Water Pollution Overview

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Questions and Answers

What is the main function of a demineralizer?

To filter out visible contaminants from water

To remove dissolved ionic material from water (correct)

To enhance the taste of water

To produce salt water from fresh sources

Which type of resin is not commonly used in demineralization?

Strong Base Cation (correct)

Weak Base Anion

Strong Acid Cation

Weak Acid Cation

What does the mixed bed in a demineralizer consist of?

Activated carbon and sand

Only cation resins

Only anion resins

Both cation and anion resins (correct)

Where is desalination primarily used to produce fresh drinking water?

In water-short nations worldwide Signup and view all the answers

Which process has the highest removal efficiency for ions in water treatment?

Mixed bed demineralization Signup and view all the answers

What is the purpose of softening water?

To remove calcium and magnesium ions Signup and view all the answers

How did desalination processes begin historically?

Using evaporative techniques by Greek sailors Signup and view all the answers

How many desalting plants are currently in operation in the United States?

Approximately 1,200 Signup and view all the answers

What primarily determines whether water is considered polluted?

The type and concentration of impurities Signup and view all the answers

Which type of pollutant is typically easier to manage?

Point sources pollutants Signup and view all the answers

What is a common misconception about sewage in relation to water pollution?

Sewage is the only source of water pollution. Signup and view all the answers

What is the main purpose of water desalting?

To remove salt and other dissolved minerals from water Signup and view all the answers

Which of the following is NOT a classification of water pollutants based on health or environmental effects?

Financial contaminants Signup and view all the answers

Which of the following is NOT a process used in water desalting?

Evaporative cooling Signup and view all the answers

What is essential for effectively controlling dispersed sources of water pollution?

Setting appropriate land use restrictions Signup and view all the answers

What percentage of the world’s desalted water is produced by distillation methods?

About 60% Signup and view all the answers

Which of the following substances is classified as a pollutant in water quality definition?

Inorganic chemicals Signup and view all the answers

In distillation processes, what is the main energy source used to produce water vapor?

Heat energy Signup and view all the answers

What is the typical range of salt concentrations in distilled water from a desalinization plant?

5 to 50 ppm Signup and view all the answers

How can water quality be affected by concentration?

High concentrations of pollutants can alter water properties. Signup and view all the answers

Which factor contributes most to the classification of water pollutants by origin?

Whether the source is point or dispersed Signup and view all the answers

Which factor is NOT considered when selecting a desalting process?

Cost of local property taxes Signup and view all the answers

What term is used for the water that contains concentrated salts after desalting?

Brine Signup and view all the answers

What is the primary role of aerobic bacteria in aerobic digestion?

To break down and digest waste Signup and view all the answers

What is one method used to reduce energy costs in distillation processes?

Boiling in successive vessels Signup and view all the answers

Which of the following is a byproduct of aerobic digestion?

Carbon dioxide Signup and view all the answers

How does the presence of oxygen affect microbial digestion processes?

It allows aerobes to thrive and decompose waste Signup and view all the answers

What happens to sewage in sewer lines if it is left for more than 1.5 days?

It becomes anaerobic Signup and view all the answers

What characterizes anoxic decomposition?

It uses chemically combined oxygen from nitrates Signup and view all the answers

Which statement is true regarding the benefits of aerobic digestion compared to anaerobic processes?

Aerobic digestion usually results in better effluent quality Signup and view all the answers

Which of the following is NOT a product of aerobic decomposition?

Methane gas Signup and view all the answers

What factor significantly increases the rate of aerobic digestion?

Adequate oxygen supply Signup and view all the answers

What is the concentration in mg/L if 0.3 g of salt is dissolved in 1500 mL of water?

200 mg/L Signup and view all the answers

How is one part per million defined in the context of water concentration?

1 mg of solute per 1 million mg of water Signup and view all the answers

What is the equivalent concentration in parts per billion (ppb) for a value expressed as micrograms per liter (µg/L)?

The same numerical value Signup and view all the answers

What is the percentage concentration if 125 mg of salt is dissolved in 500 g of solvent?

0.025 percent Signup and view all the answers

What mass per unit volume is used to express air concentrations of particulate matter and gases?

Micrograms per cubic meter Signup and view all the answers

If a concentration exceeds 10000 mg/L, how is it typically expressed for convenience?

As a percentage Signup and view all the answers

What is the converted concentration in pounds per million gallons if the concentration is 250 mg/L?

2090 lb/mil gal Signup and view all the answers

What term is used to describe very small or trace amounts of toxic inorganic and organic substances in water?

Trace amounts Signup and view all the answers

What main health hazard is associated with consuming radioactive substances in water?

It poses a serious public health hazard. Signup and view all the answers

Which of the following heavy metals is considered toxic?

Mercury Signup and view all the answers

What is the consequence of having a wide variety of different species in a stream or lake?

It indicates a healthy aquatic environment. Signup and view all the answers

What type of chemical is known to cause cancer?

Carcinogenic substances Signup and view all the answers

Which microorganisms are primarily involved in biological sewage treatment?

Microbes Signup and view all the answers

What is a primary source of radiation pollutants in water?

Wastes from uranium refinement Signup and view all the answers

What is suggested by the disappearance of certain species in aquatic environments?

The presence of pollution. Signup and view all the answers

Which process involves degrading organic material in wastewater?

