Top range dewatering of digested and THP sludge with the Bucher HPS press in the UK

Huppert, M.1,Asaadi, M.2, Shana, A.3, Fountain, P.3 and Hofmann, F.1, 1Bucher Unipektin AG, Switzerland, 2AD Technologies, UK, 3Thames Water Utilities, UK,



Bucher HPX presses are widely used in the fruit juice & cider industries and are well known for their reliability and durability. The batch wise operation that involves alternating loosening / pressing of the filter cake can in many cases achieve higher filter cake dry solids than decanters, belt presses and chamber filter presses.

The main objective of this study was to benchmark the performance of the adopted Bucher HPS dewatering technology on sludges of different type (Digested and THP-pre-treated) from several of Thames Water Sewage Treatment Works, as well as performing a polymer-optimisation on selected sludges.

To conduct these trials, an integrated pilot plant that allows straightforward scale-up to industrial scale machines was installed at Basingstoke STW and operated for more than 5 weeks.

Different polyelectrolytes, both emulsion and powder, were tested with a concentration range of 0.3 – 1.0% active substance.

The results showed that anaerobically digested sludges could be dewatered to an average dry solids (DS) of 27% and maximum of 32.2%. Digested sludges which were pre-treated with THP could be dewatered from 40% to 54% DS. The loading rate of the machine for digested sludges was 350 Kg DS/hr and for THP+digestion was 750 kg DS/h. The respective throughput may be doubled at expense of 4-6% lower filter cake DS.

Detailed results can be found in this report.

The filtrate quality in most cases was 400 mg/l and in all cases less than 700 mg/l.

Key words:
Bucher press, dewatering enhancement, digested sludge, thermally hydrolysed sludge


Current dewatering technologies involve mechanical dewatering of various types of sludges using belt presses, decanting centrifuges and chamber filter presses. Subsequent to dewatering, the dewatered cake is mostly used in agriculture and in some cases incinerated.

Apart from high dry solids content, and high quality filtrate (i.e. low suspended solids), a non-odorous, stable and stackable product is desired.

The aim of the trials, carried out at Thames Water R&D compound at Basingstoke STW, was to benchmark the performance of the Bucher HPS sludge dewatering technology on a range of sludges from different Thames Water sites. The sludges of interest were from conventional anaerobic digestion sites as well as digested sludges from sites with THP pre-testament.

A second series of trials were also carried out on THP digested sludges only, with the aim to optimise the operational parameters, in particular polymer consumption.

A third series of trials were conducted which were aimed to investigate a potential performance increase when sludges were subjected to the “Kemicond” pre-treatment prior to dewatering. Kemicond is a two-stage chemical process, with the aim of chemically hydrolysing the extracellular polymeric substances (EPS) associated with secondary sludges and hence it is likely to lead to a significant improvement in dewaterability of sewage sludge.

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