Why a Makkah Data Center Cannot Discharge Blowdown Untreated
A data center in Makkah that runs evaporative cooling generates two coupled water streams: cooling-tower blowdown, which typically measures 6–19 L/s and peaks around 20 L/s for a medium-sized site at maximum ambient temperature and IT load (Arup/LinkedIn, 2024), and any sanitary or process wastewater produced by the campus. In the Makkah region, where ambient temperatures regularly exceed 35 °C and feedwater is high in TDS and hardness, the realistic treatment train is screening, multi-media filtration, lime/soda or ion-exchange softening, ultrafiltration, and a polishing reverse osmosis (RO) stage to lift the water back to cooling-tower makeup quality — with the option of reusing RO permeate for humidification or adiabatic systems.
Discharges to sewer or wadi must align with Saudi limits on TDS, residual chlorine, temperature, and oil/grease, and the project's Water Usage Effectiveness (WUE) target should be benchmarked against the Climate Neutral Data Centre Pact's 0.4 L/kWh ceiling for water-stressed areas.
Three forces make an untreated blowdown discharge non-viable in the Makkah region. First, the site sits in a basin that, like the 66% of US power generation tied to medium-high or extremely high water-stress watersheds flagged by Ceres in 2024, leaves little buffer for careless consumption (NCSU, citing Ceres, 2026). Second, blowdown is a continuous industrial discharge that cannot be throttled back like residential demand; NCSU's Sprenger (2026) describes evaporative cooling as a 24/7 water user that fundamentally alters a watershed. Third, blowdown carries documented pollutants: elevated salinity, residual biocides, and anti-scalants picked up from the cooling-water chemical programme, plus a thermal load above ambient sewer acceptance (NCSU/Sprenger, 2026). Treating blowdown as a resource to be recovered — not a residual to be dumped — is the only path that keeps the operator compliant and the local water balance intact.
Makkah Feedwater Profile and Blowdown Stream Quality
The research corpus does not include numeric Makkah feedwater values, so any specific TDS, chloride, or hardness figure must be sourced from the National Water Company (NWC) or an on-site analysis before design. Qualitatively, Makkah's municipal and groundwater supplies trend high in TDS, chloride, and hardness relative to US/EU averages, and a single "softener plus RO" train is rarely adequate without polishing or anti-scalant chemistry on top. The cooling-tower blowdown stream concentrates dissolved solids 4–6-fold relative to makeup (cycles of concentration, or CoC), carries suspended solids picked up in the tower, and contains residual phosphonates, dispersants, corrosion inhibitors, biocides, and scale inhibitors from the chemical programme (Genesis Water Tech). Temperatures of blowdown from indirect or hybrid cooling remain well below high-temperature industrial effluent levels, but they are still above ambient sewer or wadi acceptance in many jurisdictions (Arup/LinkedIn, 2024).
Engineers should confirm local feedwater data with NWC and a recent analysis of any on-site well or treated-wastewater reuse line before fixing the design basis, because a high-iron or high-silica source will change the softening and anti-scalant strategy on the polishing RO. The table below summarises the qualitative feedwater and blowdown parameters the designer should expect in the Makkah context, with the explicit note that numeric values must be confirmed on a per-site basis.
| Parameter | Typical Makkah feedwater (qualitative) | Cooling-tower blowdown (4–6 CoC) | Design implication |
|---|---|---|---|
| TDS | High relative to US/EU baseline | Concentrated 4–6× versus makeup | RO polishing required for reuse; discharge TDS limits apply |
| Hardness (Ca/Mg) | High; site-specific value required | Scaled up at CoC | Lime/soda or ion-exchange softening upstream of RO |
| Chloride / sulfate | Elevated; site-specific value required | Concentrated | Material selection (stainless / FRP); RO membrane chloride tolerance |
| Suspended solids | Low–moderate | Picked up in tower basin; varies with CoC | Clarification or DAF before media filtration |
| Residual treatment chemicals | Negligible in feed | Phosphonates, dispersants, biocides, scale inhibitors | Antiscalant/dosing control; downstream biological fouling |
| Temperature | Ambient (≥ 30 °C summer) | Above ambient sewer acceptance | Cooling before discharge if path A is chosen |
Cycles of Concentration, Blowdown Volume, and the Cost of Pushing Too Hard
The blowdown ratio is 1 / (CoC − 1). At 4 CoC, blowdown is roughly 25% of makeup; at 6 CoC, it is about 20% — a 5-percentage-point reduction, not the 50% that operations teams often assume (Genesis Water Tech). Pushing CoC higher with chemicals alone tends to add dissolved solids to the blowdown and raise downstream treatment cost, so the better direction is physical treatment that reduces scaling and biological fouling without adding solids (Genesis Water Tech). Operating above 5–6 CoC without advanced treatment increases microbiologically influenced corrosion, scaling, and biological fouling risk exponentially and typically forces CoC back down to a manageable level (Genesis Water Tech).
