Modelling biological sulphate reduction in anaerobic digestion using WEST.
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Date
2010-09-03
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Abstract
Researchers at Rhodes University conducted investigations into the anaerobic co-disposal of
primary sewage sludge (PSS) and high sulphate acid mine drainage (AMD) resulting in the
development of the Rhodes BioSURE Process® which forms the basis for the operation of a
pilot recycling sludge bed reactor (RSBR). Further research has been conducted by researchers
at the University of Cape Town (UCT), with the principle aim of determining the rate of
hydrolysis of PSS under rnethanogenic, acidogenic and sulphate reducing conditions in
laboratory-scale anaerobic digesters.
The University of Cape Town's Anaerobic Digestion Model No.1 (UCTADMI) which
integrates various biological anaerobic processes for the production of methane was extended
with the development of a mathematical model incorporating the processes of biosulphidogenic
reduction and the biology of sulphate reducing bacteria (SRB). Kinetic parameters used in the
model were obtained from SOtemann et al. (2005b) and Kalyuzhnyi et al. (1998).
The WEST® software was used as a platform in translation of the basic UCTADMI from
AQUASIM, and subsequently applied to data sets from UCT laboratory experiments.
Incomplete closure of mass balances was attributed to incorrect reaction stoichiometry inherited
through translation of the AQUASIM model into WEST®. The WEST® implementation of the
model to the experimental methanogenic systems gave fairly close correlations between
predicted and measured data for a single set of stoichiometric and kinetic constants, with
regressed hydrolysis rate constants. Application of the extended UCTADMI to experimental
sulphidogenic systems demonstrated simulation results reasonably close to measured data, with
the exception of effluent soluble COD and sulphate concentrations. Except for a single system
with a high COD:Sat ratio, sulphidogens are out competed for substrate by methanogens within
the model. Therefore the model does not properly represent the competition between
methanogenic and sulphidogenic organism groups.
Trends observed in application of the model to available pilot plant RSBR data were similar to
those observed in sulphidogenic systems, resulting in methanogens out-competing
sulphidogens. The model was used as a tool to explore various scenarios regarding operation of
the pilot plant. Based on the work conducted in this study, various areas for further information
and research were highlighted and recommended.
Description
Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2009.
Keywords
Sewage--Purification--Biological treatment., Sewage--Purification--Anaerobic treatment., Theses--Chemical engineering.