Carbon monoxide in the atmosphere: threshold value changed from 50 to 250 mg / Nmc, applicable for an asphalt production plants and established by a Services Conference in Tuscany, in response to a “particular” application of Decree February 5, 1998 concerning to the recovery of road milled 17.03.02 CER “at cold temperature.”
Generally the existing asphalt production plants are not able to respect the threshold value of 50 mg/Nmc for Carbon Monoxide (CO) due to intrinsic issues of the productive processes that implies the transfer of thermal energy coming from a rotational furnace (normally feed by oil or natural gas) to a the aggregates that constitute the basic conglomerate. Is a highly energy demanding process that must ensure a really elevated temperature at the moment of the aggregates and other ingredients mixture, including the bitumen. In some plants it is also possible the addition of different percentages of road milled to the mixture, added as such after a volumetric reduction: the recovery of the road milled are about 20% in plants “non-specialized,” and in those “specialized” for the recovery of milled material is up to 99%.
The ventilation system of the plant, which ensures the “breathing” of the production process, is equipped with a dust filter before discharge into the atmosphere: with proper precautions, this line can guarantee very low concentrations of the effluent, even for the most elderly and unspecialized plants for the recovery of milled for the most of the parameters limits prescribed by Part V of Decree no. 152/2006. Nevertheless for the carbon monoxide, within the current state of technology, we cannot guarantee the limit of 50 mg / Nm³. Technical reasons were shared with the Environment Office of SITEB (Italian Association Bitumen Asphalt Road) and exposed to these institutions and was sought the change of the Unique Environmental Authorization-UEA (Decre 59/2013) for the point concerning carbon monoxide and raise the limit imposed by 50 mg / Nm³ to 250 mg / Nm³.
The authorities have shared the technical reasons outlined by Ecosurvey® and approved a variant for the UEA applicable for the specific site with new emission limit for carbon monoxide parameter: 250 mg / Nm³.
Considering the significant attendant environmental benefits the recovery of the milled road, given that almost all of the patrons of asphalt are public administrations, such purchases should necessarily be subject to the requirements of green procurement (GPP Ministry of Environment) and provide that any provision asphalt includes significant percentages of recovered milled road: a resource, not waste.