Achieving optimum flocculation using the flomix high energy in-line mixer

Barnett, J., Neilson, A., Singleton, N., and Kelley, D.

SNF (UK) Ltd, United Kingdom



This paper shares the experience of plant trials using the SNF FloMix high energy in-line mixer to aid flocculation of ‘difficult sludge’s’ at two UK sewage treatment works.  It aims to explore the gaps in performance that were identified at each site, and from there how the solution to those performance gaps were proved via plant trials using the SNF FloMix high energy in-line mixer. The payoffs identified are also reported.  The paper is intended to give practical advice based on experience of ‘making the polymer work’ on plant as seen under laboratory conditions.


Polymer split dosing, sludge dewatering, high energy in-line mixer, flocculation, FloMix


The objective of commissioning/operation of any sludge dewatering process is to achieve performance targets in terms of sludge throughput, cake solids, return liquors, and polymer dosage.  Typically, these performance targets will be to produce cake solids as dry as possible, return liquors as low in solids as possible, at the lowest possible polymer dosage.

Experience as a polymer supplier during commissioning/operation of a dewatering process that is not achieving the desired performance targets is that when this happens the polymer is the first variable that is questioned but to give the polymer a chance to work, it must be ensured that it is being applied properly by effectively incorporating it into the feed sludge.

Using the SNF FloMix high energy in-line mixer to aid incorporation of the polymer solution into the feed sludge has allowed significant improvements against performance targets during two full scale plant trials at sewage treatment works in the UK.

High energy in-line mixers are not new technology and there are several other types in the market, so what differentiates the SNF FloMix from the rest?  Put simply the SNF FloMix high energy in-line mixer has been developed by a company who first and foremost are the largest manufacturer of polymer in the world, so we know about polymer.  We have the technical expertise and know-how to optimise the application of polymer – ‘make it work’.

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