Water Quality 

1. Drinking Water Standards
2. Safe Drinking Water Act
3. Reverse Osmosis
4. Hard Water

Federal Drinking Water Standards

The list of federal drinking water standards is a large and growing one. However, this module presents an initial list that includes standards that have existed for some time. In the early history of the standards, a distinction was made between primary and seconary standards:

Primary standards refer to health based standards that are federally enforceable, usually in the form of an MCL (maximum contaminant level). The enforcement level in these standards is reflected in the legal language of "shall not exceed MCL."

Secondary standards refers to more aesthetically related guidelines given to the states (i.e., are not federally enforceable). The enforcement level in these standards is reflected in the legal language of "should not exceed MCL."

 We finish this module with a list of primary standards. With the clear warning that this list is not complete and the effects are not discussed in detail, this nevertheless starts an initial review of the range of health effects from contaminants in drinking water.

Inorganics

digestive: arsenic (As): GI tract cadmium (Cd): kidneys chromium (Cr): liver, kidneys	neurological: selenium (Se): neurotoxin lead (Pb): anemia, kidneys, CNS mercury (Hg): inorganic form: kidneys. organic form: nervous system (Minamata disease)
other: barium (Ba): muscle stimulant flourides (Fl): dental mottling nitrates (NO3-): methemoglobinemia silver (Ag) argyrosis (discolors skin,mucous membranes, whites of eyes)

Organics:

digestive: 1,1 dichloroethylene: liver and kidneys p-dichlorobenzene: liver and kidneys 1,1,1 trichloroethane: liver, circulatory, nervous system	neurological: endrin: lindane methoxychlor
cancer: 2,4,5-T cancer; 2,4-D; vinyl chloride; benzene; trichloroethylene; carbon tetrachloride; 1,2 dichloroethane; trihalomethanes

The Safe Drinking Water Act (SDWA)    

PRE-SDWA:  

The U.S. Public Health Service originally issued standards for drinking water. They developed the primary and secondary standards that were covered in our last lecture.    

SDWA:  

1974 saw the passage of the Safe Drinking Water Act (SDWA). Several things were fundamentally different about this law:

• EPA was required to set these standards,
• EPA was required to add to these standards, and
• Health-based standards were reissued as MCLs (maximum contaminant levels) and recommended MCLs.  

The primary federal agency that oversees water quality is the Environmental Protection Agency. However, a number of federal agencies are involved with various aspects of water quantity and quality, including:

• National Oceanic and Atmospheric Administration
• U.S. Fish and Wildlife Service
• U.S. Department of Energy: Office of Environment, Safety, and Health
• U.S. Geological Survey
• U.S. Army Corps of Engineers

Progress in adding standards was slow, however, as scientists in 1974 were just beginning to detect many of the synthetic organics that find there way into water.  

1986 AMENDMENTS:  

Congress gradually became disenchanted with the EPA's progress, which led to the 1986 SDWA Amendments. This law required addition of 83 contaminants by 1989, and required adding 25 contaminants to the list every 3 years thereafter. Examples of new standards from this law include various VOCs in water, and inorganics such as aluminum, nickel, and beryllium. At the same time, the new law designated "best available technologies" for water treatment.    

1996 AMENDMENTS:

The 1996 SDWA amendments canceled the schedule of 25 new standards every three years, and in its place set up a mechanism to set standards based on the occurrence and assessed risks of contaminants.   The law also authorized $1 billion in federal grants to individual states for upgrading water treatment systems. Research programs were set up for a consortium of American and Mexican Universities (especially for states on the Mexican border), for estrogen screening programs, and for general research.  

Reverse Osmosis in Water Treatment

To understand reverse osmosis, we first have to understand normal osmosis. And to understand normal osmosis, we have to define diffusion. So here we go...

