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European Commission “feasibility study” considers two sewage sludge management options: 1 = ongoing land use of treated sludge with tighter monitoring and contaminant limits; 2 =mandatory sludge incineration with P-recovery. The study rejects options for ongoing sewage sludge land use without EU regulatory contaminant limits. The study does not select a preferred option of the two considered because of uncertainties about levels of contaminants and related risk, and with the aim of enabling further stakeholder input. The scenario (1) proposes that sewage sludge from larger sewage works applied in agriculture must qualify under the EU Fertilising Products Regulation and that other quality requirements would be applicable to sludge from smaller sewage works used in agriculture or forestry etc. (p31), and also that all sludge used on land should be applied according to crop phosphorus needs and with good management practice requirements (p34).

The study indicates that the EU generates just over 8 Mt/y dry matter (DM) of sewage sludge of which c. 32% is incinerated (based on Eurostat 2021). 10% of EU sewage sludge still goes to landfill, resulting in significant methane emissions.

Table 1 (p8) shows that heavy metal limits are generally lower in current Member State national legislation than in the EU Sewage Sludge Directive (which dates from 1986 and has not been updated), and also that the lowest national heavy metal limits for sewage sludge are in all cases lower than EU Fertilising Products Regulation (FPR) limits (for Organic Fertiliser / Organic Soil Improvers). The average observed heavy metal levels in sewage sludge are also lower than the EU FPR limits for all eight metal contaminants considered. However, JRC note concerns about other chemicals potentially found in sewage sludge, including industrial chemicals, pesticides, pharmaceuticals, personal care chemicals, PFAS, microplastics, and consider (p26) that risk assessments of these chemicals in sludge are inadequate, in particular because they do not take into account local context and combination effects of chemicals in sludge.

The study suggests (p 19-20) that benefits to society are highest for mono-incineration of sewage sludge with phosphorus recovery (option 1). Use of composted or digested sewage sludge in agriculture has net positive benefits (assuming tight contaminant limits and application of nutrients according to crop requirements and not in excess) but significantly lower than for option 1, whereas co-incineration (phosphorus not recovered) has negative net societal impacts and landfilling has strongly negative societal impacts. On the other hand the cost of mono-incineration (option 2) is estimated to be 2-3 x higher than agriculture application (option 1).

Organic carbon returned to soil by use of treated sewage sludge is not considered significant (fig. 5 p 11, p 35) compared to manure and bio-waste.

Short-term agronomic P-efficiency is considered to be higher in mineral P-fertiliser products recovered from sewage sludge incineration ash than in agricultural application of sewage sludge, so leading to lower expected nutrient losses in scenario 2 (p 43-44).

Option 2 (mono-incineration and P-recovery from sewage sludge incineration ash) is estimated to result in additional annualised total EU costs (Capex plus Opex, compared to agricultural sludge application) of 138 – 569 million € per year, depending on the  size of sewage works above which this is mandated (138 M€ if sewage works > 500 000 p.e. – 569 M€ if > 20 000 p.e.). If mandated for sewage works > 50 000 p.e. estimated additional cost is 1.4 – 3.3 €/person/year, that is 1-3% of wastewater treatment costs. Correspondingly, option 2 ( > 50 000 p.e.) would generate 3 000 – 4 200 full time job equivalents across Europe.

The study underlines that cost to operators of societally positive sludge management options are higher than for options with negative societal impacts, so that policy action is therefore necessary.

ESPP will make comments to JRC on the content, methodology and conclusions of this study, probably in early 2024. Any input to these comments is welcome, to ESPP  by end 2023.

“Feasibility study in support of future policy developments of the Sewage Sludge Directive (86/278/EEC)”, European Commission, JRC Science for Policy Report, L. Egle et al., 2023

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