Technical Background Small Scale Biogas production

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Information about Technical Background Small Scale Biogas production
Education

Published on October 8, 2009

Author: RembrandtK

Source: slideshare.net

Description

Presentation by Iemke Bisschops of Lettinga Associates Foundation (LeAF) held at the biogas information seminar in Wageningen the Netherlands, 4 October 2009, organized by the Wageningen Environmental Platform & the Community Composting Network

Technical background on small scale anaerobic digestion of food waste Iemke Bisschops, Els Schuman, Kasia Kujawa, Henri Spanjers

Anaerobic digestion

Anaerobic digestion

What is anaerobic digestion A chain of biological processes Carried out by different groups of microorganisms In absence of oxygen Products: biogas and digestate Different digester configurations are employed depending on substrate and local conditions/preferences

A chain of biological processes

Carried out by different groups of microorganisms

In absence of oxygen

Products: biogas and digestate

Different digester configurations are employed

depending on substrate and local conditions/preferences

Types of digesters Completely mixed Plug flow Batch Fed-batch Percolation systems (type of batch system)

Completely mixed

Plug flow

Batch

Fed-batch

Percolation systems (type of batch system)

Slurry digestion Digestion of animal manure is the most widespread AD application worldwide. It produces: Valuable fertiliser Biogas Farm-scale digestion plants widespread use throughout the world plants in both developing and technically advanced countries

Digestion of animal manure is the most widespread AD application worldwide. It produces:

Valuable fertiliser

Biogas

Farm-scale digestion plants

widespread use throughout the world

plants in both developing and technically advanced countries

Digesters Rural communities: typically small-scale units Nepal 50,000 digesters; China > 8 million. These small plants are generally used for providing gas for cooking and lighting for a single household. (images references in CCN phase 1 report)

Rural communities: typically small-scale units

Nepal 50,000 digesters; China > 8 million.

These small plants are generally used for providing gas for cooking and lighting for a single household.

Digesters Western countries: normally medium- to large-scale Germany, Austria and Switzerland are leading countries Farm-scale digesters: Germany > 2000; Austria ~ 120; Switzerland > 70.

Western countries: normally medium- to large-scale

Germany, Austria and Switzerland are leading countries

Farm-scale digesters: Germany > 2000; Austria ~ 120; Switzerland > 70.

AD systems - Suitability Small plants used in developing countries seem attractive from engineering point of view relatively simple design, construction, operation Not suitable for use in Western Europe Regulations to meet Temperature too low At low temperature Very large systems needed And/or heating

Small plants used in developing countries seem attractive from engineering point of view

relatively simple design, construction, operation

Not suitable for use in

Western Europe

Regulations to meet

Temperature too low

At low temperature

Very large systems needed

And/or heating

AD systems - Suitability Current systems used for AD of organic solid waste Large to very large scale systems Usually batch systems with percolation & recycling of leachate Percolation systems not suitable for very small scale Technically too difficult Moving parts, risk of clogging,… Slurry digester seems most feasible option Technically quite simple Experience exists at small scale

Current systems used for AD of organic solid waste

Large to very large scale systems

Usually batch systems with percolation & recycling of leachate

Percolation systems not suitable for very small scale

Technically too difficult

Moving parts, risk of clogging,…

Slurry digester seems most feasible option

Technically quite simple

Experience exists at small scale

Small scale AD interest growing http://www.patervis.com/sintex.html

http://www.patervis.com/sintex.html

Anaerobic digestion of food waste

Anaerobic digestion of food waste

Food waste Main substrate considered in project with CCN Weekly production on average 3 kg per household Complex substrate carbohydrates proteins lipids nutrients, minerals Usually very concentrated and highly degradable

Main substrate considered in project with CCN

Weekly production on average 3 kg per household

Complex substrate

carbohydrates

proteins

lipids

nutrients, minerals

Usually very concentrated

and highly degradable

Anaerobic Conversion of Organic Matter CH 4 / CO 2 Methanogenesis Acetogenesis Suspended, colloidal organic matter Hydrolysis Acidogenesis volatile fatty acids alcohol H 2 / CO 2 acetic acid proteins carbohydrates lipids amino acids sugars free fatty acids glycerol ammonia

Biological stability - Acidification Overloading may lead to process deterioration – A vicious circle Overloading Methanogenic capacity exceeded Poor buffering capacity VFA increase pH decrease Unionised VFA increase Methanogenic toxicity increase

Overloading may lead to process deterioration –

A vicious circle

Biological stability - Acidification 50% inhibition by acetic acid Methanogenic capacity exceeded Poor buffering capacity VFA increase pH decrease Unionised VFA increase Methanogenic toxicity increase 30000 8 3000 7 300 6 30 5 Concentration (mg/l) pH

Food waste as AD substrate Characteristics of reactor feed and as a result the reactor performance depend on: composition particle size storage time Fast acidification, already starting during storage Acidification continues inside reactor Careful process operation is essential

Characteristics of reactor feed and as a result the reactor performance depend on:

composition

particle size

storage time

Fast acidification, already starting during storage

Acidification continues inside reactor

Careful process operation is essential

Food waste as AD substrate In principle suitable substrate for AD Challenging for a small system without advanced monitoring and control But: Normally contains waste from animal origin -> regulatory barriers

In principle suitable substrate for AD

Challenging for a small system without advanced monitoring and control

But:

Normally contains waste from

animal origin

-> regulatory barriers

Examples of regulations Animal by-product regulation (ABPR) Environmental permitting rules Planning regulations Regulations for fertiliser use Rules on gas safety etc… Important factor!

