Page 18 - Waste-to-Energy in the Danube Strategy Region. Challenges and Prospects

incineration. On the other hand, both have been reported to be more advantageous in terms of

environmental impact and energy recovery. Both also offer the benefit of waste volume reduction,
while neither requires the same level of flue-gas cleaning as does incineration (Kumar and

Samadder 2017).

Biological conversion uses microbes to decompose organic fractions of waste streams and

thereby produce biogas. The primary technology currently in use for this process is anaerobic

digestion (AD). Appropriate waste for this process is characterized by high moisture content and
high percentage of organic biodegradable material. The specifications of the process and waste

stream determine the quality of the resulting biogas. In addition to biogas, the other by-product

is sludge, which may have additional applications, for example, in agriculture. The process of AD
proceeds through a series of stages ultimately converting the biodegradable waste primarily into

methane and carbon dioxide. Factors influencing the end product include the type of reactor

(single or multi stage) and process (wet or dry), and the choice between each pair of options

depends on the characteristics of the available feedstock and the desired final product. The
resulting biogas is further treated to remove the carbon dioxide (and other gases) in order to

produce biomethane for use in transportation or as a substitute for natural gas in various domestic

and industrial applications. While this form of WtE treatment is regarded as economically and

environmentally viable, its major disadvantage is the necessary duration of the process (20–40
days) (Kumar and Samadder 2017).

The final form of WtE introduced above is sanitary landfilling. As opposed to standard

landfilling, this process incorporates systems for the recovery of landfill gas (LFG) and

management of leachate. LFG is a natural product of the complex biological and chemical
processes that affect landfilled waste. As with other WtE technologies, the characteristics and rate

of production of this gas depend on various factors, including type of landfill, waste composition,

climate conditions and moisture content. LFG is mostly comprised of methane. Successful

implementation of sanitary landfilling depends first on proper estimation of a given landfill’s LFG
production. Various models exist for this purpose, including several developed in a European

context. Nevertheless, given the EU’s current efforts towards a circular economy and reduced

Project co-funded by the European Union
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