Activated Sludge:
The term "activated sludge" refers to a brownish flocculent culture of organisms developed in aeration tanks under controlled conditions. It is also Sludge floc produced in raw or settled waste water by the growth of zoological bacteria and other organisms in the presence of dissolved oxygen. Activated sludge is normally brown in color.
Activated Sludge Process: A common
method of disposing of pollution in wastewaters.
In the process, large quantities of air are bubbled
through wastewaters that contain dissolved organic
substances in open aeration tanks. Bacteria and
other types of micro-organisms present in the
system need oxygen to live, grow, and multiply
in order to consume the dissolved organic "food"
or pollutants in the waste. After several hours
in a large holding tank, the water is separated
from the sludge of bacteria and discharged from
the system. Most of the activated sludge is returned
to the treatment process, while the remainder
is disposed of by one of several acceptable methods.
Aeration: The process or method of bringing about intimate contact between air and a liquid.
Aeration Tank: A chamber for injecting
air into water.
Aerobic Bacteria:
Bacteria that requires free (elementary) oxygen
for growth.
Alkalinity:
The capacity of water to neutralize acids, a property imparted by the water's content of carbonates, bicarbonates, hydroxides, and occasionally borates, silicates, and phosphates. Alkaline fluids have a pH value over 7.
Anaerobic:
A biological environment that is deficient in all forms of oxygen, especially molecular oxygen, nitrates and nitrites. The decomposition by microorganisms of waste organic matter in wastewater in the absence of dissolved oxygen is classed as anaerobic.
Anaerobic Bacteria:
Bacteria that grows in the absence of free oxygen
and derive oxygen from breaking down complex substances.
Anoxic: A biological environment that is deficient in molecular oxygen, but may contain chemically bound oxygen, such as nitrates and nitrites.
Bacteri:a
Bacteria are microscopic living organisms They are a group of universally distributed, rigid, essentially unicellular, microscopic organisms lacking chlorophyll. They are characterized as spheroids, rod-like, or curved entities, but occasionally appearing as sheets, chains, or branched filaments.
Biological Oxidaiton: The process
by which bacteria and other types of micro-organisms
consume dissolved oxygen and organic substances
in waster water, using the energy released to
convert organic carbon into carbon dioxide and
cellular material.
Biochemical Oxygen
Demand (BOD): A quantitative measure
of the oxygen needed by bacteria and micro-organisms
for the biological oxidation of organic wastes
in a unit volume of waste water. BOD is generally
measured in milligrams per liter (mg/l) of oxygen
consumed over a five day period. Although complete
biological decomposition of organic waste requires
about 20 days, the five day BOD is about two-thirds
of the total oxygen required and, therefore, is
a practical measure of waste concentration. In
waste treatment language, BOD is most frequently
stated as the percentage removed during treatment,
or remaining after treatment.
Bulking Sludge:
A phenomenon that occurs in activated sludge plants whereby the sludge occupies excessive volumes and will not concentrate readily. This condition refers to a decrease in the ability of the sludge to settle and consequent loss over the settling tank weir. Bulking in activated sludge aeration tanks is caused mainly by excess suspended solids (SS) content. Sludge bulking in the final settling tank of an activated sludge plant may be caused by improper balance of the BOD load, SS concentration in the mixed liquor, or the amount of air used in aeration.
Chemical Oxygen
Demand (COD): A quantitative measure
of the amount of oxygen required to oxidize all
organic compounds in a unit volume on waste water
- non-biodegradable as well as the BOD. The COD
level can be determined more readily than BOD,
but this measurement does not indicate how much
of the waste can be decomposed by biological oxidation.
Chlorination: The application of chlorine to water, sewage,
or industrial wastes, generally for the purpose
of disinfection, but frequently for accomplishing
other biological or chemical results.
Coagulation: The agglomeration of colloidal or suspended matter
brought about by the addition of some chemical
to the liquid, by contact, or by other means.
Coliform Organisms: A group of
bacteria recognized as indicators of fecal pollution
(see also escherichia coliform).
Combined Sewer: Carries both sanitary sewage and storm water run-off.
Composite Sample:
To have significant meaning, samples for laboratory tests on wastewater should be representative of the wastewater. The best method of sampling is proportional composite sampling over several hours during the day. Composite samples are collected because the flow and characteristics of the wastewater are continually changing. A composite sample will give a representative analysis of the wastewater conditions.
Denitrification:
A biological process by which nitrate is converted to nitrogen gas.
Diffused Air: Method of aeration.
Digestion: The biochemical decomposition of organic matter
that results in the formation of mineral and simpler
organic compounds.
