The exceptions are onion white rot, potato wart disease, root-knot nematodes, potato cyst nematodes and Japanese knotweed. If these organisms are spread, the consequences can be very negative.

Thus concludes a risk assessment carried out by the Norwegian Scientific Committee for Food and Environment (VKM) for the Norwegian Food Safety Authority and the Norwegian Environment Agency.

Methods

VKM has assessed methods for the treatment of organic waste from composting and biogas plants, and examined the negative consequences the spread of harmful alien organisms can have on plant health and on biodiversity in Norway.

VKM has identified relevant organisms, processes and parameters through workshops and discussions. VKM has also visited composting facilities, been in contact with stakeholders in Norway, and done an extensive literature search.

VKM has used qualitative risk assessment, and has identified uncertainty and knowledge gaps.

Results and conclusions

"In order to avoid the spread and establishment of harmful alien organisms from composting and biogas facilities, it is crucial that the feedstock entering the plants does not contain the harmful alien organisms that cannot be removed through the treatment process," says Beatrix Alsanius, Scientific leader of the project team.

According to VKM, it is not possible to draw a general conclusion about how many times a vine or mattress must be turned.

"The reason is that process and facility conditions vary, and that the level of precision for monitoring the processes is limited," Alsanius explains. With a few exceptions, harmful alien organisms are unlikely to establish themselves in new areas if they spread from composting and biogas plants, according to VKM.

“Alien organisms from feedstocks that have only been exposed to mesophilic processes, that is, moderate temperatures, can spread and establish themselves. The result has low uncertainty," says Alsanius.

Risk-reducing measures

VKM has also considered measures that can reduce risk. VKM emphasizes that, in general, it is important to prevent highly contaminated material from getting into composting facilities.
"To keep the most serious pests and pathogens from surviving, one can use pre- and post-treatment in addition to various other methods of conversion of organic matter. This is especially true for anaerobic degradation," says Alsanius.

Organisms that may pose a risk are associated with potato and onions. Compost containing material from gardens and parks does not pose a plant health risk if it has been properly processed or if the compost has been processed during ripening.
"Without pre- or post-treatment, such material can pose a risk to plant health, if used in agriculture and horticulture," Alsanius emphasizes.

The risk assessment has been approved by VKM's Panel on Plant Health.