Animal by-product regulation (ABPR)

Environmental permitting rules

Planning regulations

Regulations for fertiliser use

Rules on gas safety

etc…

Important factor!

Legislation - ABPR Animal by-product regulation (ABPR) regulates all waste from animal origin including kitchen waste Classified as “category 3 catering waste” Hygienisation of kitchen waste necessary Treatment standards for category 3 catering waste: minimum 57°C for 5 hours, maximum particle size 50 mm 70°C for 1 hour, maximum particle size 60 mm

Animal by-product regulation (ABPR) regulates all waste from animal origin including kitchen waste

Classified as “category 3 catering waste”

Hygienisation of kitchen waste necessary

Treatment standards for category 3 catering waste:

minimum 57°C for 5 hours, maximum particle size 50 mm

70°C for 1 hour, maximum particle size 60 mm

Digestate Organic nitrogen is converted into ammonia Directly available to crops Possibly higher ammonia emissions from the field Reduced viability of pathogens and weed seeds Legislation Important to ensure safe use Probably largest barrier Quality protocols e.g. UK: “Quality Protocol for the Production and Use of Quality Compost from Source-Segregated Biowaste” Defines the point at which the material ceases to be a waste and instead becomes a product.

Organic nitrogen is converted into ammonia

Directly available to crops

Possibly higher ammonia emissions from the field

Reduced viability of pathogens and weed seeds

Legislation

Important to ensure safe use

Probably largest barrier

Quality protocols

e.g. UK: “Quality Protocol for the Production and Use of Quality Compost from Source-Segregated Biowaste”

Defines the point at which the material ceases to be a waste and instead becomes a product.

Digestate use – Practical When all regulations are complied with, the digestate can be used as fertiliser It should be worked into the soil to prevent ammonia emissions Separation in liquid and solid fraction Solid fraction can be composted together with green waste (might be more attractive) Liquid fraction can be used as liquid fertiliser Will still contain solids and salts, this might limit its application in drip systems.

When all regulations are complied with, the digestate can be used as fertiliser

It should be worked into the soil to prevent ammonia emissions

Separation in liquid and solid fraction

Solid fraction can be composted together with green waste (might be more attractive)

Liquid fraction can be used as liquid fertiliser

Will still contain solids and salts, this might limit its application in drip systems.

Biogas Composition (most important compounds) Methane Carbon dioxide Hydrogen sulphide Examples of uses: Heating Steam production CHP: electricity and heat Transport fuel (e.g. car, lift truck, city busses) Supply to normal natural gas network (so called Green Gas) End use determines the needed gas quality

Composition (most important compounds)

Methane

Carbon dioxide

Hydrogen sulphide

Examples of uses:

Heating

Steam production

CHP: electricity and heat

Transport fuel (e.g. car, lift truck, city busses)

Supply to normal natural gas network (so called Green Gas)

End use determines the needed gas quality

Biogas use on small scale In developing countries very common, e.g. cooking and lighting In Western Europe not common gas quality upgrading normally necessary economy of scale But: starting to gain interest

In developing countries very common, e.g. cooking and lighting

In Western Europe not common

gas quality upgrading normally necessary

economy of scale

But: starting to gain interest

Proposed system concept for CCN project

Proposed system concept

for CCN project

Summary of system criteria Digester volume fixed at 1 m 3 Amount of waste will be made to fit system size Robust and easy to build Steel and plastic as preferred building materials Focus on kitchen waste as a substrate

Digester volume fixed at 1 m 3

Amount of waste will be made to fit system size

Robust and easy to build

Steel and plastic as preferred building materials

Focus on kitchen waste as a substrate

Process design Biodegradability Hydrolysis rate of substrates ( particle size!) Applied conditions Temperature (mesophilic / thermophilic) Retention time Presence of toxic or inhibitory compounds All combined determine overall process performance Stability of process and products Biogas production

Biodegradability

Hydrolysis rate of substrates ( particle size!)

Applied conditions

Temperature (mesophilic / thermophilic)

Retention time

Presence of toxic or inhibitory compounds

All combined determine overall process performance

Stability of process and products

Biogas production

Proposed system concept Simplified process flow diagram, not to scale. Dashed connecting lines: slurry/liquid flow could be done manually

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