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Know your bubbles

While some biological reactions are key to the waste management process, some are most unwelcome and, while the process of foaming can have its place in the industry, it can also bring operations to a grinding halt.

Antifoams are chemicals that reduce and prevent foam forming in liquids that are used in industrial processes. They are also known as de-foamers or antifoaming agents, and are added to a foam to break it up or to prevent formation.

Foam can occur from bacterial activity or wherever liquids are moved, for example in production and filling processes, blending and mixing, distillation and filtration. The change in pressure can result in air being created in a solution. This can work its way to the surface creating bubbles, and foam and can have an adverse effect on how equipment operates.

Antifoams are particularly useful in the treatment of industrial waste water. They can effectively eliminate the build-up of foam in recirculating water systems or where foam occurs following the use of pumps and other aeration devices.

Antifoams are also commonly found in the biological stages of waste management. Air is mixed into the process to oxygenate the water, which promotes the biological oxidation of waste water. Silicones have a limited effect on the chemical oxygen demand and, as such, do not hinder this breakdown process.

But without the correct use of antifoam, unwanted foam can quickly overrun waste plants and interfere directly with the oxygen uptake of the micro-organisms in the process.

The two main varieties of antifoam available are silicone or non-silicone based. The former are available in aqueous emulsions or non-aqueous forms, depending on how you wish to disperse and apply the antifoam.

Aqueous emulsions can be dispersed easily into water-based systems or polar solvents, so they are best used in situations where accurate dosages are required and close process control is needed.

Waste management operators should also consider how long they need the antifoam to be active. Some products are fastacting to quickly reduce a rapidly growing foam. Others have more longevity and can be used continually to maintain a steady level of foaming at low concentrations.

Two other major influences on choice of antifoam are pH level and temperature.

The pH of the waste to be treated can have a direct effect on antifoam choice and dosage level. Large fluctuations in pH can make the effluent unstable and increase foam production. Therefore, the correct dilution rates are vital to a smooth running facility.

Operations which are based in rural or outdoor locations may be more susceptible to freezing. In these cases, non-aqueous antifoams are likely to be more suitable due to their greater resistance to freezing. But in facilities where materials can be stored indoors, aqueous options can be more suitable.

When one of Airedale Chemical’s long-term customers, Urbaser Balfour Beatty, began work on a new on-site bioreactor, it was banking on the chemical process of transforming organic waste and accelerating its decomposition and stabilisation. But while this is what drives a bioreactor, other potentially foaming reactions had to be curbed so it could function correctly.

Antifoams were required for the suppression system around the top of the bioreactor, where they were injected using a nozzle system as leacheate from biohalls. These feed the bacteria from the bioreactor and, due to the aerobic process, inevitably create foam.

If antifoams were not used as part of the system, the foam would keep on being produced and the bioreactor would become ineffective due to the amount of foam falling out of the top. Eventually it would stop working altogether because it would cause an unmanageable mess which would keep foaming up and overun the site if left untreated.

Airedale therefore advised on a non-silicone based antifoam which would not block the fine membranes in the filtration equipment rather than a silicone-based antifoam which is insoluble in water and could obstruct the system.

Adam Duxbury is a product development chemist at Airedale Chemical

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