processes. Their purpose is to facilitate or regulate the nutrients absorption by plants
or improve their resistance to abiotic stress.
The apprehension of the legal definitions of the terms waste and products applied
to WWTPs sludge as fertilizing materials brings out a harmony and the coherence
between these terms for the use of sludge as fertilizer for agricultural applications
after their stabilization, as required and legislated. Nevertheless, before being considered as a recoverable waste that can be integrated into a circular economy process,
sludge should be safe for human health and without any harm to the environment,
creating hence no risk for surface water or groundwater, neither air nor soil or flora
and fauna (L125-1) [12]. Therefore, an assessment of the hazardous properties
should be made taking into account the complex composition of the sludge [1].
Considering the sludge formation process, its composition closely related to that
of the initially treated effluent, and the nature of its pollutant load, various types of
compounds with negative impacts on health and soil could be present (Fig. 2). The
persistent substances concentration effects and their mixing may reinforce the
danger of the product resulting from the WW treatment. The key point of ethical
issues about sewage sludge valorization is related to the nature of the product
emanating from a depollution process to become a fertilizer with added agricultural
value. In fact, the sludge use will depend first on its legal status: Is it a by-product
of effluent treatment used as an input into a second activity that is agriculture
according to the circular economy principles? Should we first ensure the safety of
this by-product before considering its recycling in a circular economy?
A comparison of recent data available on the dangerousness of persistent compounds that can be found in sludge is required with the implementation of direct tests
and methods of specific analysis and calculation considering the different hazardous
properties to be evaluated [1].
Taking into account the limitations of the biological treatment of certain polluting
substances such as endocrine disruptors and metalloids, as well as the risk of
cultivable and non-cultivable pathogenic microorganisms’ presence [91, 98] for
humans, animals, and the environment, could we continue to exploit agricultural
sludge without concern? In addition, without being exempted of toxic compounds or
pathogens whose quantification should be possible, mustn’t we take a strong decision regarding their safe recycling?.
As it is known, a standard is a viable tool that responds to a specific problem.
Should it be required to revise the standard specific to sludge reuse in agriculture
(NF U 44-095) [99] and update its specifications to meet a crucial need for safety and
of the environment protection?
In France, most of the produced WW sludge is used in agricultural farming
(47%), particularly in cereal crops (3% of the agricultural area). WW sludge is
also mixed with green waste and composted (26%); of the ten million tons of sewage
sludge produced each year in France, three million are now valued this way. The
compost is then sold to farmers with the objective to reduce the use of chemical
fertilizers, although this practice is still limited to 1% of the useful agricultural area.
However, the “Waste Directive” adopted in 2018 by the European Union, Directive (EU) 2018/850, requires Member States to reduce significantly waste disposal
70
E. Ammar et al.
or improve their resistance to abiotic stress.
The apprehension of the legal definitions of the terms waste and products applied
to WWTPs sludge as fertilizing materials brings out a harmony and the coherence
between these terms for the use of sludge as fertilizer for agricultural applications
after their stabilization, as required and legislated. Nevertheless, before being considered as a recoverable waste that can be integrated into a circular economy process,
sludge should be safe for human health and without any harm to the environment,
creating hence no risk for surface water or groundwater, neither air nor soil or flora
and fauna (L125-1) [12]. Therefore, an assessment of the hazardous properties
should be made taking into account the complex composition of the sludge [1].
Considering the sludge formation process, its composition closely related to that
of the initially treated effluent, and the nature of its pollutant load, various types of
compounds with negative impacts on health and soil could be present (Fig. 2). The
persistent substances concentration effects and their mixing may reinforce the
danger of the product resulting from the WW treatment. The key point of ethical
issues about sewage sludge valorization is related to the nature of the product
emanating from a depollution process to become a fertilizer with added agricultural
value. In fact, the sludge use will depend first on its legal status: Is it a by-product
of effluent treatment used as an input into a second activity that is agriculture
according to the circular economy principles? Should we first ensure the safety of
this by-product before considering its recycling in a circular economy?
A comparison of recent data available on the dangerousness of persistent compounds that can be found in sludge is required with the implementation of direct tests
and methods of specific analysis and calculation considering the different hazardous
properties to be evaluated [1].
Taking into account the limitations of the biological treatment of certain polluting
substances such as endocrine disruptors and metalloids, as well as the risk of
cultivable and non-cultivable pathogenic microorganisms’ presence [91, 98] for
humans, animals, and the environment, could we continue to exploit agricultural
sludge without concern? In addition, without being exempted of toxic compounds or
pathogens whose quantification should be possible, mustn’t we take a strong decision regarding their safe recycling?.
As it is known, a standard is a viable tool that responds to a specific problem.
Should it be required to revise the standard specific to sludge reuse in agriculture
(NF U 44-095) [99] and update its specifications to meet a crucial need for safety and
of the environment protection?
In France, most of the produced WW sludge is used in agricultural farming
(47%), particularly in cereal crops (3% of the agricultural area). WW sludge is
also mixed with green waste and composted (26%); of the ten million tons of sewage
sludge produced each year in France, three million are now valued this way. The
compost is then sold to farmers with the objective to reduce the use of chemical
fertilizers, although this practice is still limited to 1% of the useful agricultural area.
However, the “Waste Directive” adopted in 2018 by the European Union, Directive (EU) 2018/850, requires Member States to reduce significantly waste disposal
70
E. Ammar et al.