Do hydrolysis processes effect digested sludge rheology?
Dawson, M.K. and Ozgencil, H., BHR Group Ltd, UK
(free)
Sludge hydrolysis processes of various types are being adopted upstream of mesophilic anaerobic digestion on an increasing number of sewage treatment works in the UK. The objectives of hydrolysis are to maximise pathogen kill and (if possible) achieve enhanced treated standard, to enable higher digester solids loadings and to maximise gas production.
The cost effective design, sizing or selection of equipment for sludge pumping, transport, handling, mixing, thickening, de-watering, heat exchange and other processing depends on reliable sludge rheology measurement. There is no published information on hydrolysed sludge rheology or on how hydrolysis prior to digestion effects digested sludge rheology.
In the water industry sponsored WWM research programme, BHR has established the worlds largest database of sludge rheological properties (SRDB) (currently 500+ rheograms) to enable improved property prediction for a wider range of sludge types than the obsolete WRc Report TR185. The new SRDB has been established from a combination of existing data and sludge samples obtained from WWM members and measured using the BHR rheology laboratory. The SRDB covers both potable and wastewater sludges and includes many types of hydrolysed sludge before and after digestion. The SRDB has enabled predictive sludge rheology correlations to be built up for different sludge types including hydrolysed sludges.
In this paper, comparisons of the rheology of ‘ordinary digested’, alpha biotherm, enzymically hydrolysed (EH & EEH), thermally hydrolysed (CAMBI), acid phase digested and sonicated sludges pre- and post-digestion are made. Some hydrolysis processes have a definite influence on digested sludge rheology whilst others appear to have no effect.
