Mohaideen, Katheem Kiyasudeen Seeni
(2018)
Eudrilus Eugeniae As A Plug Flow
Reactor.
PhD thesis, Universiti Sains Malaysia.
Abstract
Earthworms are referred as ecological engineers and their guts are often
compared to chemical reactors, however, modeling experiments to substantiate it are
lacking. The aim of this study was to apply established reactor models on the gut of
the composting earthworm Eudrilus eugeniae to better understand its digestive
kinetics. Firstly, a mathematical model based on first-order kinetics was applied to
determine the pattern of digestion rates of indicators, namely total carbon (%), total
nitrogen (%), C/N ratio, 13C (‰), and 15N (‰) at 5 intersections (pre-intestine,
foregut, midgut A, midgut B, and hindgut) along the gut of E. eugeniae. Secondly, an
enzyme model of digestion and absorption was used to test two probable hypotheses,
(i) digestion limitation, and (ii) absorption limitation to identify the mode of gut
operation in E. eugeniae. To achieve that, the concentration profiles of crude protein
(%) and 17 amino acids (%) were experimentally determined as substrate and
breakdown products at the 5 intersections along the guts of E. eugeniae. The data
then were used to determine the rates of digestion and absorption using the curve-fit
simulation analysis. Lastly, a model based on deactivation kinetics was used to
understand how three deactivation rates (β=0.05, 0.1, and 0.15) affect the rates of
digestion at those 5 intersections along the gut. The experimental results based on the
first-order model revealed that all the indicators exhibited a linear pattern of
digestion along the gut, while, the enzyme model reflected that the rate of digestion
to be higher than that of absorption. The deactivation model revealed that an increase
in deactivation rates result in the reduction of digestion rates
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