UNIVERSITI KEBANGSAAN MALAYSIA
FAKULTI SAINS DAN TEKNOLOGI
SARJANA PENGURUSAN KESELAMATAN INDUSTRI
Z1LK 6193
PENGURUSAN BIOLOGY DAN ALAM SEKITAR
TUGASAN 1
9hb November 2008
Nama :
No. Matriks :
1.
HAFIZ IZUWAN BIN OTHMAN
G76867
2.
EDMUND MAHAI AMBOH
G72697
PENSYARAH :
DR FATIHAH
QUESTION NO 1:
Explain how the following classes of biodegradation processes differ from each other. In
what respects are they similar?
a)
Aerobic heterotrophic process
b)
Anaerobic heterotrophic process
c)
Anoxic heterotrophic process
ANSWER:
a) Aerobic Heterotrophic Process.
Aerobic heterotrophic process is a bacterial process occurring in the presence of oxygen.
Under aerobic conditions, bacteria rapidly consume organic matter and convert it into
carbon dioxide. In other explanation it can says that this biological treatment is performed
in the presence of oxygen by aerobic microorganisms (principally bacteria) that
metabolize the organic matter in the wastewater, thereby producing more microorganisms
and inorganic end-products (principally CO2, NH3, and H2O). Several aerobic biological
processes are used for secondary treatment differing primarily in the manner in which
oxygen is supplied to the microorganisms and in the rate at which organisms metabolize
the organic matter. In aerobic processes (i.e. molecular oxygen is present) heterotrophic
bacteria (those obtaining carbon from organic compounds) oxidize about one-third of the
colloidal and dissolved organic matter to stable end products (CO2 + H2O) and convert
the remaining two-thirds into new microbial cells that can be removed from the
wastewater by settling.
Organic Matter + O2
CO2 + H2O + new cells
b) Anaerobic Heterotrophic Process.
Aerobic heterotrophic process is a bacterial process that breaks down organic materials
within waste in the absence of oxygen. It is generally run in closed tanks. Generally,
biomass consisting of sewage or processing wastes is mixed with water and fed into the
digester without air. The waste stream generally contains fats, oils, greases. These waste
streams are produced in processes involving the manufacture of detergents and soaps, as
well as within the petrochemical industry. Municipal sewage treatment facilities also use
sludge digesters. The generalized equation for anaerobic sludge digestion is:
Organic Matter + Combined Oxygen’s  Anaerobic Microbes + New Cells
+ Energy for life processes + CH4 + CO2 + Other gases
The combined oxygen consists of CO3-2, SO4-2, NO3-1, and PO4-3 which no O2 present.
Microbial action during anaerobic processes consists of three stages:
i. liquefaction of solids
ii. Digestion of the soluble solids
iii. Gas production
Organic Matter
Organic Acids
Acid –forming
CH4 + CO2
Acid-splitting methane
methane-forming bacteria
In this process, the digestion is accomplished by two groups of heterotrophic bacteria:
i. Organic-acid forming heterotrophs –
The organic-acid forming heterptrophs use the complex organic substrates
such as, carbohydrates, proteins, fats, oils to produce organics fatty acids,
primarily acetic and propionic with some butyric and valeric acids. These
final breakdown products frequently called volatile acids. Most of the
organics-acid forming bacteria are soil microorganisms and are facultative
anaerobes.
ii. Methane-producing heterotrophs –
The methane-producing heterotrophs use the organic acids produced by the
acid formers as substrates and produce methane and carbon dioxide.
(c) Anoxic heterotrophic process
It is a process in which microorganisms use bound oxygen, for example from NO3 for
denitrification. Under continuing aerobic conditions, autotrophic bacteria (those obtaining
carbon from inorganic compounds) then convert the nitrogen in organic compounds to
nitrates, as shown below:
Organic N
NH3 (decomposition)
And
NH3 + O2
NO2
nitrifying
NO3 (nitrification)
bacteria
No further changes in the nitrates take places unless heterotrophics bacteria convert the
nitrates to odorless nitrogen gas, by using bound oxygen.
