A problem with sludge
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A problem with sludge
A transportation model becomes an effective planning tool for Southern Water Keith Parramore, Colin Wllsdon and Chris Gostick
Sludge processing equipment In the Sussex Division is located at 23 of the 184 treatment works. Sludge has to be transported from the 161 satellite works by road tanker to these treatment centres. Some 15,000 tds of sludge are treated per year, 5,000 of which are produced by the small satellite works and transported to treatment
The Sussex Division of the Southern Water Authority sought to rationalize their management of the handling of sludge produced at sewage treatment works. This
article describes a project undertaken with the
assistance of a placement student and consulting staff from Brighton Polytechnic. The result proved to be a very
satisfactory partnership between Southern Water, the placement student and the consultants. No off-the-peg package was available to do the job required, andin the process of tackling the problem a useful method was developed for solving large transportation problems. The Sussex Drainage Manager, Mr J. Foxley, now has a tool to optimize his operations and plan effectively for future investment.
centres.
The sludge can be processed in a number of different
ways, for disposal into the ground or for long-term storage. The various processing methods include gravitational and mechanical dewatering, hot or cold
digestion in large tanks (to destroy pathogens), drying beds and lagooning. The processed sludge may be used as a fertilizer and
Crude sewage is treated ¡n a variety of ways at sewage
soil improver, provided that various constraints are satisfied (e.g. metal content, proportion of rags and
treatment works to produce a cleaned effluent and a residue of sludge. This is a liquid suspension containing up to 7% of solid material (measured as tds - tonnes dry solid). The treatment and disposal of this material involves the Division in considerable expense, In total something of the order of £2 million per annum.
plastic, pathogen levels). If In cake form (15%-30% dry
solids) it may be surface-spread and ploughed in; otherwise it may be surface-sprayed or injected, in compliance with various codes of practice.
Figure 1: Henfield Sewage Treatment Works, West Sussex Foreground: primary tanks from which initial separation of sludge takes place Background: filter beds
Copyright © Operational Research Society 1989 3
OR Insight Vol. 2 No. 3 July-September 1989
The availability of land for disposal is further
(wherepj is the production at satellite works j)
constrained by the use of the land (grassland, arable), the season and the state of the land (heavy machinery cannot access "heavy land in wet conditions). Furthermore, care must be exercised to avoid polluting acqulfiers.
plus other constraints (e.g. metal content) as required.
Whilst the model was mathematically satisfactory, it was not acceptable to the DMslon as a working system. The ideal was for a model which could be run on a hard disk micro within the drainage o
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