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of digestate. To combat this,
struvite can be recovered from
the digestate by increasing the
pH and adding magnesium
to precipitate out the struvite
which can then be processed
into pellets and sold as an
inorganic fertiliser.
Ammonia stripping – this
has the dual benefit of remov-
ing ammonia from the diges-
tate, which reduces the risk of
volatilisation during storage,
and producing ammonium
sulphate or ammonium nitrate
which can be used as a liquid
fertiliser. Ammonia is removed
from the digestate liquor by
mixing it with air at high
temperature and high pH. The
ammonia gas is then scrubbed
with sulphuric or nitric acid
to produce an ammonium
salt which can be used as a
nitrogen-rich fertiliser.
Ion exchange – liquid di-
gestate can be passed through
a column containing adsorp-
tion media such as zeolite
or an ion exchange resin to
remove ammonia from the di-
gestate. The resin can then be
regenerated, and an ammonia-
rich liquid drained off. This
liquid has potential for use
in the chemical production
industry.
A number of "second-
generation" technologies
are emerging that may offer
further opportunities for pro-
duction of valuable resources.
Many of the technologies are
based on the manipulation
(Source: Agler et al. 2011)
