Dr. Martin T. Auer MTU Department of Civil & Environmental Engineering Water Treatment

Charge Neutralization

Bridging negatively- charged particle negatively- charged particle hydroxo- metallic complex floc

Particle Settling Velocities ParticleDiameter (mm)Velocity (m/s) Sand1.02x10 -1 Fine sand0.11x10 -2 Silt0.011x10 -4 Clay0.0011x10 -6 Source: Vesilind & Morgan

sorption Chlorine Distribution

Drinking Water Process Train

Equilibrium Chemistry

Iron and Manganese

Hardness

The most commonly used adsorbent is granular activated carbon (GAC). These irregular particles, mm in diameter, are a char of carbon material (wood or coal). They are ‘activated’ or made more porous by exposure to steam at high temperature. Activated carbon has 1000 m 2 of adsorbing surface area per gram (~ 1 teaspoon) or equivalent to that of a 40 acre farm in one handful! Source: Sontheimer et al Source: Chemviron Carbon Source: Millenium Inorganic Chemicals Granular Activated Carbon

Organic chemicals are typically removed from a water supply prior to distribution through the process of adsorption: the physical-chemical attraction of a solid material for a chemical in solution. In adsorption, the chemical being adsorbed is termed the adsorbate and the solid to which it sorbs is the adsorbent. Influent stream Effluent stream The Adsorption Process

For adsorption to be effective, the chemical must sorb strongly. Poorly soluble (hydrophobic) compounds (e.g. the components of gasoline) adsorb more strongly than highly soluble (hydrophilic) compounds (e.g. table salt) Time (d) Concentration (mg/L) Poorly sorbed Strongly sorbed … tendency to sorb

In drinking water treatment, adsorption with GAC is accomplished using a packed bed column. The untreated water is introduced at the top of the column and trickles down through the GAC. Contaminants are removed en route and clean water emerges at the bottom of the column. In application, columns 6 feet in diameter and 30 feet in height are not uncommon. GAC columns Bed Carbon … application in water treatment

Water flows thru the column and contaminants are adsorbed. With time, the GAC becomes saturated (sorption capacity is reached) and contaminants exit the bed (breakthrough). The exhausted carbon must then be replaced. C in C eq C out exhaustion breakthrough … column operation

Asbestos/Arsenic/Metals Removal Sorption with Ferric sulfate: asbestos, arsenic, cadmium, chromium, copper, lead, mercury, molybdenum, selenium, silver Coagulation with Alum: asbestos, nickel, uranium

Reverse Osmosis

Ultrafiltration

300 µm ID 500 µm OD polypropylene fiber

Ultrafiltration 0.2 µm nominal pore size

Ultrafiltration Technology epoxy seal permeate flow raw water in

Ultrafiltration banks of fiber bundles

Ultrafiltration contaminants backwashing

Home Water Treatment Reverse osmosis unit (salt) Softening by ion exchange (hardness)

Home Water Treatment Three step process: sieve and bottom filter – rust, sand, turbidity activated carbon filter – chlorine, color and SOCs ion exchange resin – metals Bottled Water: $8 /gallon Tap Mount: $0.25 / gallon Municipal: $ / gallon Achieves 99.99% removal of Giardia and Cryptosporidium cysts, but does not remove all pathogenic organisms.