Biomedical Engineering Reference
In-Depth Information
input and equipment maintenance in the operation will lead to dramatic increase in the
investment.
Table 1. Some physical techniques for cell lysis [25]
Lysis method
Apparatus
Method description
Sonication
Sonicator/homogenizer
Shear cells via cavitation and impaction by
pulsed, high frequency sound waves
(typically 20-50 KHz)
Agitation with beads
Electric motor
Disrupt cells through vigorous agitation
provided by electric motor
Freeze/thaw cycle
Freezer or dry
ice/ethanol
Repeat cycles of freezing and thawing to
disrupt cells through ice crystal formation
nitrogen
bomb/nitrogen burst
High pressure nitrogen
Rapid release of high pressure nitrogen gas
(usually 25,000 psi) as bubbles inducing
cell lysis
The Photo-Fenton reaction, one of the advanced oxidation processes (AOPs), has been
exploited for minimization of excess sludge. In this process, the cell wall of a microbe is
destroyed and becomes easily decomposable. The results by Tokumura et al. [12] showed that
the chemical oxidation of excess sludge by Photo-Fenton reaction contained two phases: (i)
oxidative decomposition of the cell wall leading to the increased dissolved COD due to the
discharge of organic substances into the medium; (ii) the maximum COD release and
followed by gradual decrease. Solubilization of suspended solids and mineralization of
dissolved organic substances by the Photo-Fenton reaction might be dominant in these two
interrelated phases.
Settling tank
Aeration tank
Effluent
Influent
Returned sludge
Ozone contact tank
Figure 2. The flow sheet of ozonation process. The returned sludge is contacted with ozone and then re-
circulated to the aeration tank for biodegradation.
The lysis-cryptic growth techniques sound reasonable in practice to achieve effective
minimization of excess sludge production in CAS process; however, there are some
constraints in those approaches, i.e. two-step correlative reactions (solubilization and
oxidation of autochthonous substrate) may limit the efficiency of excess sludge reduction
[23]. According to previous research, these techniques on the basis of lysis-cryptic growth
also incur additional costs because cumbersome equipments are always needed, and other
shortcomings, such as difficulty in control, not suitable for large scale application, make their
capabilities unacceptable in the environmental engineering sense.
