Chapter 17 - Review Questions

27/10/2010 01:08

1.    Define pollution, pollutant, nonbiodegradable, point source, and nonpoint source of pollutants.

·       Pollution: “the presence of a substance in the environment that, because of its chemical composition or quantity, prevents the functioning of natural processes and produces undesirable environmental and health effects” (EPA). (pg. 438)


Pollutant: are almost always by products of worthy and essential [human] activities and of our basic biological functions. / ... almost anything may be a pollutant. The only criterion is that the addition of a pollutant results in undesirable changes [pollution]...(pg. 438)


·       Nonbiodegradable: resit attack and breakdown by detritus feeders and decomposers (pg. 438)


Point Source: ...easily identified sources.... (i.e. involve the discharge of substances form factories, sewage systems, power plants, underground coal mines and oil wells). (pg. 440)


[External definition: Is a single, identifiable, confined source (often in a stationary location or fixed facility) of pollutant emissions]


·       Nonpoint Source: ...are poorly defined and scattered over broad areas. Pollution occurs as rainfall and snowmelt move over and through the ground, picking up pollutants as they go... (pg. 440)


[External definition: Pollution discharged over a wide land area, not from one specific location, e.g. source is not readily identifiable. Induced by natural processes, including precipitation, seepage, percolation, and runoff]


2.    Discuss each of the following categories of water pollutants and the problems they cause: pathogens, organic wastes, chemical pollutants, and sediments.


·       most serious water pollutants (can cause sickness and death)

·       Origin: contained primarily in human and animal excrement; poor sanitation regarding water and sewage

·       Effects: public health issues (million chronically infected with disease-causing bacteria, viruses and other parasitic organisms).(pg. 440 - 441)


Organic waste:

·       Origin: human and animal excrement, leaves, grass clippings, trash, etc.

·       Effects: When bacteria and detritus feeders decompose organic matter in water, they consume oxygen gas dissolved in the water [creating 'dead zones']. (pg. 442)


Chemical pollutants:

·       water is an excellent solvent and thus it is able to hold many chemical substances in solution

·       Origin: inorganic chemicals> heavy metals (lead, mercury, arsenic, nickel, etc.), acids from mine drainage (sulfuric acid), acid form precipitation (sulfuric and nitric acids) and road salts. organic chemicals> petroleum, pesticides, etc.

·       Effects: low concentrations of these chemicals in water can render it useless for human and animal use. Some may become concentrated up the food chain (biomagnification) (pg. 443)

[An excess of inorganic chemicals classified as nutrients -phosphorus and nitrous- (originating from: point source: sewage outfalls; nonpoint source: agricultural runoff), can enter streams, rivers, lakes and oceans, causing eutrophication and/or undesirable plant growth.] (pg. 444)



·       sediments enter streams and rivers because of storms and wind

·       Origin: erosion from farmlands, deforested slopes, overgrazed rangelands, construction sites, mining sites, stream bank, roads, etc.

·       Effects: large amount of sediments can make the water unclear reducing the amount of light penetrating the water, and hence, reducing photosynthesis. Kills animals by clogging their gills and feeding structures. Smothers eggs and other organisms at the bottom, clogs hiding and resting places and prevent reestablishing of organisms, because the bottom is a constantly shifting bed of sand. (pg. 444)


3.    How are water quality standards determined? Distinguish between water quality criteria pollutants and maximum contaminant levels. (pg. 446)

The EPA has established the National Recommended Water Quality criteria. EPA has listed 167 chemicals and substances as criteria pollutants (including: toxic chemicals, natural chemicals, nutrients, level of dissolved calcium, pH level, etc). The list identifies the pollutant and then recommends concentrations for fresh water, saltwater, and human consumption.

For drinking water, EPA has established the Drinking Water Standards and Health Advisories which are stricter.


4.    Give a brief history of how humans' handling of sewage wastes has changed as the risks and potential benefits have become better understood. (pg 447)

Before the 1800s the most common mean of disposing excrements was the outdoor privy. They contaminated underground drinking water reservoirs due to leakage of fluids. Louis Pasteur proofed that sewage bacteria present in underground drinking water reservoirs were the cause of many diseases.

This discovery made cities use the drain systems for storm water to flush out sewage too (flush toilets were introduced). Rain water, sewage & industrial waste started to be flushed into natural waterways. They were soon overloaded of decomposing organic matter and filth, depleting the oxygen and the rest of the organic life in the waters.

To alleviate this problem, wastewater treatment plants were constructed. However, the combined volume of storm water and sewage was too much to handle. Regulation were created to enforce different systems for draining storm water and sewage (for easier treatment).

