Enzymic Hydrolysis Technology Demonstration – Production of Enhanced Treated Biosolids for Agricultural Recycling

Le, S.1, Briddon,T.1, Harrison,D.2 and Werker, A.3
1United Utilities, 2Monsal, 3AnoxKaldnes AB, Sweden.


The Sixth Community Environment Action Programme re-instates Europe’s commitment to a sound use of sludge on land and
the LIFE Instrument is one of the Measures aimed to achieve the long-term goal of 75% of urban sludge as being suitable for
land spreading in the whole of the EU. The Blackburn Sludge Treatment Scheme was chosen by LIFE to demonstrate best
practice. Thermophilic pre-treatments were the preferred bolt-on upgrades for the Blackburn Digestion facility to guarantee an
enhanced treated sludge for agricultural recycling. As conventional thermal pasteurisation techniques with their short
treatment times and high temperatures do not allow sufficient biological activity to develop, the United Utilities Enhanced
Enzymic Hydrolysis (EEH) process was selected for its combined advantage of simple yet robust operation and optimum
enzyme activity at 55°C. Operation at 55°C allows the plant to guarantee the minimum 6-log E. coli reduction using only lowgrade heat. This is important, as it would enable any standard CHP scheme to use a greater proportion of the biogas for
electricity production. To date the first full scale EEH plant at Blackburn has shown excellent pathogen control capability with
indicative VS destruction rate of 55%, even under highly overloaded hydraulic conditions. The enhanced treated cake has
been used as a seedbed fertiliser for maize and cereal crops. It has proved to be of low odour and has provided the
opportunity for surface spreading on grassland, even in close proximity to residential areas. Increasingly the ability to produce
a low odour product will help to make sludge recycling more sustainable where the land bank is limited and more acceptable
to the public.

Anaerobic digestion; enzymic hydrolysis; pathogen; sewage sludge; agricultural recycling

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