Anaerobic digestion to biogas renewable energy resources def

RENEWABLE ENERGY RESOURCES
Lecture # 22
Presented by:
Dr. Bilal Ahmad Zafar Amin
Anaerobic Digestion (AD) od Biomass to Biogas
Solar Energy
Wind Energy
Biomass Energy
Thermal Energy
Renewable
Resources
Oil
Coal
Natural Gas
Nuclear
Non-Renewable
Resources

Week # 12, Lecture # 2 Renewable Energy Resources
 Biomass waste potential of Pakistan
 Mechanism and composition of Biogas by Anaerobic Digestion (AD)
 Types of anaerobic digestion system
 AD Technologies used globally
 Commonly usedAD technologies
 Classification of biogas plants
 Visual presentation of AD technologies
 Research article regarding AD technologies and implications
Lecture Outlines:

 Pakistan generates about 20 million tons of solid waste a year, which has been increasing
more than 2 percent annually.
 The Government of Pakistan (GOP) estimates that 71,000 tons of solid waste is
generated per day, mostly from major metropolitan areas.
 Karachi, Pakistan’s largest city generates more than 9,000 tons of municipal waste daily.
 Solid waste generation in Pakistan ranges between 0.283 to 0.612 kg/capita/day and the
waste generation growth rate is 2.4% per year.
 The most common types of solid waste in Pakistan are:
 Municipal solid waste
 Agricultural waste
 Industrial waste
 Hazardous waste
Biomass waste potential of Pakistan

Mechanism of AD biomass conversion to energy

Typical composition of Biogas by AD

Classification
Methods
Loading Schedule
Flow Pattern
Mixing
Temperature Regime
HRT SRT
Batch Continuous
No Mixing Complete
Mix
Mesophilic Thermophilic
There are many types of AD Systems depending on different classification methods as highlighted
on this page
Types of AD Systems

Hydraulic Retention Time (HRT)
Solid Retention Time (SRT)
The hydraulic retention time (HRT) is the amount
of time in hours for waste water to pass through a
tank, such as aeration tank.
It can be determined by dividing the volume of
aeration tank in million gallons by the flow rate
through the aeration tank. The flow rate must be
expressed as gallons per hour (gph)
HRT = Volume of aeration tank, (gal)
Flow rate (gph)
Solid retention time is the amount of time in days
that solid or bacteria are maintained in the activated
sludge system. To calculate SRT of an activated
sludge, it is necessary to know the amount of solids
(pounds) or suspended solids and the amount of
suspended solids leaving the activated sludge
system
SRT = Suspended solids in the system (pounds)
Suspended solids leaving system per day

AD Technologies Used Globally
Liquid Anaerobic Digestion
High Solids Anaerobic Digestion
Plug Flow Anaerobic Digestion
High Rate Anaerobic Digestion
Co-digestion
Micro Anaerobic Digestion

Sources: Biogas World, Wales AD Centre
 Designed to process a dilute organic slurry with typically
<15% total solids
 Successful track record in treating low solid materials
such as sewage sludges and food industry effluents
 Require comparatively larger digesters, more and greater
capacity water pumping and piping/valving, more
extensive digestate storage and / or de-watering, higher
capacity wastewater treatment facilities and more energy
required to heat the larger volumes
 Providing that the above points are considered at the
design stage, a wet system can provide an effective and
robust means of treating low solid content waste, or high
solid waste that has been adjusted to <15% total solid
content
Liquid Anaerobic Digestion
17
Companies offering
Liquid AD

 High-solids systems can handle up to 35 percent solids,
which could be some materials other than organics,
though at a minimum.
 Successful track record in treating low solid materials
such as sewage, sludge and food industry effluents
 More expensive than liquid digestive systems
 Municipalities and waste haulers tend to select this
system type because of a higher solid, higher
contaminant mix
High SolidsAnaerobic Digestion
Companies offering High
Solids AD Systems

 It can be considered a type of high solids anaerobic
digester - it can handle greater amounts of solids than
both a covered lagoon and a complete mix digester
 Total solid content of input should be at least 15% to as
high as 20%
 The contents within the plug flow digester are thick
enough to keep particles from settling to the bottom of
the tank
 Plug flow digesters do not require mechanical mixing as
in other types of digesters
 Hydraulic retention times are generally in the 15 days to
21 day time-frame
Plug Flow Anaerobic Digestion
Companies offering Plug
Flow AD

 System where liquids stay in the digester for a short
period of time; where-as, solids are held longer. This
allows for a smaller reactor size, while maintain high gas
production
 Decouples the hydraulic retention time (HRT) from the
solids retention time (SRT)
 Methane-forming microorganisms are trapped in the
digester to increase efficiency
 High rate systems are more commonly used and are
characterized by supplemental heating, auxiliary
mixing, uniform feeding rates, and sludge thickening
before digestion
High Rate Anaerobic Digestion
Companies offering High
Rate AD

