Steel Tanks for Wastewater Treatment and Collection
Wastewater treatment is one of the most demanding storage environments in the tank industry. Tanks face continuous exposure to hydrogen sulfide (H₂S), variable pH, high biological oxygen demand, abrasive suspended solids, and thermal cycling. The coating fails before the steel does — unless the tank was engineered for the application from the start.
MMI Tank designs, fabricates, and erects bolted and field-welded steel tanks specifically for wastewater treatment plants, industrial pretreatment systems, and collection infrastructure across the western United States. Our in-house coatings division applies chemical-resistant linings that match the aggressiveness of your specific waste stream — not a generic spec pulled from a catalog.
Wastewater Tank Applications
Equalization Basins
Flow equalization (EQ) tanks that buffer peak flows and stabilize influent characteristics before downstream treatment. Sized to your diurnal flow pattern with proper inlet diffusion and mixing. Bolted construction is ideal for EQ basins — fast to install and relocatable if plant capacity changes.
Primary and Secondary Clarifiers
Circular steel clarifiers with center-feed wells, peripheral weirs, and sludge collection mechanisms. Field-welded construction for custom diameters and depths. Interior coatings resist the corrosive combination of biological activity and dissolved gases.
Anaerobic Digesters
Gas-tight welded steel digesters for biogas production from primary and waste activated sludge. Engineered for internal pressure, temperature, and mixing system loads. Insulated jacket systems available for mesophilic and thermophilic operation. Roof-mounted gas collection and safety venting.
Aerobic Digesters and SBRs
Sequencing batch reactor (SBR) tanks and aerobic digester vessels. Designed for cyclic fill-draw operation with internal baffles, diffuser supports, and decant system mounts.
Sludge Holding and Thickening
Tanks for waste activated sludge (WAS), thickened sludge, and biosolids storage before dewatering or land application. Heavy-duty floor slopes and drain configurations for viscous and abrasive slurries. Chemical-resistant coatings for high-H₂S environments above the waterline.
Biosolids Storage
Long-term Class B biosolids storage for seasonal land application. Bolted tanks with factory-coated panels provide fast deployment and excellent corrosion resistance in the aggressive headspace environment.
Industrial Pretreatment
Neutralization tanks, oil-water separators, DAF units, and chemical feed tanks for industrial users discharging to municipal systems. Sized and coated for the specific waste stream — food processing, metal finishing, pharmaceutical, petrochemical, and manufacturing.
Lift Station and Wet Well Storage
Collection system surge tanks and wet well overflow storage. Designed for intermittent submersion and H₂S exposure with appropriate corrosion allowances and coatings.
Codes and Design Standards
| Standard | Application |
|---|---|
| AWWA D100 | Welded steel tanks for water/wastewater storage |
| AWWA D103 | Factory-coated bolted steel tanks |
| API 650 | Industrial wastewater and process tanks |
| ASME BPVC Sec. VIII | Pressure-rated digester vessels |
| NFPA 820 | Fire protection in wastewater treatment plants |
| ASCE 7 | Seismic and wind loading |
| Ten States Standards | Recommended standards for sewage works |
Coatings for Wastewater Service
Wastewater environments are significantly more aggressive than potable water. Above the waterline, H₂S gas attacks unprotected steel rapidly. Below the waterline, biological films, fluctuating pH, and abrasive grit accelerate coating wear. MMI’s coatings division specifies and applies systems matched to each exposure zone:
- Glass-fused-to-steel (bolted tanks) — ceramic bond resists H₂S, acids, and biological attack. Ideal for digester covers, EQ basins, and sludge holding where coating integrity is critical.
- High-build epoxy — interior/exterior systems with SSPC SP-10 surface prep. Minimum 16-mil DFT for immersion service.
- 100% solids epoxy — zero-VOC option for enclosed spaces and high-humidity cure conditions.
- Polyurea — rapid-cure elastomeric for rehabilitation, relining, and secondary containment.
- Vinyl ester — for extremely aggressive chemical environments (low pH, high chloride, high temp).
- Zinc-rich primer + epoxy/urethane — exterior atmospheric protection.
Bolted vs. Welded for Wastewater
| Factor | Bolted | Welded |
|---|---|---|
| EQ basins, sludge holding, biosolids | ✅ Fast install, factory coating | Available |
| Anaerobic digesters (gas-tight) | Limited | ✅ Welded for gas integrity |
| Clarifiers with internal mechanisms | Limited | ✅ Custom geometry |
| SBRs with complex internals | Limited | ✅ Custom baffles/supports |
| Remote or space-constrained sites | ✅ Ship flat, small crane | Needs welding access |
| Future capacity expansion | ✅ Add rings or relocate | Permanent |
Wastewater Tank FAQ
What is the biggest corrosion risk in wastewater tanks?
Hydrogen sulfide (H₂S) gas in the headspace above the waterline. H₂S is produced by anaerobic bacteria in sewage and attacks unprotected steel and concrete aggressively. Glass-fused-to-steel and high-build epoxy coatings are the primary defenses.
Can a bolted tank be used for an anaerobic digester?
Bolted tanks can serve as digester covers or secondary digesters where gas-tightness requirements are less stringent. Primary digesters requiring full pressure containment and gas-tight integrity are typically field-welded.
How long do wastewater tank coatings last?
Glass-fused-to-steel linings in wastewater service routinely last 30+ years. Field-applied epoxy systems typically provide 15–20 years before recoating, depending on exposure severity and maintenance. MMI performs in-service coating assessments and relining when coatings reach end of life.
Does MMI work with engineering firms on design-build wastewater projects?
Yes. We regularly partner with consulting engineers, EPC firms, and design-build contractors on municipal and industrial wastewater projects. We can work from your engineer’s drawings or provide turnkey engineering from our in-house team.
What states does MMI serve for wastewater tank projects?
We are licensed in Arizona, California, Colorado, Nevada, New Mexico, Oregon, Washington, Wyoming, Hawaii, Alaska, and South Dakota.
Request a Wastewater Tank Quote
Related: Water Treatment Tanks · Bolted Tanks · Field-Erected Welded Tanks · Coating Selection Guide · Municipal Tanks
Tell us your application (EQ, clarifier, digester, sludge, etc.), target capacity, stored product characteristics, and site location. Our engineering team will recommend the right construction and coating system.
📞 (602) 272-6000 · 📧 info@mmitank.com · Request a quote online →
