Wastewater Treatment Ventilation: Polypropylene vs. Stainless Steel and GRP

Corrosive Gases in Water Treatment

Environmental wastewater treatment plants face a number of challenges in terms of ensuring safe and effective ventilation due to the release of corrosive and toxic gases that occWastewater Treatment Plant Corrosion Resistant Ventilationur across the various treatment processes. During the treatment process, the ventilation system 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. To ventilate wastewater treatment plants, engineers have a choice of materials for the fans and systems. Typically, these materials are stainless steel, glass reinforced plastic (GRP) and polypropylene, each with their own positive and negative attributes towards handling corrosion and explosions. The range of corrosive gases present in the plants is so vast that it is essential to select ventilation equipment resistant to the largest array of chemicals possible.

 

Safe Ventilation for Personnel

Water Treatment

 

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.

 

Drinking Water

Drinking WaterWastewater treatment plants reduce pollutants in the water used by homes, businesses and industries before it is released back into the environment. Water builds up from rainstorms is also a hazard to our environment, harmful substances can wash off buildings and road surfaces and run into our rivers and lakes. The survival of a wide array of species and plants living in the water relies on this treatment process to keep the water clean and habitable. Harmful bacteria are also removed from water preventing the risk of disease spreading. The inability to treat water efficiently would result is serious harm to the ecosystems and human health.

To provide water that is safe for human consumption, there are a number of processes that the water treatment industry use.

Coagulation and flocculation are often the first steps in water treatment. Chemicals with a positive charge are added to the water. The positive charge of these chemicals neutralises the negative charge of dirt and other dissolved particles in the water. When this occurs, the particles bind with the chemicals and form larger particles, called floc. To separate the floc from the water, it is allowed to settle and fall to the bottom of the water during the sedimentation process. The clear water is then passed through various filtration compositions and sizes to remove any remaining dissolved particles. Finally, the water is disinfected with further chemicals, such as chlorine, to kill any bacteria and protect the water as it is piped to homes and businesses.

The chemicals used during the water treatment process pass through metering equipment in a dosing system. In the system, the solution is at its strongest and the chemicals are often corrosive and can be flammable. Such chemicals and gases include methane, ammonia, phosphorous, pesticides and carbon dioxide. Consequently, wastewater treatment plants are, by their nature, one of the harshest engineering environments. The plant room or dosing cabinet needs to be ventilated to prevent a harmful build-up of chemicals in the air around the equipment. Plant room and cabinets can be vented directly to the outside air or, more commonly, through an air filtration system. A filtration system is the more environmentally friendly option as it helps keep the air surrounding the water treatment site clear of harmful chemicals.

 

“According to the World Health Organisation, contaminated drinking water causes 485,000 diarrheal deaths every year. Contaminated water can transmit diseases such diarrhoea, cholera, dysentery, typhoid, and polio. However, the UK’s water is one of the safest and purest supplies of water in the world.”

 

Desalination Plants

Desalination PlantDesalination plants produce water for drinking and agriculture on coastal regions. The process uses chemicals to remove excess salts and minerals from sea water, rivers, streams, wastewater, industrial feed and process water. A build up of concentrated brine is produced in the process which would usually end up back in the sea so a pumping system is needed to prevent any harm to the eco system and marine life.

However, in 2019 Engineers at MIT News completed a study to show that through a fairly simple process the waste material from this process can be converted into useful chemicals -including ones that can make the desalination process itself more efficient.

 

 

Sludge Treatment Plants

Sludge Treatment PlantSewage sludge is the accumulation of solid or semi solid waste produced during the water treatment process. The sludge is separated from the wastewater and treated in sewage treatment plants so that it is safe to be recycled or disposed of. The sludge is either formed from the separation of the solids in the water or is created as a resulted of biological treatments to the water. These treatment plants often receive waste material contained in or removed from a septic tank from on site wastewater treatment systems.

The treatment and disposal of sludge is an important process in all wastewater treatment plants. The sludge needs to be reduced in volume to reduce the cost of pumping and storage and its organic compounds need to be stabilized so that it can be handled without causing harm or any offensive odours. Sewage sludge treatments may include a combination of thickening, digestion, and dewatering processes.

Most large sewage treatment plants use a two-stage digestion system where organics are broken down by bacteria anaerobically. In the first stage, the sludge, thickened to a dry solids (DS) content of about 5 percent, is heated and mixed in a closed tank for several days. Acid-forming bacteria hydrolyse large molecules such as proteins and lipids, breaking them into smaller water-soluble molecules, and then ferment those smaller molecules into various fatty acids. The sludge then flows into a second tank, where the dissolved matter is converted by other bacteria into biogas, a mixture of carbon dioxide and methane. Methane is combustible and is used as a fuel to heat the first digestion tank as well as to generate electricity for the plant.

 

Methane is combustible and is used as a fuel to heat the first digestion tank as well as to generate electricity for the plant.”

 

 

Choosing A Suitable Industrial Fan for Water Treatment Ventilation

The corrosive nature of the air to be extracted during a lot of these process in water treatment plants means that standard metal fans would be adversely affected by rust and degradation and not withstand the environment for long. Therefore, fans manufactured from polypropylene corrosion resistant materials are needed in this application. Axair’s ‘Storm’ range of polypropylene fans are best suited to this application as they are designed to perform against a wide range of chemicals to resist 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 supplied industrial fans for use within the water treatment and corrosive air industry for many years  supplying 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.

 

Stainless Steel

Benefits:

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

Drawbacks:

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.”

 

GRPGlass Reinforced Plastic (GRP) Fans

Benefits:

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.

Drawbacks:

 

The cost of making GRP corrosion resistant can cause it to have a considerably greater manufacturing cost that material counterparts like polypropylene. GRP can also be subject to fibre shedding due to the nature of the material. This can cause problems with longevity and overall durability.

 

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%).’

 

 

polypropylenePolypropylene

Benefits:

Polypropylene 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.

 

Corrosion Resistant Polypropylene Fans

 

s30 seat corrosion resistant polypropylene fanOur 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 [email protected].

 

 

 

 

Download Key Fan Information for Water Treatment Below:

 

Extraction Fans for Water Treatment Cover

 

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