Nonetheless, not all cities in developed countries have this nor wastewater treatment plants. In non-developed countries sewage treatment is still in a primitive state.


5.    Name an describe the facility and the process used to remove debris, grit, particulate organic matter, colloidal and dissolved organic matter, and dissolved nutrients from freshwater. (pg. 449)

Preliminary treatment (Removal of Debris and Grit)

Debris is removed by letting raw sewage water flow though a bar screen (a row of bars mounted about 2.5cm apart). Debris is removed from the screen and burned in incinerators.

Grit is removed by slowing down the velocity of the water in the grit chamber (a swimming pool – like tank). Grit settles at the bottom and is taken to landfills.



Primary Treatment (Removal of Particulate Organic Material)

Water flows slowly through large tank called primary clarifiers. Flow is so slow that particulate organic material settles at the bottom and fat and oily substances float on the top. Both, the organic material as well as fat and oil are removed and combined into what is referred to raw sludge.


Secondary Treatment (Removal of Colloidal and Dissolved Organic Matter)

An environment is created where decomposers and detritus feeders can feed on the colloidal and dissolved organic material and break it down to CO2, mineral nutrients, and water via cell respiration. Oxygen is added to the water to enhance the organisms respiration and growth.


Biological Nutrient Removal – optional- (see question 7)


Final Cleansing and Disinfection

Water is subjected to final clarification and disinfection. Disinfecting agents include:

·       chlorine gas (cheap,effective but can harm aquatic animals),

·       sodium hypochlorite (Clorox),

·       ozone gas (effective but costly and unstable -explosive-)

·       ultraviolet light


6.    Why is secondary treatment also called biological treatment? What is the principle involved? What are the two alternative techniques used?

Because it uses decomposers and detritus feeders that can feed on the colloidal and dissolved organic material.

The wastewater from primary treatment is a food- and water rich medium for the decomposers and detritus feeders. The only thing that needs to be added is oxygen to enhance the organism's respiration and growth.

There are two system that may be used:

·       Trickling-filter system: water from primary treatment is sprinkled onto, and allowed to percolate through, a bed of fist-sized rocks. Space between the rocks allows good aeration as well as the growth of various bacteria, protozoan, rotifiers, worms, etc. that live in/are attached to the rocks.

·       Activated sludge system: Most common type. [I suggest you read this process directly from the book -pg 449 last paragraph-]


7.    What are the principles involved in, and what is accomplished by the removal of biological nutrients from waste? Where do nitrogen and phosphate go in the process? (pg.450)

Due to the increased awareness of the problem of cultural eutrophication, secondary active-sludge systems have been added to the process in order to remove nutrients and oxidize detritus. This process is called biological nutrient removal (BNR).


Nitrogen: Various bacteria convert nutrient forms of nitrogen (ammonia and nitrate) back to non nutrive nitrogen gas in the atmosphere through denitrification.


Phosphorus: Bacteria take up phosphate from solution and store it in their bodies. Thus phosphate is removed as the excess organisms are removed from the system. These organisms, together with the phosphate they contain, are added to, and treated with, the raw sludge, ultimately producing a more nutrient-rich treated-sludge product.


8.    Name and describe three methods of treating raw sludge, and give the end product(s) that may be produced from each method. (pg. 451 - 452)

Aerobic Digestion:

·       Raw sludge is put into large airtight tanks called sludge digesters. In the absence of oxygen, a consortium of anaerobic bacteria breaks down the organic matter.

·       End products of this process include:CO2, methane, water and a nutrient-rich humus-like material suspended in water.

·       Treated sludge (or biosolids) makes an excellent organic fertilizer that may be applied directly to lawns and agricultural fields.



·       Raw sludge is mixed with wood chips or some other water-absorbing material to reduce the water content. It is then place in long, narrow piles (windrows) that allow air to circulate conveniently through the material. Bacteria and other organic decomposers break down the organic material to rich humus-like material.



·       After raw sludge is dewatered, the resulting sludge is put into ovens that heat it sufficiently to kill any pathogens.

·       The product is dry, odorless organic pellets.


9.    How may sewage from individual homes be handled in the absence of municipal collection systems? What are some problems with these on-site systems? (pg. 452 - 453)

On site Wastewater Treatment Systems:

·       Wastewater flows into a septic tank, where particulate organic material settles to the bottom. Water containing colloidal and dissolved organic material, as well as dissolve nutrients, flows into a leaching field and gradually percolates into the soil. Organic material that settles in the tank is digested by bacteria, but accumulation must be pumped our regularly.

