Wastewater treatment plants don't belong in a catalogue
Saturday, 01 September, 2018
Dissolved Air Flotation (DAF) systems have been around for a long time and it would seem that they are here to stay. That said, if anything, DAF manufacturers are getting more — rather than less — enthusiastic about the application of DAF technology in new areas of treatment or processing.
Applying existing technology such as DAF for a new purpose can have its rewards, although it can be dangerous unless the principles of DAF are fully understood. There are far too many companies selling DAF systems from a catalogue without taking into consideration exactly what they are going to be used for.
The specific design and features of a DAF system really do matter, and not only because the unit is expected to fulfil its duties. An incorrectly designed system can absorb considerably more power than it needs to, and it can take up unnecessary space.
Many companies simply quote standard sizes of DAF systems which are based on a flow rate that the unit is deemed to be able to treat. You may get lucky if the stream that you want to treat is similar to what that particular design is based on. However, to invest considerable money while leaving a successful outcome to chance is not a particularly virtuous or smart business decision.
There could be deemed to be two general areas to a DAF design being firstly, the actual hardware and secondly, the process. The hardware could be defined as the actual DAF vessel, the sludge removal technology, an efficient means of dissolving air in water and injecting it at the inlet of the DAF and a system that ensures laminar conditions. We would have to assume that most DAF manufacturers have this part of the equation correct otherwise they wouldn’t have built enough systems to devise their catalogue.
The process side of the equation is where knowledge, experience, skill and — equally as important — having the ability to apply the technology to the application is critical.
The most commonly overlooked aspect of designing a DAF is getting the air-to-solids ratio correct. This is basically a ratio of the mass of air that is dissolved and released into the incoming stream to the mass of solids that are present. Many text books will suggest a range of anywhere between 0.01 and 0.2 but this is 20-fold difference. Given that the pumps used to generate the dissolved air stream are by far the most power-hungry component in a DAF system, if you are generating 20 times as much dissolved air than you need to, you are paying way too much in electricity.
The dissolved air flow also affects the surface loading rate. Thus for a given size DAF system with a defined surface area, decreasing the recycle stream flow will reduce the surface loading rate, thereby allowing treatment of a greater flow in the same unit.
Like many DAF suppliers, Hydroflux has adopted a range of standard DAF vessels, the design of which is based on ensuring that the hardware is optimised from a process point of view and also that it is designed for economical fabrication. How we apply the range is where we differ. At Hydroflux, we have a deep understanding of both DAF systems and the DAF process. We design each DAF system to suit the application in question.
Our intelligent software program considers a wider range of factors including solids load, temperature, surface loading rate, solids loading rate, fluid density and air solubility. This is to ensure that the dissolved air system is ideal for your application and not simply based on a text book guideline. Furthermore, one would be hard pressed to find a DAF related project that at least one of our engineers does not have knowledge of or experience in.
DAF systems are not inexpensive and are required to be extremely reliable — often having to operate 24 hours a day, 365 days a year. So making sure that your system is designed specifically to meet your needs is of paramount importance.
The capital cost for a properly designed DAF system may be a little more, but it may actually be a lot less, and you can be assured that a DAF system from Hydroflux will present far less problems and certainly incur lower costs in the long term.
For more information: https://www.hydrofluxindustrial.com.au/industrial-wastewater/dissolved-air-flotation-daf/.
About the Hydroflux Group
The Hydroflux Group comprises eight companies based in Australia, the Pacific and the UK, providing design and build, equipment, processes and operational services in water and wastewater treatment. Hydroflux Industrial specialises in industrial wastewater treatment including designing and constructing plants and supplying equipment across all sectors. Hydroflux Industrial is a wholly owned subsidiary of the Hydroflux Group.
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