MODELLING THE ECONOMIC AND ENVIRONMENTAL IMPACT OF ENZYMIC HYDROLYSIS IN SLUDGE TREATMENT
M.S. Le1, D. Harrison2 and A. Werker3
1United Utilities PLC, Lingley Mere Business Park, Warrington, WA5 3LP.
2Monsal, Oak House, Ransom Wood Park, Southwell Road West, Mansfield, NG21 0HJ.
3AnoxKaldnes AB, Klosterängsvägen 11A, S-226 47 Lund, Sweden.
(free)
Environmental release of pathogens and green house gas emissions are the two key
concerns in sludge management. In this paper mathematical modelling has been presented
as a new approach to account for the different kinetics of various pre-treatments in the
anaerobic digestion of sludge. The models were used to predict pathogen and volatile solid
reduction in digestion as well as biogas release in secondary digestion.
Thermal de-activation and Enzymic Hydrolysis de-activation of pathogens were found to have
the same type of kinetics. For enhanced pre-treatment, the observed median E. coli removal
at Blackburn was 6 log. Using mathematical modelling it was possible to demonstrate that
the Enhanced Enzymic Hydrolysis process had a pathogen removal capability of at least 6.86
log.
There was good agreement between the model and the VS reduction data for the anaerobic
digestion of EEH treated sludge at Blackburn. Mixing was shown to have a significant impact
on the VS reduction performance of the digesters.
The substrate conversion model was able to predict accurately the emissions of green house
gases from secondary digestion.
An economic model for VFA has been developed. It is based on the cost saving resulting
from the use of EBPR as an alternative to ferric dosing for phosphorus removal. The model
suggested that VFA may be worth up to £1,090 per tonne in an EBPR application.
KEY WORDS
Enzymic Hydrolysis; environmental; modelling; pathogen; sludge; VS reduction; VFA
