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

Drinking Water Treatment Objectives Potable: safe to drink - may be consumed with low risk of immediate or long term harm. Palatable: pleasant to taste

U.S. EPA Standards National Primary Drinking Water Regulations Microorganisms Disinfectants & Disinfection Byproducts Inorganic Chemicals Organic Chemicals Radionuclides Enforceable

U.S. EPA Standards National Primary Drinking Water Regulations Microorganisms Viruses: hepatitis A, gastroenteritis Bacteria: cholera, dysentery, legionellosis, typhoid Protozoa: Giardia and Cryptosporidium Turbidity: standard is 1 NTU; microorganism contamination is associated with turbidity; particles also shield microorganisms from agents of disinfection. Indicator organisms: standard for microbial contamination is based on E. coli, a species of bacteria originating from animal or human fecal material. Most strains of E. coli are not pathogenic, but their presence indicates the presence of fecal material and thus, potentially, pathogenic microbes. No E. coli may be present in finished drinking water.

U.S. EPA Standards National Primary Drinking Water Regulations Chemicals Inorganic: arsenic, cadmium, copper, lead, mercury, nitrate Organic: herbicides (e.g. atrazine), insecticides (methoxychlor), industrial residues (e.g. polychlorinated biphenyls, dioxin) Radionuclides:  and  particles, radium, uranium MCLs: Maximum Contaminant Levels

U.S. EPA Standards National Primary Drinking Water Regulations Disinfectants Chlorine Chlorine dioxide Chloramines Disinfectants & Disinfection Byproducts Trihalomethanes

U.S. EPA Standards Secondary Drinking Water Regulations Cosmetic Effects (tooth color, excess fluoride) Total Dissolved Solids (chloride, sulfate) Taste, Odor, Color Non-Enforceable (federally)

U.S. EPA Standards National Primary Drinking Water Regulations Microorganisms Viruses: hepatitis A, gastroenteritis Bacteria: cholera, dysentery, legionellosis, typhoid Protozoa: Giardia and Cryptosporidium Turbidity: standard is 1 NTU; microorganism contamination is associated with turbidity; particles also shield microorganisms from agents of disinfection. Indicator organisms: standard for microbial contamination is based on E. coli, a species of bacteria originating from animal or human fecal material. Most strains of E. coli are not pathogenic, but their presence indicates the presence of fecal material and thus, potentially, pathogenic microbes. No E. coli may be present in finished drinking water.

Drinking Water Process Train Basic treatment for turbidity and pathogens

Particle Settling Velocities ParticleDiameter (mm)Velocity (m/s) Sand1.02x10 -1 Fine sand0.11x10 -2 Silt0.011x10 -4 Clay0.0011x10 -6 Source: Vesilind & Morgan Stokes Law Thus, the small, clay particles settle extremely slowly.

Coagulation Particle populations are stable because their net negative charge repels one another. Chemicals such as alum are added to neutralize the negative charge and destabilize the particle populations and allow them to come together, i.e. coagulate. Addition of the chemical occurs in a flash mix of 1-3 minutes where the chemical dissolves and mixes with the raw water

Flocculation The alum reacts with calcium bicarbonate naturally present in most waters to form a precipitate or floc, aluminum hydroxide. Destabilzied smaller particles can be attracted to the floc or simply swept up by the larger particles (sweep floc) as they settle and removed from the system. Flocculation proceeds through a slow mix of minutes.

Sedimentation Sedimentation takes place over a period of 1-4 hours.

Disinfection sorption Chlorination Thus above HOCl dominates below pH 7.5 and OCL - dominates above pH 7.5

Disinfection sorption Design Chick’s Law The Surface Water Treatment Rule Requires a 4-log or 99.99% removal and

Disinfection The Surface Water Treatment Rule Requires a 4-log or 99.99% removal Design Ct = concentration, time It = irradiance, time

Disinfection Residual

Disinfection Disinfection By-products (DBPs) Formed through reaction of chlorine and natural organic matter (NOM) e.g. trihalomethanes such as chloroform, Design – reduce NOM through pre-oxidation with ozone.

Iron and Manganese

Hardness Ca 2+, Mg 2+ Adding lime and soda ash, Ca(OH)2, Na2CO3 Precipitates, CaCO 3, Mg(OH) 2

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

Membrane Processes

Ultrafiltration 300 µm ID 500 µm OD polypropylene fiber

Ultrafiltration 0.2 µm nominal pore size

Ultrafiltration epoxy seal permeate flow raw water in

Ultrafiltration banks of fiber bundles backwashing contaminants

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.