While some biological reactions are key to the waste management process, some are most definitely unwelcome and whilst the process of foaming can have its place in the waste management industry, it can also bring operations to a grinding halt.
Adam Duxbury, New Product Development Chemist here at Airedale Chemical advises on the essential role of antifoams in the world of waste management.
1. Know your antifoams
Antifoams are a range of chemicals that reduce and prevent foam forming in liquids used in industrial processes. They are also known as de-foamers or anti-foaming agents and are added to foams which have already formed 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.
2. Applications in waste management
In the waste management industry antifoams are particularly useful in the treatment of industrial waste water. They can effectively eliminate the build up of foam in re-circulating 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.
3. Making the right choice
The two main varieties of antifoam available are silicone or non-silicone based. Silicone antifoams are available in aqueous emulsions and non-aqueous forms depending upon how you wish to disperse and apply the anti-foam. Therefore, at Airedale Chemical our first step is to ascertain whether customers require an aqueous or non-aqueous form of antifoam.
Aqueous emulsions can also be easily dispersed into water based systems or polar solvents so they are best used for situations where accurate dosage levels 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 fast-acting to quickly reduce a rapidly-growing foam. Whereas, 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 impact on antifoam choice and dosage level. Large fluctuations in pH can make the effluent unstable and consequently 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. However, in facilities where materials can be stored indoors, aqueous options can be more suitable.
4. Antifoams in action
When one of Airedale’s long-term customers, Urbaser Balfour Beatty (UBB (Essex) Construction JV) began work on its 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 in order for it to carry on functioning correctly.
We began consultation with UBB to help them navigate the range of antifoams on the market and explore the benefits of using them in its new bioreactor at its site in Basildon, Essex.
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 as it would cause an unmanageable mess which would keep foaming up and overun the site if left untreated.
Therefore we advised on a non-silicone based antifoam which would not block the fine membranes in the filtration equipment, as oppose to a silicone based antifoam which is insoluble in water and could obstruct the system.