4.4 Thermochemische Reststoffbehandlung und Wertstoffrückgewinnung
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Organisationseinheit der BAM
- 4.4 Thermochemische Reststoffbehandlung und Wertstoffrückgewinnung (188) (entfernen)
Paper des Monats
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Gleichwertigkeit der nach AbfKlärV zulässigen Verfahren zur Phosphorbestimmung in Klärschlamm
(2021)
In dem Meeting wurde den Notifizierern und Ausrichtern des jährlichen länderübergreifenden Ringversuchs Klärschlamm die Ergebnisse zu Untersuchungen hinsichtlich der Gleichwertigkeit verschiedener nach AbfKlärV zulässiger Verfahren zur Phosphorbestimmung in Klärschlamm vorgestellt. Die Untersuchungen an 15 Klärschlammproben ergaben die höchsten Ergebnisse für das Messverfahren ICP-OES und das Aufschlussverfahren in der Mikrowelle. Diese Ergebnisse wurden im Ringversuch bestätigt.
Die landwirtschaftliche Klärschlammverwertung ist in der Bundesrepublik Deutschland seit Jahren rückläufig. Neben den Risiken durch Schadstoffeinträge gibt es in Deutschland Regionen mit einem stark erhöhten Nährstoffüberschuss. Um die Grundwasserbelastung zu verhindern wurde u.a. das Düngerecht verschärft, was die Flächenkonkurrenz zwischen Klärschlamm und Wirtschaftsdünger vergrößern wird.
Es ist davon auszugehen, dass sich die neuen Regelungen im Düngerecht und der Klärschlammverordnung massiv auf die landwirtschaftliche Verwertung von Klärschlamm und damit auf die Kreislaufwirtschaft verschiedener Nährstoffe auswirken werden. In diesem Beitrag werden erste Ergebnisse des Projekts extraWERT vorgestellt.
Es wurden erste Ergebnisse des Projekts extraWERT vorgestellt. Im Projekt werden monatlich Klärschlammproben von 10 kommunalen Kläranlagen untersucht, deren P-Gehalt im Grenzbereich der AbfKlärV liegt zwischen 1,7 und 2,3%. Die ersten Ergebnisse lagen zu fünf Kläranlagen vor, es wurden Daten zum TS-Gehalt, zur oTS und zu den Nährstoffgehalten präsentiert.
New developments in legislation and technology development for P-recovery were presented with focus on the situation in Germany.
Im Projekt extraWERT geht es um die Ermittlung von Nährstoffpotenzialen in Abwasser und Klärschlamm. Neben kommunalen Kläranlagen soll auch die Industrie als Quelle für nährstoffreiche Abfallströme betrachtet werden. Mit dem Vortrag sollten Mitglieder des MIV zu einer Projektbeteiligung bewegt werden. Es sollen rohes und gereinigtes Abwasser von direkt einleitenden Betrieben auf Makronährstoffe untersucht werden, neue Erkenntnisse werden insbesondere für die Nährstoffe Calcium und Magnesium erwartet.
Vorstellung des REFOPLAN-Projekts extraWERT Erhebung zusätzlicher Wertstoffpotenziale in Klärschlamm
(2019)
Auf dem Regionalgruppentreffen wurden erste Projektergebnisse vorgestellt und die Probenahmestrategie diskutiert. Vorgestellt wurde eine Rückberechnung der mittleren Wertstoffgehalte aus dem Klärschlamm-Monitoring 2014 (Krüger und Adam) und erste Auswertungen der Klärschlammbericht-Rohdaten aus NRW und Hessen.
Agricultural sewage sludge utilization becomes less important in Germany. In 2017, new fertilizer and waste laws caused the agricultural sewage sludge utilization to collapse by more than a quarter. From 2029, in German wastewater treatment plants (WWTPs) phosphorus (P) must be recovered from sewage sludge ifit contains more than 2 wt % P. Agricultural utilization will be prohibited for large WWTPs > 100,000 population equivalents (pe) from 2029 and > 50,000 pe from 2032. In Germany, each federal state must annually report amounts and quality of agriculturally utilized sewage sludge which was 17 % of the total disposal in 2019. The reports of 10 States were evaluated for 2016 and 2017 representing approx. 60 % ofthe total agriculturally used sludge volume. Whereas phosphorus recovery is mandatory this does not apply to other nutrients. However, many P recovery processes recover other nutrients, too.
