7/11/2014 Lesson 1: Wastewater Treatment http://water.me.vccs.edu/courses/ENV108/Lesson1_print.htm 1/13 Lesson 1: Wastewater Treatment Objective In this lesson we will learn the following: What is involved in treating wastewater. What microbes are beneficial and harmful in the wastewater treatment process. Reading Assignment Along with the online lecture, read Chapter 1 in Wastewater Microbiology. Lecture Introduction The purpose of this lesson is to provide a fundamental background on the relationship between microbes, wastewater, and wastewater treatment. It will explain why we are concerned about microbes in wastewater, what role do they play in wastewater treatment, and what happens when "clean" water is released into the environment. The main focus of wastewater treatment plants is to reduce the BOD (biochemical oxygen demand) and COD (chemical oxygen demand) in the effluent discharged to natural waters, meeting state and federal discharge criteria. Wastewater treatment plants are designed to function as "microbiology farms", where bacteria and other microorganisms are fed oxygen and organic waste. Wastewater is teaming with microbes. Many of which are necessary for the degradation and stabilization of organic matter and are beneficial. On the other hand, wastewater may also contain pathogenic or potentially pathogenic microorganisms, which pose a threat to public health. Waterborne and water-related diseases caused by pathogenic microbes are among the most serious threats to public health today. Waterborne diseases whose pathogens are spread by the fecal-oral route (with water as the intermediate medium) can be caused by bacteria, viruses, and parasites (including protozoa, worms and rotifers). Diarrhea is one of the most common features of waterborne disease. Fecal pollution is one of the primary contributors to diarrhea. Examples of bacteria commonly associated with diarrheal disease are Shigella dysenteriae and Salmonella typhi . Two protozoans commonly associated with diarrheal disease are Giardia lamblia and members of the genus Cryptosporidium.
What is involved in treating wastewater.What microbes are beneficial and harmful in the wastewater treatment process.
Reading Assignment
Along with the online lecture, read Chapter 1 in Wastewater Microbiology.
Lecture
Introduction
The purpose of this lesson is to provide a fundamental background on the relationship between
microbes, wastewater, and wastewater treatment. It will explain why we are concerned about
microbes in wastewater, what role do they play in wastewater treatment, and what happens when
"clean" water is released into the environment.
The main focus of wastewater treatment plants is to reduce the BOD (biochemical oxygen demand)and COD (chemical oxygen demand) in the effluent discharged to natural waters, meeting state and
federal discharge criteria. Wastewater treatment plants are designed to function as "microbiology
farms", where bacteria and other microorganisms are fed oxygen and organic waste.
Wastewater is teaming with microbes. Many of which are necessary for the degradation and
stabilization of organic matter and are beneficial. On the other hand, wastewater may also contain
pathogenic or potentially pathogenic microorganisms, which pose a threat to public health.
Waterborne and water-related diseases caused by pathogenic microbes are among the most
serious threats to public health today. Waterborne diseases whose pathogens are spread by the
fecal-oral route (with water as the intermediate medium) can be caused by bacteria, viruses, and
parasites (including protozoa, worms and rotifers).
Diarrhea is one of the most common features of waterborne disease. Fecal pollution is one of theprimary contributors to diarrhea. Examples of bacteria commonly associated with diarrheal disease
are Shigella dysenteriae and Salmonella typhi. Two protozoans commonly associated with
diarrheal disease are Giardia lamblia and members of the genus Cryptosporidium.
Water quality has inspired development of tests designed to measure its suitability for drinking,
bathing, and release back to the environment. Water that looks clear and pure may be
contaminated with pathogenic microorganisms. Even water that appears "pure" must be tested to
ensure that it contains no microorganisms that might cause disease. On the other hand, there are so
many potential pathogens that it is impractical to test for them all. Because of this, tests have been
developed for indicator organisms. These are organisms that are present in feces (or sewage),
survive as long as pathogenic organisms, and are easy to test for at relatively low cost.
