Side Stream Filtration – Closed Loops
- MoO₄ (Molybdate), pH, and Azole treatment program used in a data center closed-loop system, including functionality, control limits, testing log, and consequences of poor treatment.
Component | Function | Mechanism |
Molybdate (MoO₄²⁻) | Corrosion inhibitor for ferrous metals (carbon steel) | Forms a passive film on metal surfaces, protecting against oxygen corrosion. |
pH Control | Ensures corrosion minimization and chemical stability | Maintains water chemistry in a range that minimizes attack on copper, steel, and elastomers. |
Azole (e.g., TTA, BTA) | Copper and brass corrosion inhibitor | Bonds to copper surfaces forming a protective molecular film; prevents galvanic corrosion and staining. |
- Recommended Control Ranges
Parameter | Lower Limit | Target | Upper Limit |
Molybdate (as MoO₄²⁻) | 100 ppm | 150 ppm | 200 ppm |
pH | 8.5 | 9.0 | 9.5 |
Azole (as TTA/BTA) | 2.0 ppm Plus 2 ppm per ppm Fe | 4.0 ppm Plus 2 ppm per ppm Fe | 6.0 ppm Plus 2 ppm per ppm Fe |
- Weekly Closed Loop Testing Log Template
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| pH | MoO₄ (ppm) | Azole (ppm) | Iron (ppb) | Copper (ppb) | Conductivity (µS/cm) | Comments / Actions | Additions | |||
| LCL | 8.5 | 100 | 2 | NA | NA |
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| Gallons | Gallons | Gallons | Gallons |
| T | 9.0 | 150 | 4 | <.1 | <.05 | < 1500 |
| Added | Added | Added | Added |
| UCL | 9.5 | 200 | 6 | <.15 | <0.1 | < 2000 |
| Mo | Azol | Caustic | Water |
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- Notes:
- Iron and copper levels >0.1 ppm indicate active corrosion.
- Risks of Improper Water Treatment
Problem | Impact on System | Energy / Cost Implications |
Low Molybdate | Increased steel corrosion (rust, sludge) | Blocked exchangers, reduced flow, pump wear |
Low Azole | Copper/brass pitting, galvanic corrosion | Heat exchanger leaks, system shutdowns |
Incorrect pH (<8.5) | Enhanced corrosion of all metals | Shortened equipment life, higher iron/copper |
Neglected Monitoring | Biofouling, under- or overfeed | Fouled coils, inefficient heat transfer, high ΔT |
- Poor treatment can cause up to 20–30% efficiency loss in heat exchange equipment due to fouling and corrosion layer buildup, increasing chiller and pump load.
Weekly Activity Table
Week | Filter Media Installed | Pore Size (µm) | Sampling & Analysis | Target / Milestone | Actions |
1 Minus 1 day | None | None | Pref filtration location | Establish Baseline | Submit for PSA, TSS and NTU |
1 | Nominal | 100 | Testing PreF – Pre Filtration PostT – Post Filtration Particle size analysis – PSA ( Count and Volume – C and V ) Turbidity – NTU Total Suspended Solids – TSS Test and adjust Inhibitor Value – TA – IV Test and adjust pH – TA – pH | Reduce Visible Solids | Weekly actions Install new and smaller µm filter; Sample inlet and outlet Record DP (differential pressure) initial Record DP (differential pressure) daily Change filters every other day or if DP > 10 psi Look for gel – like deposits Photo dirty filters and save |
2 | 50 µm depth filter (melt-blown PP) | 50 | Testing Battery | Reduce visible solids | Complete Weekly Actions |
3 | 25 µm nominal cartridge | 25 | Testing Battery | 80% removal of >50 µm particles | Complete Weekly Actions |
4 | Dual-stage: 25 µm pre + 10 µm final | 10 | Testing Battery | <25 µm peak size | Complete Weekly Actions |
5 | 5 µm nominal pleated filter | 5 | Testing Battery | >95% removal of >10 µm particles | Complete Weekly Actions |
6 | Dual-stage: 5 µm + 1 µm absolute | 1 (final) | Testing Battery | <5 µm peak; dissolved iron only | Complete Weekly Actions |
7 | Add 0.5 µm final stage (if available) | 0.5 | Testing Battery | Peak <1 µm | Complete Weekly Actions |
8 | Maintain <1 µm filters | 0.5 (or 1 µm) |
Confirm <1 µm peak with <5% >1 µm particles | Final validation | Lock-in final filter sizing Monthly PSA, NTU & TSS |