Considering three differentscenariosfor future German sewage sludge disposal Shows that 70 - 77 % ofthe P load in sewage sludge will probably be recovered in the future.
At the same time, this applies for about 0 - 16 % of nitrogen, 36 - 52 % of calcium, 31-53 % of potassium, and 40 - 52 % of magnesium. However, these recovered nutrient loads can substitute only 1 % or less ofthe commercial fertilizer demand except from phosphorus which is about 45 % ofthe demand.
Die landwirtschaftliche Klärschlammverwertung ist in der Bundesrepublik Deutschland seit Jahren rückläufig, hatte im Jahr 2017 jedoch noch einen Anteil von rund 18 % [20]. Diese Art der Verwertung wird kontrovers diskutiert, da der Klärschlamm im Rahmen der Abwasserreinigung eine Schadstoffsenke darstellt. In vergangenen Jahrzehnten wurden insbesondere die hohen Gehalte an Schwermetallen im Klärschlamm als kritisch für eine landwirtschaftliche Verwertung eingestuft. Diese Belastung konnte allerdings durch Absenkung der Einträge von Schmermetallen in das Abwasser signifikant gesenkt werden. Neben Schwermetallen kamen jedoch auch organische Schadstoffe wie Pharmazeutika, Kosmetika und Haushaltschemikalien in den Fokus der Diskussion über den Einsatz von Klärschlamm auf Agrarflächen. Heute geraten zunehmend weitere Inhaltsstoffe in den Fokus, deren Auswirkungen noch nicht abschließend geklärt sind, weshalb eine einheitliche Bewertung über Grenzwerte nicht darstellbar ist. Beispiele für diese neuen Stoffgruppen sind Mikroplastik, Nanopartikel, Antibiotikaresistenzen und persistente organische Spurenstoffe. Neben den angesprochenen Risiken gibt es in Deutschland Regionen mit einem stark erhöhten Nährstoffüberschuss. In der Kritik steht vor allem eine nicht ordnungsgemäße Düngung mit Stickstoff, welche mit Nitratauswaschungen in das Grundwasser einhergeht. Um diese Grundwasserbelastung zu verhindern wurde u.a. das Düngerecht erneut verschärft, was die Flächenkonkurrenz zwischen Klärschlamm und Wirtschaftsdünger weiter vergrößern wird. Auf Druck der EU-Kommission stehen zudem weitere Anpassungen im Düngerecht bevor, da die beschlossenen Änderungen aus Kommissionssicht nicht ausreichen, um die Nitratrichtlinie einzuhalten. Vor dem Hintergrund der angeführten Probleme wurde im Koalitionsvertrag der 18. Legislaturperiode (2013) festgeschrieben, „die Klärschlammausbringung zu Düngezwecken [zu] beenden und Phosphor und andere Nährstoffe zurück[zu]gewinnen“ [5]. Die novellierte AbfKlärV beinhaltet allerdings kein grundsätzliches Aufbringungsverbot und eine Rückgewinnungspflicht besteht lediglich für den Nährstoff Phosphor. Es ist davon auszugehen, dass sich die neuen Regelungen im Düngerecht und der Klärschlammverordnung massiv auf die landwirtschaftliche Verwertung von Klärschlamm und damit auf die Kreislaufwirtschaft verschiedener Nährstoffe auswirken werden. Zur Ermittlung dieser Auswirkungen wird seit Oktober 2018 im Auftrag des Umweltbundesamtes das REFOPLAN-Projekt „extraWERT“ (FKZ 3718 26 330 0) von der Bundesanstalt für Materialforschung und -prüfung (BAM) in Kooperation mit dem Institut für Siedlungswasserwirtschaft (ISA) der RWTH Aachen durchgeführt. In diesem Beitrag werden erste Ergebnisse dieses Projekts vorgestellt.