Sustainability directors often mandate CoC increases without addressing the chemistry; engineers should pre-empt this by modelling both the water saving and the chemistry/health cost together. The table below sets out the math with the values supplied in the research, so the engineer can defend the chosen CoC to a project sponsor.
| Cycles of concentration (CoC) | Blowdown ratio (1 / (CoC − 1)) | Blowdown as % of makeup | Operating envelope |
|---|---|---|---|
| 3 | 1 / 2 | 50% | Conservative; high blowdown, low scaling risk |
| 4 | 1 / 3 | ~25% | Common baseline for many facilities (Genesis Water Tech) |
| 5 | 1 / 4 | ~20% | Upper edge of stable operation without advanced treatment |
| 6 | 1 / 5 | ~20% | Biologically and chemically risky without advanced physical treatment (Genesis Water Tech) |
| > 6 | < 1 / 6 | < 17% | Requires RO/IX polishing, anti-scalant chemistry, and tight biological control |
Recommended Treatment Train: From Cooling-Tower Blowdown to Reusable RO Permeate
The defensible end-to-end process flow for a Makkah blowdown treatment and reuse train, with each stage's role and the parameter ranges the supplier must meet, is as follows.
- Screening. A rotary mechanical bar screen protects downstream pumps and media from rags, plastics, and debris typical of cooling-tower basin water.
- Clarification / DAF. A DAF system removes suspended solids, oils, and light biological floc, and is well-proven in industrial cooling-water duty; a lamella clarifier is an alternative where space is tight and load is steady.
- Multi-media filtration. A sand/anthracite/garnet multi-media filter reduces turbidity and SDI to a level that protects downstream RO membranes.
- Softening or antiscalant dosing. Either a twin-tank industrial water softener or a PLC-controlled chemical dosing skid is used to control hardness and silica scaling on the RO; the dosing skid is the standard delivery vehicle when anti-scalant chemistry is preferred over ion exchange.
- Ultrafiltration. A PVDF ultrafiltration system at 0.03 µm removes colloids, bacteria, and remaining turbidity, providing stable RO feed.
- Polishing RO. An industrial RO system polishes UF permeate to cooling-tower makeup quality at recovery up to 95%; concentrate is sent to ZLD or authorised discharge.
- Disinfection. A UV steriliser or on-site chlorine dioxide generator controls biological fouling in the reuse loop without the high-DP residuals of chlorine gas.
The table below maps each stage to the parameter the supplier must commit to, with the scope flagged where the research does not provide a value.
| Stage | Equipment | Key parameter / duty | Design note for Makkah |
|---|---|---|---|
| 1. Screening | Rotary mechanical bar screen | Bar opening to suit pump solids tolerance | Outdoor-rated enclosure for > 35 °C ambient |
| 2. Clarification / DAF | DAF or lamella clarifier | TSS, oil/grease removal | Skid-mounted to reduce civil works on fast-track sites |
| 3. Multi-media filtration | Multi-media filter | SDI reduction to RO-grade | Backwash water recycled to cooling-tower basin |
| 4. Softening / antiscalant | Industrial softener or dosing skid | Hardness, silica, LSI control | Site-specific feedwater analysis required |
| 5. Ultrafiltration | PVDF UF system | 0.03 µm; up to 300 ppm feed turbidity with automatic backwash and air scour | Pre-RO barrier against biological fouling |
| 6. Polishing RO | Industrial RO | Recovery up to 95%; permeate to makeup quality | Energy-recovery device recommended at > 10 L/s |
| 7. Disinfection | UV or ClO₂ generator | Reuse-loop biological control | Avoid chlorine gas in occupied buildings |
Sizing the Train for Representative Makkah Loads
The 6–19 L/s blowdown flow range and ~20 L/s peak from the Arup/LinkedIn review (2024) anchor a medium-site design at roughly 350–1,150 m³/day average and ~1,700 m³/day peak; these figures are derived from the cited L/s ranges, not from site measurements. A 10 MW facility at 4 CoC could intake on the order of 15 million gallons (≈ 57,000 m³) per month with ~25% as blowdown (Genesis Water Tech, citing a 10 MW example) — again, a published example figure rather than a Makkah-specific value. Right-size the treatment train to the actual site load; do not copy hyperscale (100+ MW) treatment architecture, because the per-gallon capital cost is typically 3–4× higher at 5 MW colocation scale and operational complexity exceeds available staff (Genesis Water Tech). Modular, skid-mounted, PLC-controlled systems reduce installation risk on a fast-track Saudi site and ease future capacity additions, and an MBR-integrated wastewater treatment module can be added if sanitary or process streams are co-treated on the same site.
| Reference load | CoC | Approx. blowdown range | Train sizing implication |
|---|---|---|---|
| ~ 10 MW facility, evaporative cooling, 4 CoC example | 4 | ~ 25% of ~ 57,000 m³/month intake | Modular skid around 100–300 GPM (Genesis Water Tech) |
| Medium site, average blowdown | 4–6 | 6–19 L/s (Arup/LinkedIn, 2024) | 350–1,150 m³/day average; sized to peak |
| Medium site, peak demand (high ambient, high IT load) | 4–6 | ~ 20 L/s (Arup/LinkedIn, 2024) | ~ 1,700 m³/day peak; RO sized to peak recovery |
| 5 MW colocation reference | — | — | Avoid hyperscale RO/IX architecture; capex per gallon 3–4× higher (Genesis Water Tech) |
Discharge, Reuse, or ZLD: A Decision Framework for the Makkah Operator
Four paths are available to a Makkah operator, and the right one is driven by site-specific water cost, sewer capacity, and the corporate water-positive target.