Indicator organisms indicate that fecal pollution has occurred and microbial pathogens might bepresent. Total and fecal coliforms, and the enterocci -fecal streptocci are the indicator organisms
currently used in the public health arena.
Biological Wastewater Treatment
Principal Goals
It was mentioned earlier that many of the microbes present in wastewater are beneficial. In fact,
many wastewater treatment technologies are dependent on these beneficial microorganisms forremediation of wastewater so that it won't detrimentally impact the environment. One of the primary
goals of biological treatment is the removal of organic material from wastewater so that excessiveoxygen consumption won't become a problem when it is released to the environment.
Another goal of biological treatment is nitrification/denitrification. Nitrification is an aerobicprocess in which bacteria oxidize reduced forms of nitrogen. Denitrification is an anaerobic
process by which oxidized forms of nitrogen are reduced to gaseous forms, which can then escapeinto the atmosphere. This is important because the release of nitrogen to the aquatic environment
Overview of nitrification and denitrification at the wastewater treatment plant.
Another goal of biological treatment is elimination of pathogenic microorganisms either throughpredation or out-competition. The oxidation/stabilization of organic sludge is also of importance in
biological treatment of wastewater.
Biochemical Oxygen Demand and Eutrophication
Organic material in wastewater originates from microorganisms, plants, animals, and syntheticorganic compounds. Organic materials enter wastewater in human wastes, paper products,
detergents, cosmetics, and foods. They are typically a combination of carbon, hydrogen, oxygen
and nitrogen and may contain other elements.
The oxidation of organic materials in the environment can have profound effects on the maintenance
of aquatic life and the aesthetic quality of waters. Biochemical oxidation reactions involve theconversion of organic material using oxygen and nutrients into carbon dioxide, water and new cells.
The equation that expresses this is:
Organic material + O2 + nutrients CO2 + H2O + new cells + nutrients + energy
It can be seen from this equation that organisms use oxygen to breakdown carbon-based materialsfor assimilation into new cell mass and energy. A common measure of this oxygen use is
biochemical oxygen demand (BOD). BOD is the amount of oxygen used in the metabolism of
biodegradable organics. If water with a large amount of BOD is discharged into the environment, it
can deplete the natural oxygen resources. Heterotrophic bacteria utilize deposited organics andoxygen at rates that exceed the oxygen-transfer rates across the water surface. This can cause
anaerobic conditions, which leads to noxious odors. It can also be detrimental to aquatic life by
reducing dissolved oxygen concentrations to levels that cause fish to suffocate. The end result is an
overall degradation of water quality.
Wastewater often contains large amounts of the nutrients, particularly nitrogen and phosphorous,
which are essential for growth of all organisms and are typically limiting in the environment. Nitrogenis a complex element existing in both organic and inorganic forms. The forms of most interest from a
water quality perspective are organic nitrogen, ammonia, nitrite, and nitrate. Phosphorous is found
in synthetic detergents and is used for corrosion control in water supplies.
The introduction of large concentrations of these nutrients from untreated or improperly treated
wastewater can lead to eutrophication. Eutrophication is the process by which bodies of water
become rich in mineral and organic nutrients causing plant life, especially algae, to proliferate, then
die and decompose thereby reducing the dissolved oxygen content and often killing off otherorganisms.
Fundamentals of Biological Treatment
The basic mechanisms of biological treatment are the same for all treatment processes.
Microorganisms, principally bacteria, metabolize organic material and inorganic ions present inwastewater during growth. Which brings us to the fundamental differences between catabolic and
anabolic processes. Catabolic processes are those biochemical processes involved in the
breakdown of organic products for the production of energy or for use in anabolism. Catabolicprocesses are dissimilar because the reactants can be though of as redox reactions because they
involve the transfer of electrons resulting in the generation of energy to be used in cell metabolism.
