Organic Waste Bio-Methanisation
Why Treat Waste Using Bio-methanisation?
The main benefits of organic waste bio-methanisation are:
| • |
It is a net energy producing process |
| • |
It eliminates odours |
| • |
It produces sanitised compost that is nutrient rich |
| • |
It recycles carbon back into the soil |
| • |
It maximizes recycling benefits |
| • |
It provides a source of carbon credits |
What Types of Waste Can Be Treated by Bio-Methanisation?
Generally any waste that is organic in nature, including:
| • |
Food waste |
| • |
Green waste like grass clippings and leaves |
| • |
Animal manure |
| • |
Industrial organic sludge |
How is it Different from Open-Air Composting?
Open-air composting requires large tracts of land and noxious odours are released from the compost piles if it is not turned frequently enough. On the other hand, with bio-methanisation a smaller plant footprint is required and any noxious odours are contained within the digester vessel.
IUT's Organic Waste Bio-Methanisation Solution - Anaerobic Treatment Using the ADOS Process
ADOS stands for “Anaerobic Digestion of Organic Slurry”, with the name itself strongly reflecting the special nature of IUT’s waste bio-methanisation process.
The ADOS process is positioned between the so-called “wet” and “dry” digestion processes. This allows the ADOS process to exploit both the benefits of the “wet” and “dry” processes, including:
| • |
Maximum purity of digestate in the digestion process |
| • |
Insensitivity to variances in feedstock composition |
| • |
Thermophilic operating temperatures |
| • |
A very simple digester design that avoids the risk of clogging or foaming |
| • |
A process which is adaptable to different water contents during operation |
| • |
A variety of feedstock that can be composted without waste water emissions |
| • |
Simple and effective automated PLC control |
| • |
A high bio-gas yield |
| • |
Economical solution, even with small throughputs |
|
|
The ADOS process is carried out in four main stages:
STAGE 1: MECHANICAL TREATMENT
 |
Organic waste from households, restaurants and food courts, agriculture, commerce and industry is treated as needed in a mechanical segregation system, and the organic fraction is concentrated. Recyclables and undesirable/inorganic materials are removed to a large extent. |
STAGE 2: ADOS MILLING
The heart of the ADOS process is the ADOS mill, a patented wet mill performing a size reduction of organic solids while also effectively removing the reminent of inorganics and inerts (sand, metals, glass, plastics, etc.) prior to introduction into the digestor.
The segregation efficiency and performance of this robust machine can be varied during operation as required and can thus be easily adapted to different types of organic waste streams and impurities.
STAGE 3: ANAEROBIC DIGESTION
 |
The product discharged from the ADOS mill is an organic “slurry”. This slurry is pumped into a buffer silo, the sole function of which is to homogenise the stream of feedstock material before entering the digester and thus maximise bio-gas production during digestion.
Within the digestor, the decomposition and digestion process occurs at a temperature of between 52°C - 55ºC, under thermophilic conditions, with the material moving in the digester from top to bottom, where a portion is discharged for dewatering and composting and the balance is recycled with fresh waste to the top of the digestor.
Fresh waste is pre-heated to the operating temperature before entering the digestor. |
STAGE 4: DEWATERING & COMPOSTING
The finished material is pumped from the digester, dewatered and mixed with bulking material before proceeding to the
organic composting process.
The End Products
Compost – In a downstream composting facility, high-quality compost is obtained after about 4 weeks, which owing to feedstock segregation by the ADOS mill, boast excellent levels of purity. The bulking material is sieved off and reused.
|
 |
Bio-gas – The bio-gas produced is buffered, compressed and used as fuel in gas engines. The electrical power generated is fed into the power grid. Waste heat is recovered to heat the material being digested and fresh material being introduced into the digestor. Excess heat may be used for district heating, absorbent chillers, regeneration of dessicants for dehumidifying fresh air prior to chillers or processes that require 80ºC-90ºC heat. |
Because of the low energy requirements of the ADOS bio-methanisation process, it is very economical even in “small scale” facilities (e.g. 30 to 40 tons/day).
Thus, IUT’s organic waste bio-methanisation solution using the patented ADOS process sets new standards for the economics of digestion systems.
