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Biofiltration: a cost-effective effluent solution

06 June 2016

Good wastewater bio-filtration solutions are important to virtually all food production processes. Peter Brewer talks us through the benefits of biofiltration and a typical project. 

Reducing trade effluent loads will minimise a company’s environmental impact, ensure Environmental Agency compliance and help reduce costs. Complying with Environment Agency and other legislation relating to wastewater is getting more difficult and disposing of trade effluent into a sewer or watercourse is becoming ever more heavily-regulated.

Trade Effluent Consents, pollution prevention and control (PPC) permits and Waste Management Licences are designed to protect the environment from pollutants. For most food processors this now requires the installation of on-site effluent treatment plant to remove contaminants and to produce environmentally-safe, treated wastewater.

There are many physical, chemical, and biological wastewater treatment solutions available, which can make it hard to identify which offers the best solution for a particular application. One of the most effective technologies is biofiltration. If a factory has sufficient available space, it can offer a relatively low-cost, low-maintenance effluent treatment with very low power consumption and practically no operator input. It can also be used alongside, or in conjunction with, other technologies. Wastewater is processed through screening, pH control, balancing, primary clarification, secondary biological treatment and secondary clarification to an effluent that is clean enough to go into the local watercourse.

Biofiltration also provides a tried and tested method for processing wastewater and is used by many food producers around the world, including Bairds Malt.

Pencaitland Maltings plant near Edinburgh is one of five plants operated by UK maltster, Bairds Malt. New bio-filters at the plant are treating an effluent flow of 550m3 per day. With an annual malt production capacity of 47,000 tonnes the plant uses significant quantities of water in the steeping and germination processes. The specific role of the biofilter is to reduce the BOD (Biological Oxygen Demand) load in the effluent to acceptable levels which reduces trade effluent charges. The previous BOD load at the Pencaitland Maltings plant was 100kg per day and this has now been reduced by 90% to just 10kg per day.

This biofiltration project comprised the decommissioning and demolition of an outdated and inefficient bio-filter and the design, supply, installation and commissioning of new bio-filter, recirculation pumps, electrical works and minor civil works. The biggest challenge encountered during the project was to keep the treatment plant operational while the bio-filters were replaced. This was achieved by hiring a temporary SAF unit (Submerged Aerated Filter) to operate in parallel with the existing biofilters to enable each one to be replaced in turn.

The Pencaitland Maltings' new biofiltration plant was designed to be robust and environmentally friendly with low noise, low maintenance and low energy requirements. Its operational life is expected to be at least 20 years.

Peter Brewer is general manager of ACWA Services Ltd

How it works…
A bio-filter is a bed of media to which micro-organisms attach and grow to form a biological layer – a biofilm. This biofilm comprises different micro- and macro-organisms which stick to each other and to the surface of the media.

Wastewater is applied intermittently or continuously over the media. Organic matter and other water components diffuse into the biofilm where the treatment occurs, mostly by biodegradation.

Biofiltration processes are usually aerobic, which means that micro-organisms require oxygen for their metabolism. Oxygen is supplied to the biofilm counter currently with water flow. Aeration occurs passively by the natural flow of air through the process.

Some biofilters have a rigid structured plastic media which offers high specific surface area and good air/water distribution. Wastewater is distributed over the media via a series of nozzles above the media. A proportion of the wastewater is recirculated through the media to ensure there is a minimum volume passing over the media (at times of low influent flow) to ensure the biofilm is kept moist and that the micro-organisms remain healthy and productive.

The specific role of the biofilters is to reduce the BOD (Biological Oxygen Demand) load in the effluent to acceptable levels which reduces trade effluent charges.


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