In contrast, anabolic processes are the biochemical processes involved in the synthesis of cell
constituents from simpler molecules. These processes usually require energy and are assimilatory.That is the processes result in the incorporation of the reacting molecules or compounds into new
The growth of bacteria in pure culture has been the mainstay of microbiology, specifically the
mainstay of microbiological technique. Solid media techniques have allowed the isolation of
individual species from complex natural populations. In natural environments and in pathogenicrelationships, bacteria are different than the same organisms grown in vitro. In natural systems,
mixed bacterial populations grow as biofilms.
There are three steps necessary for the formation of biofilms. First, there must be a macromolecularconditioning of the surface to be colonized. This is a purely chemical process that occurs on the
order of microseconds. If you put any clean surface into the environment, low molecular weight
compounds possessing their own unique hydrophilic (readily absorbing or dissolving in water) andhydrophobic (repelling, tending not to combine with, or unable to dissolve in water) character will
bind to that surface. Step two, microbial binding, is a two-step process. First there is reversible
binding (colonization) by bacteria. Next if the cell senses the proper conditions, irreversible binding
takes place, often triggering capsule formation. Finally, there is further permanent attachment ofcells and cell division leading to microcolony formation and biofilm generation.
One important distinction of biofilms is that they can provide a variety of microenvironments and are
chemically heterogeneous throughout. They establish their own gradients of nutrients, oxygensaturation, and pH relative to the bulk environment. Because the capsule is hydrated, biofilms are
greater than 95% water and thus they will trap inorganic and organic material that is soluble or
particulate in nature. The solid/liquid interface between the biofilm and the environment is important
as well to current/flow rates. There is a critical role of transport and transfer processes which aregenerally rate controlling in biofilm systems. For example, high flow rates in oligotrophic ( Lacking
in plant nutrients and having a large amount of dissolved oxygen throughout. Used of a pond or
lake) environments will be well nourished due to high transfer rates across the interface.
In natural systems, biofilms are responsible for the removal of dissolved and particulate
contaminants and are important in the cycling of chemical elements. These concepts are equally
important in wastewater treatment systems. Also, in the natural environment, enhanced growth mayresult from nutrient trapping.
Microbiology of On-Site Systems
The septic tank works by a combination of sedimentation and anaerobic digestion. Anaerobic
bacteria are responsible for the digestion. Anaerobic bacteria are non-pathogenic and are present inlarge numbers in the human intestine. A new supply of these bacteria are regularly added to the
septic tank with each flush of human fecal material. Anaerobic digestion represents an incomplete
digestion. Methane, hydrogen sulfide, and sulfur dioxide gases are produced, as well as a sludge of
high molecular weight hydrocarbons. This sludge will readily decompose further when exposed tooxygen and aerobic bacteria. This further decomposition will take place in the municipal sewage
treatment plant or landfill if either of these places is used to dispose of sludge pumped periodically
Wastewater treatment refers to the process of removing pollutants from water previously employedfor industrial, agricultural, or municipal uses. The techniques used to remove the pollutants present
in wastewater can be broken into biological, chemical, physical and energetic. These different
techniques are applied through the many stages of wastewater treatment.
Primary treatment usually includes the removal of large solids from the wastewater via physicalsettling or filtration. The first step in primary treatment is screening.
Secondary treatment typically removes the smaller solids and particles remaining in the
wastewater through fine filtration aided by the use of membranes or through the use of microbes,
which utilize organics as an energy source. Energetic techniques may also be employed in tandem
with biological techniques in the secondary phase to break up the size of particles thus increasing
their surface area and rate of consumption by the microbes present. A common first step in thesecondary treatment process is to send the waste to an aeration tank.
Tertiary treatment involves the disinfection of the wastewater through chemical or energetic
means. Increasing the number of steps in a wastewater treatment process may insure higher quality
of effluent; however employing additional technologies may incur increased costs of construction,
Screening is the first technique employed in primary treatment, which is the first step in thewastewater treatment process.
This step removes all sorts of refuse that has arrived with the wastewater such as plastic, branches,
rags, and metals. The screening process is used primarily to present the clogging and interference of
the following wastewater treatment processes.
