Water Quality and Treatment: Key Concepts for Drinking Water Safety

Potable Water

water that is safe to drink

Palatable

Water that is aesthetically pleasing

Major Inorganic Constituents

Calcium, chloride, fluoride, iron, manganese, nitrate, sodium, sulfur

Minor Inorganic Constituents

Cadmium, chromium, copper, lead, mercury, nickel, zinc, arsenic

Natural Organic Compounds

Naturally occurring organic matter (NOM) that is measured as total organic carbon

Anthropogenic Organic Constituents

Synthetic organic chemicals (SOCs) and emerging chemicals of concern used in industry, households, and agriculture(benzene, methyl tert-butyl ether, tetrachloroethylene, trichloroethylene, vinyl chloride, alachlor)

Living Organisms

Bacteria, algae, viruses

Turbidity

Measures the optical clarity of water. Turbidity of <5 NTU is usually acceptable

Particles

Suspended Particles

Larger than 1 um

Colloidal particles

001 < CP < 1 um

Dissolved Particles

DP < .001 um

Calcium and magnesium

Above 60 mg/L can be considered nuisance as hardness

Chloride

Above 250 mg/L can impart salty taste. Below 50 mg/L can be corrosive to some metals

Fluoride

Toxic to humans at concentrations of 250-450 mg/L; Fatal at concentrations above 4 g/L

Iron and Manganese

Taste threshold of iron for many consumers is around 0.01 mg/L. Iron can impart a brownish color to laundry and bathroom fixtures. Manganese ion can impart a dark brown color. At concentrations around 0.4 mg/L, manganese can impart an unpleasant taste to water and can stain laundry and fixtures.

Nitrate

Very high nitrate concentrations may produce baby blue syndrome.

Sulfur

Groundwater low in dissolved oxygen can contain reduced sulfur compounds, which impart objectionable odors such as that of rotten eggs. Sulfates are also corrosive in concrete structures and pipes.

Disinfection

NOM reacts with, and consumes, disinfectants, which increase required dose to achieve effective disinfection and produces harmful disinfection byproducts (DBPs) (e.g., trihalomethanes).

Coagulation

NOM reacts with, and consumes, disinfectants, which increase required dose to achieve effective disinfection and produces harmful disinfection byproducts (DBPs) (e.g., trihalomethanes).

Adsorption

NOM reacts with, and consumes, disinfectants, which increase required dose to achieve effective disinfection and produces harmful disinfection byproducts (DBPs) (e.g., trihalomethanes).

Membranes

NOM reacts with, and consumes, disinfectants, which increase required dose to achieve effective disinfection and produces harmful disinfection byproducts (DBPs) (e.g., trihalomethanes).

Distribution System

NOM may lead to corrosion and slime growth in distribution system

Escherichia Coli Bacteria

Causes Diarrhea

The Safe Drinking Water Act

Protect public health by regulating public water supply/ Maximum contaminant level goals(suggested)/ Maximum contaminant levels (enforced)

Coagulation

Neutralizes the electrical charge of constituents (fast mixing)

Flocculation

Destabilized particles slowly clump together/ Form larger particles called floc

High Rate Filtration

Process used by nearly all U.S. filtration plants

Membrane Process

Involve water pumped under pressure, called feedwater, into a housing containing a semipermeable membrane, where some of the water filters through the membrane and is called permeate

Flux Rate

Rate at which the permeate flows through the membrane area

MCL

Standard based on health risk plus costs and technology

MCLG

Based solely on health and risk information

Surface Water

Turbidity 1-20 NTU, high flows, high TSS, TOC 1-20 mg/L, easy contaminate

Ground Water

< 1 NTU, lower flows, natural filter removes TSS, TOC .1-2, high TDS, difficult to decontaminate

Calcium and Magnesium cause:

Hard water and flakes

Chloride causes:

Salty taste

Iron/manganese causes:

Brown water

Nitrate causes:

Infant methemoglobinemia (Baby blue syndrome)

Sulfur causes:

Stink and corroded pipes

Sedimentation

Particles settle overtime

Filtration

Used for removing small flocs or participated particles