Odour control in sewage treatment

Odour Control in Sewage

Sewage treatment plants must route odours through odour control systems to control air pollution. Ventilation systems are useless on their own for odour control if all they do is vent odours out into the atmosphere.

This setup would only pollute the atmosphere and cause a nuisance with the local population. It may even get you in trouble with the local council. For these reasons, odour control should be a top priority for all treatment works.

Getting to the root of your odour problem

The most common cause of a foul odour in sewage treatment plants is the release of hydrogen sulphide (H2S). This offensive odour is also known as “sewer gas” and it can cause health problems.

Other types of odours include amines which possess an ammonia smell and mercaptans which give off the stench of rotting food.

Sewage moves through pipes and is treated by a number of processes contained in large tanks. This environment is contained. The screenings and sludges are separated and pumped away into containers. Again, the environment is contained. So, you might be wondering how odours escape and make a plant smell?

The main cause is biological overload and odour overload. Quite simply, tanks and process rooms have to be ventilated and sludge has to be removed at least once a year and tanks have to be cleaned. This can allows odours to escape. Plants can also have spills and accidents that can also cause significant odour problems.

Odour control systems in sewage plants

Controlling odours so that they are not a problem for the local population is important for several reasons, chief of which is a social responsibility to ensure that your operation does not impact on the lives of local residents.  

Thankfully, there are a number of odour control systems we can use in sewage treatment plants so that the air vented is clean and odourless.

Some of these systems include:

Tube vents and a passive filter

These are an activated carbon-based, passive odour control unit. They are commonly utilised to absorb vent gases from sewerage processes.

One stage carbon filtration

Our CuCarb® activated carbon dry scrubbers can operate as a single standalone unit or as a polishing unit downstream of biological or chemical treatment systems. OSIL’s selected activated carbons serve as media to purify air streams by concentrating and retaining odorous gases and vapours.

Single-stage chemical scrubbing

Our ChemKlean®  Scrubbing System has no moving parts to reduce maintenance. This system works by using a liquid to absorb odour-causing components in gasses. The gas is then released into the atmosphere.

Dual systems

Dual systems combine two systems for odour control, such as biofiltration + carbon filtration or chemical scrubbing + carbon filtration. We call this process multi-stage filtration, and it is used to control powerful odours.

What’s the right solution for your sewage plant?

The scale of your operation, the types of equipment you use, and the design of your building and ventilation system will determine the right solution. There is no one-size-fits-all approach. It’s important to note that the size of the systems used in odour control vary. You need bigger systems for higher air volumes. We can recommend a few options if you’d like. Feel free to call us on (0) 1543 506855 for a chat.

LEV & GEV Surveys


Where a business produces airborne contaminants in the workplace, there is a legal and insurance-based requirement to protect workers’ health by controlling exposure to contaminants. Control is achieved with an LEV or GEV system.

The question of whether LEV and GEV surveys are necessary is a plain matter of requirement. HSE’s Control of Substances Hazardous to Health Regulations state businesses have a legal obligation to control dust and fumes.

LEV and GEV systems are used to extract and ventilate airborne contaminants and pollutants (e.g. dust, fumes and gas). These systems require regular checks to ensure they are fit for purpose, and surveys enable compliancy to be checked.

LEV & GEV survey process

Health and safety law, says you must assess the risks to your workers from hazardous substances – dusts, fumes, vapours, etc. – and decide what measures to use to protect their health.

Common Elements of LEV Systems

If the measures you adopt include extraction systems (LEV) to remove the dusts, fumes, vapours etc. produced by your work processes or activities, then you must maintain the LEV in efficient working order, so it continues to provide the necessary protection. You should also have a periodic thorough examination and test (at least every 14 months) and must keep this record for at least 5 years. In addition, you should have information on the installed LEV system to confirm it provides adequate protection, which should be kept for the life of the equipment.


You must ensure that your LEV is still working as effectively as originally intended and is helping to protect your employees’ health. To be able to tell if it is still working as it should, you should be able to provide the examiner with information about the intended or designed performance of your system.

An examination will test:

  • Process flow functionality and comparison against the design intent
  • Hoods, seals and ductwork
  • Parts that deteriorate, such as filters
  • Parts that need attention, such as volume control dampers and their settings

Each piece of LEV / GEV equipment in a system is inspected to ensure system conformity with design specifications. The system is then tested to establish if it provides an adequate level of exposure control.

This information might be in the form of an initial appraisal or commissioning report, if one was carried out, or for simple ‘standalone’ systems it could have been provided as standard operating data by the suppliers of the extraction equipment. Alternatively, it might be found in recognised guidance (including that from HSE) on simple processes/systems (For example  LEV Guidance hsg258 ). If none of this is available, you could consider getting someone competent to advise you.

During a survey, extraction systems are visually inspected and tested to determine if they are fit for purpose and functioning as intended.