Screens are considered coarse if their opening are larger than 6mm, fine if their openings arebetween 1.5 and 6mm, and very fine if their openings are between 0.2 and 1.5mm.
This type of screen, called a bar screen, removes debris from wastewater.
Screens are cleaned manually if the object caught is larger and mechanically if finer particles are
caught. The angle of the screen may also be varied to affect the efficiency of filtration.
In order to remove coarse solids, numerous types of detritus tanks, grinders, and cyclonic inertial
separation are utilized, including a comminutor and a grit chamber. The type of grit removalseparation depends upon the characteristics of the grit itself.
A comminutor, also known as the grinding pump, houses a rotating
cutting screen. This cutting screen shreds any large chunks of organic
matter in the wastewater into smaller pieces. This makes it easier for themicroorganisms to use the organic matter as food and prevents the large
chunks from harming the internal workings of the treatment plant.
A grit chamber allows pieces of rock, metal, bone, and even egg
shells, which are denser than organic materials, to settle out of thewaste stream. Removal of grit prevents damage to machinery through
abrasion or clogging.
The last step in primary treatment is sedimentation, which occurs in the primary
clarifier.
Sedimentation simply entails the physical settling
of matter, due to its density, buoyancy, and the
force of gravity. Certain chemicals known as
coagulants and flocculants are often used to
expedite this process by encouraging
aggregation of particles. Through sedimentation,the larger solids are removed in order to
facilitate the efficiency of the following
procedures and also to reduce the biological
oxygen demand of the water.
The biochemical oxygen demand (BOD) refers to the amount of oxygen required by themicrobes within the wastewater to digest the matter that they are using for food. By removing these
solids early on, the efficiency of the microbial digestion at later stages in increased.
Secondary Treatment
Once the wastewater leaves the primary treatment steps, it enters secondary
treatment. The first step in the secondary treatment process is the aeration
tank.
Bacteria are single celled organisms, which have basic requirements for existence and reproduce
rapidly. Many occupy unique niches and consume only certain types of food. Many types ofbacteria have been utilized in wastewater processing. If certain bacterium is supplied with an
environment in which the proper pH, temperature, micro and macronutrients, and oxygen levels are
present, it can quickly and effectively break pollutants present in wastewater down into less harmful
The types of bacteria utilized in wastewater processing can be
categorized based upon their necessary or intolerance of oxygen to
survive. Those bacteria that require oxygen to convert food into energy
are called aerobic, those that will perish in the presence of oxygen are
anaerobic, and finally facultative anaerobes may thrive in either thepresence or absence of oxygen. Typically aerobes, which can degrade
pollutants 10-100 times faster than anaerobes, are utilized most
frequently. Increases in temperature and pollutant food source have
shown to increase the rate of degradation, but if all elements necessary
for conversion of food to energy are not in balance, the microbial
degradation will be thwarted.
The wastewater is then passed through a secondary clarifier, which performssedimentation again, which is described earlier and occurs in primary treatment as
well.
The disinfection of wastewater through the sue of chemicals such as chlorine typically
acts as the final step in wastewater treatment. Disinfection seeks to remove harmful
organics and pathogens causing cholera, polio, typhoid, hepatitis, and a number of
other bacterial, viral, and parasitic diseases from the water.
Due to security concerns, some wastewater treatment facilities are using sodium hypochlorite to
eliminate the need for chlorine. Sodium hypochlorite is more expensive than liquid chlorine, but is
also safer. Although chlorine is considered the tried and true solution to reducing pathogens in
contaminated water, the method of disinfection, such as UV disinfection, must fit the type of
pathogen the wastewater harbors, to be truly effective.