Ab 2029 gilt für alle Kläranlagen in Deutschland eine Pflicht zur Rückgewinnung von Phosphor (P) aus Klärschlamm. Ausgenommen sind nur Anlagen mit Schlämmen mit weniger als 20 g P/kg bezogen auf die Trockenmasse (TM). Für eine Überprüfung der Phosphorschwankungen im Klärschlamm wurden neun verschiedene Kläranlagen ausgewählt mit Phosphorgehalten nahe der "Rückgewinnungsgrenze" von 20 g/kg TM. Der entwässerte Klärschlamm dieser Anlagen wurde monatlich beprobt und auf seinen Phosphorgehalt geprüft. Die Phosphorschwankungen betrugen je nach Anlage zwischen 4 % und 13 % (relative Standardabweichung), im Mittel rund 7 %.
Phosphorus (P) recovery is obligatory for all sewage sludges with more than 20 g P/kg dry matter (DM) from 2029 in Germany. Nine wastewater treatment plants (WWTPs) were chosen to investigate variations of phosphorus contents and other parameters in sewage sludge over the year. Monthly sewage sludge samples from each WWTP were analyzed for phosphorus and other matrix elements (C, N, H, Ca, Fe, Al, etc.), for several trace elements (As, Cr, Mo, Ni, Pb, Sn) and loss of ignition. Among the nine WWTPs, there are four which have phosphorus contents both above and below the recovery limit of 20 g/kg DM along the year. Considering the average phosphorus content over the year, only one of them is below the limit. Compared to other matrix elements and parameters, phosphorus fuctuations are low with an average of 7% over all nine WWTPs. In total, only hydrogen and carbon are more constant in the sludge.
In several WWTPs with chemical phosphorus elimination, phosphorus fuctuations showed similar courses like iron and/or aluminum. WWTPs with chamber flter presses rather showed dilution efects of calcium dosage. As result of this study, monthly phosphorus measurement is highly recommended to determine whether a WWTP is below the
20 g/kg DM limit.
Phosphorus recycling from sewage sludge will be obligatory in Germany from 2029. Phosphorus content determination in sewage sludge is crucial to assess the prescribed recycling rates. Currently, German law regards sample preparation using aqua regia digestion in a microwave or under reflux conditions as well as instrumental phosphorus determination by ICP-OES, ICP-MS, or photometric determination with ammonium molybdate as equivalent. However, it is questionable whether these methods are indeed equivalent regarding phosphorus quantification in sludges near the limit of 20 g/kg for mandatory recycling. To answer this question, 15 sewage sludges of 11 different wastewater treatment plants were investigated with all permitted method (digestion and measurement) combinations. Moreover, one sewage sludge was also examined in an interlaboratory comparison (ILC) with 28 participants. This study shows that the above-mentioned methods differ in some cases significantly but across all method combinations and sludges, phosphorus recovery was between 80 and 121% after normalization to the grand mean (average of 15 sludges between 85 and 111%). The ILC and the examination of 15 sludges produced largely similar results. There is a tendency to higher phosphorus recovery after microwave digestion compared to reflux digestion and ICP-OES measurements determine higher phosphorus contents than ICP-MS and photometric phosphorus determination. As a result, the authors recommend ICP-OES determination of phosphorus in sewage sludge after microwave digestion.
Future nutrient recovery from sewage sludge regarding three different scenarios - German case study
(2022)
Agricultural sewage sludge utilization becomes less important in Germany. In 2017, new fertilizer and waste laws caused the agricultural sewage sludge utilization to collapse by more than a quarter. From 2029, German wastewater treatment plants (WWTPs) must recover phosphorus (P) from sewage sludge if it contains more than 2 wt % P. Agricultural utilization will be prohibited for large WWTPs >100,000 population equivalents (pe) from 2029 and >50,000 pe from 2032. In Germany, each federal state must annually report amounts and quality of agriculturally utilized sewage sludge which was 16% of the total disposal in 2019. The reports of 10 states were evaluated for 2016 and 2017 representing approx. 60% of the total agriculturally used sludge volume. In 2016, 60% of the WWTPs’ sludges exceeded the recovery limit of 2 wt % P which is 70% of the amount of sludge and 85% of the phosphorus load. Other nutrients are not affected by the recovery obligation. However, many P recovery processes recover other nutrients, too. Considering three different scenarios for future German sewage sludge disposal shows that 70–77% of the P load in sewage sludge will probably be recovered in the future. At the same time, this applies for about 0–16% nitrogen, 36–52% of calcium, 31–53% of potassium, and 40–52% of magnesium. However, these recovered nutrients loads can substitute only 1% or less of the commercial fertilizer demand except from phosphorus which is up to 43% of the demand.
