1. AEROBIC AND ANAEROBIC DIGESTERS
DEPARTMENT OF MICROBIOLOGY
SUBJECT: BIOREMEDIATION
VIVEKANANDHA ARTS AND SCIENCE COLLEGE FOR WOMEN,
VEERACHIPALAYAM,SANKARI,SALEM, TAMILNADU.
PRESENTED BY,
P.DEVADHARSHINI,
| M.SC MICROBIOLOGY.
PAPER IMCHARGE,
Dr.R.DINESHKUMAR,
ASSISTANT PROFESSOR,
DEPARTMENT OF MICROBIOLOGY.
2. AEROBIC DIGESTERS :
• Aerobic digestion is a process in sewage treatment designed to reduce the volume of
sewage sludge and make it suitablefor subsequentuse.
• More recently, technology has been developed that allows the treatment and reduction
of otherorganic waste, such as food, cardboardand horticulturalwaste.
• It is a bacterial process occurring in the presence of oxygen. Bacteria rapidly consume
organic matter and convert it into carbon dioxide, water and a range of lower molecular
weight organic compounds.
• As there is no new supply of organic material from sewage, the activated sludge biota
begin to die and are used as food by saprotrophicbacteria.
• This stage of the process is known as endogenousrespiration and it is process that
reduces the solid concentrationin the sludge.
4. PROCESS OFAEROBIC DIGESTERS:
• Aerobic digestion is typically used in on activated sludge treatment plant.
• Waste activated sludge and primary sludge are combined, where appropriated, and passed to a thickener where the
solids content is increased.
• This substantially reduces the volume that is required to be treated in the digester.
• The process is usually run as a butch process with more than one digester tank in operation of any one time
• Air is pumped through the tank and the contents are stirred to keep the contents fully mixed. Carbon
• dioxide, waste air and small quantities of other gases including hydrogen sulfide are given off. These waste gases
require treatment to reduce odours in works close to housing or capable of generating public nuisance.
• The digestion is continued until the percentage of degradable solids is reduced to between 20% and 10% depending
on local conditions.
• Where non se wage waste is being processed, organic waste such as food, cardboard and horticultural waste can be
significantly reduced in volume leaving an output that can be used as soll improver or biomass fuel.
7. ADVANTAGES OFAEROBIC DIGESTER:
• Aerobic digestion occurs much faster than anaerobic digestion.
• The process is usually run at ambient temperature and the process is much less complex and easier to
manage than anaerobic digestion.
• Aerobic treatment usually yields better
• effluent quality that that obtained in anaerobic processes.
• The aerobic pathway also releases a substantial amount of energy.
• A portion is used by the microorganisms for synthesis and growth of new microorganisms.
8. DISADVANTAGES OF AEROBIC DIGESTERS:
• The operatingcosts are typically much greater for aerobic digestion than for anaerobic
digestion because of energy used by the blowers, pumps and motors needed to add oxygen to
the process.
• However, recent technological advances includenon-electricallyaerated filter systems that
use natural air currents for the aeration instead of electricallyoperated machinery.
• The digested sludge is relatively low in residual energy and although it can be dried and
incinerated to produceheat, the energy yield is very much lower than that produced by
anaerobicdigestion.
9. ANAEROBIC DIGESTERS:
• Anaerobic digestion, or mechanization, uses the process of fermentation to break down
organic matter from animals, plantsor sewage to producebiogas.
• The process takes place within a centralized system in a unit called an anaerobicdigester,
also known as a biogas reactor or a biodigester.
• A digester is a tank, whose size and appearancevaries considerablydependingon what it
is used for.
• A householddigester for a single family can have a volume of less than one cubic meter,
whereas an industrial-scaleunit can easily surpass 5,000 cubic meters.
• A digester on a farm or a ranch typically has a capacity of a few dozen cubic meters.
10.
11. PROCESS OFANAEROBIC DIGESTERS:
• Many microorganisms affect anaerobic digestion, including acetic acid-forming bacteria (acetones and
methane- forming archon (methanogens)
• These organisms promote a member of chemical processes in converting the biomass to biogas
Gaseous oxygen is excluded from the reaction by physical containment.
• Anaerobes utilize electron acceptors from sources other than oxygen gas
• These acceptors con be the organic material or may be supplied by inorganic oxides from within the
input material.