- Path A — Discharge to municipal sewer after treatment. Simplest if the receiving NWC sewer has capacity and tariff; the train ends at clarification, media filtration, and disinfection to meet Saudi effluent limits for TDS, residual chlorine, oil/grease, and temperature.
- Path B — Reuse as cooling-tower makeup via RO. Closes the loop on cooling water and reduces makeup by 15–25% at typical facilities (Genesis Water Tech); concentrate requires separate handling and is the main complication.
- Path C — Industrial–agricultural reuse of treated blowdown. Conceptually attractive in arid regions, but in Saudi Arabia this is constrained by irrigation-water quality rules and proximity to farmland — confirm with MOMRA and the Ministry of Environment, Water and Agriculture before designing for it (Arup/LinkedIn, 2024).
- Path D — ZLD for hyperscale or constrained sites. A combination of RO plus thermal/crystallisation stage; appropriate where sewer capacity is absent, concentrate disposal is restricted, or the operator has a corporate water-positive target. The selection logic is laid out in the zero-liquid-discharge (ZLD) plant buyer's guide, and the ETP compliance picture in a similar inland, arid context is covered in Saudi ETP compliance in a similar inland, arid context.
| Path | Best fit | Main complexity | KSA compliance hook |
|---|---|---|---|
| A. Sewer discharge after treatment | Site with available NWC sewer and tariff | Thermal, TDS, residual chlorine limits | NCEC / MOMRA sewer acceptance criteria |
| B. Reuse as cooling-tower makeup via RO | Site with water-positive target and enough load to justify RO | Concentrate handling and RO membrane fouling | Reuse permit; concentrate disposal route |
| C. Industrial–agricultural reuse | Site near irrigation canal authority | Irrigation-water quality rules; off-take agreement | MEWA / MOMRA irrigation reuse approval (Arup/LinkedIn, 2024) |
| D. ZLD | Hyperscale or constrained site; no sewer | Capex, energy for thermal stage, brine handling | NCEC brine disposal permit; ZLD buyer's guide (2026) |
Frequently Asked Questions
What CAPEX band should a Makkah engineer plan for a 10 MW blowdown treatment and reuse train?
The supplied research gives a worked payback example at $200,000 capital for a 15 MW facility recovering 60% (3 million gallons/year) — a 6.7-year simple payback before avoided costs, improving to 3–5 years once avoided costs are included (Genesis Water Tech). For a Makkah tender, request a CAPEX breakdown by skid (screening, DAF, multi-media, softener or dosing, UF, RO, disinfection) rather than a single lump sum, and ask the vendor to quote the concentrate-handling option separately so paths B and D can be compared like-for-like.
What should a Makkah buyer screen for when shortlisting blowdown-treatment suppliers?
Ask for documented SDI performance on the multi-media filter, recovery and energy per cubic metre on the RO, and PVDF UF tolerance to feed turbidity. Require evidence that the RO and UF skids have been factory-integrated, not field-assembled, and ask for a reference list of operating sites in hot, high-TDS climates. For a Makkah project specifically, the supplier should commit to documentation that aligns with NCEC, SWCC, NWC, and MOMRA submission packages, and should provide a concentrate-handling option that fits the site-specific ZLD or sewer-discharge decision.
What feedwater and blowdown data does an engineer need before fixing the design basis?
Get a recent NWC feedwater analysis (TDS, chloride, sulfate, hardness, silica, iron, manganese), an on-site well analysis if a well is in use, and a 12-month blowdown composite from the existing cooling-water chemical programme. The Genesis Water Tech review warns that measured blowdown typically exceeds theoretical calculations by 15–30% due to unmeasured losses and emergency dumps, so the monitoring plan must cover makeup, blowdown, evaporation, conductivity, pH, and suspended solids before the design is frozen.
How do cycles of concentration and WUE interact in a Makkah design?
Blowdown ratio is 1 / (CoC − 1): 4 CoC ≈ 25% of makeup, 6 CoC ≈ 20% — a 5-percentage-point improvement, not 50% (Genesis Water Tech). WUE under the Climate Neutral Data Centre Pact is capped at 0.4 L/kWh in water-stressed areas (Climate Neutral Data Centre Pact, 2025 Revision, cited via Arup/LinkedIn, 2024). The Makkah engineer should set the WUE target from the Pact, then back-solve the CoC and reuse percentage that hits it, rather than chasing CoC in isolation, because pushing CoC above 5–6 without advanced treatment increases scaling, microbiologically influenced corrosion, and biological fouling risk exponentially (Genesis Water Tech).