The present work demonstrates a sustainable approach of using relatively coarser iron ore particles for ironmaking. The motivation is to reduce the energy consumption in the milling of the iron ore by utilizing coarser iron ore particles (+0.05 mm) and to select a suitable binder for improving pellet properties. Iron ore fines in the range of 0.05–0.25 mm was selected and classified into three size ranges. Fluxed iron ore pellets were prepared using lime as a binder for the basicity of 0, 1, and 2. Reduction of these pellets with a packed bed of coal fines was performed in the temperature range of 900–1200 °C for a duration of 30–120 min. The direct reduction kinetics of the iron ore pellets were studied by employing diffusion and chemical reaction control models to the experimental data. The results show that pellets made with coarser iron ore particles have improved reduction behavior and kinetics. The reduction reaction is found to be a mixed control. The activation energy for the reduction reaction varies from 44.3 to 74.76 kJ mol−1 as iron ore particle size decreases from 0.25 to 0.05 mm and basicity increases from 0 to 2.
In the transition to the Circular Economy (CE) model, where the added value of products is kept as long as possible and waste is eliminated, the sustainable management of raw materials plays a key role. In above CE model, especial attention is paid to CRMs which are economically and strategically important for the European economy, but have a high-risk associated with their supply.
One of the most important element which can not be replaced and is an essential element for human nutrition, yet limited resource is phosphorus (P). An importance of issues related to sustainable P management results from EU legislation, which indicated P as a Critical Raw Material (CRM).
The sustainable management of P-resources is especially important for the Baltic region. A consequence of waterborne loads passing into the sea, mainly as wastewater with a high P content is the eutrophication of the Baltic Sea environment. Due to the largest inputs of P (37%) into the Baltic Sea originate from Poland, the development of sustainable solutions aimed at more rational P management for this country is externally important.
Due to the vital importance of phosphorus (P) and its increasing scarcity as a natural resource, phosphorus recovery has recently gained significant scientific and technical interest. An interesting sources of phosphorus are sewage sludge (SS) and sewage sludge ash (SSA) due to the major part of the phosphate from P rich wastewater is transferred to the sludge (approx. 90%). Despite the fact that the raw materials base is large (PURE report indicates that in 2020 the amount of sewage sludge generated in Poland will reach 180% of the dry matter of sewage sludge produced in 2010), at present recycling of phosphorus is not a commonly used practice in Poland.
More sustainable waste management practices are an important element in the Transformation towards a circular economy (CE). Activities in this area should be dedicated to all groups of waste, including those generated in the water and sewage sector. This paper presents the characteristics of sewage sludge ash (SSA) coming from Polish municipal waste incineration plants. Due to the high content of nutrients such as phosphorus (8.01% P2O5), calcium (5.11% CaO) and magnesium (2.75% MgO), the analyzed SSA may constitute a valuable source of raw materials for the fertilizer industry.
Despite the good fertilizing properties of the SSA, in some cases the presence of heavy metals such as cadmium (0.74–1.4 mg/kg dry matter), lead (49.8–99 mg/kg dry matter), mercury (3.93 mg/kg dry matter) and arsenic (4.23–4.43 mg/kg dry matter) and poor bioavailability of P from SSA disqualifies this waste from direct use as a fertilizer. Therefore, it is necessary to look for methods that will allow the municipal SSA to be processed, for example, technologies for the extraction of phosphorus and the production of phosphate fertilizer. This way of SSA management is in the line with the CE assumptions, in which waste becomes a valuable source of secondary raw materials. Fertilizer produced from waste meeting quality, safety and labelling requirements and limits of organic, microbiological and physical contaminants will be able to be traded freely within the European Union (EU) and receive the CE marking. The idea of use of SSA for fertilizer purposes is consistent not only with the objectives of the CE but also with the Polish National Waste Management Plan 2022 and the Municipal Sewage Sludge Strategy 2019–2022, which emphasizes the necessity to maximize the use of biogenic substances contained in wastewater. Therefore, sustainable management of SSA, in particular its storage in a way enabling the recovery of phosphorus, should be promoted.
