Environmental Engineering Reference
In-Depth Information
residues, slaughterhouse and rendering wastes) must be sanitized prior to AD.
More details about quality issues can be found in Chapter 12 of this topic.
Another important limitation refers to a shortage of such organic wastes,
especially methane boosters, in countries with well-developed biogas
markets. It is likely that industrial organic wastes will continue to be
used, when available and mainly because of their high methane yields,
especially as co-substrates for animal manure. The environmental benefits
related to AD and the high costs of other disposal methods are further
incentives in favor of using suitable industrial organic wastes, by-products
and residues as biogas feedstocks.
2.2.3 Municipal waste biogas feedstock
Source-separated organic waste
Source-separated organic waste refers to the organic fraction of household
waste such as food waste, garden waste and other similar organic wastes,
separately collected. Increasing urbanization and consumption patterns
makes adequate waste management mandatory. Separate collection is a
solution that is capable of providing clean and high-quality materials for use
as AD feedstock, at the same time reducing the stream of organic materials
going to landfills and incineration (Favoino, 2002; Rutz et al., 2011) in favor
of recycling and nutrients recovery. Separately collected organic household
wastes are often co-digested with animal manure and slurries in manure-
based AD plants. Increasingly high amounts of household wastes generated
in society indicate a very high AD potential. The use of household wastes as
a feedstock for biogas does not compete for land use and does not have
negative sustainability impacts (Rutz et al., 2011).
To be suitable for recycling as AD feedstock, organic household wastes
must have high purity. Amon and Boxberger (1999) show that low-purity
waste, due to the presence of foreign materials, can cause technical
malfunctions of the biogas plant, be a source of pollutants and can have a
negative impact on the utilization of digestate as fertilizer. For this reason,
the authors indicate that the content of foreign materials in organic wastes
may not exceed 0.1%. Effectively, this is only possible if organic wastes are
collected separately, according to their composition materials, at their place
of production or utilization. Separate collection is an integrated part of the
overall waste management system, as shown in Fig. 2.2, and ensures the high
quality and purity necessary for their optimal use as AD feedstock.
Compared with source separation, mixed collection followed by a central
separation implies higher costs and considerable losses of organic matter
(Favoino, 2002) as well as high contamination risk. For this reason, the
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