Water treatment

Treatment plants and wastewater treatment with biogas

Wastewater plants with anaerobic digestion produce biogas with methane and H2S and need corrosion-resistant ATEX equipment. Maffioletti supplies it.

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Aerial view of the tanks at a water treatment plant

Where the hazardous areas are

In wastewater plants, hazardous areas come mainly from the biogas produced by anaerobic sludge digestion: digesters, gas holders, biogas pipework, desulphurisation, flares and CHP engine rooms. Biogas is mostly methane and carbon dioxide, with traces of hydrogen sulphide. The inside of digesters and gas holders is Zone 0 or 1 depending on the assessment; Zones 1 and 2 are typically found around relief valves, vents and condensate drains.

Sewage pumping stations and enclosed rooms may need assessment for sewer gas, and sludge drying can lead to Zones 20, 21 and 22. Methane is IIA T1; H2S is IIB T3, toxic and corrosive: group and temperature class must be based on the actual composition.

Typical requirements

H2S corrosion: with moisture it attacks copper, brass and unprotected steel, so stainless steel, GRP or coated materials are preferred for enclosures and glands.
Outdoor installation: rain, frost and UV call for UV-stable materials and a rating such as IP66.
Gas detection: methane, H2S and oxygen are monitored in enclosed rooms, chambers and confined spaces.
Inspection: the aggressive environment degrades seals and glands, so inspection under IEC/EN 60079-17 matters.
Standards: Directive 1999/92/EC, IEC/EN 60079-10-1 for classification, Directive 2014/34/EU and IEC/EN 60079-14 for selection and installation.

Products for this sector

Gas detection: fixed and portable detectors for methane, H2S and oxygen, also for entry into chambers and confined spaces.
Enclosures, junction boxes and control stations: junction boxes and control stations for pumps, blowers and valves on the biogas line.
Lighting: LED luminaires for digesters, CHP rooms and outdoor areas.
Measuring instruments: WIKA pressure and level instruments and BEKA field indicators.
Supports and cable trays: fibreglass and aluminium cable trays and Eaton B-Line supports for damp, aggressive environments.

How we help

We design and assemble custom Ex enclosures, junction boxes, control stations and panels in-house, with the 72-hour Express service on junction boxes and control stations; the online configurator lets you set up your request yourself.

If your plant runs around the clock, the energy-saving calculator estimates what switching to LED is worth. Through Atex Italia we offer consulting on area classification, training and inspections. Contact us to review your plant together.

FAQ

Frequently asked questions

What ATEX zone is an anaerobic digester?

The inside of digesters and gas holders is classified Zone 0 or Zone 1 depending on the assessment: biogas on its own is not explosive, but during start-up, shutdown and maintenance it can mix with air and enter the explosive range. Zones 1 and 2 are usually identified around pressure relief valves, vents and condensate traps, with an extent that depends on release rate and ventilation.

What gas group is biogas?

Biogas consists mainly of methane, classified IIA T1, together with carbon dioxide and traces of H2S, which on its own is IIB T3. Group and temperature class should therefore be set on the actual composition; IIB or IIC equipment is also suitable for Group IIA.

Why is H2S a problem for electrical equipment?

Besides being toxic, hydrogen sulphide combined with moisture corrodes copper, brass and unprotected steel, damaging contacts, terminals and cable glands. That is why resistant materials are chosen and shorter inspection intervals are considered.