Environmental Engineering Reference
In-Depth Information
available for transporting liquid. Regeneration of the adsorbent and the cost for
carbon replacement are issues to be concerned with. In addition, the surface
functionalization by solvent deposition and covalent attachment on ceramic sup-
ports as commonly used failed to demonstrate high ligand coverage and stability
of the attached functional groups. These drawbacks can be overcome by applying
the sol-gel processing method to form a silica network with functional ligands [10].
6.2.3 Ion Exchange
The ion-exchange process relies on the exchange of certain undesirable cations
or anions in wastewater with sodium, hydrogen, chloride, etc., in porous poly-
mer resins of either a styrene or an acrylic matrix. The ion-exchange process
continues until the solution being treated exhausts the resin exchange capacity.
The exhausted resin must be regenerated by other chemicals which replace the
ions captured in the ion-exchange operation, thus converting the resin back to
its original composition for reuse in the next cycle. Many chelating resins have
been reported but they do not show physical rigidity due to swelling of the
polymeric skeleton, poor wettability, small surface area, poor selectivity, slow
adsorption rate, and challenge in regeneration [11, 12]. Clogging and regenera-
tion of resins, similar to that encountered in the adsorption process by activated
carbon, may also be experienced in this approach. In practice, wastewater to be
treated by ion exchange is generally pre-filtered to remove suspended solids
which could mechanically clog the resin bed.
6.2.4 Reverse Osmosis
In industry, reverse osmosis removes minerals from boiler water at power
plants. The water is boiled and condensed over and over again and must be as
pure as possible to avoid fouling or corrosion of boilers. It is also used to clean
effluent and brackish groundwater. The apparent limitations of this approach
are concerns with membrane lifetime, loss in flux rate, relatively small amount
of effluent that can be treated and limited types of materials that can be
removed. Some solutions (strong oxidizing agents, solvents, and other organic
compounds) can cause dissolution of the membrane materials. Fouling of
membranes by suspended solids in wastewater is another concern. Pre-
treatment of effluents is thus necessary for reverse osmosis system.
6.2.5 Ion Flotation
Ion flotation involves the removal of surface-inactive ions from aqueous solu-
tions by the addition of surfactants capable of forming ion-surfactant pairs,
