Excellence Repeated Maximises the AD Mixing Process

The reality for today’s AD operators is that in addition to achieving higher gas yields reducing foaming and minimising maintenance issues, they now need to fully maximise the sustainability benefits of their AD process plant, which means that each part of the AD process is subject to ever closer scrutiny.

Huntingdon based System Mix LTD in conjunction with P&M Pumps, who market the Rotamix System incorporating the Vaughan chopper pump, are an established supplier of digester mixing systems to all of the UK’s waste water companies over the past 20 years and more recently to numerous private sector food waste AD plants. One example of the success of the Rotamix System is at Southern Water where currently over 90% of their total digester volume (82007m³) is being mixed using the Rotamix System.

The basis of the success of these plants depends on a durable mixing technology supported by reliable Vaughan Chopper Pumps. Andy Parr, Director of System Mix underlines the reasons for the success of System Mix with a reference to the quotation made by Aristotle the Greek Philosopher and Scientist, “We are what we do repeatedly…excellence then, is not a single act, but a habit”. Explaining the mixing process in more detail, Andy continues, “It is crucial to the AD process that suitable pre-conditioning of solids is carried-out prior to digestion and our system has been proven to be one of the most effective in achieving this. The Vaughan pump prevents re-accumulation of fibrous and fatty material in the digester and this means that material continues to pass through the nozzles.

This in turn ensures that digestate is adequately conditioned and actually benefits all post-digestion equipment”. He concluded, “As many AD operators now need to maximise the sustainable credentials of their plant and equipment even further, we are confident that the benefits of our mixing systems are becoming even more important”.

Over last few years System Mix Ltd has been involved with ‘retrofit’ projects at existing AD plants where existing mixing systems were contributing to operational and biological issues. For example, high grit deposition was reducing the active volume of digesters and threatening to significantly reduce output outside compliance requirements. Also, compressors were requiring high levels of maintenance and were proving costly to keep running. Furthermore, as deposition increased, the maintenance issues escalated because not only did the rag mass reweaving within the digester impair their efficiency, it also caused blockage problems in the heat exchangers and further downstream pumps and systems.