UHT is well known to be better for the environment, see e.g. https://www.newscientist.com/article/dn27898-so-many-milks-but-do-their-health-claims-really-stack-up/
However, our local council does not recycle the UHT milk cartons (but does recycle plastic bottles). Is it still more sustainable?
I am thinking so because recycling Tetra Paks provides only limited benefit, and plastic bottles can only be recycled so many times anyay; However but I haven't seen any study that considers the benefit of UHT over the cost of unrecycled cartons.