Issue a Complete Request for Proposal
A comparable bid requires bidders to price the same physical scope. Request separate packages or clearly priced alternatives for source segregation and equalization, pretreatment, RO or other recovery equipment, sanitary MBR, disinfection, controls, concentrate management and commissioning. This prevents a bidder from hiding an unresolved design gap in a turnkey price.
The mandatory bid schedule should include the representative influent analysis, water balance, average and peak flows, operating hours, recovery target, reuse specification, current Dortmund discharge criteria, available utilities and future expansion assumptions. Each bidder must state design flow, turndown, recovery, permeate and concentrate quality, membrane materials and replacement interval, chemical consumption, electrical load, controls, alarm response and maintenance requirements.
| Bid package | Mandatory evidence | Acceptance requirement |
|---|---|---|
| Segregation and equalization | Stream diagram, flows, storage and pumping calculations | Peak-condition verification |
| Pretreatment | Design flow, feed assumptions, cleaning and redundancy | Representative-wastewater test |
| RO or recovery | Recovery, rejection, membrane materials and replacement plan | Guaranteed performance at agreed feed conditions |
| Sanitary MBR | Design flow, effluent quality and operating controls | Representative wastewater testing |
| Disinfection | Generation or dosing method, residuals and monitoring | Demonstration under operating conditions |
| Concentrate management | Composition, volume and authorized destination | Documented route and contingency |
| Controls and commissioning | PLC scope, alarms, training and site acceptance protocol | Witnessed functional and performance testing |
Require proof-of-performance criteria and a site acceptance protocol based on representative wastewater, not clean-water assumptions. Specify spare parts and support through the membrane and filter-element supply package and treatment-parts schedule. The supplied research explicitly limits final design values: they must be verified against current permits, influent testing and the final equipment proposal.
Frequently Asked Questions
How should a data center in Dortmund size cooling blowdown treatment?
Size from the site water balance, not IT load alone. Obtain make-up, evaporation, drift, average and peak blowdown, cooling configuration and future demand, then size equalization and treatment for the actual operating window. The 4 CoC and 6 CoC relationships are calculation examples from the 2026 Frankfurt guide, not Dortmund flow assumptions.
Is industrial RO or full zero-liquid discharge the better choice?
Use industrial RO when the recovered water has a defined reuse value and the concentrate has an authorized destination. The industrial RO equipment specification supports recovery up to 95%, but actual performance depends on feed chemistry, scaling control and system design. Choose full ZLD only where project constraints justify its additional equipment, energy and operating burden; the supplied 2026 Frankfurt comparison reports potential capital costs of 2–3× and an order-of-magnitude increase in power per cubic metre.
What should the budget estimate include?
Request a vendor quotation using the measured site flow, representative water analysis, Dortmund discharge criteria, reuse target, operating hours, concentrate route and utility conditions. Do not transfer the Frankfurt reference saving of roughly €25,000–€35,000/month, which relates to approximately 9,000 m³/month at 60% recovery and an indicative €4–6/m³ Frankfurt tariff band. Ask for capital cost, annual power, chemicals, membranes, maintenance, concentrate disposal and disposal-savings assumptions separately.
How should a buyer assess a wastewater-treatment supplier?
Check whether the supplier performs the sizing calculations, identifies incompatible cooling chemicals, guarantees permeate and concentrate quality at representative feed conditions, defines redundancy and maintenance, and accepts a site acceptance protocol. Confirm that the integrated MBR wastewater treatment system or industrial reverse osmosis system is offered with the required process performance—not equipment capacity alone—and obtain current Dortmund sewer requirements and confirmed influent data before selecting the supplier.