LEV and GEV surveys produce a report that highlights defects, problems and advises where maintenance is recommended. Businesses must implement critical recommendations to comply with health and safety standards.

LEV Systems

For example, the survey may find an issue with ducting that leaks. The ducting would need to be repaired or replaced for the system to pass the test.


Businesses must also keep records of all examinations and tests for at least five years. A logbook or dedicated LEV/GEV file is the standard way of doing this. Following a survey, the survey report should be read, and any queries/actions addressed. A presentation of the survey should be carried out to the client from the examiner, if possible. If a logbook is used, then this should be stamped so the business has a record of compliance.


Another important aspect of surveys is ensuring the people who use the extraction system know how it functions and what settings have been established during the commissioning process. Training should be provided by the installer in this respect. Adjustments to any settings should not be made by anyone except the company’s maintenance engineer, the commissioning engineer or the LEV system examiner.

Routine checks (maintenance)

  • Know the parts of the LEV system and their function.
  • How the LEV system should be used.
  • How to recognise a damaged part.
  • Simple checks to show that the LEV system is delivering its design performance and what to do if it is not.

The importance of regular surveys

Regular LEV and GEV surveys are a legal requirement, so you are breaking the law if you have a ventilation system that isn’t regularly tested.

To put it another way, surveys are necessary to determine the ventilation system is functioning as intended and providing the necessary protection against airborne contamination. They will also detail the requirements to prove compliance with health and safety legislation.

If you require assistance with your LEV or GEV surveys OSIL would be pleased to discuss your requirements.

The Consequences if Odour Control isn’t implemented

The Consequences if Odour Control isn't implemented

Wastewater treatment, chemical processing, waste incineration and food production can all contribute to industrial odours.

Many industrial sectors and municipal wastewater treatment works can release unpleasant odours into the air which can travel for miles before becoming a nuisance. Different environmental factors can also play a key role in increasing the effect of offensive odours. One of the common examples that intensifies odour at the source is an increase in the air temperature and air distribution can also transfer odours from one place to another.

What are the impacts of Odour emissions?

Continuous odour emissions of a pungent type can be categorised as a part of air pollution and such odours can have a detrimental effect on local neighbourhoods. Constant exposure to offensive and aggressive odours inside a factory, food manufacturing facility or waste treatment plant can cause severe mental and physical health problems to the employees as well as causing detrimental corrosion to plant and machinery.

A large number of research studies have suggested that odour emissions could be more dangerous to the most susceptible sections of the population. It can particularly affect; children, the elderly and asthmatic sufferers. The correct type of odour control can lead to a better and a healthier environment for people living in the neighbourhood of a plant that is producing foul odour.

The offensive release of harmful gases like hydrogen sulphide, ethyl methyl sulphide and trimethylamine can result in serious health issue. These health issues can produce symptoms that range from mild discomfort, to being extremely serious. Chemicals with strong odour have the capacity of causing lung, eyes, nose and throat irritation. Employees working inside factories can experience a mild burning sensation in their throat that eventually leads to coughing, wheezing and other breathing problems.

What can be done to eliminate odour emissions?

There are a comprehensive range of odour abatement processes that can be used to maintain an odour free environment both internally or externally.

Here is a list of multiple processes that can be used for eliminating odour problems:

  • Wet Scrubbing: Often the technology of choice for companies seeking a flexible and efficient way to eradicate unwanted odours.
  • Biological Treatment: OSIL’s LavaRok biological systems which is often the favoured solution for clients looking for a reliable and flexible process for treating high volumes of odour – without the addition of chemicals.
  • Photo- ionisation: This process involves applying a high intensity UV light combined with a specialised catalyst to eliminate odours from contaminated air.
  • Activated Carbon: This adsorption process is ideal for treating VOCs and other organic contaminants.
  • Misting and Dosing System: This is a process for masking odours with the careful use of essential oils, surfactants and organic compounds.

With the continual development of towns and cities, foul odour emissions are becoming more and more problematic for all types of manufacturing, production and treatment processes as well as for the conurbations surrounding these facilities.

Odour elimination has gradually become one of the primary concerns that need to be resolved. It is imperative that odour is controlled so as not to materially affect people’s enjoyment of their property or outdoor space and decrease their legitimate use of the environment.

If problems do occur, or are likely to occur in the near future, it is important that the appropriate actions to prevent or minimise the risk are taken. While for some activities it may not be practicable to avoid all odours, any neighbourhood has the right to expect that there must not be any odour produced that will detract from their quality of life. It is unlikely; however, that action will be taken over occasional or slight odours.

By “neighbourhood” we mean anyone living, working, visiting or making use of public space outside a site that is producing odour. It means any sensitive receptor.

Rather than simply installing turnkey equipment, OSIL is one such odour controlling partner that focuses on finding the right solution to resolve odour problems.

