It might be a common practice for consulate to do that:
Russian consulate in SF did it in 2017 in response for an eviction related to "Russian gate" [1]
The U.S used shredder to destroy document in Iran in 70s but
Iranians were able to piece back the document to get intel from it so I guess the intelligence community learned a lesson there.
Shredding is absolutely fine. The modulating factor is the size of the pieces and total number of pieces that are shuffled. The problem scales with N^2 (?).
If the shredder shreds with 1mm particles, it will be pretty much impossible to piece it together and it will depend on how each page mixes with other particles. Even if the particle size is 100mm, if you throw those pieces in a pile of 500 tons of paper, and shuffle it sufficiently, then it will be impossible to piece together the original source.
The U.S used shredder to destroy document in Iran in 70s but Iranians were able to piece back the document to get intel from it so I guess the intelligence community learned a lesson there.
[1]: https://www.msnbc.com/all-in/watch/why-was-the-russian-consu...