Environmental Engineering Reference
In-Depth Information
12.9
Overview of the distribution of industrial-scale applications of
further treatment of the liquid fraction of digestate in Gemany, Austria
and Switzerland in 2009.
Combined processes
There are several systems for complete processing of the digestate into
concentrated fertilizer products by combining solid-liquid separation with
one or more refinement steps of varying degrees of technical maturity. There
are agricultural biogas plants operating with digestate processing facilities in
Denmark and more plants are considering establishing such facilities (Al
Seadi and Møller, 2003). There are several industrial-scale plants with
combined digestate processing concepts in Germany. Figure 12.9 gives an
overview on the distribution of technologies for the further treatment of the
liquid fraction of digestate in Germany, Austria and Switzerland.
12.3.6 Advantages and limitations of digestate processing
Intensive animal farming has come under increasing legislative pressure over
recent decades as requirements for environmental protection through better
nutrient management have necessitated export and redistribution of the
excess nutrients and regulated the application of fertilizers. This has led to
an increase in the costs of nutrient management in both manure and
digestate, as their high volume and low dry matter content made transport
over long distances very expensive. Partitioning digestate into a solid
fraction and a liquid fraction, where only the solid fraction is exported, thus
has the potential to reduce transport and application costs of digestate.
Separation by decanter centrifuges and screw press separators has gained
popularity because of the simplicity, efficiency and low cost of these systems.
Several combined technologies and separation concepts have been devel-
oped, of which some are still documented and implemented at full scale
while others are still
in various stages of development. Biogas plants
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