 Micro anaerobic digesters can be applied to anywhere
where there is a need and benefit for AD but a full-sized
system wouldn’t be appropriate because of cost and
footprint constraints
 It is generally anticipated that micro scale biogas plants
are on farm installations using only own (waste) biomass
resources, where livestock manure is a main source
 Micro-scale digestion involves the production of biogas,
but on a small scale within farms
 The small-scale digestion production units are below 80
kW
Micro Anaerobic Digestion
Companies offering Micro
AD

 Co-digestion is the simultaneous digestion of a
homogenous mixture of two or more substrates.
Traditionally, anaerobic digestion was a single
substrate, single purpose treatment
 The most common situation is when a major amount of
a main basic substrate (e.g. manure or sewage sludge)
is mixed and digested together with minor amounts of a
single, or a variety of additional substrate
 The use of co-substrates usually improves the biogas
yields from anaerobic digester due to positive
synergisms established in the digestion medium and the
supply of missing nutrients by the co- substrates
Co-digestion Anaerobic Digestion
Companies offering Co-
digestion AD

Following factors must be considered while selecting the site for a
biogas plant:
1.Distance
2.Minimum gradient
3.Open space
4.Water table
5.Seasonal run off
6.Distance from wells
7.Space requirements
8.Availability of water
9.Sources of cow dung/materials for biogas generation
Site selection

Complete Mixed Reactors
Mixed Plug Flow Reactors
Covered Lagoons
Up-flow Anaerobic Sludge Blanket
Sequential Batch Reactor
Fixed FilmAnaerobic Digester
Commonly UsedAD Technologies

Schematic of an anaerobic digester as part of a sanitation system.
It produces a digested slurry (digestate) that can be used as a fertilizer, and biogas that can
be used for energy.

Classification of Biogas Plants:
Biogas plants are mainly classified as:
1.Continuous and batch type(as per the process)
a)Single stage process
b)Double stage process
2. The dome and drum type
3. Different variation in the drum type

Schematic diagram of Single stage and Double
stage Continuous Plant:

Continued…
The main features of continuous plant are as
follows:
1.It will produce gas continuously.
2.It require small digestion chambers.
3.It needs smaller period of digestion.
4.It has less problem compared to batch type and
it is easier in operation.

The main features of Batch type plant are:
1.The gas production is intermittent, depending upon the
clearing of the digester.
2.It needs several digesters or chambers for continuous gas
production, these are fed alternately.
3.Batch plants are good for long fibrous materials.
4.This plant needs addition of fermented slurry to start the
digestion process.
5.This plant is expensive and has problems comparatively, the
continuous plant will have less problems and will be easy for
operation.

The Dome and the Drum Type
Mainly two types of biogas plants are normally used:
1.The floating gas holder plant (Also known as KVIC plant)and
other is :
2.Fixed dome digester. (Also known as Chinese Plant)
In a floating gas holder, gas holder is separated from the digester.
While in fixed dome digester, the gas holder and the digester are
combined.
The fixed dome is best suited for batch process especially when
daily feeding is adopted in small quantities.
The fixed dome type plant is generally built below the ground level
and is suitable for cooler regions.

Floating Drum plants

Floating-drum plants consist of a digester and a
moving gasholder.
The gasholder floats either direct on the
fermentation slurry or in a water jacket of its own.
The gas collects in the gas drum, which thereby
rises.
If gas is drawn off, it falls again. The gas drum is
prevented from tilting by a guide frame.

Advantages
• High gas yield.
• No problem of gas leakage.
• Works under constant pressure naturally.
• No problem of mixing of biogas
with external air, thus no danger of explosion.
• It has higher cost.
• Heat is lost through metal gas holder.
• Requires painting of drums to avoid corrosion
at least twice a year.
• Requires maintenance of pipes and joints.
Disadvantages

A fixed-dome plant consists of an enclosed digester
with a fixed, non-movable gas space. The gas is
stored in the upper part of the digester.
When gas production commences, the slurry is
displaced into the compensating tank.
Gas pressure increases with the volume of gas
stored; therefore the volume of the digester should
not exceed 20 m³. If there is little gas in the holder,
the gas pressure is low.

Advantages
 Cost of plant is less compare to floating drum
type plant.
 Loss of heat is negligible since these are
constructed underground.
 No corrosion problems as in fixed dome
type. It is maintenance free.

Disadvantages
 Needs skilled labour to operate.
 Gas production per m3 of digester volume is
less. Gas is produced at variable pressure.

Different variations in the drum type
There are mainly two variation in floating type plant. One
with water seal and other without water seal.
Water sealing makes the plant completely anaerobic.
Cylindrical shape of the digester is preferred because cylinder
has no corners and so that there will be no chances of cracks
due to faulty construction. This shape also needs smaller
surface area per unit volume, which reduces heat losses also.
Moreover the scum formation may be reduced by rotating gas
holder in the cylindrical digester.

Anaerobic digestion to biogas renewable energy resources def

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Anaerobic digestion to biogas renewable energy resources def

Similar to Anaerobic digestion to biogas renewable energy resources def (20)

More from DrBilalAhmadZafarAmi

More from DrBilalAhmadZafarAmi (10)

Recently uploaded

Recently uploaded (20)

Anaerobic digestion to biogas renewable energy resources def