New German Sewage Sludge Regulation sets the Standard for Phosphorus Recovery
Apart from nitrogen, phosphorus is one of the hidden treasures in sewage sludge. As phosphate, unlike nitrogen, is a finite resource that cannot be reproduced, the new German Sewage Sludge Regulation requires sewage plant operators to recycle phosphates.
Pursuant to the new German Sewage Sludge Regulation in force since 03 October 2017 sewage sludge must now be recycled to recover phosphorus. The aim is to gradually close the phosphorus cycle and reduce Germany’s dependence on phosphorus imports. This will save phosphorus resources and reduce soil contamination.
Phosphorus as Fertiliser
Phosphorus is primarily used as fertiliser. When it comes to producing mineral-based phosphorus fertilisers, Germany - as most of the other EU states – depends almost entirely on imports. If the new German Sewage Sludge Regulation is complied with, 50% to 60% of imports can be replaced by phosphorus recovered from sewage sludge. To achieve that aim, the new German Sewage Sludge Regulation requires operators of larger sewage plants (population equivalent of > 50,000) to recover phosphorus from sewage sludge. To develop and optimise respectively recovery processes, the regulation provides for transition periods. Large sewage plants (population equivalent of > 100,000) have 12 years to comply with the new regulation. The transition period for smaller sewage plants (population equivalent of 50,000 to 100,000) is 15 years. By the end of 2023 however the operators of sewage plant of the above sizes must have submitted their phosphate recycling concept to the regulatory authorities.
Upon expiry of the transition periods the sewage plants of the sizes mentioned above are no longer allowed to supply sewage sludge for agricultural use.
Phosphorus Recovery from Sewage Sludge
Currently it is possible to recover phosphorus from ash, which however excludes any mixing with other fuels and requires the incineration of phosphorus-containing sewage sludge in so-called mono-incineration plants. However the ash produced there cannot be used for agricultural purposes. An additional recovery plant is required that extracts the phosphates from the ash. As ash recovery rates are high, the new German Sewage Sludge Regulation requires a recovery rate of 80% in relation to the sewage plant’s phosphorus input.
Currently no large-scale processes to recover phosphorus from sewage sludge ash have been tested and capacities at mono-incineration plants are not sufficient to process all suitable sewage sludge available. The capacity of existing mono-incineration plants (Germany currently has 19 plants) is about 450,000 mg dry solids/a, which is equivalent to roughly 25% of the total dry sewage sludge mass produced. New plants are definitely needed.
Another option is to eliminate phosphates from sludge using a precipitation method. Here, P recovery requirements are lower: The dry solid content of sewage sludge after treatment must be lower than 20gP/kg DS. If the dry solid content of sewage sludge is very high (> 40gP/kg DS), a 50% reduction in phosphate concentrations is acceptable.
In the precipitation plants already installed phosphate is usually recovered as magnesium ammonium phosphate (MAP) which has a track record of excellent plant availability. A second process step to ecologically recycle phosphorus as needed in the mono-incineration process can be dispensed with.
The P recovery rates of existing large-scale processes however need to be optimised.
Contact us if you require more information or would be interested in a bespoke concept to increase phosphate recovery rates at your sewage plant. We will be happy to assist you.