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Anaerobic Digestion Presentazione Si
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Transcript of Anaerobic Digestion Presentazione Si
ANAEROBIC DIGESTION
ANAEROBIC DIGESTION
Anaerobic digestion is a series of microbiological processes that convert
organic compounds to methane. Anaerobic digestion con take place only
in an air tight chamber kept at a temperature not lower than 20° C. The maximum temperature for a digester is 65°C: such a high temperature reduces
processing time and digester dimensions, but the digestion is more prone to upset,
so it requires close control.
The digestion takes place thanks to four different types of bacteria which operated at
different stages of the digestion process:
HYDROLYTIC BACTERIA
The hydrolytic bacteria break down complex organic waste into sugars and amino acids.
Hydrolytic bacteria form a variety of reduced end-products from the fermentation of a given substrate. One fundamental question which arises, concerns the metabolic
features which control carbon and electron flow to a given reduced end-
product during pure culture, and mixed methanogenic cultures of
hydrolytic bacteria.
FERMENTATIVE BACTERIA The fermentative bacteria turn sugars
and amino acids into organic acids.
Fermentation bacteria are anaerobic, but use organic molecules as their final
electron acceptor to produce fermentation end-products. Bacteria
are a large group of unicellular or multi-cellular organisms which can
tolerate different temperatures. While most bacteria have a temperature
optimum of between 20 to 30ºC, there are some which prefer higher
temperatures (50 to 55ºC) and those with colder temperature optima (15 to
20ºC).
ACIDOGENIC MICRO ORGANISMS
The acidogenic micro organism converted organic acids into hydrogen, carbon dioxide and acetic acid.
Acidogenesis is a biological reaction where simple monomers are
converted into volatile fatty acids ; is one of the main reactions of this stage, in this, the intermediary
metabolites produced are metabolized to acetate, hydrogen and carbonic gas by the groups of
bacteria.
METHANOGENIC BACTERIA
Produce biogas from acetic acid, carbon dioxide and acetate.
Methanogens are microorganisms that produce methane as a
metabolic byproduct in anoxic conditions. They are common in
wetlands, where they are responsible for marsh gas, and in the guts of animals such as ruminants and
humans, where they are responsible for the methane content of
flatulence.
There a three traditional main types of digester , and more recently developed one which is promising but not yet largery tested:
- They have different building;- Operating and maintaining cost;- Each one can digester manure with a
specific total solid content.
COVERED LAGOON
It consist of a manure storage lagoon with an air-tight impermeable floating cover of industrial fabric that traps the gas produced during decomposition of the manure and a suction pipe which extracts the gas for use.
Heating the waste reduces retention time to less than 20 days. It can be used for large manure volumes with concentration of solids from 3% to 10%.
PLUG-FLOW
Plug Flow is a simple model of the velocity profile of a fluid flowing in a pipe. In plug flow, the velocity of the fluid is assumed to be constant across any cross-section of the pipe perpendicular to the axis of the pipe. The plug flow model assumes there is no boundar layer adjacent to the inner wall of the pipe.
The manure remeins in the digester for 20-30 days.
It is mosty used for ruminant manure which contains a solid concentration of 11% to 13%.
TPAD
Temperature-phased anaerobic digester (TPAD) has a potential to enhance digestion of the lignocellulose present in the solids and improve biogas production.
It consist of a two-staged reactor, which first operates at a high
temperature (57°C), then at a lower temperature (35° C) in order to
optimize methane recovery from the manure by enhancing the digestion
of lignocellulosic solids -50% of them usually passes thorough anaerobic
digester undigested.
Anaerobic digester is very important because produce methane for industrial purposes is an effective , reduce greenhause gases, global warming, good for enviromental and
producing energy from waste.