NO3
NO2
N2 (denitrification)
Under continuing anoxic conditions, any sulfates present are reduced to odorous
hydrogen sulfide gas
SO4
sulfate- reducing
H2S
bacteria
In term of similarity for the above classes of biodegradation processes, the volatile solid
loading and percent solids destruction are about the same. Anoxic conditions in which no
free, elemental oxygen is present. The only source of oxygen is combined oxygen, such
as that found in nitrate compounds. Also used to describe biological activity of treatment
processes that function only in the presence of combined oxygen. Oxidized inorganic
compounds such as nitrate and nitrite can function as electron acceptors for some
respiratory organisms in the absence of molecular oxygen. Anoxic process is the
biological treatment processes that exploit these microorganisms.
Anoxic process in producing methane is favored by high organic levels and low nitrate
and sulfate levels. Methane production plays a key role in local and global carbon cycles
as the final step in the anaerobic decomposition of organic matter. This process is the
source of about 80% of the methane entering the atmosphere. The carbon from microbial
produced methane can come from either the reduction of CO2 or the fermentation of
organic matter, particularly acetate. The anoxic production of methane can be represented
in the following simplified manner. When carbon dioxide acts as an electron receptor in
the absence of oxygen, methane gas is produced:
1/8CO2 +
H+ + e- 1/8CH4 + 1/4H2O
(01)
This reaction is mediated by methane-forming bacteria. When organic matter is degraded
microbial, the half-reaction for one electron-mole of {CH2O} is
1/4{CH2O}
+ 1/4H2O 1/4CO2 + H+ + e-
(02)
Adding half-reactions 01 and 02 yields the overall reaction for the anaerobic degradation
of organic matter by methane-forming bacteria, which involves a free energy change of 5.55 kcal per electron-mole:
1/4{CH2O}
1/8CH4 + 1/8CO2
(03)
QUESTION NO.2
What is the significance of microbial growth rate in biological waste treatment processes?
What growth rate characteristics would be desirable for efficient treatmnet process
development?
ANSWER:
The rate of microbial growth varies directly with the amount of available substrate. In a
batch culture when food is not limiting, the microbial population, after an initial lag
period, grows rapidly at a logarithmic rate. As food decreases, growth slows until, at
some time, growth stops and the number of new cells produced is balanced by the
number of old cells that are dying. When the substrate is exhausted, the numbers of
microorganisms’ declines as old cells decompose release theirs nutrients for use by new
microorganisms. Wastewater treatment uses microbes to decompose organic matter in
sewage. If too much untreated sewage or other organic matter is added to a lake or stream,
dissolved oxygen levels will drop too low to support sensitive species of fish and other
aquatic life. Wastewater treatment systems are designed to digest much of the organic
matter before the wastewater is released so that this will not occur. The objectives of
biological treatment are to coagulate and remove the colloidal solid and to stabilize organic
matter to a reasonable extent (Fogler 1997; Wesley 1989). The advantages of using microbes
in liquid waste treatment are efficiency, effectiveness, and minimal cost of maintenance and
do not require the use of toxic or hazardous chemical. However it must be noted that after
treatment the cell tissue of the microbes has to be removed or else it would constitute a
source of BOD, which implies treatment has not achieved (Micheal 1987; Wesley 1989). The
removal of the cell tissue can be achieved by introducing predators like protozoan and
rotifers to clean up the water before it is discharged. The microorganisms, which treat this
wastewater, like any other living things, grow; and their growth is an indication of the degree
of treatment (Horan 1990).
Exponential growth rate
Bacterial growth is comprised of four phases: lag phase, log-growth phase, stationary
phase, and log-death phase. During the lag-phase, microorganisms acclimate to their new
environment and begin to reproduce. In the log-growth phase, bacterial cells multiply at a
rate determined by their generation time and ability to process the substrate. When the
microorganisms enter the stationary phase, they have exhausted the substrate necessary
for growth, and their population is at a standstill. If no new substrate is added, the
microorganisms begin to die; hence, in the log-death phase, the death rate exceeds the
production of new cells. The death rate is usually a function of the viable population and
environmental characteristics. In some cases, the log-death phase is the inverse of the
log-growth phase (Metcalf and Eddy, Inc. 1991). Moreover, a phenomenon occurs when
the concentration of available substrate is at a minimum: the microorganisms are forced
to metabolize their own protoplasm without replacement. This process, known as lysis,
occurs when dead cells rupture and the remaining nutrients diffuse out to furnish the
remaining cells with food. This type of cell growth is sometimes referred to as cryptic
growth and occurs in the endogenous phase. While bacteria play a primary role in waste
degradation and stabilization, other groups of microorganisms described previously also
take part in waste stabilization. The position and shape of the growth curve, with respect
to time, of a microorganism in a mixed-culture system depend on the available substrate
and nutrients and environmental factors such as temperature, pH, and oxygen
concentrations.
