A sewage treatment plant in turn produces waste. These are sewage sludge, the final residue that comes from the purification treatment of urban and suburban wastewater, civil and industrial.
These sludge are produced at various stages of purification and flow into the so-called sludge line of the sewage treatment plant. Among the various ways of disposal is the reuse of sludge in agriculture, the subject of regulatory intervention in recent months and the comparison of different opinions.
Treatment and disposal of sewage sludge
Before being disposed of, sludge can undergo various treatments to stabilize the organic component, to reduce the presence of water and increase the dry component.
Depending on the origin and quality of the sludge, the bestowal may be in an incinerator, in landfill for special waste or in agriculture as fertilizers.
Disposal of sludge in agriculture in Italy
Among the ways of disposing of sludge, in Italy reuse in agriculture affects about 30% of the sludge produced.
Treated sludge is allowed to stabilise organic components, they must not contain harmful or toxic substances and remain within certain thresholds for substances such as heavy metals.
The 1992 Decree governing the sector was joined by regional initiatives and intervention by the Supreme Court which sometimes created conflicting situations in the management of sludge; as recently in Lombardy, where stalls in disposals have been created, reducing the supply to agriculture and on the other hand not making it possible to resort massively to incinerator or landfill.
The latest developments
The issue of sludge in agriculture is a contentious issue because it clashes with the protection of the environmentand soil, as well as with the safety of agricultural products. And in recent months the debate in Italy has been intense.
This comparison of different positions is part of a recent state intervention withArticle 41 of the so-called “Genova Decree”. With this regulatory initiative, the limits allowed for the presence of hydrocarbons in sludge for agriculture have been increased in an attempt to keep the disposal needs together and environmental protection. In the absence of a comprehensive regulatory framework, the risk is that of excessive storage, which is also risky. However, these new limits have been criticized by environmental groups for increasing the permissible threshold under the previous Supreme Court ruling in 2017.
More recently Alessandro Bratti, Director General of the Ispra (Institute for Environmental Protection and Research), has been critical of the use of sludge in agriculture, especially if mixed, i.e. if they come from both urban and industrial wastewater, due to the risk of dispersion of pollutants.
But, according to Alessandro Bratti, the regulatory framework is still to be defined and deepened, especially with regard to traceability and controls. This is in the face of European countries that have decided to ban sludge altogether in agriculture, believing that there are more risks than benefits.
If sludge can be a resource in reuse, an overall picture of the real costs and benefits of their disposal in agriculture is needed, as part of a comprehensive review of the regulatory framework that ensures safety for people and environmental protection.