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@PHDTHESIS{Schnell:974487,
author = {Schnell, Matthias},
othercontributors = {Quicker, Peter and Wintgens, Thomas Josef},
title = {{I}ntegration des additivgestützten thermochemischen
{P}hosphor-{R}ecyclings in die {K}lärschlammverbrennung},
volume = {89},
school = {RWTH Aachen University},
type = {Dissertation},
address = {Düren},
publisher = {Shaker Verlag},
reportid = {RWTH-2023-11377},
isbn = {978-3-8440-9297-4},
series = {Schriftenreihe zur Aufbereitung und Veredlung},
pages = {1 Online-Ressource : Illustrationen},
year = {2023},
note = {Druckausgabe: 2023. - Auch veröffentlicht auf dem
Publikationsserver der RWTH Aachen University 2024;
Dissertation, RWTH Aachen University, 2023},
abstract = {The recovery of phosphorus from municipal sewage sludge
will be legally required in Germany from 2029. This
obligation serves to improve the utilization efficiency of
the nutrient phosphorus within a sustainable and
resource-efficient circular economy as well as to reduce the
high import dependency on other countries. Since sewage
sludge, as a pollutant sink, contains both nutrients and a
variety of undesirable components, agricultural utilization
as an option for nutrient recirculation will be largely
stopped by the year 2031. In addition, no well-established
or suitable processes are available to fulfill the
phosphorus recovery requirements to date. Established
treatment pathways for sewage sludge, such as
co-incineration in waste-to-energy plants and cement plants,
are increasingly restricted because downstream phosphorus
recovery is not possible in these cases. Co-incineration in
coal-fired power plants is also limited due to the phase-out
of coal-fired power generation. As a result, a large number
of sewage sludge mono-incineration plants are being
realized. The mono-incineration of sewage sludge does not
hinder phosphorus recovery, but enables downstream
phosphorus recovery from sewage sludge ash, in which
phosphorus is enriched during incineration.Sewage sludge ash
can be used directly or as a feedstock for fertilizers, if
the requirements and limits of the Sewage Sludge and
Fertilizer Ordinance are complied with. However, during
sewage sludge incineration, numerous heavy metals such as
lead, nickel, copper and zinc are accumulated in the ash in
addition to phosphorus. Furthermore, phosphorus in sewage
sludge ash is predominantly present in poorly soluble
compounds that are not accessible to plants. Without
post-treatment in wet-chemical or thermochemical processes,
the majority of sewage sludge ash from conventional sewage
sludge incineration, which according to the state of the art
is predominantly carried out in the stationary fluidized
bed, cannot be used as a fertilizer. A specific improvement
of the ash quality during incineration, consisting of
reduction of the heavy metal content and increase of the
phosphorus availability, makes it possible to dispense with
additional post-treatment. This is the aim of the
additive-assisted thermochemical phosphorus recycling
approach. According to the current state of knowledge,
alkali and alkaline earth chlorides are used for heavy metal
reduction. During thermochemical sewage sludge treatment,
heavy metal chlorides are formed using these additives,
which are transferred to the gas phase at the prevailing
incineration temperatures due to lower boiling points
compared to the elemental form of the heavy metals.
Phosphorus availability is improved by recrystallization or
formation of new phosphorus compounds during thermochemical
treatment with additive addition. Besides alkali and
alkaline earth chlorides, carbonates and sulfates are also
used for this purpose. On the basis of the current state of
knowledge, existing research deficits were identified, and
comprehensive laboratory investigations were carried out to
remedy these deficits, with the aim of expanding data
availability and comparability and establishing a basis for
explaining the observed effects. The main focus of the
investigations was on the determination of heavy metal
reduction and phosphorus recovery during sewage sludge
incineration. For this purpose, laboratory-scale tests were
carried out in a muffle furnace, which were supplemented by
trial tests at a full-scale incinerator with stationary
fluidized bed technology. Chlorides (MgCl2, MgCl2 ∙ 6H2O,
CaCl2, CaCl2 ∙ 2H2O, NaCl, KCl, NH4Cl, PVC), sulfates
(Na2SO4, K2SO4), and carbonates (Na2CO3, K2CO3, CaCO3) were
used as additives. The feedstocks and sewage sludge ashes
were characterized by means of fuel and elemental analyses,
thermogravimetric investigations, analyses of ash melting
behavior and investigations of phosphorus solubility. In
addition, thermodynamic equilibrium calculations were
performed to enable a discussion of the results beyond the
analytical results. The reduction of heavy metals by the
addition of chlorine-containing additives during
thermochemical sewage sludge treatment was confirmed in the
laboratory tests carried out. Increasing heavy metal
reductions were obtained with increasing chlorine
concentration and treatment temperature. The highest
reductions were determined using the additives CaCl2, NaCl
and KCl. In addition, influences on the transfer of
phosphorus contained in the sewage sludge to the produced
sewage sludge ash were observed. The solubility of
phosphorus was improved using most of the additives only in
two percent citric acid. Relevant increases for solubility
in water and neutral ammonium citrate were not observed. On
the basis of the investigation results, a generally valid
identification of a most suitable additive or preferred
treatment parameters is not possible. The tested additives
have different advantages and disadvantages. An individual
evaluation based on the sewage sludge to be treated is
therefore mandatory for the suitability of the process. With
regard to compliance with the requirements and limit values
of the Fertilizer Ordinance, the element nickel in
particular is to be classified as critical according to the
investigations carried out, as it could only be reduced by
the use of NaCl and KCl at high treatment temperatures and
chlorine concentrations. However, these parameters also
caused a decrease in the proportion of phosphorus
transferred to the ash. In addition, the phosphorus
solubilities in water and neutral ammonium citrate required
by the fertilizer regulations could not be achieved. A
possible improvement in phosphorus availability or
solubility, as described in some published studies, must
therefore be part of further investigations to verify the
approach for large-scale application. The preparation of a
concept for the integration of additive-assisted
thermochemical phosphorus recycling into sewage sludge
incineration, including the identification of open
challenges, serves as a decision-making aid and basis for
comparison for further process development. Compared to
conventional sewage sludge incineration, the integration of
thermochemical phosphorus recycling resulted in an increase
of treatment costs by 40-62 €/Mg related to the sewage
sludge dry mass or by 10-16 $\%.$ Product earnings were not
considered in this analysis due to the unresolved
challenges.},
cin = {512220 / 510000},
ddc = {620},
cid = {$I:(DE-82)512220_20140620$ / $I:(DE-82)510000_20140620$},
typ = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
doi = {10.2370/9783844092974},
url = {https://publications.rwth-aachen.de/record/974487},
}
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