·       This system often fail (leakage or clogging) resulting in: sewage backup into homes, pollution of groundwater and surface water due to nutrient and pathogen pollution.


Using Effluents for Irrigation:

·       Nutrient-rich water from the standard secondary-treatment process is beneficial for growing plants. However it has to be free of pathogens and toxic material to do so.


Reconstructed Wetland Systems:

·       It is possible to make use of the nutrient-absorbing capacity of wetlands in suitable areas and under suitable climatic conditions.


10.                    Describe and compare submerged aquatic vegetation and phytoplankton. Where and how does each get nutrients and light? (pg. 454)

Submerged Aquatic Vegetation (SAV):

·       Grows totally under water, thus requiring water that is clear enough to allow sufficient light to penetrate to allow photosynthesis.

·       SAVs absorb its required mineral nutrients from the bottom sediments through the roots.



·       Consists of numerous species of photosynthetic algae, protists and chlorophyll-containing bacteria. Phytoplankton lives suspended in the water constantly exposed to sunlight for photosynthesis.

·       Phytoplankton absorbs nutrients directly from the water, thus its population density is directly related to the level of nutrients dissolved in the water.


11.                    Explain the difference between oligotrophic and eutrophic waters. Describe the sequential process of eutrophication. (pg. 455)

Oligotrophic water:

·       low in nutrients (limited phytoplankton)

clear water (light penetrates)

·       allows growth of SAVs


Eutrophic water:

·       nutrient-rich (large amount of phytoplankton)

·       accumulation of detritus of dead algae

·       decomposers feed on detritus (depletion of dissolved oxygen → fish and shellfish suffocate)

·       water is turbid

·       SAVs are shaded out


Eutrophication process:

1.    As water of an oligotrophic body become enriched with nutrients, phytoplankton rapidly grows and multiplies, increasing turbidity in water.

2.    Increasing turbidity shades out the SAV

3.    With the death of SAVs, there is a loss of food, habitats and dissolved oxygen form their photosynthesis.

4.    As phytoplankton dies, it settles at the bottom of the water body. The abundance of detritus supports an abundance of decomposers (mainly bacteria).

5.    Explosive growth of bacteria consume oxygen via respiration, creating an additional demand for dissolved oxygen.

6.    The result is the depletion of dissolved oxygen, creating hypoxic conditions.


12.                    Distinguish between natural and cultural eutrophication. (pg. 455)

Natural eutrophication: Over periods of thousands of years, bodies of water are naturally subjected to gradual enrichment of nutrients. This process is part of natural succession.


Cultural eutrophication: Accelerated eutrophication by nutrient enrichment of water bodies due to human activities (sewage treatment plants water disposals, poor farming practices, urban runoff, etc.).


13.                    What is being done to establish nutrient criteria? (pg. 457)

In 2001 EPA began publishing water quality nutrient criteria aimed at preventing and reducing the eutrophication. It listed recommended criteria for causative factors (nitrogen and phosphorus) and criteria for response factors (chlorophyll – a measure of phytoplankton density and water clarity).


The EPA divided the country into ecoregions and determined criteria levels deemed appropriate for the specific region (natural levels of these criteria are different for different water bodies / regions)


14.                    How does the NPDES (National Pollution Discharge Elimination System) program address point-source pollution by nutrients? (pg. 457)

The program enforces that “anyone discharging pollutants from any point source into waters of the US [must] obtain and NPDES permit from EPA or an authorized state”. The permit must be drawn up in the context of the total pollutants sources (point and nonpoint) impacting a watershed or body of water.


15.                    Describe the TMDL (Total Maximum Daily Load) program. How does it address nonpoint-source pollution, and what role do water quality criteria play in the program? (pg. 458)

The TMDL program evaluates all sources of pollutants entering a body of water, especially nonpoint sources, according to the water body's ability to assimilate the pollutant.


It regulations include:

·       Identify the pollutants responsible for degrading a body of water

·       Estimate the pollution coming from all sources (point and nonpoint)

·       Estimate the ability of the body of water to assimilate the pollutants while remaining below the threshold designating poor or inadequate water quality (water quality criteria play an important role in this process as they will determine the allowed levels of pollutants that the water body is allowed to absorb).

·       Determine the maximum allowable pollution load.

·       Within a margin of safety, allocate the allowable level of pollution among the different sources such that the water quality standards are achieved.


16.                    What are some of the important issues relating to water quality in the public policy? (pg. 461)

Nonpoint sources of pollution is the most important water pollution problem. Other importa