Popioły pochodzące z instalacji do spalania komunalnych osadów ściekowych, znajdującej się na terytorium Polski, poddano procesom termochemicznego przekształcania, dzięki czemu otrzymano produkty nawozowe spełniające kryteria dopuszczające je do obrotu jako nawozy mineralne. Ponadto dokonano analizy możliwości wykorzystania popiołów na cele nawozowe zgodnie z obecnie przyjętymi dokumentami strategicznymi i planistycznymi dotyczącymi gospodarki odpadami na poziomie krajowym i europejskim.
This paper presents an inventory of sewage sludge ashes (SSA) generated in the mono-incineration plants for municipal sewage sludge in Poland. This research focused on the detailed study of mass flows, chemical composition, and phosphorus recovery potential. There are currently 11 sludge mono-incineration plants operated with a total capacity of 160,300 Mg dry weight (d.w.) of sludge annually. Recently, a significant increase in the amount of SSA generated in these plants has been observed, reaching 26,756 Mg in 2018. Chemical composition of SSA showed significant amounts of the main nutrients: calcium (~14%), phosphorus (~13%), magnesium (~3%), and potassium (~1%). Additional main elements were iron (~14.5%), silicon (~13%), and aluminium (~6%). The main trace elements in the SSA were zinc (~3750 mg/kg) and copper (~899 mg/kg). Pollutants, according to fertilizer regulations of different countries, present in Polish SSA were chromium(~703 mg/kg), nickel (~260 mg/kg), lead (~94 mg/kg), and Cadmium (~9 mg/kg). The radionuclides, uranium, and thorium often present in higher amounts in commercial phosphate rock-based fertilizers, were only detected in SSA t low levels of 4–9 mg/kg and 2–3 mg/kg, respectively. Theoretical phosphorus recovery potential from the SSA (from plants in Cracow, Lodz, Gdansk, Gdynia, Szczecin, and Kielce) was estimated at 1613.8 Mg, of which 33.9% is bioavailable. Currently, in Poland, the recommended approach is the production of fertilizers as a result of the extraction of phosphorus from the SSA with its use in the production of secondary mineral fertilizers.
Further research in this area is required considering Polish conditions and legislation.
Phosphorus (P) recovery from sewage sludge ash (SSA) is one of the most promising approaches of phosphate rock substitution in mineral fertilizers and might be a sustainable way to secure supply of this raw material in the future. In the current investigation, the process of thermochemical treatment of SSA was applied to SSA coming from selected mono-incineration plants of municipal sewage sludge in Poland (Cracow, Gdansk, Gdynia, Lodz, Kielce and Szczecin).
The Polish SSA was thermochemically converted in the presence of sodium (Na) additives and a reducing agent (dried sewage sludge) to obtain secondary raw materials for the production of marketable P fertilizers. The process had a positive impact on the bioavailability of phosphorus and reduced the content of heavy metals in the obtained products. The P solubility in neutral Ammonium citrate, an indicator of its bioavailability, was significantly raised from 19.7–45.7% in the raw ashes and 76.5–100% in the thermochemically treated SSA. The content of nutrients in the recyclates was in the range of 15.7–19.2% P2O5, 10.8–14.2% CaO, 3.5–5.4% Na2O, 2.6–3.6% MgO and 0.9–1.3% K2O. The produced fertilizer raw materials meet the Polish norms for trace elements covered by the legislation: the content of lead was in the range 10.2–73.1 mg/kg, arsenic 4.8–22.7 mg/kg, Cadmium 0.9–2.8 mg/kg and mercury <0.05 mg/kg. Thus, these products could be potentially directly used for fertilizer production. This work also includes an analysis of the possibilities of using ashes for fertilizer purposes in Poland, based on the assumptions indicated in the adopted strategic and planning documents regarding waste management and fertilizer production.