The topic of nutrient recovery takes on a new meaning in Germany due to the amendment of the Fertilizer Ordinances (DüV / DüMV). In particular, the discussion about the upcoming EU infringement proceedings due to excessive nitrate concentration in groundwater led to the identification of numerous nitrate and phosphate-sensitive areas in which fertilization of agricultural areas is only allowed within very strict limitations. This means that many farms have to find new ways of using digestate and liquid manure.
Also aimed at nutrients - in particular phosphorus - the new sewage sludge regulation specifies requirements for the recovery of phosphorus from sewage sludge. This means that from 2029 at the latest there is compulsory to recover phosphorus from sewage sludge with a phosphorus content of 20 grams or more per kilogram of dry matter. Exceptions to the recovery obligation only apply to sewage sludge with low phosphorus content (less than 20 grams of phosphorus per kilogram of sewage sludge (dry matter)).
Overall, the regulations increase the pressure on waste management and the agriculture sector to close material cycles and establish a circular economy
Recycling of Phosphorus
From 2029 at the latest, there is an obligation to recover phosphorus from sewage sludge with a phosphorus content of 20 grams or more per kilogram of dry matter.
When these stricter requirements became known, numerous processes for the recovery of phosphorus from sewage sludge were developed, which start at different points in the treatment process:
- Drainage of the secondary sedimentation
- Sludge liquor
- Digested sludge / sewage sludge
- After the mono-incineration from sewage sludge ash
Depending on where in the treatment process the phosphorus recovery starts, the phosphorus is available in different chemcial forms and concentrations. Accordingly, the recovery potential (based on the inflow loads of the sewage treatment plant) varies (see table, source DWA, 2013).
Since the obligation to recover phosphorus will not exist until 2029, many processes are currently still being tested or are slowly moving into industrial operation.
Liquid Manure and Digestate Processing
In the regions of Germany that have large agricultural areas, nutrient recovery has a special role in relation to the agricultural products of manure and digestate. From a technical point of view, numerous processes and concepts have been optimized, newly developed or interconnected in a suitable manner in the past few years so that digestate or manure can be processed.
The aim of the treatment is usually to reduce the accruing volume so that a form of nutrient concentrate / fertilizer is produced on the one hand and an effluent that can be discharged on the other hand.
Overall, nutrient recovery is becoming increasingly important against the background of Europe-wide legislation and discussion about sustainability and climate change.
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