FRP Grating Case Study | Municipal WWTP Tank-Top Catwalk — ZeAllgrate
Water & Wastewater — Project Background
A 200,000 m³/day municipal wastewater treatment plant in East Asia required new tank-top access walkways and catwalks around 12 aeration tanks and clarifiers. The previous aluminum catwalks had suffered H₂S (hydrogen sulfide) corrosion on fasteners and frame members, and biological slime growth on the walking surface made the catwalks dangerously slippery after rain or during wet-weather operation. The plant wanted a single material that would survive continuous damp H₂S atmosphere without painting and without becoming a slip trap.
Engineering called for a cost-effective molded grating system, with anti-slip upgrade only in the chemical-dosing zones where hypochlorite and caustic are handled. Client identity is kept confidential; the project is described as Confidential Client, a large municipal wastewater treatment plant in Southeast Asia.
Engineering Specification
Working values agreed with the client's engineering team during design review.
| Parameter | Selected Value | Standard / Reference |
|---|---|---|
| Pedestrian live load | 3.0 kN/m² (≈ 62 lb/ft²) | EN 1991-1-1 / local building code |
| Clear span | 1.0 m across tank rails | ZeAllgrate molded grating design guide |
| Deflection limit | L/150 at design load | ZeAllgrate standard |
| Resin system | ZeAll ISO (isophthalic polyester) | H₂S / moisture / mild chemicals resistance |
| Panel size | 1220 × 3660 mm standard panels | ZeAllgrate standard molded grating |
| Panel thickness | 38 mm, mesh 38×38 mm | ZeAllgrate standard molded grating |
| Surface | Concave standard (grit-top in dosing zones) | ZeAllgrate molded surface options |
| Fixings | SS304 clamps and bolts | ASTM A276 304 |
| Custom work | Cut-outs for pipe penetrations and equipment | Fabricated in factory |
What Was Supplied and How It Went In
ZeAllgrate supplied 850 m² of 38 mm ZeAll ISO molded grating in 1220 × 3660 mm standard panels, plus grit-top upgrade in the chemical dosing corridors. All cut-outs for pipe penetrations, mixer supports and sample-point equipment were fabricated in the factory rather than on site, reducing field welding and measuring errors.
Installation was staged across two planned maintenance shutdowns so the plant never lost aeration capacity. Existing aluminum catwalk frames were removed, tank rails were reused as support, and FRP panels were clip-fixed with SS304 hardware. The concave standard surface provides drainage of rainwater and eliminates standing puddles; the grit-top zones handle the occasional chemical splash.
Molded FRP grating catwalk over wastewater clarifier tanks
Tank-top walkway in municipal wastewater treatment plant
Tank-top access grating around aeration basins
Outcomes and Inspection Findings
At 3-year inspection, plant maintenance reported the walkways in excellent condition: no corrosion, no delamination, no loose clips. Biological slime growth was limited to a thin film that washes off during routine high-pressure cleaning — a marked improvement over the aluminum catwalks, where slime had adhered permanently.
- Corrosion: zero H₂S attack on FRP panels and SS304 hardware at 3 years.
- Slip safety: wet-surface slip incidents reported by operators dropped to zero in the first two years of operation.
- Maintenance: no painting, no recoating, no replacement hardware required.
- Weight: the FRP system is approximately 65% lighter than an equivalent steel grating deck, reducing dead load on the existing tank rails.
- Schedule: completed inside the two planned shutdown windows with no extension.
Engineering Notes
Tank-top catwalks sit over process tanks in wet, corrosive, UV-exposed service: the resin is matched to the tank atmosphere and chemistry, UV-stabilised grades are used for the open exposure, and grit-top handles the wet traffic surface. SS316 hardware avoids the corrosion that wet service inflicts on galvanized fixings, and the lightweight panels install over the tank grid without interrupting the process. The corrosion-proof construction removes the repaint and replacement cycle of steel catwalks over the same tanks.
What to Specify
- Resin matched to the tank atmosphere/chemistry; UV-stabilised for exposure.
- Grit-top on the wet catwalk surface.
- SS316 hardware throughout.
- Lightweight panels installed without process interruption.
- Resin matched to the tank atmosphere/chemistry; UV-stabilised for exposure.
- Grit-top on the wet catwalk surface.
- SS316 hardware throughout.
- Lightweight panels installed without process interruption.
Planning a Similar FRP Grating Project?
Send us your layout drawings, service chemicals and span requirements — ZeAllgrate will return a design proposal, load calculation and reference pricing within 48 hours.
- ZeAllgrate molded grating design guide, load tables and deflection criteria.
- EN 1991-1-1 — Eurocode 1: actions on structures, imposed loads for walkways.
- AWWA manual of practice on municipal wastewater treatment plant access structures.
- Project inspection records supplied by Confidential Client; values quoted as-reported.