Through disinfection a significant portion of the pathogens are inactivated, however, it is difficult to
identify individual pathogens within wastewater, and therefore indicator pathogens are used. In
wastewater, fecal coliform acts as the indicator pathogen, but there has been discussion of using
E. coli or total coliform, the indicator for potable water, to check wastewater.
Coagulants and flocculants are chemicals used to precipitate insoluble substances. The purpose
of coagulation and flocculation is to cause small pollutant particles such as metals to aggregate and
form large enough floc so that they can be separated from the wastewater through sedimentation.
There are three main types of coagulants that are used to overcome the repulsive forces of
particles, thus causing them to aggregate. Electrolytes, organic polymers, and synthetic
polyelectrolites are added to wastewater and then flocculation tanks mix the water to promote flocs
and subsequent physical separation.
Rate of flocculation is dependent upon many factors including concentration of particles, particlecontact, and range of particle sizes. Coagulation targets dissolved ions such as metal and
radionuclides. Some difficulties with this technology include the frequent need to adjust pH levels,
the creation of toxic sludge that must be eventually mitigated, and the difficulty that results in trying
to address the chemical nature of multiple compounds. This technology has been used consistently
in the electronics and electroplating industry as well as for applications in groundwater treatment.
Membrane Filtration
The three main types of membrane-based filtration technologies include reverse osmosis,
nanofiltration, and ultrafiltration. Although categorized as different technologies, the three types
of membrane filtration have a great deal in common. All three act as membranes created by coating
a thin layer of a very porous polymer, or plastic, onto a backing material. The end result is the finest
form of filtration presently known, with reverse osmosis being the smallest, nanofiltration being aslight step larger and ultrafiltration being a bit larger again.
The pore sizes are typically measured in angstroms (one billionth of a meter) and thus are extremely
tiny. These membrane technologies offer a host of advantages over traditional filtration. Due to thefine pore space and indiscrimination of influents of these membrane filtration systems, a very high
quality effluent emerges. Additionally, membrane technologies take up only a fraction of the space
needed for other tertiary treatment systems. The disadvantage of having extremely fine pores means
that clogging is a frequent and costly problem with membrane filtration technologies.
Constructed Wetlands
Scientists have long recognized the abilities of wetlands to purify water. Through the correct
sequencing of base media, plant species, and microbe species, constructed wetlands can
successfully reduce nitrogen content, filter out solids, and reduce the presence of heavy metals.
The type and amount of pollutant removed depends upon the species and oxygen affinity of the
organisms present in the wetland. Wetlands utilize physical and chemical processes to clean
wastewater and typically serve as the secondary and tertiary steps.
Although constructed wetlands tend to take up a great
deal of space, they require less investment of time and
money than traditional waste treatment procedures.
Ultimately, constructed wetlands area cost-effective and
In this lesson we learned the relationship between microbes, wastewater, and wastewater
treatment. One goal of biological treatment is nitrification/denitrification. Nitrification is an
aerobic process in which bacteria oxidize reduced forms of nitrogen. Denitrification is ananaerobic process by which oxidized forms of nitrogen are reduced to gaseous forms, which can
then escape into the atmosphere. If water with a large amount of BOD is discharged into theenvironment, it can deplete the natural oxygen resources. Eutrophication is the process by which
bodies of water become rich in mineral and organic nutrients causing plant life, especially algae, toproliferate, then die and decompose thereby reducing the dissolved oxygen content and often killing
off other organisms. Wastewater treatment in the plants involve primary, secondary and tertiarytreatment. Primary treatment deals with removing large solids while secondary treatmentremoves the smaller solids and tertiary treatment involves the disinfection of the wastewater
Complete the interactive assignment on Wastewater Treatment .
This assignment will give you practice with the topics covered in Lesson 1. You should print the
assignment and become familiar with the exercises before doing them online. You may do theAssignment online to get credit or print it out and send it to the instructor. It will require the Flash
player to view, which should already be installed on your machine.
In addition, the first Project paper is due this week. Once you have completed the project either
Answer the questions in the Lesson 1 quiz . When you have gotten all the answers correct, printthe page and either mail or fax it to the instructor. You may also take the quiz online and directly