Nutritional Requirements
For microorganisms, nutrients (1) serve as an energy source for cell growth and
biosynthetic reactions, (2) provide the material required for synthesis of cytoplasmic
materials, and (3) serve as acceptors for the electrons released in energy-yielding
reactions. To sustain reproduction and proper function, microorganisms require an energy
source, a carbon source for synthesis of new cellular material, and inorganic nutrients
such as nitrogen, phosphorus, sulfur, potassium, calcium, and magnesium. In addition,
organic nutrients (growth factors) may also be required for cell synthesis. Table below
lists the primary nutritional requirements.
Table 1: Classification of nutrient requirement.
Function
Sources
Energy Source
Organic compounds, inorganic compounds, and sunlight.
Carbon Source
Carbon dioxide, bicarbonate, and organic compounds.
Electron Acceptor
Oxygen, organic compounds, and combined inorganic oxygen
(nitrate, nitrite, sulfate).
The nutritional requirements of microorganisms provide a basis for classification.
Microorganisms are classified on the basis of the form of carbon they require:
Autotrophic: These microorganisms use carbon dioxide or bicarbonate as their sole
source of carbon, from which they construct all their carbon-containing biomolecules.
Heterotrophic: These microorganisms require carbon in the form of complex, reduced
organic compounds, such as glucose.
Temperature Effects
Since microbial growth is controlled mostly by chemical reactions, and the nature and
rate of chemical reactions are affected by temperature, the rate of microbial growth and
total biomass growth are affected by temperature. The microbial growth rate increases
with temperature to a certain maximum where the corresponding temperature is the
optimum temperature (see Figure below). Then, growth does not occur after a small
increase in temperature above the optimum value, followed by a decline in the growth
rate with an increase in temperature beyond the optimum. For example, bacteria can be
divided into three different classes on the basis of their temperature tolerance:
psychrophilic, mesophilic, and thermophilic. Psychrophilic bacteria tolerate temperatures
in the range of 210 to 30°C, with the temperature for optimum growth in the range of 12
to 18°C. The mesophilic group tolerates temperatures in the range of 20 to 50°C, with an
optimum temperature between 25 and 40°C, while thermophilic bacteria survive in a
temperature range of 35 to 75°C and have optimum growth at temperatures in the range
of 55 to 65°C (Metcalf and Eddy, Inc. 1991). In their respective classes, facultative
thermophiles and facultative psychrophiles are bacteria that have optimum temperatures
that extend into the mesophilic range. Optimum temperatures for obligate thermophiles
and obligate psychrophiles are outside the mesophilic range.
pH Effects
Since enzymes are responsible for microorganism activity, pH effects on enzymes
translate to effects on the corresponding microorganism. Some enzymes like acidic
environments, while some like a medium environment and others prefer an alkaline
environment. When the pH increases or decreases beyond the optimum, enzyme activity
decreases until it disappears. For most bacteria, the extremes of the pH range for growth
are 4 and 9, while the optimum pH for growth is within the range of 6.5 to 7.5. Bacteria,
in general, prefer a slightly alkaline environment; in contrast, algae and fungi prefer a
slightly acidic environment. Biological treatment processes, however, rarely operate at
optimum growth. Full-scale, extended-aeration, activated sludge and aerated lagoons can
successfully operate at pH levels between 9 and 10.5; however, both systems are
vulnerable to a pH less than 6 (Benefield and Randall 1980).
QUESTION NO.3
(a)
What are the principal pollutant parameters in a biodegradable wastewater
that can be removed by common biological treatment techniques?
(b)
List all the various biological treatment methods that can be used to
against each of parameters.
ANSWER:
a) Many industries wastewater, the most principles pollutant in biodegradable which
common using by biological treatment technique can divide by several categories
in which are Biochemical Oxygen Demand (BOD),Chemical Oxygen Demand
(COD) and Mixed Liquor Suspended Solid (MLSS).
b) List all the various biological treatment methods that be used to against each the
parameters.
a) The various biological treatment method used in typical waste-treatment
usually conducted during secondary treatment which is Aerobic treatment and
Anaerobic treatment.
In this stage, there are two treatment method are used which is biological
oxidations or anaerobic treatment of soluble and insoluble organic compound.
