1. Mass Exchangers Direct-contact mass-transfer unit Utilizes a Mass Separating Agent (MSA) to selectively remove pollutants from rich streams (waste streams). The MSA should be partially or completely immiscible in the rich phase.

2. Mass Exchangers Absorption, liquid solvent removes certain components from a gas. Examples: 1. Desulfurization of flue gas using alkaline solutions. 2. VOC’s recovery using light oils 3. NH 3 removal from air using water.

3. Mass Exchangers Adsorption, a solid adsorbs specific components from a gaseous or liquid solution. Examples: The use of granular activated carbon 1. For the removal of benzene/toluene/xylene mixture from underground water. 2. Separation of ketones from aqueous wastes of an oil refinery. 3. Recovery of organic solvents from the exhaust of polymer manufacturing facilities.

4. Mass Exchangers Extraction, employs a liquid solvent to remove components from other liquid. Examples: Wash oils are used 1. To remove phenol and polychlorinated biphenyls from aqueous wastes of synthetic-fuel plants. 2. To remove Chlorinated hydrocarbons for organic wastewater.

5. Mass Exchangers Ion Exchange, cation and/or anion resins are used to replace undesirable anionic species in liquid solution with non-hazardous ions. Examples: Removal of dissolved metals, cyanides, phenols, and halides from wastewater. Cation-exchange resins may contain mobile, positive ions such as, Na + or H + which are attached to immobile acid groups, such as sulfonic or carboxylic. Anion-exchange, OH - or Cl - attached to amine.

6. Mass Exchangers Leaching, selective solution of specific components of a solid mixture when brought in contact with a liquid solvent. Examples: Removal of metals from solids or sludge.

7. Mass Exchangers Stripping, desorption of relatively volatile components from liquid or solid streams using a gaseous MSA. Examples: 1. Recovery of VOC’s from wastewater using air. 2. Removal of NH 3 from wastewater using steam. 3. Regeneration of spent activated carbon using steam or N 2.

8. Mass-Exchange Network Synthesis Given a number N R of waste (rich) streams (sources) and a number N S of MSAs (lean streams), it is desired to synthesize undesirable species from the rich streams to the MSAs.