What does high biochemical oxygen demand indicate?

Question

What does the presence of high biochemical oxygen demand (BOD) indicate?

Answer 1

The presence of a lot of animals???

Answer 2

Oxygen demand is an important parameter for determining the amount of organic pollution in water. High influent BOD requires extensive treatment to provide the oxygen necessary to break down the water's organic contents.

Answer 3

That the water contains high numbers of organisms or decaying matter. Anything that uses up lots of dissolved oxygen.

Answer 4

Biochemical Oxygen Demand, or BOD, is a measure of the quantity of oxygen consumed by
microorganisms during the decomposition of organic matter. BOD is the most commonly used
parameter for determining the oxygen demand on the receiving water of a municipal or industrial
discharge. BOD can also be used to evaluate the efficiency of treatment processes, and is an
indirect measure of biodegradable organic compounds in water.
Imagine a leaf falling into a stream. The leaf, which is composed of organic matter, is readily
degraded by a variety of microorganisms inhabiting the stream. Aerobic (oxygen requiring)
bacteria and fungi use oxygen as they break down the components of the leaf into simpler, more
stable end products such as carbon dioxide, water, phosphate and nitrate. As oxygen is
consumed by the organisms, the level of dissolved oxygen in the stream begins to decrease
Water can hold only a limited supply of dissolved oxygen and it comes from only two sourcesdiffusion
from the atmosphere at the air/water interface, and as a byproduct of photosynthesis.
Photosynthetic organisms, such as plants and algae, produce oxygen when there is a sufficient
light source. During times of insufficient light, these same organisms consume oxygen. These
organisms are responsible for the diurnal (daily) cycle of dissolved oxygen levels in lakes and
streams.
If elevated levels of BOD lower the concentration of dissolved oxygen in a water body, there is a
potential for profound effects on the water body itself, and the resident aquatic life. When the
dissolved oxygen concentration falls below 5 milligrams per liter (mg/l), species intolerant of low
oxygen levels become stressed. The lower the oxygen concentration, the greater the stress.
Eventually, species sensitive to low dissolved oxygen levels are replaced by species that are
more tolerant of adverse conditions, significantly reducing the diversity of aquatic life in a given
body of water. If dissolved oxygen levels fall below 2 mg/l for more than even a few hours, fish
kills can result. At levels below 1 mg/l, anaerobic bacteria (which live in habitats devoid of
oxygen) replace the aerobic bacteria. As the anaerobic bacteria break down organic matter, foulsmelling
hydrogen sulfide can be produced.
BOD is typically divided into two parts- carbonaceous oxygen demand and nitrogenous oxygen
demand. Carbonaceous biochemical oxygen demand (CBOD) is the result of the breakdown of
organic molecules such a cellulose and sugars into carbon dioxide and water. Nitrogenous
oxygen demand is the result of the breakdown of proteins. Proteins contain sugars linked to
nitrogen. After the nitrogen is "broken off" a sugar molecule, it is usually in the form of ammonia,
which is readily converted to nitrate in the environment. The conversion of ammonia to nitrate
requires more than four times the amount of oxygen as the conversion of an equal amount of
sugar to carbon dioxide and water.
When nutrients such as nitrate and phosphate are released into the water, growth of aquatic
plants is stimulated. Eventually, the increase in plant growth leads to an increase in plant decay
and a greater "swing" in the diurnal dissolved oxygen level. The result is an increase in microbial
populations, higher levels of BOD, and increased oxygen demand from the photosynthetic
organisms during the dark hours. This results in a reduction in dissolved oxygen concentrations,
especially during the early morning hours just before dawn.
In addition to natural sources of BOD, such as leaf fall from vegetation near the water's edge,
aquatic plants, and drainage from organically rich areas like swamps and bogs, there are also
anthropogenic (human) sources of organic matter. If these sources have identifiable points of
discharge, they are called point sources. The major point sources, which may contribute high
levels of BOD, include wastewater treatment facilities, pulp and paper mills, and meat and food
processing plants.
Organic matter also comes from sources that are not easily identifiable, known as nonpoint
sources. Typical nonpoint sources include agricultural runoff, urban runoff, and livestock
operations. Both point and nonpoint sources can contribute significantly to the oxygen demand in
a lake or stream if not properly regulated and controlled.
Performing the test for BOD requires significant time and commitment for preparation and
analysis. The entire process requires five days, with data collection and evaluation occurring on
the last day. Samples are initially seeded with microorganisms and saturated with oxygen (Some
samples, such as those from sanitary wastewater treatment plants, contain natural populations of
microorganisms and do not need to be seeded.). The sample is placed in an environment suitable
for bacterial growth (an incubator at 20o Celsius with no light source to eliminate the possibility of
photosynthesis). Conditions are designed so that oxygen will be consumed by the
microorganisms. Quality controls, standards and dilutions are also run to test for accuracy and
precision. The difference in initial DO readings (prior to incubation) and final DO readings (after 5
days of incubation) is used to determine the initial BOD concentration of the sample. This is
referred to as a BOD5 measurement. Similarly, carbonaceous biochemical oxygen test
performed using a 5-day incubation is referred to as a CBOD5 test.
Water Quality Standards for BOD
Although there are no Michigan Water Quality Standards pertaining directly to BOD, effluent
limitations for BOD must be restrictive enough to insure that the receiving water will meet
Michigan Water Quality Standards for dissolved oxygen.
Rule 64 of the Michigan Water Quality Standards (Part 4 of Act 451) includes minimum
concentrations of dissolved oxygen that must be met in surface waters of the state. This rule
states that surface waters designated as coldwater fisheries must meet a minimum dissolved
oxygen standard of 7 mg/l, while surface waters protected for warmwater fish and aquatic life
must meet a minimum dissolved oxygen standard of 5 mg/l.
Biochemical Oxygen Demand Limitations in NPDES Permits
Typically, CBOD5 limits are placed in NPDES permits for all facilities which have the potential to
contribute significant quantities of oxygen consuming substances to waters of the state. These
limits are developed in direct correlation with limits for ammonia nitrogen and dissolved oxygen.
The nitrogenous oxygen demand is computed separately because of the difference in oxygen
demand (as explained above) and because the rate of oxygen consumption over time varies from
carbonaceous oxygen demand. Ammonia is further considered separately because in sufficient
levels (dependant upon several variables) it can also be toxic to living organisms.
In determining CBOD5 limits, stream modelers use computer models which simulate actual
stream conditions. Model inputs include the flow of the receiving stream, the quantity of water to
be discharged, the decay rate for the particular type of wastewater, the stream's slope, and
temperature. Other upstream or downstream dischargers are also considered in the model. The
modeler determines maximum limits for CBOD5 and ammonia nitrogen and minimum limits for
dissolved oxygen. These limits are selected to insure that Water Quality Standards for dissolved
oxygen are met in the receiving water.

Answer 5

indicate how many animals,protozoa, and algae.