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Forbes design, manufacture & install large pasteurising digestate tanks on AD Plant

Forbes Technologies Ltd, UK’s largest custom plastic & composite tank manufacturer was faced with an extremely demanding application, where digestate is pasteurised from a large Mechanical Biological Treatment AD plant. The plant located in the south of England and processes feed stock derived from residual municipal waste and generates electricity.

All six tanks, manufactured in a dual composite of high heat resistant polypropylene & NPG isophthalic glassfibre laminate, have a working capacity of 40 cubic metres and are 2.5 metres diameter with an overall height of 10.4 metres including a conical base. The tank tops incorporated a steel support bridge for a large top mounted slow speed agitator with four one meter diameter blades with the shaft terminating in a foot step bearing in the base of the cone. To aid the agitation process three full height vertical standoff baffles are welded to the internal wall, split to allow for thermal expansion

One major requirement is thermal insulation to permit liquid digestate to enter the tank at 75 degrees Centigrade & to hold the temperature for a given period without any further heating being required.  The tank being constructed in thermoplastic glassfibre laminate assisted in the insulation. To maintain this temperature 100mm thick polyurethane insulation foam covered with a GRP laminate was added externally.

This very physically demanding duty demonstrates the robustness of composite tanks when designed correctly. The combined strength & insulation factors are a big plus point being manufactured throughout in composites.

One of the strengths of Forbes is the range of materials & types of constructions they are able to apply to the construction of tanks, vessels & towers.  The company has dedicated factories for specific types of manufacture including helically wound polyethylene tank up to capacities of 100 cubic metres; composite single & dual laminate tanks & towers in excess of 200 cubic metre capacity & free standing tanks in polypropylene & HDPE from a few litres to 100 cubic metres.

Unlike many plastic fabrication companies, this wide choice of materials & designs allow Forbes to select the correct material & design for your specific application.

Sales contact:  Des Dibley  +44 (0) 1366 389650   email:

Press contact: Melvyn Jupp +44 (0) 1366 389640  email:

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