44    ANAEROBIC BIODEGRADATION OF INDUSTRIAL
SOLVENTS-THE CASE OF ACETONE AND ISOPROPANOL
E. Terzis, Experimental Officer
J. Diaper, Student
Dept. of Environmental Science
University of Bradford
Bradford, W. Yorkshire, BD7 1DP
England
INTRODUCTION
Increased industrial water usage in recent years has resulted in higher volumes of waste water, rich
in organic pollutants. Waste waters from pharmaceutical, cosmetic, textile, rubber and other industries will inevitably contain solvents, often in high concentrations. The presence of solvents is undesirable in an industrial effluent. Direct disposal in a river or to the sewage system is prohibited in U.K.
because of their effect in living organisms,' on the sewage reclamation system itself and also because
of their flammability. Iso-propanol and acetone are two commonly used solvents and easily found in
an industrial effluent.
Anaerobic treatment of organic waste has long been incorporated in the biological treatment of
waste waters. Anaerobic digestion of waste organic matter is a very complex process. Any description
can only be a simplified account of the real and complex processes taking place in an anaerobic
system. Such an account is given in Fig. 1. Experience in the U.K. is primarily associated with the
anaerobic digestion of sewage sludge but the field of application is by no means restricted to that
process and it is increasingly applied to industrial wastes.2 To investigate the applicability of the
anaerobic digestion of iso-propanol and acetone the Monod kinetic model was employed.3,4 The
estimation of the kinetic parameters of the Monod model provides a quantitative description of the
anaerobic degradation of iso-propanol and acetone and also offers useful design information for such
process.
THE KINETICS OF THE ANAEROBIC PROCESS
In a completely mixed continuous flow system with solids recirculation (Fig. 2, see also list of
symbols) the rate of change of the bacterial mass and substrate concentration are described by two
differential equations.
(dX/dt) = u.X.V - Kd.X.V - [W.X + (Q - W)].Xe (1)
(ds/dt) = [Q.(S0 - S)] - tji/Y).X.V (2)
Assuming that anaerobic digestion exhibits Monod type kinetics the bacterial growth rate can be
linked with the concentration of the limiting substrate (S).
p - ^.S/GCj+S) (3)
Under steady-state conditions Equations 1 and 2 yield;
e,-1 - *. - Kd <4)
H = Y.[Q.(SC - S)]/(X.V) (5)
The growth (Y) and decay (Kd) parameters can be determined as the slope and the intercept,
respectively, of the plot of Equation 4 as l/6\ vs. in. The maximum specific growth rate (/*„,) and half-
velocity coefficient (Ks) can be determined by rearranging Equation 3 to obtain linearity and plotting
l//i vs. 1/S. Such plots are shown in Fig. 3.
45th Purdue Industrial Waste Conference Proceedings, CO 1991 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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