Environmental Engineering Reference
In-Depth Information
CHAPTER 6
Organic waste as a biomass resource
Eva Thorin, Thorsten Ahrens, Elias Hakalehto &Ari Jääskeläinen
6.1 INTRODUCTION
The waste hierarchy promotes reuse and recycling of waste material but substantial amounts of
wastes cannot be reused or recycled. However, the energy content of this waste can be utilized.
Waste is constantly produced in agriculture, municipalities and industries and part of that thus
provides a secure and a local source of energy. Wastes and biomass fuels are usually viewed as
sustainable energy sources (Kothari et al. , 2010). Waste can consist of many different materials.
Considering using waste as a biomass resource, the organic fractions containing material of
biological origin is of interest, see the examples in Table 6.1.
Packed foodwaste fromgrocery shops is one important source of organicwaste in industrialized
countries. In Finland, for example, grocery shops' food wastage due to overdated products totaled
5.4
10 3 kg per M€. This includes
products that have exceeded the “use-by date” such as fresh meat, mince, fresh fish, fresh cheese,
uncooked ready-made food and other food easily contaminated microbiologically. It is prohibited
to sell or even give away these after the use-by date. “Best before” marking is used for other
groceries, such as bread, grain products, other dry products, frozen food and canned food. It is
possible to decrease their wastage by selling them at a discount. Moreover, contaminated groceries
and groceries with damaged packages are thrown away. In addition, frozen food that has melted
or for which the cold chain has otherwise been broken, cause wastage of groceries (Ekoleima Ay,
2008).
In Table 6.1 possible conversion processes for examples of organic wastes are also given.
Anaerobic digestion and fermentation are microbiological conversion methods while combus-
tion, pyrolysis and gasification are thermochemical conversion methods. The product of the
conversion processes of organic waste can be used as fuel in further energy conversion. Ethanol
from fermentation and up-graded gas from anaerobic digestion can be used as a fuel in trans-
portation. The gas from anaerobic digestion can also be used directly in an oven, gas engine or
gas turbine for heat and power production. The gas from gasification and pyrolysis can be used
in a similar way but can also be further reformed for production of other types of transportation
fuels for example dimethylether (DME) or Fischer-Tropsch fuel.
10 7 kg in 2007. This corresponds, on average, to 4.15
×
×
6.2 PRE-TREATMENT
To utilize the organic waste as an energy resource, pre-treatment of a waste flow is required.
The aim of the treatment will be to sort out the organic fractions and by that increase the energy
content but also to get a more homogeneous, dense and/or less contaminated material. The latter
reasons can simplify handling and use of the material as an energy source and also the handling
of by-products and emissions from the conversion processes.
Pre-treated municipal solid waste with the purpose to prepare a fuel for thermal conversion
processes is often called Refuse Derived Fuel (RDF). This fuel normally includes the plastic,
paper, wood, textile and rubber parts of the solid waste. In addition, other terms are in use,
109
Search WWH ::




Custom Search