• When the oxygen source in an anaerobic system is derived from the organic material itself, the
“Intermediate end products are primarily alcohols, aldehydes, and organic acids, plus carbon dioxide.
• In the presence of specialized methanogens, the intermediates ore converted to the final end products of
methane,
12. PROCESS STAGES:
• The four key stages of anaerobic digestion involve,
• hydrolysis
• acidogenesis
• acetogenesis
• methanogenesis
• The overall process can be described by the chemical reaction, where organic
• material such as glucose is biochemically digested into carbon dioxide (CO2) and methane (CH4) by
the anaerobic microorganism.
• C6H12O6 3CO2 + 3CH4
13. HYDROLYSIS :
Hydrolysis is the first step of anaerobic digestion in which insoluble complex
molecules such as carbohydrates and fats are broken down to short sugars, fatty
acids and amino acids.
Fermentation:
Fermentation is the second step of anaerobic digestion. Fermentative bacteria
transform sugars and other monomeric organic products from hydrolysis into organic
acids, alcohols, carbon dioxide (CO2), hydrogen (H) and ammonia (NH3).
14. ACETOGENESIS:
Acetogenesis is the third step of anaerobic digestion. Products from fermentation (organic acids,
alcohols) are converted into hydrogen (H2), carbon dioxide (CO2) and acetic acid (CH3COOH). To produce
acetic acid, acetogenic bacteria need oxygen and carbon.
METHANOGENESIS:
Methanogenesis is the fourth and final step of anaerobic digestion. Methanogenic bacteria
(methanogens), which are strictly anaerobic, transform the acetic acid (acetate), carbon dioxide and hydrogen
into a mixture of methane and carbon dioxide (biogas)
17. ADVANTAGES OFANAEROBIC DIGESTERS:
• Almost any organic material can be processed with anaerobicdigestion.
• This includesbiodegradablewaste materials such as waste paper, grass clippings, leftover
food, sewage and animal waste.
• The exception to this is woody wastes that are largely unaffected by digestion as most
anaerobesare unableto degrade lignin found in wood.
• Stabilizationin the absence of oxygen
• Pathogen reduction
• Reductionin mass
• Productionof methane
18. DISADVANTAGES OF ANAEROBIC DIGESTERS:
• Longer start-up time to develop necessary biomass inventory
• May require alkalinity and/orspecific ion addition
• May require further treatment with an aerobic treatment process to
• meet discharge requirements
• Biological nitrogen and phosphorusremoval is not possible
• Much more sensitive to the adverse effect of lower temperatureson reaction rates
• May need heating (often by utilization of process gas) to achieve adequatereaction rates
• May be more less stable after ‘toxic shock’ (eg after upsets due to toxic substances in the
feed)
• Increased potential for productionof odors and corrosive gases.
• Hazards arise from explosion..
19. VARIOUS TYPES OF DIGESTER:
• Wet Digesters
• Dry Digesters
• Stand Alone-Digesters
• On- Farm Digesters
Wet Digesters: Wet digesters are more common that dry. A wet digester or low solids AD system generally
processes feedstock with less than 15 percent solids content. The feed stocks for a wet digester are typically in
slurry form and can be pumped.
Types:
• Conventional digesters
• Sludge retention digesters
• Fixed films digesters
20. Dry digesters: A dry digester or a high solids AD system generally processes feedstock with greater than
15 percent solids content. The feed stocks for a dry digester are often described as stackable.
Types:
• Continuous dry digesters
• Batch dry digesters
• Large-scale dry digesters
On- Farm Digester Wet Digester
21. INDUSTRIAL EFFLUENTS
It is caused by emission of industrial waste (effluent) into water bodies. It is main source
of water pollution.Industrial waste includesorganic pollutantstoxic chemical that is
heavy metals, acid and alkalis, Oils, lubricant, petroland grease.
Types of Industries:
Followingare some major types of industries responsiblefor industrial effluents.
• Food industry
• Organic chemical industry
• Iron and steel industry
• Offshore drilling
22. FOOD INDUSTRY
• Vegetable washing-generate waste water with increased particulate matter
• Animal processing waste water generate with-added antibiotics, pesticides
23. ORGANIC CHEMICAL INDUSTRY:
These industries manufacture or use, complex organic chemicals which
includes pesticides, paints, detergents, plastics etc.
24. IRON AND STEEL INDUSTRY:
Conservation of iron to steel, contaminates waste water with hydraulic oils.
