A chemical mixing basin is to be designed to blend chlorine and treated wastewat

Question

A chemical mixing basin is to be designed to blend chlorine and treated wastewater. The basin flow is 700 gallons per minute and the basin dimensions are 5 feet by 5 feet by 5 feet water depth. The basin will have a single mechanical blender that will transfer 100% of the mixing energy from the blades to the water. The wastewater temperature will vary from 35 F to 70 F. The selected mixing intensity in the basin shall be a minimum of 600 1/sec. What size motor (horsepower) is required for the mixer?

Answer the following:

What is hardness in water and why is it important?

Why is too much fluoride in drinking water a problem?

What is the drinking water standard for fluoride?

For benzene, what are the federal epa and State of NJ drinking water standards?

What is considered a safe level of benzene in drinking water?

If you were designing a drinking water treatment facility for the removal of benzene, what

would you set as a treatment goal and why? How would you involve the client in the decision?

Explanation / Answer

1)Water hardness is important to fish culture and is a commonly reported aspect of water quality. It is a measure of the quantity of divalent ions (for this discussion, salts with two positive charges) such as calcium, magnesium and/or iron in water. There are many different divalent salts; however, calcium and magnesium are the most common sources of water hardness.

Hardness is traditionally measured by chemical titration. The hardness of a water sample is reported in milligrams per liter (same as parts per million, ppm) as calcium carbonate (mg/l CaCO3). Calcium carbonate hardness is a general term that indicates the total quantity of divalent salts present and does not specifically identify whether calcium, magnesium and/or some other divalent salt is causing water hardness. Hardness can be a mixture of divalent salts. In theory, it is possible to have water with high hardness that contains no calcium. Calcium is the most important divalent salt in fish culture water.

Calcium has an important role in the biological processes of fish. It is necessary for bone formation, blood clotting and other metabolic reactions. Fish can absorb calcium for these needs directly from the water or food. The presence of free (ionic) calcium at relatively high concentrations in culture water helps reduce the loss of other salts (e.g. sodium and potassium) from fish body fluids (i.e. blood). Sodium and potassium are the most important salts in fish blood and are critical for normal heart, nerve and muscle function. In low calcium water, fish can lose (leak) substantial quantities of these salts into the water. Fish must then use energy supplied by their feed to re-absorb lost salts. That can reduce the energy available for growth and may extend the time necessary to grow fish to market size. For some species (e.g. red drum and striped bass), environmental calcium is required for good survival.

It is easy to see that the presence of calcium in water for fish culture is important. A low CaCO3 hardness value is a reliable indication that the calcium concentration is low. However, high hardness does not necessarily reflect a high calcium concentration. A high hardness reading could result from high magnesium concentrations with little or no calcium present. Since limestone commonly occurs in the soil and bedrock of Kentucky, it would be reasonably safe to assume that high hardness readings reflect high calcium levels


2) Exposure to excessive consumption of fluoride over a lifetime may lead to increased likelihood of bone fractures in adults, and may result in effects on bone leading to pain and tenderness. Children aged 8 years and younger exposed to excessive amounts of fluoride have an increased chance of developing pits in the tooth enamel, along with a range of cosmetic effects to teeth.

This health effects language is not intended to catalog all possible health effects for fluoride. Rather, it is intended to inform consumers of some of the possible health effects associated with fluoride in drinking wate

3)the MCLG for fluoride is 4.0 mg/L or 4.0 ppm.

Fluoride is an ionic compound containing fluorine, which is the single most reactive element; it is naturally found in many rocks.

About 90 percent of the fluoride added to public water supplies comes from silicofluorides, chemicals produced mainly as byproducts from the manufacture of phosphate fertilizers, according to the CDC.

Fluoride is added to public water supplies at an average concentration of about 1 part per million (1 ppm), or slightly below. Naturally occurring fluoride concentrations in surface waters depend on location but are generally low and usually do not exceed 0.3 ppm. Groundwater can contain much higher levels, however.

4) & 5) Benzene in soft drinks has to be seen in the context of other environmental exposure. Taking the worst example found to date of a soft drink containing 87.9 ppb benzene,[1] someone drinking a 350 ml (12 oz) can would ingest 31 ?g (micrograms) of benzene, almost equivalent to the benzene inhaled by a motorist refilling a fuel tank for three minutes. While there are alternatives to using sodium benzoate as a preservative, the casual consumption of such a drink is unlikely to pose a significant health hazard to a particular individual (see, for example, the EPA IRIS document on benzene[5]). However, spread out over millions of people consuming soft drinks each day, there might be a small number of cancers caused by this exposure.[citation needed]

The UK Food Standards Agency has stated that people would need to drink at least 20 litres (5.5 gal) per day of a drink containing benzene at 10 ?g to equal the amount of benzene they would breathe from city air every day.[6] Daily personal exposure to benzene is determined by adding exposure from all sources.

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