Diffusion simply says that molecules spread from areas of higher concentration to areas of lower concentration. A simple example may help: if you're boiling a tasty soup in the kitchen, those delicious molecules don't just stay concentrated in the pot -- they gradually move throughout the house, filling the area with the wonderful smells of cooking. In other words, they diffuse from areas of higher concentration (the pot of soup) to lower concentration (the rest of the house).

Osmosis is a special case of diffusion in which all the molecules are in water, and the water crosses a barrier called a semipermeable membrane. A semipermeable membrane allows water to pass right through it, but not ions (e.g., Na⁺, Ca⁺⁺, Cl^-) and not larger molecules (e.g., hydrocarbons). Semipermeable membranes can be made of many types of materials, but typically are made of cellulose acetate or polyamide resins. An example of a material that is not a semipermeable membrane is Saran wrap, simply because it keeps just about everything sealed in.

Now here's the twist: in normal osmosis, water moves from areas of lower concentration to higher concentration. That's because the water is acting to dilute or diffuse the higher concentration of other molecules. In the first diagram given below, we see normal osmosis in action. The contaminant molecules are represented by the yellow dots.

Normal osmosis doesn't do us much good in water treatment, because the water is moving into a contaminated area. We're interested in reversing the direction. Osmosis can be reversed if sufficient pressure is applied to the membrane from the concentrated side of the membrane. This is shown in the next diagram below. Notice that the semipermeable membrane essentially acts as a filter for the water to pass through, and in fact reverse osmosis is sometimes called "ultrafiltration."

Reverse osmosis (or "RO systems") is a standard in water treatment. The system is normally located beneath the kitchen sink since it is used to treat water for drinking and cooking purposes. A typical RO system is shown in the diagram below.

The numbers in the diagram indicate :

1. a pre-filter for larger sediments, which helps extend the life of the semipermeable membrane,
2. the semi-permeable membrane unit,
3. a pressurized container that stores the treated water,
4. a carbon adsorption post-filter, and
5. a separate tap for the treated water.

If there are any disadvantages to reverse osmosis, they would have to include:

1. RO units use a lot of water. They recover only 5 to 15 percent of the water entering the system. The remainder is discharged as waste water. However, since the water is used for drinking and cooking only, the amount of wastewater can be small compared to other sources.
2. Some systems have built-in monitors, but many do not. Therefore, leaks through the semipermeable membrane (or other problems) may go undetected.
3. They're relatively expensive -- a few hundred dollars may not seem like a lot, but for people with lower incomes, it may be just enough to discourage its use.

To summarize the main points:

1. Diffusion is the movement of molecules from a higher to lower concentration.
2. A semipermeable membrane lets water pass through it but not various other kinds of molecules.
3. Osmosis is water moving through a semipermeable membrane from lower to higher concentrations.
4. Reverse osmosis, also called ultrafiltration, is water moving through a semipermeable membrane from higher to lower concentrations.
5. RO units recover only 5 to 15 percent of all the water entering the system.

Hard Water    

Objective: The purpose of this assignment is:

• to define water hardness
• to define a grain per gallon
• to explain the problems with hard water

Hard water is water that contains hardness minerals (e.g., calcium, manganese and magnesium) above 1 GPG (grain per gallon). 1 GPG is equal to 17.1 PPM of water hardness as defined by Standard Methods. Hard water is not as efficient or convenient as "soft water" for bathing, washing (dishes, clothes or cars), shaving, and many other uses. For example:

• soft water requires only 1/2 as much soap for cleaning.
• hard water and soap combine to form "soap scum," 'bathtub ring," and spots on your dishes.
• when hard water is heated, hardness minerals form hardness scale; this scale can plug your pipes and hot water heater.
• soap scum remains on your skin even after rinsing, causing diaper rash, itching, and skin irritation

If the hardness is over 3 GPG, softening can usually save enough to pay for the cost and maintenance of a water softener. Water softeners can also remove copper, iron, and other minerals. De-ionization is a more extensive form of water softening that removes anions as well as cations.

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