Dissolved Air Flotation: Method of removing oil and suspended solids.
Dissolved Oxygen (DO):
The oxygen dissolved in water, wastewater, or other liquid. DO is measured in milligrams per liter. If the DO of a sample of water is 2 mg/L, it means that there are 2lbs of oxygen in 1 mil lb of water.
Dissolved Solids: Solids physically suspended in sewage that cannot
be removed by proper laboratory filtering.
Effluent: The liquid that comes out of a treatment plant
after completion of any treatment process.
Escherichia Coliform: A species of bacteria found in large numbers in
the intestinal tract of warm-blooded animals.
Extended Aeratio:
A modification of the activated sludge process which provides for aerobic sludge digestion within the aeration system.
Floc: The
agglomeration of smaller particles in gelatinous
mass that can be more easily removed from the
liquid than the individual small particles.
Flocculation: The coming together of coalescing and minute particles
in a liquid.
Grease
In wastewater, a group of substances, including fats, waxes, free fatty acids, calcium and magnesium soaps, mineral oils, and certain other non-fatty materials.
Grit: Heavy, inorganic matter, such as sand or pebbles.
Inorganic Material: Material that will not respond to biological action
(sand, cinders, stone). Non-volatile fraction
of solids.
Infection: Introduction of presence of pathogenic organisms
in potable water supply. This is determined in
two ways:
1. Bacterial Count - Number
of bacteria developed under controlled conditions
after 25 hours incubation period. In unpolluted
waters count is frequently less than 10 per milliliter.
2 - Coliform Index - Escherichia
Coli is an organism normally found in the intestinal
tract of man and animals but rare elsewhere. Indicators
of this organism family are most reliable as index
of pollution, purification efficiency and potability
of water.
Mechanical Aeration: Method of aeration.
Micor-Organisms: Microscopic plants and animals such as bacteria,
molds, protozoa, algae, and small metazoa.
Milligrams per Liter (mg/L)
A unit of concentration of water or wastewater constituent. It is 0.001 g of the constituent in 1000 ml of water. The unit parts per million is identical to milligrams per liter.
Mixed Liquor: The combination of primary effluent and active
biological solids (return sludge) in the activated
sludge process that is fed into the aeration tank.
Mixed Liquor Suspended Solids (MLSS):
The milligrams of suspended solids per liter of mixed liquor that are combustible at 550 degrees Centigrade. An estimate of the quantity of MLSS to be wasted from the aeration tank of an extended aeration plant may be determined by the rate of settling and centrifuge tests on the sludge solids.
Mixed Media Gravity
Filter: A filter using more than
one filtering media (such as coal and sand.)
Nitrification:
The conversion of nitrogen matter into nitrates by bacteria.
Nitrogen:
Nitrogen is present in wastewater in many forms: total Kjeldahl nitrogen, ammonia nitrogen, organic nitrogen.
Nitrogen Cycle:
The cycle of life, death, and decay involving organic nitrogenous matter is known as the nitrogen cycle. In the nitrogen cycle ammonia is produced from proteins.
Nutrient: Any
substance assimilated by organisms that promotes
growth and replacement of cellular constituents.
Organic Matter: The waste from homes or industry of plant or animal
origin. Volatile fraction of solids.
Organic Material: Material that can be broken down by bacteria (fats,
meats, plant life).
Orthophosphate:
A simple compound of phosphorous and oxygen that is soluble in water.
Oxic:
A biological environment which is aerobic
Oxidation: The conversion of organic material to a more stable
form using bacteria, chemicals, or oxygen.
Oxidation Ponds
or Lagoons: Holding ponds designed
to allow the decomposition of organic wastes by
aerobic or anaerobic means.
pH Value: A convenient method of expressing small differences
in the acidity or alkalinity of solutions. Neutrality
= pH 7.1; lower values indicate increasing acidity,
higher values indicate increasing alkalinity.
Potable Water: Water
fit for human consumption.
Polyelectrolytes: Synthetic chemicals used as a coagulant aid.
Polyphosphate
A large compound formed of several orthophosphate molecules connected by phosphate-storing microorganisms.
Primary Waste Treatment: Mechanical separation of solids, grease, and scum
from waste-water. With the aid of flocculating
agents, primary treatment can eliminate 50% t
65% othe suspended solids. Solids removed by
the primary treatment may comprise as much as
30% t40% othe original BOD of the water.
Raw Wastewater:
Wastewater before it receives any treatment.
Reactor:
A tank where a wastewater stream is mixed with bacterial sludge and biochemical reactions occur.