Contact us today to find out more about our cost-effective odour control solutions.

Odour Masking Vs Odour Control

It is a common misconception that these two terminologies are identical to each other but in reality, they are poles apart. We at OSIL are here to guide you through the differences.

odour control vs odour masking.png

Odour Masking

The simplest comparison of industrial Odour Masking is the domestic air-fresheners when introduced into a room at a high concentration they mask the unpleasant pungent odour present in the room or particular area. As a result, the human nose detects the highly concentrated fragrance and not the bad odour. The drawback to this technique is that the odour still exists in the background and when the masking fragrance fades away, the bad odour resumes its presence, thus demonstrating that it is a short-term solution.

Industrial Odour Masking differs only slightly from the above but is not an entirely unique concept. In the industrial sector, odour masking is achieved by releasing a highly concentrated masking agent in numerous kinds of fragrant odours. The process is used on Industrial Waste, Sewage, Farming, and similar industries to mask the odours being generated. Large areas like septic tanks, sewage ponds, refuse tips, offal processing plants, often use masking agents to deodorise the noxious odour, being produced which would otherwise make the surrounding local area very unpleasant.

There are special odour masking products for the industrial sector that are easy-to-use and can be mixed with water in a range of varying dilutions. As a result, these can be applied by mist machines, sprayers or direct drip-feed into the water source.

Odour Control

Numerous facilities such as sewage treatment plants are prone to odour issues due to the residual components from the treated wastewater. These screenings and sludges can produce an excessive amount of hydrogen sulfide gas which smells like rotten eggs. To control this type of odour, various odour control technologies are used:

  1. Micronutrient Dosing- A healthy way to combat this type of odour is by adding micronutrient additives as they biologically breakdown the organic waste and reduce the amount of odour released. These additives increase the growth of facultative bacteria, which prohibits the emission of Hydrogen Sulfide (H2S).
  2. Extraction and Filtration- Extracting the odorous vapours from waste treatment is another method via which the odour in the sewage treatment plants can be controlled. This is an effective method that prevents the odour from infiltrating the surrounding neighbourhoods.  Activated carbon filters and biofilters can be used to treat the extracted vapours.

The above details the differences between these two odour treatment solutions. We at OSIL can ensure that your employees work in an environment with the best possible atmosphere, one that is odourless and safe from noxious gases. We can help create a workplace environment that employees deserve, reach out to our engineering staff for assistance in removing your odour problems.

Case Study: May Gurney

Whitlingham SBT, Odour Abatement System: LavaRok® Biofilter, CuCarbs®, Fans, Ductwork & Covers

Project Description

Odour abatement of H2 S and ammonia extracted from covered tanks through an OSIL LavaRok® Biofilter followed by dual CuCarb® activated carbon polishing units capable of a 99% removal of 30ppm NH3 and 100ppm H2 S from a 12,500mÑ/h air stream. Final effluent water is continually sprayed over the graded LavaRok® pebbles to provide the correct environment for the inoculum.

The porous nature of the LavaRok® provides a large surface area for the inoculum to react with the odorous air. The CuCarb® units polish any odour not removed by the Biofilter. The benefit of CuCarb® over other carbons is the ability to continue the polishing process in a damp environment.

“While OSIL presented three options to help us prevent nuisance odours being produced, together with the relative capital and running costs, their LavaRok® bio-filtration system was clearly the way forward. Bio-filtration fits with our business ethics, from the unique long life media to employing natural biological processes.”

Chris Penn, Project Manager May Gurney.

OSIL Scope

Turnkey design, manufacture, supply, installation and commissioning of OSIL LavaRok® and CuCarb® odour control system including fans, ducting, electrical panels.

Project Duration: 22 weeks

Case Study: Timothy Taylor & Co. Ltd

Keighley Brewery – Odour Control Plant 

Project Description

OSIL were invited to design, supply and install an odour control plant to capture and treat the odours from Timothy Taylor’s new effluent plant. The system was designed to extract 1,550m³/h from the sludge thickening building and comprises a range of interconnecting ducting, an extraction fan and a CuCarb® activated carbon unit with an H2S removal efficiency in excess of 99%. To ensure quiet operation the fan is housed within an acoustic enclosure.

OSIL Scope

Turnkey design, manufacture, supply, installation and commissioning of complete OSIL CuCarb ® odour control system.

Project Duration: 4 weeks

“After analysing our emissions to atmosphere from our new effluent treatment plant we sought a company that could ensure we met exacting standards of odour reduction consistently and cost effectively. OSIL offered us a cost effective practical solution with a high level of industry expertise, design capability and customer service. It continues to work reliably and cost effectively and importantly helps us to meet the high environmental standards set by the company.”

Nick Berkovits, Senior Brewer, Timothy Taylor & Co. Ltd.