Anaerobic Digestion Flashcards
What is anaerobic digestion of MSW?
Microorganisms break down organic matter, in the absence of oxygen, into biogas (a mixture of CH4 and CO2) and digestate.
Can you draw a diagram showing the anaerobic digestion process?
1) Slurry & Manure, Food and amenity waste, Crops and residues.
2) Anaerobic digester > Digestate and biogas
3) Biogas > heat, biomethane and power.
4) Biomethane > transport fuel, gas grid
What are the three key stages of AD?
Pre-treatment, digestive process, by-products
What does the first key stage of AD consist of?
1) Mixes different feedstocks - adds water and removes undesirables. 2) Better digestate quality - efficiency. 3) Necessary - specific products desired and suited to digester type.
What does the second key stage of AD consist of?
1) Digester classified by temp, water content and stage number. 2)i) Single stage wet systems, ii) single stage dry system, iii) two-stage systems, and iv) batch systems.
What does the third key stage of AD consist of?
1) Biogas and digestate can be used for income - need to be upgraded for use.
2) Biogas used in CHP for electricity and heat - needs H20 removed as it damages the boilers.
3) Digestate used as fertiliser or compost.
4) Biogas = 55-70% CH4.
How can digestate be used as compost?
1) Has the ability to improve the humus balance in a soil and contains beneficial nutrients for plant growth.
2) Properties differ to compost and therefore its efficiency is different.
3) Often combined with compost to add value to the digestate.
What operating parameters must be controlled for AD?
Soild content, temperature, retention time, carbon:nitrogen ratio, pH, mixing and organic loading rate/volatile solids.
What are the advantages of AD?
1) Mass reduction of waste (70-90%) and maximises methane production without releasing it into the atmosphere.
2) Source of energy with no net increase of carbon in atmosphere (doesn’t add to GHGs).
3) Feedstock is renewable.
4) Energy generated reduces fossil fuel demand.
5) Use of the digestate decreases synthetic fuels used in fertiliser manufacturing
(an energy intensive process).
6) Residues sellable: biogas, soil conditioner and liquid fertiliser.
What are the disadvantages of AD?
1) Creates some risk and potential negative environmental impacts. 2) AD plants have big capital and running costs, i) 10-20% more than aerobic composting, ii) best of all by-products are sold.
3) Potential human health risk from pathogens in feedstock.
4) Visual impact.
What is Harry Foreman?
A cunt
