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TY  - THES
AU  - Schnell, Matthias
TI  - Integration des additivgestützten thermochemischen Phosphor-Recyclings in die Klärschlammverbrennung
VL  - 89
PB  - RWTH Aachen University
VL  - Dissertation
CY  - Düren
M1  - RWTH-2023-11377
SN  - 978-3-8440-9297-4
T2  - Schriftenreihe zur Aufbereitung und Veredlung
SP  - 1 Online-Ressource : Illustrationen
PY  - 2023
N1  - Druckausgabe: 2023. - Auch veröffentlicht auf dem Publikationsserver der RWTH Aachen University 2024
N1  - Dissertation, RWTH Aachen University, 2023
AB  - 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 
LB  - PUB:(DE-HGF)11 ; PUB:(DE-HGF)3
DO  - DOI:10.2370/9783844092974
UR  - https://publications.rwth-aachen.de/record/974487
ER  -