Error occurs when Titanium, Krastorio 2 Spaced Out, and Planet Rubia are all enabled.
I already reported this to the Titanium discussion, but I found that all BZmods that use the redo_recycling function have the same error (Silica & Silicon, Lead, etc.). I decided to report this issue here as well, as I thought it might be better if it could be resolved on the Planet Rubia side.
I am not a native English speaker, so I apologize if my wording is rude. Thank you for making this mod to add such a unique planet.

bztitanium/data-util.lua:1899: bad argument #1 of 2 to 'pairs' (table expected, got nil)
stack traceback:
[C]: in function 'pairs'
bztitanium/data-util.lua:1899: in function 'redo_recycling'
bztitanium/data-updates.lua:10: in main chunk

4.637 Loading mod bztitanium 2.0.25 (data-updates.lua)
4.650 Error ModManager.cpp:1758: MOD "bztitanium" の読み込みに失敗しました: bztitanium/data-util.lua:1899: bad argument #1 of 2 to 'pairs' (table expected, got nil)
stack traceback:
[C]: in function 'pairs'
bztitanium/data-util.lua:1899: in function 'redo_recycling'
bztitanium/data-updates.lua:10: in main chunk
4.683 Loading mod core 0.0.0 (data.lua)
4.749 Checksum for core: 1117214423
4.777 Error ModManager.cpp:1758: Error in assignID: recipe-category with name 'recycling' does not exist.

Thank you for your very detailed report.
BZTitanium was looking at a recipe called "kr-crush-makeshift-biorecycling-science." The issue is on the BZ mod side. I fixed it on my computer by changing:

in bztitanium/data-util.lua:1899:
Old Line: for _, product in pairs(recipe.results) do
New line:for _, product in pairs(recipe.results or {}) do

Unfortunately, I can't update their mod for them, so all I can do is report it. Thank you for your time.

Thank you for your response.
Until BZmods is updated, I will apply the fixes you have presented myself.