Environmental Engineering Reference
In-Depth Information
industrial by-products and energy crops. Waste fractions include the organic
fraction of municipal solid waste, source-separated organic wastes, food and
feed leftovers, kitchen waste and grass cuttings. In industrial processes,
significant quantities of organic by-products are accumulated, including
agro-industrial by-products (manure, harvest residues, etc.) and food
processing by-products (e.g. slaughter house wastes, whey, brewers' spent
grains, distillery slops, fruit and vegetable wastes, sugar beet residues).
High-strength industrial wastewaters can also be of interest as feedstock in
biogas plants. Finally, purpose-grown crops for anaerobic digestion include
maize, grass and beets.
Not all waste products and crops are equally suitable for biogas
production and in some cases biogas production might not be profitable.
To assess the suitability and profitability of biogas feedstocks, a reliable way
of characterising and analysing feedstocks is necessary. A preliminary
assessment of a feedstock can be carried out using data available in the
literature combined with feedstock process and production data. Legal
issues should also be considered, such as environmental and safety laws
regulating the use of waste products. If the preliminary assessment indicates
that the feedstock might be suitable, a detailed laboratory analysis should
follow. Concise information about the different analysis methods (such as
total solids (TS), volatile solids (VS), nitrogen content, chemical oxygen
demand (COD)) and their limitations are discussed in this chapter.
Furthermore, the availability of macro- and micronutrients should also be
evaluated, as well as the possibility of the accumulation of inhibitory
substances (antibiotics, heavy metals, disinfectants, ammonia, hydrogen
sulphide, etc.). An important test for the anaerobic degradability and
acceptability of a feedstock is a batch test for the biochemical methane
potential (BMP). The best information on the behaviour of a biogas
feedstock in a biogas plant can be obtained from continuous fermentation
trials. However, a major disadvantage of these continuous trials is their
complexity and cost.
After a detailed characterisation of the biogas feedstock has been carried
out and if the results seem promising, a detailed economic evaluation should
follow. This is essential before realising a biogas project. Feedstock analysis
and characterisation allow estimation of the price of a substrate when sold
to a biogas plant operator.
3.2
Preliminary feedstock characterisation
3.2.1 General suitability as feedstock for anaerobic digestion
Using basic data such as water content and content of inorganic matter or
bulky/fibrous material, a rough estimation of the suitability of a specific
Search WWH ::
Custom Search