Environmental Engineering Reference
In-Depth Information
Respirometry is an effective method to monitor polymer mineralisation by measuring
carbon dioxide produced or oxygen consumed in a closed system. Respirometric
systems use a measuring technique such as a cumulative respirometric measurement
and a direct respirometric measurement. The cumulative respirometry uses acid
base titration. The released carbon dioxide gas is trapped into a sodium hydroxide
or barium hydroxide solution. Then, a known concentration of hydrochloric acid is
used to titrate the solution in the trap. In direct respirometry, the concentration of
released carbon dioxide is obtained directly from the exit using gas chromatography
(GC) or a gas analyser [37]. The drawback of this technique is that a knowledge
of the metabolic pathway is required otherwise this method is not reliable [38].
For automated systems the air low must be known and the detectors should give
stable results for very slow degradation.
Incomplete degradation of polymers can form intermediate products, which can
be detected using GC-MS, LC-MS, HPLC and so on. A combination of LC with
IR spectroscopy can be used to detect the degradation products of polymers.
This combined technology can also be used to measure the mass distribution of all
the components throughout the chromatographic distribution of a sample. LC-FTIR
yields a chromatographic separation of mixed solutes integrated to a spectrometer
which provides the spectra for all the eluting resolved constituents [23].
6.1.2.4 Bioilm Characterisation
Development of a bioilm on a polymer surface can cause a variety of problems such
as biofouling, biodeterioration and degradation. A number of techniques have been
used such as turbidity measurement with a ibre optical device, microscopic methods,
spectroscopic methods and electrochemical methods. Various bioilm characterisation
techniques are listed in
Table 6.3
.
Microscopy gives information on the morphology of microbial cells and colonies,
their distribution on the surface, the presence of exopolysaccharide (EPS) and bioilm
thickness [24, 39]. These include: light microscopy, SEM, epiluorescence microscopy,
CLSM and AFM. SEM is a commonly used technique but requires dehydrating the
samples during sample preparation, which distorts the bioim structure. A new imaging
technique Wet-STEM can be used for bioilm determination that can overcome the
drawbacks of conventional SEM [11]. For thin bioilms, epiluorescence microscopy
is the most feasible and for bioilms with a thickness greater than 3 μm, CLSM is the
preferred method. CLSM and AFM allow real time monitoring as well as analysis of
hydrated bioilms [15]. A combination of CLSM and AFM provides an insight into
bioilm structure with high resolution.
