Environmental Engineering Reference
In-Depth Information
reaction in the anaerobic digester, increase the decomposition of organic compounds nor-
mally found in wastewater, and increase digester gas generation [34].
6.7.5 Emerging Contaminants
Endocrine disruptors, pharmaceuticals, and other emerging compounds are now gaining
interest in the treatment of both wastewater and drinking water. With the increase in soluble
COD observed through cavitation, a potential result would be an increase in bioavailability
of these organics. In addition, research has shown that with increased digester retention
time, these compounds are removed to a greater degree. With cavitation, the removal may
be similar but in a shorter amount of time. The generation of hydroxyl radicals as a result
of hydrodynamic cavitation to remove trace amounts of endocrine-disrupting compounds,
ECs, and microconstituents of concern has been shown to be very effective [35-37].
6.7.6 Biodiesel
A fuel alternative to conventional petroleum-based diesel engine fuel is manufactured
from vegetable oils or animal fats by catalytically reacting these with a short-chain aliphatic
alcohol, usually methanol or ethanol, using a process that is called either transesteriica-
tion or alcoholysis. A current bottleneck is the reaction between the oil and the methanol.
An improvement in eficient product conversion would be very desirable. Preliminary
results show that the reaction time is reduced considerably and reaction temperatures are
reduced from 140°F to 100°F. With some recent modiications, glycerin is formed almost
immediately, a desired result not previously observed. The observed improvements in
batch mode lend to evaluate and investigate hydrodynamic cavitation for both batch and
continuous production of biodiesel on a commercial scale.
6.7.7 Ballast Water Treatment
Ballast water treatment before discharge is now becoming regulated worldwide because
the discharge of ballast water from one environment into another has resulted in consid-
erable ecological harm. The damage stems from the introduction of nonnative or exotic
organisms into an environment such as the zebra mussels. Cavitation gives good results
in eliminating small marine creatures in ballast water. If a certain amount of pressure and
low rate are used, the marine copepods will be crushed by the imploding vacuum bub-
bles. On the basis of the ability to control bacteria and other microorganism, the potential
for ballast water applications is ideal.
6.7.8 Enhanced Organic Reactions
Cavitation can be effectively used for intensiication of chemical reactions owing to the
production of free radicals and conditions of high temperatures and pressures locally.
Under the optimized conditions of soniication, the yield of sulfone was about ive to six
times than the conventional approach of using mechanical agitation only. In the oxidation
of
p
-xylene, seven times more product could be obtained in the case of hydrodynamic
cavitation than in the case of acoustic cavitation. The reaction was found to be consider-
ably accelerated at ambient temperature by the introduction of air bubbles into water. Of
course, all other gases can be introduced in this way, and they all share the same proper-
ties; the smaller the bubbles, the better transfer rate.
