Evaluation of the Effects of Fibre Content when De-watering Sludge

SNF (UK) Ltd provides technical support to various water companies throughout the UK.  The technical team routinely visit sites to monitor and optimise the polymer performance on thickening and dewatering applications.

Monitoring sludge characteristics has allowed SNF (UK) Ltd to identify an apparent correlation between fibre content and centrate quality when dewatering primary sludges.

This appears to be a seasonal phenomenon, with the lowest fibre readings being recorded during the warmer months of the year as biological activity within the sludge increases due to the higher temperatures.  Initial indicators of a potential problem are a drop-in sludge pH to ≤ 4.5 as the sludge becomes septic; this is then typically followed by a fall in fibre content as the increased acidity breaks down the fibrous material, figure 1.


This reduction in fibre content can lead to a significant deterioration in cake and centrate quality, figures 2 & 3, particularly when using powder polymers and linear emulsions, leading to potentially costly processing issues on site.


Using the data collected from the routine sampling of water company sites and extensive laboratory trials, we can inform our customers that the fibre content of the primary sludge may be becoming compromised and advise them to amend their treatment regime accordingly, usually to a structured or crosslinked emulsion, thus pre-empting any potential processing problems on site and preventing major issues such as consent to discharge failures which can result in extremely punitive consequences to the water company.





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