ESPP organised a one day dialogue meeting between scientists, stakeholders and ESPP members and partners on questions around the use of sewage biosolids in agriculture. This will be presented in detail in a future SCOPE Newsletter. In conclusion, it is clear that different stakeholders, industries and countries have widely varying positions. On the one hand, there are concerns about the proven presence of different contaminants, which the “precautionary principle” suggests to not disseminate. However, there seems to be no evidence that these contaminants pose significant risk to health or to the environment where sewage biosolids are appropriately managed (this should include monitoring zinc and copper, and limiting spreading as a function of their levels if necessary). Accumulation of contaminants or leaching to groundwater should also be avoided, including heavy metals, organic contaminants and microplastics. On the other hand, agricultural valorisation of sewage biosolids offers benefits: recycling of phosphorus, nitrogen and other nutrients; return of carbon to soil, and is cost-effective for both taxpayers and farmers.
Technical phosphorus recovery processes enable recycling of phosphorus without release of contaminants to the environment, so ensuring depollution and safety. Most participants however agreed that there is no one best solution: different options for sewage biosolids management fit different local contexts. Thermal valorisation responds to the needs of regions with low agricultural demand, for example densely urban areas and regions with significant supply of animal manures. In countries with high agricultural demand, farmland application of biosolids under strict quality control conditions can enable nutrient and organic carbon recycling.
Anaerobic digestion of sewage biosolids is effective for energy recovery, as well as sanitising and stabilising sewage sludge, and some phosphorus recovery processes, such as struvite precipitation, are compatible with both thermal sludge valorisation or agronomic application of biosolids organic content. Many of the contaminants which currently generate concerns in sewage sludge are also found in animal manures and other organic secondary materials (in particular pharmaceuticals and antibiotic resistance genes). Further research and monitoring are strongly needed, including into improving organic contaminants removal in biosolids treatment, optimisation of energy recovery, and development and implementation of nutrient recovery processes. In all cases, the priority should be reduction at source and preventing that contaminants enter municipal sewage.
It was underlined that a strong point of ESPP is to bring together in dialogue a heterogeneous range of industries and stakeholders. ESPP should not promote a particular route or technologies for sewage biosolids management and phosphorus recycling, but should promote the advantages of different approaches appropriate to different regional contexts, subject in all cases to quality control, transparency and to effective nutrient recycling.
Meeting presentation slides are available (soon) at www.phosphorusplatform.eu/activities/conference/meeting-archive/1788-espp-meeting-sludge-2018