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Tekniska processer för fosforåtervinning ur avloppsslam
RISE - Research Institutes of Sweden, Built Environment, Energy and Circular Economy.
RISE - Research Institutes of Sweden, Built Environment, Energy and Circular Economy.
2019 (Swedish)Report (Other academic)
Abstract [en]

This report is written within the framework of the state's public inquiries M 2018:08, committee directive 2018:67 "Non-toxic and circular recycling of phosphorus from sewage sludge". One of the tasks in the directive is a task about mapping the technological development for phosphorus recovery, which this report highlights.

The methodology for answering the question has been to examine scientific articles published in recent years, and to review documentation from recent years' conferences, seminars and EU projects (completed and ongoing) in the field. Among the sources available on the internet, the German, Swiss and European phosphorus platforms have been the most important. A selection has been made of relevant processes, where the selection criteria are reported in the report. The starting point for recovering phosphorus is inside the waste water treatment plant (WWTP) where the sludge occurs. The reported processes have been subdivided on the basis of where in the process scheme they have their starting point, which is also the most common classification according to the literature.

The result is that the choice of method must be a balance of what one wants to achieve because no method meets all the wishes. A vast majority of processes meet the criterion of depollution, ie the degree of detoxification is very high, which is an important driving force for introducing them. The recycling potential of the processes is very variable, from 20 % of incoming phosphorus to the WWTP (usually struvite processes etc.) to just over 95 % of incoming phosphorus (usually thermal processes, e.g. biokol and extraction from ash), since it involves the whole sludge stream. In order to achieve a high recovery rate when internal processes are applied, it is also required that the phosphorus in the remaining dewatered sludge is recycled.

Only one category of processes is assessed to be fully developed, namely the struvite processes. All other processes are considered "new technology" or "promising innovations". Most of the internal processes in WWTP do not fit well in Sweden because most Swedish WWTPs use chemical precipitation of phosphorus instead of biologically.

An important aspect from the system- and economic point of view is in what form the phosphorus comes out of the process, which is highly variable for the processes studied. The processes in which phosphorus comes out in a form known to the agriculture (or industry) are considered to have the greatest potential to be viable in the long term. It has been difficult to obtain costs for introducing the studied processes, this because the processes are under development. It is often pointed out that phosphorus recovery processes are very expensive, but compared to today's costs that WWTPs has to get rid of the sludge, it is unclear how large the cost difference actually becomes.

The report also highlights the environmental impacts from a life-cycle perspective. The general conclusion is that it is difficult to obtain knowledge because most of the processes are under development, and that it is difficult to draw any clear results from the analyzes that have been fulfilled.

Three different ways of taking care of the entire sludge flow have been identified; bio-coal, ash and ash extraction. The first means that the entire sludge amount is dried and pyrolyzed and the remainder is a bio char which should be regarded as a carbon-sink and a long-term phosphorus source. The second way is to burn ash and direct spread of this ash. The third way involves the extraction of phosphorus from this ash in different ways and here there are three methods of this type that are at approximately the same level of development. Two other methods that are regarded as promising innovations are about HTC processes (hydrothermal carbonization) and extraction using CO2. Assessed advantages and disadvantages for these and other categories of processes can be found in the report.

Place, publisher, year, edition, pages
2019. , p. 48
Series
RISE Rapport ; 2019:59
Keywords [en]
phosphorus, sewage sludge, recycling, waste water treatment, struvite, combustion, biochar, pyrolysis
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:ri:diva-43258ISBN: 978-91-88907-86-8 (electronic)OAI: oai:DiVA.org:ri-43258DiVA, id: diva2:1386080
Available from: 2020-01-16 Created: 2020-01-16 Last updated: 2020-01-16Bibliographically approved

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