Aluminum vs. Fiberglass Tank Covers: How to Choose
Choosing the right material for your wastewater tank cover — aluminum or fiberglass (FRP) — is one of the most critical decisions in any treatment plant project. The wrong choice can lead to premature corrosion, costly repairs, odor control failures, or compliance issues on federally funded projects. The best option depends on your tank size, H₂S levels, chemical environment, budget, installation constraints, and funding source.
At RPS Engineering, we manufacture both aluminum and fiberglass wastewater tank covers under one roof — the only major fabricator that offers this unbiased advantage. That means we’ll recommend the material that truly fits your application, not the one we happen to produce.
Request a QuoteAluminum vs. Fiberglass Tank Covers: Quick Comparison
Choosing the right cover material for your wastewater tank is one of the most important decisions in a cover project. The wrong choice can mean premature corrosion, compliance issues on federally funded projects, or a cover system that doesn’t hold up in your specific process environment.
RPS Engineering manufactures both aluminum and fiberglass (FRP) wastewater tank covers — the only major cover fabricator to do so under one roof. That means we help you choose the right material for your application, not the one we happen to make.
| Feature | Aluminum | Fiberglass (FRP) |
|---|---|---|
| Best for | Large-span clarifiers, digesters, standard municipal tanks | High H₂S environments, aggressive chemical atmospheres |
| Span capability | Up to 180′ diameter (geodesic dome) | Flat covers any span; domes up to 32′ dia. |
| H₂S resistance | Good with proper alloy selection | Excellent — FRP is inert to hydrogen sulfide |
| BABA compliance | Yes — all RPS aluminum is domestically sourced & fabricated | No — FRP produced via fabrication partner |
| Cold climate | Standard; insulation can be added | Insulates naturally; preferred in cold climates |
| Maintenance | Very low; anodized finish resists corrosion | Very low; FRP does not corrode or rust |
| Lifecycle cost | Low; durable 30+ year service life | Low; no painting or coating required |
| Custom fabrication | Yes — cut to fit any equipment, pipe, or sensor | Yes — via RPS partner to your tank specs |
| Walkable | Yes — 5×6 plank with bidirectional safety tread | Yes — flat panel systems |
| SRF / federal grants | BABA compliant — qualifies for federally funded projects | Check project requirements; may not qualify |
| Weight | Lightweight; 5×6 plank at 3.65 lbs/LF | Lightweight; comparable to aluminum flat covers |
| Dome size limit | Up to 180′ diameter | Maximum 32′ diameter |
When to Choose Aluminum
Aluminum is the most widely specified material for wastewater tank covers, and for good reason. It offers an excellent combination of strength, longevity, and corrosion resistance across the widest range of municipal and industrial applications.
Best applications for aluminum covers:
- Circular clarifiers and thickeners — aluminum geodesic domes span up to 180′ diameter
- Aeration tanks and equalization basins — flat aluminum covers with 5×6 M/F interlocking planks
- Wet wells and pump stations — formed aluminum covers with airtight seals for suction pipes
- Headworks and channel areas — 2×7 low-profile planks for tight clearances
- Any SRF or federally funded project requiring BABA compliance
BABA: All RPS aluminum cover products are domestically sourced and fabricated at our Elgin, IL facility. This makes them compliant with the Build America, Buy America Act — a requirement on SRF loans, USDA grants, and most federal infrastructure funding. If your project has federal funding, confirm BABA requirements before specifying.
Aluminum alloy matters — not all aluminum is equal
RPS flat covers use 6005A-T5 alloy for planks and flashing — not the more common 6061-T6 used for structural components. This is a deliberate engineering choice. 6005A-T5 offers better extrudability for consistent, code-compliant profiles and performs well in the corrosive environments typical of wastewater treatment.
Structural framing components (CS8 channels, L3×3 angles, mounting brackets) are fabricated from 6061-T6. All fasteners are 316 stainless steel throughout.
When to Choose Fiberglass (FRP)
Fiberglass reinforced plastic (FRP) covers are the preferred choice when chemical resistance is the primary concern. In high H₂S environments — digesters, sludge holding tanks, and industrial process tanks with aggressive gases — FRP outperforms aluminum over the long term.
Best applications for FRP covers:
- Digesters and gas-tight applications — FRP flat covers with silicon perimeter seal
- High H₂S environments where metal corrosion is a concern
- Cold climate installations — FRP dome covers provide natural insulation
- Industrial wastewater — food processing, chemical, pharmaceutical facilities
- Applications where budget is a driver and aluminum is overspecified
Note: RPS fiberglass dome covers max out at 32′ diameter. Larger span requirements should use aluminum geodesic domes. RPS FRP flat covers are produced through our fabrication partner to the same quality standards as our aluminum products.
FRP and odor control
FRP covers offer outstanding performance for odor containment. The material is inert to hydrogen sulfide and other corrosive gases produced in anaerobic digestion and primary treatment. For facilities in H₂S-heavy environments, FRP can significantly extend the service life of the cover system compared to metal alternatives.
The Case for Having Both Options
Most cover manufacturers specialize in one material. The result: you get quoted the product they make, not necessarily the product your project needs.
Because RPS fabricates both aluminum and FRP covers in-house (or through our qualified partner), our engineering team can give you an honest recommendation based on your tank geometry, process environment, project funding, and budget — without steering you toward a particular material for business reasons.
In practice, many large WWTP projects use both: aluminum flat covers or geodesic domes for clarifiers and aeration tanks, and FRP for digesters or high-H₂S applications elsewhere on the same site. RPS can supply both, coordinating submittals and field measurements across the full project.
Material Selection Checklist
Before requesting a quote, consider these factors:
| Consider aluminum when… | Consider FRP when… |
|---|---|
| Your project uses SRF or federal funding (BABA required) | H₂S levels are high or the environment is highly corrosive |
| Tank diameter exceeds 32′ (requires aluminum geodesic dome) | Budget favors lower upfront cost on smaller spans |
| You need a walkable cover with bidirectional safety tread | Cold climate performance and insulation are priorities |
| You want both materials specified by one manufacturer | The tank is a digester or other gas-tight application |
Talk to RPS Engineering
Not sure which material is right for your project? RPS engineers work directly with plant operators, consulting engineers, and EPC contractors to recommend the right cover system for each application. We’ll review your drawings, answer RFIs, and provide a complete submittal package — including a bill of materials with all parts numbered and located.
Budget pricing is available from dimensions alone. A firm quote requires drawings and a completed Work Info Sheet.
Contact RPS Engineering: Gina | gina-wwtp@rpsengineering.com | (847) 931-1950
