1 Introduction
There are several reports on microbial treatment of cyanidation
wastewater with successful operational efficiency
[1-4]. The impact of various factors
such as temperature, pH, substrate and bioreactor configuration on the
performance of organisms in cyanidation wastewater have been reported
[5-7]. In addition, thermodynamic
tools have been used to validate the microbial performance and the
cyanide degraded [8-10]. However, the
uptake of the microbial remediation by the industry have not been
inspiring even though Homestake and LaRonde gold mine in Canada,
including Gold Fields Limited have demonstrated the robustness and
feasibility of the biological process
[11-13]. Analysis of process
performance should not only be based on microbial growth and toxicant
degraded but also on the impact of the toxicant on the physical
properties of the organism. This will provide further insight on the
capability of the organism to manage their environment under stress.
Thermodynamic properties of a material are an essential tool for
predicting the feasibility of any chemical and biological reaction
including processes such as the microbial growth process and the biomass
conversion of nutrient media to useful products. Among these
thermodynamic properties, heat capacity of biological molecules such as
starch, glucose, proteins and amino acids reportedly measured based on
rudimentary heat capacity quantifications can be used to estimate
entropy increments and/or changes at low temperatures (0 to 298.15 K);
however, there is high uncertainty associated with this estimate
[14]. Recently, some researchers have
reported on the use of an adiabatic calorimeter for measuring heat
capacity of biological materials at low temperature; based on the
application of the third law of thermodynamics, for which incremental
entropy and/or absolute entropy can be estimated
[15,
16]. Nevertheless, the results were
determined to be unreproducible because there was no reference material
used and that each researcher had to fabricate their own calorimeter.
This maybe the reason for Pyda’s [15]
preference for Differential Scanning Calorimeter (DSC) measurements over
adiabatic calorimeter measurements. Overall, there is only one report on
heat capacity of microbial dried biomass thus far
[17] which reported on the use of an
adiabatic calorimeter for quantifying the heat capacity of lyophilised
cells of Saccharomyces cerevisiae, subsequent to the estimation
of entropy changes as a function of temperature based on the third law
of thermodynamics.
From the second law of thermodynamics, the heat capacity of any material
can be estimated/quantified using heat flow curves obtained from DSC
generated profiles of the sample being studied. A DSC provides a more
reliable, accurate and reproducible results because it is calibrated
with a standard reference and/or material such as sapphire, which is
used to ascertain and/or detect any error with the equipment, a
parametric requirement not available with an adiabatic calorimeter.
Nevertheless, it is often difficult to interpret the heat flow data from
DSC experiments when multiple processes are involved, resulting in
overlapping transitions. Besides, the heat capacity of a material cannot
be determined directly from DSC data, it requires multiple experiments
including data interpretation to ascertain or determine the heat
capacity [18-21].
Furthermore, a modulated DSC (MDSCTM) overcomes these
drawbacks and thus provide an insight into the thermal properties of
materials being studied. MDSCTM uses a modulated
temperature input signal to provide information on the heat capacity,
both under isothermal and non-isothermal conditions. Further details on
theory, principles, application and instrumentation requirements of the
MDSCTM can be found in Vendonck
[18] and Knopp
[22].
Cells are known to be insoluble and using lyophilised cells, an
approximate entropy per unit mass can be obtained if cellular integrity
is not annihilated by lyophilisation
[23]. Battley
[24] in his report hypothesized that
the constituent materials of formation do not affect the molecular
weight and subsequently thermodynamic properties of lyophilised cell but
Duboc et al [25] and Akinpelu et al
[26] have proven otherwise with their
report on several yeast, bacteria, algae and filamentous fungi. And this
agrees with the basic concept that the specific heat is a function of
the property of the substance. Therefore, the objective of this study
was to determine the impact of different substrates (glucose, Beta
vulgaris and cyanide) on the heat capacity of lyophilised biomass ofFusarium oxysporum in cyanidation wastewater using a modulated
DSC (MDSCTM).