Recieving Waters: Rivers, lakes, or other water sources that recieve
treated or untreated waters.
Return Sludge:
Settled activated sludge returned to mix with incoming raw or primary settled wastewater. When the return sludge rate in the activated sludge process is too low, there will be insufficient organisms to meet the waste load entering the aerator.
Return Activated Sludge:
Activated return sludge is normally returned continuously to the aeration tank. Recycling of activated sludge back to the aeration tank provides bacteria for incoming wastewater. Its should be brown in color with no obnoxious odor and is often also returned in small portions to the primary settling tanks to aid sedimentation. Settled activated sludge is generally thinner than raw sludge. Some activated sludge will be wasted to prevent excessive solids build up.
Secondary Waste
Treatment: Secondary treatment is part of the primary treatment in that the wastewater continues from the equalization tank and sludge holding zone where it loses the most solids. From the primary stages it passes to the aeration zone where it continues to be broken down and separated from any solids. After aeration the wastewater will pass to the clarifier and disinfection zones. Some plants will include a tertiary treatment that typically involves clorination or UV treatment.
Sedimentation Tanks:
Provide a period of quiescence
during which suspended waste material settles
to the bottom of the tank and is scraped into
a hopper and pumped out for disposal. During this
period, floatable solids (fats, oils) rise to
the surface of te tank and are skimmed off into
scum pipes for disposal.
Sewage: Largely the water supply of a community after
it has been fouled by various uses. From the standpoint
of course, it may be a combination of the liquid
or water-carried wastes from residences, business
buildings, and institutions, together with those
from industrial establishments, and with such
ground water, surface water, and storm water as
may be present.
Sewers: A
system of pipes used for collecting domestic and
industrial waste, as well as storm water run-off.
Lateral sewers connect homes and industries to
trunk sewers, which channel waste into interceptor
sewers carry only domestic and industrial wastewater.
Storm sewers carry only storm water run-off. Combined
sewers carry both.
Sludge: The accumulated suspended solids of sewage deposited
in tanks or basins.
Sludge Age:
In the activated sludge process, a measure of the length of time a particle of suspended solids has been undergoing aeration, expressed in day. It is usually computed by dividing the weight of the suspended solids in the aeration tank by the weight of excess activated sludge discharged from the system per day.
Sludge Digestion:
The purpose of sludge digestion is to separate the liquid from the solids to facilitate drying. The proper pH range for digested sludge is 6.8 - 7.2.
Sludge Index:
Properly called sludge volume index (SVI). It is the volume in millimeters occupied by 1 g of activated sludge after settling of the aerated liquid for 30 minutes.
Sludge Reaeration:
The continuous aeration of sludge after initial aeration for the purpose of improving or maintaining its condition.
Splitter Box:
A division box that splits the incoming flow into two or more streams. A device for splitting and directing discharge from the head box to two separate points of application.
Suspended Solids: Solids physically suspended in sewage that can
be removed by proper laboratory filtering.
Tertiary Waste Treatment: Following secondary treatment, the clarified effluent
may require additional aeration and/or other chemical
treatment to destroy bacteria remaining from the
secondary treating stage, and to increase the
content of dissolved oxygen needed for oxidation
of the residual BOD. Tertiary treatment can also
be used to remove nitrogen and phosphorous. This is done with clorination and often times UV treatment.
Total Solids: The
total amount of solids in solution and suspension.
Trickling Filter: An aerobic biological process used as secondary
treatment of sewage. Effluent from the primary
clarifier is distributed over a bed of rocks.
As the liquid trickles over the rocks, a biological
growth on the rocks breaks down the organic matter
in the sewage. The effluent is then taken to a
clarifier to remove biological matter coming from
the filter.
Turbidity: Any finely divided, insoluble impurities that
mark the clarity of the water.
Waste Activated Sludge: That portion
of sludge from the secondary clarifier in the
activated sludge process that is wasted to avoid
a buildup of solids in the system.
Waste Treatment
Sludge: A series of tanks, screens,
filters, and other processes by which most pollutants
are removed from water.
Wastewater:
Domestic wastewater is 99.9% wer and 0.1% sids. Fresh wastewater is usually slightly alkaline. If the pH of the raw wastewater is 8.0, it indicates that the sample is alkaline. If wastewater has a pH value of 6.5, it means that it is acid. Wastewater is said to be septic when it is undergoing decomposition.
Water Pollution: A general term
signifying the introduction into water of micro-organisms,
chemicals, wastes, or sewage which renders the
water unfit for it's intended use.
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