Single-serve aluminum or plastic pods create a lot of unnecessary waste. Extracting and processing raw materials is not always cheap, and both making and recycling them are energy-intensive processes. So, even if you do recycle, a lot of raw materials and a lot of energy is used, which creates a lot of pollution and leaves a large carbon footprint.
At the heart of this, there are three big problems with the recycling schemes for coffee capsules. Firstly, it's not that easy to recycle Nespresso capsules. You have use Nespresso's own recycling scheme, since you can't throw used capsules out with other normal domestic recycling. Secondly, all that aluminium still has to be produced to make the capsules in the first place, which takes a lot of energy and raw material, then the recycling process itself takes up a lot of energy and still produces waste and pollution. Finally, most people just don't use it.