VI Purpose of Water Treatment A Objectives B

VI. Purpose of Water Treatment A. Objectives, B. Regulatory approaches, and water quality standards

Learning Objectives: List and describe some of the main objectives of drinking water and wastewater treatment. n Distinguish between two primary approaches to water quality regulation. n

Goals of Water Treatment: To Protect the health of community (Portability, or primary drinking water standards). n To supply water that is aesthetically desirable (Palatability, or secondary drinking water standard). n To protect the property of the consumers n All the above criteria should be achieved at a reasonable cost. n

Potability of water: n Microorganisms (pathogens) can contaminate water and make it unsafe for drinking (transmit infectious diseases). – Surface sources of drinking water require disinfection, as well as some groundwater sources. n Chemical contaminants (such as Arsenic, Mercury, Chromium, Cadmium, Aluminum) can also make water unsafe for drinking purposes.

Palatability of water: n Palatability is related to several factors: – Color, – Taste, – Odor, – Sediments, – Cloudiness (turbidity), etc. n These may indicate chemical or microbiological contaminants (potability).

Regulatory Approaches - for Drinking Water Drinking water standards for a variety of potential contaminants are set by the EPA to protect public health. n The 1974 Safe Drinking Water Act established Maximum Contaminant Levels (MCL’s) for water contaminants. n

Water quality criteria (MCLG) Evidence of human exposure n Threshold levels determined for long-term exposure (“No Observed Adverse Effects Levels”, or NOAEL’s) n – Educated guess – Application of mathematical models n Maximum Contamination Level Goa. L (MCLG) established.

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

Regulatory Approaches for wastewaters No-Degradation Principle (including effluent standards and stream standards) n This is an attempt to meet the “nopollutant discharge” (NPDES) objective of the Clean Water Act. n

Summary: Water treatment has two primary objectives: to make water potable (safe to drink) and palatable (aesthetically acceptable for drinking). n Water quality regulations for drinking water are primarily based on MCL, while wastewater standards are primarily based on minimum degradation. n