VI. Purpose of Water Treatment VI. Purpose of Water Treatment

A. Objectives,A. Objectives,

B. Regulatory approaches, and B. Regulatory approaches, and

water quality standardswater quality standards

Learning Objectives:Learning Objectives:

List and describe some of the main List and describe some of the main objectives of drinking water and objectives of drinking water and wastewater treatment.wastewater treatment.

Distinguish between two primary Distinguish between two primary approaches to water quality regulation.approaches to water quality regulation.

Goals of Water Treatment:Goals of Water Treatment:

To Protect the health of communityTo Protect the health of community ((PortabilityPortability, , oror primary drinking water primary drinking water standardsstandards).).

To supply water that isTo supply water that is aestheticallyaesthetically desirable desirable ((PalatabilityPalatability, , oror secondary drinking water secondary drinking water standardstandard))..

To protect the property of the consumersTo protect the property of the consumers All the above criteria should be achieved at a All the above criteria should be achieved at a

reasonable cost.reasonable cost.

PotabilityPotability of water: of water: Microorganisms (pathogens) can Microorganisms (pathogens) can

contaminate water and make it unsafe for contaminate water and make it unsafe for drinking (transmit infectious diseases).drinking (transmit infectious diseases).– Surface sources of drinking water require Surface sources of drinking water require

disinfection, as well as some groundwater disinfection, as well as some groundwater sources.sources.

Chemical contaminants (such as Chemical contaminants (such as Arsenic, Arsenic,

Mercury, Chromium, Cadmium, AluminumMercury, Chromium, Cadmium, Aluminum) can ) can also make water unsafe for drinking also make water unsafe for drinking purposes.purposes.

PalatabilityPalatability of water: of water:

Palatability is related to several factors:Palatability is related to several factors:– ColorColor,,– TasteTaste,,– OdorOdor, , – SedimentsSediments,,– CloudinessCloudiness (turbidity), etc. (turbidity), etc.

These may These may indicateindicate chemical or micro- chemical or micro-biological contaminants (potability).biological contaminants (potability).

Regulatory Approaches Regulatory Approaches - - forfor Drinking WaterDrinking Water

Drinking water standards for a variety of Drinking water standards for a variety of potential contaminants are set by the EPA potential contaminants are set by the EPA to protect public health.to protect public health.

The 1974 Safe Drinking Water Act The 1974 Safe Drinking Water Act established Maximum Contaminant Levels established Maximum Contaminant Levels (MCL’s) for water contaminants.(MCL’s) for water contaminants.

Evidence of human exposureEvidence of human exposure Threshold levels determined for long-term Threshold levels determined for long-term

exposure (“No Observed Adverse Effects exposure (“No Observed Adverse Effects Levels”, or NOAEL’s)Levels”, or NOAEL’s)– Educated guessEducated guess– Application of mathematical modelsApplication of mathematical models

Maximum Contamination Level GoaL Maximum Contamination Level GoaL (MCLG) established.(MCLG) established.

Water quality criteria (MCLG)Water quality criteria (MCLG)

How water quality standards How water quality standards (MCL) are established:(MCL) are established:

Standards are established on the basis of Standards are established on the basis of one or more of the following:one or more of the following:– Scientific evaluation (Criteria); MCLGScientific evaluation (Criteria); MCLG– Technical attainability;Technical attainability;– Economic attainability;Economic attainability;– Legal enforceability;Legal enforceability;– Established on ongoing practice,...Established on ongoing practice,...

Regulatory ApproachesRegulatory Approachesfor wastewatersfor wastewaters

No-Degradation Principle (including No-Degradation Principle (including effluent standards and stream standards)effluent standards and stream standards)

This is an attempt to meet the “no-This is an attempt to meet the “no-pollutant discharge” (NPDES) objective pollutant discharge” (NPDES) objective of the Clean Water Act.of the Clean Water Act.

Summary:Summary:

Water treatment has two primary Water treatment has two primary objectives: to make water objectives: to make water potablepotable (safe to (safe to drink) and drink) and palatablepalatable (aesthetically (aesthetically acceptable for drinking).acceptable for drinking).

Water quality regulations for drinking Water quality regulations for drinking water are primarily based on water are primarily based on MCLMCL, while , while wastewater standards are primarily based wastewater standards are primarily based on on minimum degradationminimum degradation..