Proceedings

Mobile sludge thickening: results from Anglian Water’s shop window

Rushworth, A1, Capeau, P.1, Patheyjohns, I.1, Inman, D.2, 1Orege, 2Anglian Water Services, UK

(free)

Abstract:

Mobile thickening, where a trailer-mounted thickener performs a ‘milk-round’ service on multiple sites,
has potential to make thickening possible on smaller sites, where installing a permanent thickener is
not financially viable. By opening the way to thicken on smaller sites, significant costs savings are
possible.

The paper presents results from an R&D project where a novel mobile sludge thickener, incorporating
the SLGTM (Solid-Liquid-Gas) process developed by Orege (France), was tested in Anglian Water’s
Shop Window, centred on the Newmarket sub-catchment in the East of England.

The project was undertaken over a 2-year period and the technology has been successfully used across
multiple sites. The project demonstrates the technology can consistently produce sludge of between
5.5 to 7% dry solids, at a polymer dose of 6-8 kg/tds, with a filtrate quality between 500-1000 mg/l.
The project is part of Anglian Water’s Shop Window, which is a microcosm of a future water company,
and aims to demonstrate the practical use of new technologies and behaviours.

Introduction:

Efficient thickening and dewatering of sludges from sewage treatment remains one of the key
challenges for UK water companies. Biological sludge from water recycling is known to have properties
that make it difficult to dewater such as high bound water content and compressibility (Sorensen and
Hansen, 1993; Katsiris and Katsiri, 1987). In Anglian Water, the preferred approach is either to thicken
to a 3 to 6% sludge using a drum or belt thickener, or to produce a 20 to 25% cake using a centrifuge.
In terms of the overall costs associated with operating a Water Recycling Centre (WRC), the cost of
sludge treatment and handling is second only to the electricity used for secondary aeration. The majority
of this expense is the movement of the treated and dewatered sludge. For this reason, WRC managers
are constantly seeking to reduce solids handling costs. A challenge identified by Anglian Water has
been how to cost-effectively thicken sludge on small WRCs.

Many plant operators believe this can only be achieved by switching to alternative dewatering
equipment. Such a significant change presents additional challenges as a plant operations team is
forced to learn an entirely new technology and the facility may incur new operating costs in certain areas
(e.g. staffing, energy, maintenance & repair) as they endeavour to reduce polymer usage and increase
cake dryness. Treatment plant operators would ideally install new equipment that reduces polymer
usage and produces a cake with higher dry solids content; however the high costs of replacing less
efficient equipment usually makes complete replacement economically unfeasible.

An alternative approach, presented in this paper, is to utilize existing dewatering equipment, but make it operate more efficiently by adding a pre-treatment step to improve the dewaterability of the sludge.
A new patented technology, developed by Orege in France, called the SLG™ (Solid-Liquid-Gas)
process claims to be able to improve the operational efficiency of existing thickening and dewatering
equipment. The process acts as a ‘sludge conditioning’ step, upstream of existing equipment, and by
changing the characteristics of the solids, thus improves Solids Liquid separation and improves its
dewaterability.

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