Wastewater Treatment Ventilation: Polypropylene vs. Stainless Steel and GRP

Wastewater Treatment Plant Corrosion Resistant Ventilation

Environmental wastewater treatment plants face a number of challenges in terms of ensuring safe and effective ventilation. Water treatment processes must control hazardous substances, chemicals and gases such as methane, ammonia, phosphorous, pesticides and carbon dioxide. Consequently, wastewater treatment plants are, by their nature, one of the harshest engineering environments.

Why is Ventilation Necessary?

Ventilation is necessary in providing a safe clean air environment for employees working on site. Water treatment ventilation works by removing harsh chemicals in the air and recycling it to provide fresh, clean air. Ventilation systems manage the airflow intake and outlets to prevent any harmful pollutions escaping out into the atmosphere and causing an environmental hazard.

Ventilation is fundamental in controlling the temperature in the room to suit the ideal working conditions and wellbeing of employees, but it also ensures that equipment and structures in the building are protected from condensation, corrosion or the build-up of mould. Heat from machinery such as air blowers can be effectively exhausted, preventing overheating, and smoke can also be extracted in the same way ensuring added security in the event of a fire.

Understanding Water Treatment Processes

There are a wide array of processes that take place in water treatment plants, one of these processes is cleaning wastewater that is then released back into the environment or used for various other applications. According to Defra, every day in the UK about 347,000 kilometres of sewers collect over 11 billion litres of wastewater. This is treated at about 9,000 sewage treatment works before the treated effluent is discharged to inland waters, estuaries and the sea. Without the correct treatments such a mass of contaminated water could have a detrimental effect on public health and the environment. Water companies have a duty of care to adhere to the Wastewater Treatment Directive which sets out guidelines for water treatment companies to protect human health, the environment and to sustain the overall resilience of aquatic ecosystems.

As stated by the World Health Organisation the demand for wastewater as a reliable source of water and nutrients for agriculture is growing in response to population growth, urbanisation, increasing water scarcity and the effects of climate change. Insufficient treatment of wastewater and faecal sludge spreads disease and is a driver of antimicrobial resistance. The WHO produces global guidelines and tools to improve treatment and manage health risks at all steps of the wastewater treatment process.

The corrosive nature of the air to be extracted means that standard metal fans would be adversely affected and not withstand the environment for long, therefore, fans made from polypropylene are needed in this application. Axair Fan’s ‘Storm’ range of polypropylene fans are best suited to this application as they are designed to perform in the corrosive air, providing a relatively low air flow rate against elevated system pressures. ATEX rated versions are also available on request for circumstances where the chemicals in use create the potential for explosions due to their flammable nature.

Axair has been associated with fans for various applications within the water treatment industry for many years and continue to supply fans and fan related components to a number of industry leaders involved in the build and installation of chemical dosing equipment. A full range of accessories are available including weather protecting pedestals, energy efficient speed controllers to match fan performance to the application requirements, anti-vibration mounts and flexible connectors.

To ventilate wastewater treatment plants, engineers have a choice of materials for industrial fans and their ventilation systems. Typically, these materials are stainless steel, glass reinforced plastic or polypropylene. The range of corrosive gases present in the plants is so vast that it is essential to select ventilation equipment that is resistant to the largest array of chemicals possible.

Choosing A Suitable Industrial Fan for Water Treatment Ventilation


Stainless Steel Fans


Rosenberg_ANDBStainless steel is a highly durable material that can withstand many harsh environments.


Often, a special finish, for example, marine grade powder coating is required to make stainless steel corrosion resistant in environments where highly corrosive chemicals and vapours are present. Therefore, there is an added cost implication to what can be a relatively expensive material.

Stainless steel is also the heaviest of the three options, meaning there is an extra challenge when designing the ventilation system.

Glass Reinforced Plastic (GRP) Fans


GRP, as the name suggests, is plastic reinforced with fibreglass. It can be manufactured in a way that makes it more resistant to corrosion and lighter than stainless steel.


The cost of making GRP corrosion resistant can cause it to have a considerably greater manufacturing cost that material counterparts like polypropylene.

Furthermore, the corrosion resistance achieved with GRP is often not as effective as stainless steel or polypropylene according to the HVAC and Chemical Resistance Handbook for the Engineer and Architect:

‘GRP equipment resisted only 29% of 109 chemicals in a satisfactory manner, thus affecting its durability. That same rating was higher for stainless steel (52%), and even higher for Polypropylene (79%).’

Moreover, GRP can be subject to fibre shedding due to the nature of the material. This can cause problems with longevity and overall durability.

Polypropylene Fans


SEAT corrosion resistant HVAC fansPolypropylene is thermoplastic and many of its properties are similar to polyethylene. However, it offers several additional benefits over GRP and stainless steel. Firstly, it can be up to 30% less expensive than other materials used for ventilation in environment with harsh gases and chemicals. As previously mentioned, it usually offers more durability than most other materials used in wastewater treatment plants and resists the largest number of chemicals. It is also the lightest of the three options, making polypropylene ideal in terms of ease of installation.

In certain circumstances, there may be other variables to consider when selecting the material of the ventilation system but the polypropylene option is ideally suited to the wastewater treatment environment due to its lightweight, durable, affordable, corrosion resistant properties.

Our range of polypropylene fans have scrolls which are moulded into a single piece, meaning that there are no welding joins. This improves the durability of the fan as it eliminates the risk of welded joins parting and needing to be repaired. For more information or a specification for a fume extraction application, contact our team on 01782 349 430 or email sales@axair-fans.co.uk.


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