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Meeting ever-tightening discharge requirements

16 May 2024

Ensuring trade effluent discharges meet strict water company standards, particularly for chemical oxygen demand (COD) is presenting an increasingly complex challenge. Pete Cranney argues that biological treatment could offer a solution.

Trade effluent charges have increased significantly in the last decade and water companies are tightening permit conditions to drive industrial customers to improve the quality of water entering the sewers. As a result, existing trade effluent treatment methods may no longer be enough to meet these stricter standards.

However, if designed and implemented correctly, onsite biological treatment is able to deliver full environmental compliance and ensure long-term cost efficiency, while contributing to sustainability goals.

Trade effluents are liquid waste streams discharged into public sewers. Their composition is highly variable but can include substances such as chemicals and fats that can be harmful to human health and the environment if not treated correctly.

In giving consent for organisations to discharge trade effluent, water companies may require it to be treated to a specified standard before it enters the foul sewer and becomes the responsibility of the utility to manage.

A breach of trade effluent consent is a criminal offence and penalties can range from an early-warning notice to a fine or prosecution or, in the most serious cases, imprisonment. Financial and reputational implications can also be very detrimental to brands. 

Polluting parameters 
Specified trade effluent limits are usually for pH, flow, suspended solids, temperature and COD. Limits on COD concentrations in discharges to sewers can be particularly challenging to maintain, partly because they are highly variable, prone to spikes and dips depending on flows. Because of the additional costs incurred by the water companies to treat, heavy metals in the discharge are also covered by consent limits or are being tightened if already included.

Most food processors already have some level of wastewater treatment on site, such as dissolved air flotation (DAF) systems. But many organisations are now finding that they require additional processes to keep COD within permitted levels and satisfy water companies.

Traditionally, tankering the waste away from site to be managed elsewhere has been the solution for many, but this comes at a significant financial cost, as well as the heavy environmental impact associated with the mileage of carbon-emitting vehicles on the road.

Installation of a biological treatment plant could be the bettert effective option to ensure full compliance. Many industrial trade effluents from the food and beverage sector in particular, are also ideal for biological treatment. Wastewater generated by food and drink production is typically rich in organic materials like fats, oils and sugars, so can be treated successfully without chemicals once the solids have been removed.

Biological treatment sees microorganisms naturally degrading and transforming organic pollutants without the use of chemicals – an approach that reduces chemical residues, promoting a greener and more sustainable wastewater treatment process. 

Biological treatment methods can include:

Aerobic: The aerobic treatment process uses oxygen to break down the organic contaminants in an aerated tank. Oxygen is continuously mixed into the wastewater by an aeration device, such as a blower.

Aerobic microorganisms convert the pollutants into carbon dioxide, water and biomass. This process produces sludge which can be safely disposed of or sold as agricultural fertiliser.

Anaerobic: Anaerobic treatment is an energy-efficient process that uses anaerobic bacteria to convert organic pollutants or COD into biogas, a valuable source of renewable energy.

Submerged aerated filter (SAF): SAF systems use a biological filter bed that supports the growth of microorganisms. The filters are continuously aerated to enhance the biological treatment process, allowing the microorganisms to effectively break down organic pollutants.

High-performance aerated filter (HiPAF): HiPAF systems combine the benefits of SAF technology with enhanced aeration to achieve higher treatment efficiencies.

Lab tests and trials
Before any permanent biological treatment is installed, advanced testing is advisable to ensure that the most suitable system is selected.

Industrial effluent composition can be highly variable and biological treatment processes should be tailored for each site. To inform this process, ahead of permanent installation, WCSEE undertake an in-depth advance testing in two ways – laboratory testing and onsite trials.

These reviews can help avoid performance and commercial shocks caused by discrepancies between designs and the delivery of a project. They also give the end user reassurance that the systems are suitable before committing to a capital purchase, while at the same time keeping a site compliant.

Bespoke lab-scale reviews can ascertain the profile of the effluent and ensure that the correct process is implemented, based on the requirements of trade effluent permits.

A report is produced that determines the best technology and cost of the final scheme. This kind of testing has a quick turnaround, causes little disruption and allows designers to rule out different technologies, saving time in researching options that might not work.

Following the lab review, an onsite trial is usually recommended to identify the precise equipment required. Trials will give a very accurate indication of how the plant will operate and will give a good idea of its running costs. While biological treatment plants may initially seem expensive, they may save money in the long run, and often provide a quick return on investment (ROI).

So, as trade effluent disposal costs rise, food and drink processing organisations need to explore solutions that are both cost-effective and environmentally-friendly. By adopting biological treatment, it is possible to reduce costs, minimise environmental impact, and remain competitive in a challenging market landscape.

Pete Cranney is Technical Sales Manager at WCS environment Engineering.


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