Biomedical Engineering Reference
In-Depth Information
Heater
Heating steam, M
s
, T
s
Inlet hot water,
M
w
, T
wi
Outlet cold
water, M
w
, T
co
Humidifier
Condenser
Packing
material
Condensate, M
d
Intake air,
M
a
, H
i
, W
i
Outlet
brine,
M
w
, T
wo
Inlet seawater,
M
w
, T
ci
FIGURE 19.8
Schematic.of.conventional.humidiication-dehumidiication.process..(From.Ettouney,.H.,.
Desalination
,.183,.341-
352,.2005..With.permission.)
19.3.4 Humidification-Dehumidification Desalination
Humidiication-dehumidiication. (HDH). desalination. processes. rely. on. distillation. to.
achieve.desalination.
53
.Simple.technology.is.required.due.to.their.ability.to.function.at.atmo-
spheric.pressure;.generally,.HDH.units.require.two.exchangers,.an.evaporator.to.humidify.
air.and.a.condenser.to.collect.the.freshwater.generated,.as.shown.in.the.basic.system.sche-
matic.in.Figure 19.8..The.process.begins.by.allowing.dry.air.to.absorb.vapor.from.heated.
feedwater.in.one.chamber,.transferring.the.humid.air.to.another.chamber,.where.it.comes.
in.contact.with.a.cool.surface,.thus.allowing.freshwater.collection.
27
.Energy.consumption.in.
such.a.system.is.required.by.the.heat.source.as.well.as.the.pumps.and.blowers.to.move.the.
water. and. vapor.. Recovery. rates. for. these. systems. range. from. 5. to. 20%,. and. heat. sources.
such.as.solar.or.geothermal.supplies.are.common.choices,.especially.since.the.rates.of.fresh-
water.production.are.suited.for.demands.of.a.few.m
3
/day..Temperature.differences.between.
2.and.5°C.are.required,.necessitating.heat.consumption.of.approximately.20.9.kJ/m
3
.
53
19.3.5 Microbial Desalination Cells
Microbial. fuel. cells. convert. biowaste. to. electricity. through. microbial. activity
54
. by. gen-
erating. electrons. available. for. harvesting. in. an. external. load. circuit.. In. an. innovative.
approach,.a.three-cell.system.was.converted.into.a.water.desalination.system.(Figure 19.9)..
In. a. proof-of-concept. study. it. was. shown. that. the. three-cell. design. with. an. integrated.
anion.exchange.membrane.(AEM).and.cation.exchange.membrane.(CEM).could.generate.a.
small.amount.of.potential.(typically.less.than.1 V).and.desalinate.water..The.bacteria.grow.
on.the.anode.side.and.discharge.protons.into.the.water;.however,.the.protons.cannot.pass.
