Environmental Engineering Reference
In-Depth Information
compounds are removed through complex pre-treatments. In plug flow
digesters or in dry digestion systems, the disturbing compounds can be
removed also after digestion.
Sewage sludge
Anaerobic digestion used to treat primary and secondary sludge resulting
from the aerobic treatment of municipal wastewater is a standard
technology around the world. The technology is used in thousands of
installations as part of modern treatment systems of municipal wastewaters.
Sewage sludge has a methane potential similar to animal slurries (primary
sludge has a higher methane potential than waste-activated sludge). Various
pre-treatments can be applied to increase methane yield, aiming at
disintegration of bacterial biomass and releasing organic substances easily
accessible to the subsequent anaerobic degradation, for example mechanical
disintegration, chemical hydrolyses,
thermal hydrolyses and enzymatic
degradation (Rulkens, 2008).
The limiting factor for the use of sewage sludge as biogas feedstock is the
high content of pollutants and the risks related to their subsequent presence
in digestate used as fertilizer. Because of its origin, sewage sludge contains
significant amounts of biologic and chemical pollutants. Utilization of
sewage sludge as feedstock for AD is therefore regulated by national
legislation and quality standards for the utilization of waste products as
fertilizers. There are countries in which the use of digested sewage sludge as
a fertilizer or for other agricultural purposes is banned, while in other
countries its utilization as a fertilizer is controlled by strict requirements
concerning the limit values of concentrations of heavy metals and persistent
organic pollutants as well as the sanitation requirements for inactivation of
pathogens and other biologic vectors (Smith, 2011). Sewage sludge is often
co-digested with manure or/and organic wastes from industries and
households, which improves the biogas yield and the process stability
(Kuglarz and Mroviec, 2009). More details about sewage sludge can be
found in Chapter 12 of this topic.
2.2.4 Aquatic biomass
Along with the materials produced by different sectors of society described
so far, there is growing interest in the utilization of aquatic biomass from
marine and fresh waters. This is estimated to have high potential for
utilization in food and feed production and as a raw material for various
other industries, and is also one of most promising feedstocks for biofuels
production, including biogas (Burton, 2009; Wellinger, 2009; Angelidaki
et al., 2011). In the last few decades, research on aquatic biomass has
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