Organic compounds are oxidized to CO2 and H2O by organism under aerobic
condition. Unoxidized organic compound and solid from aerobic treatment (e.g.
cell wall material, lipids-fat) are decomposed to a mixture of CH4, CO2 and H2S
under anaerobic condition.
QUESTION NO.4
Compare aerobic and anaerobic processes in terms of their advantages and disadvantages
for the treatment of organic wastes. Indicate under what conditions one is likely to choose
each.
ANSWER:
Aerobic Process
Anaerobic process
Organic loading rate:
Organic loading rate:
High loading rates:10-40 kg COD/m3-day Low loading rates: 0.5-1.5 kg COD/m3-day
(for high rate reactors, e.g. AF,UASB, (for activated sludge process).
E/FBR).
Biomass yield:
Biomass yield:
Low biomass yield: 0.05-0.15 kg VSS/kg High biomass yield: 0.35-0.45 kg VSS/kg
COD (biomass yield is not constant but COD (biomass yield is fairly constant
depends
on
types
of
substrates irrespective
of
types
of
substrates
metabolized).
metabolized).
Specific substrate utilization rate:
Specific substrate utilization rate:
High rate: 0.75-1.5 kg COD/kg VSS-day.
Low rate: 0.15-0.75 kg COD/kg VSS-day.
Start-up time:
Start-up time:
Long start-up:
Short start-up: 1-2 weeks
1-2 months for mesophilic.
2-3 months for thermophilic.
Sludge Recovery Treatment (SRT):
Sludge Recovery Treatment (SRT):
Longer SRT is essential to retain the slow SRT of 4-10 days is enough in case of
growing methanogens within the reactor.
activated sludge process.
Microbiology:
Microbiology:
Anaerobic process is multi-step process Aerobic process is mainly a one-species
and diverse group of microorganisms phenomenon.
degrade
the
organic
matter
in
a
sequential order.
Environmental factors:
Environmental factors:
The process is highly susceptible to The process is less susceptible to changes
changes in environmental conditions.
in environmental conditions.
QUESTION NO.5
Compare and contrast the distinctive characteristics of the activated sludge process versus
biofilm processes for organic waste treatment.
ANSWER:
Sludge refers to solids that settle and are removed when a liquid with suspended solids is
passed through a setting tank. There are many types of sludge, depending from which
part of wastewater treatment plant it originates. Therefore sludge has its own
characteristics, for instance solids concentration and ease of biodegradation. So forth,
waste activated sludge is excess sludge that is produced from the activated sludge process.
In other word, the secondary treatment of waste involves removing the `leftovers’ from
primary treatment. Whereby primary treatment of wastewater merely removes the solids
originally suspended in that waste. These leftovers are composed of colloidal and
dissolved organic matters. Since theirs forms are colloidal and dissolved, they can no
longer be removed by simple sedimentation. They must be transformed into solids that
can then easily be settled. This transformation involves feeding them to microorganisms,
mostly bacteria. As the bacteria feed on the colloidal and dissolved organic matters, they
grow and multiply, thus converting those which were once colloidal into solids that are
capable of settling.
In the practical application, microorganisms are either suspended or attached. The
activated sludge system and ponds and lagoons are examples of a suspended-culture
system, while trickling filters, bio towers, and rotating biological contactor are examples
of an attached-culture system.
QUESTION NO.6
An extended aeration plant consists of three oxidation ditches without primary
clarification. Each ditch has a volume of 2.0 million gallon. The average annual flow is
6.0 MGD and the BOD is 260 mg/L. The MLSS is maintained by wasting at 2200 mg/L.
Calculate the liquid detention time, BOD loading and F/M ratio.
ANSWER:
Flow rate, Q: 6.0 MGD = 6.0 Mil gallon per day.
Ditch Volume, V = 2.0 Mil gallon (3 ditches)
MLSS = 2200 mg/L
BOD = 260 mg/L
Liquid detention time, HRT = V/Q
= (2.0 Mil Gal x 3)/ 6.0 Mil Gal per day
= 1 day.
BOD loading = BOD x Q
= 260 mg/L x 6.0 MGD
= 260 mg/L x (6.0 Mil Gallon/day) x (3.785 L/1 Gallon)
= 59046 kg/day
F/M ratio
= BOD/MLSS
= (260 mg/L) / (2200 mg/L)
= 0.1182 mg BOD day per mg MLSS