Aerobic and anaerobic digestion Signup and view all the answers

Study Notes

Water Pollution

Pure water is not found outside a lab.
Water is considered polluted when it has enough foreign materials to make it unsuitable for its intended use (e.g., drinking, recreation).

Pollutant Classification

Pollutants can be categorized by their source:
- Point sources: Easier to manage; pollutants from a single source are collected and treated at a single point.
- Dispersed (non-point) sources: Harder to manage; pollutants come from many different sources making them harder to control.
Pollutants can also be categorized by their effects and origin:
- Pathogenic organisms
- Oxygen-demanding substances
- Plant nutrients
- Toxic organics
- Inorganic chemicals
- Sediments
- Radioactive substances
- Heat
- Oil

Water Quality Expression

Water quality is often expressed in quantitative terms (e.g., mass per unit volume).
Common units include milligrams per liter (mg/L), parts per million (ppm), parts per billion (ppb), and percentages.

Mass per Unit Volume

Milligrams per liter (mg/L) is a common measure of concentration.
If 0.3 grams of salt is dissolved in 1500 mL of water, the concentration is 200 mg/L.
Concentrations in air are often expressed in micrograms per cubic meter (µg/m³).

Part per Million (ppm)

1 ppm = 1 mg of solute per 1,000,000 mg of water.
1 mg/L = 1 ppm

Percentage Concentration

Concentrations above 10,000 mg/L are usually expressed as percentages.
Percentage = (mass of solute (mg) / mass of solvent (mg)) x 100

Toxic and Radioactive Substances

Toxic substances can cause immediate harm, chronic illnesses, or passing on harm to future generations (e.g., cancer, mutations).
Examples of toxic heavy metals are Cadmium (Cd), Chromium (Cr), Lead (Pb), Mercury (Hg), Silver (Ag), Arsenic (As), Barium (Ba), and Selenium (Se).
Radioactive substances are undesirable and have maximum allowable concentrations for public water.

Radiation

Radiation from unstable atoms poses a hazard and maximum allowable concentrations are set for radioactive materials.
Radon, occurs naturally in groundwater.
Sources include nuclear power plants, industrial/medical radioactive chemicals and uranium ore refining.

Biological Parameters

The presence or absence of living organisms provides a good indication of water quality.
Diversity of fish and insects indicates the health of the aquatic environment.
The disappearance of species and overabundance of others can indicate pollution.
Examples of biological indicators are bacteria, algae, protozoa, viruses and coliform.

Aerobic and Anaerobic Digestion

Aerobic digestion requires oxygen; it breaks down waste into carbon dioxide, water, nitrates, and biomass.
Anaerobic digestion does not require oxygen; it produces methane and carbon dioxide, often called biogas.

Advantages of Aerobic Digestion

Efficient at breaking down waste products.
Yields better effluent quality.
Releases substantial energy.

Anaerobic Digestion Advantages

Transforms pollutants into methane, carbon dioxide, and smaller bio-solids.
Biomass growth is less in anaerobic processes compared to aerobic ones.
More compact than aerobic bio-solids.

Anaerobic Digestion Steps

Hydrolysis: complex organic matter is broken down into simple, soluble components.
Fermentation: carbohydrates are broken down by microbes into organic acids, gases, and more microorganisms.
Acetogenesis: fermentation products are converted into acetate, hydrogen, and carbon dioxide.
Methanogenesis: acetate, hydrogen, and carbon dioxide are converted into methane by methanogenic bacteria

Aerobic Decomposition

Microorganisms use organic matter and oxygen to produce stable solids, carbon dioxide, and more organisms.
Organisms that require oxygen are known as aerobic organisms.

Anoxic Decomposition

Microorganisms use chemically combined oxygen (like Nitrates and Nitrites) from organic matter to produce nitrogen gas, carbon dioxide, stable solids, and more organisms.

Demineralization

Water in nature contains minerals that can harm both humans and animals.
Demineralization removes mineral by using ion exchange.
Positively charged ions (e.g., calcium, magnesium) are removed by cation beds while negatively charged ions (e.g., sulfate, chloride) are removed by anion beds.

Desalting

Desalting is used to obtain fresh water from salty water resources (e.g., ocean).
Greek sailors used evaporation 4th Century BC
Desalination plants produce over 6 billion gallons of water a day.
Thermal or membrane processes are used for desalting.

Desalting Processes

Thermal processes (distillation): heats water to evaporate salt, condensing the fresh water vapor.
Membrane processes (ED and RO): Use membranes to separate salts from fresh water using pressure and membranes

Electrodialysis

Electrodialysis uses membranes based on electrical charge.
Positive and negatively charged ions are attracted to oppositely charged electrodes.

Membrane Processes

Reverse Osmosis (RO): Uses pressure on salt water to push water through a membrane while salt is left behind
Electrodialysis (ED): Uses membranes and electrical current to separate ions by charge.

Conclusions

Depending on the type of water (seawater or brackish), Nanofiltration plants provide approximately 85-95% water recovery while RO systems typically recover 50-80%.

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Description

This quiz explores the various aspects of water pollution, including definitions, classification of pollutants, and methods of assessing water quality. Understand the different sources and types of pollutants that affect water and learn how water quality is expressed in measurable terms.