Bamboo needles wear out. I should have been prepared. I bought my first pair very reluctantly, thinking that the shafts would not be sturdy enough, and they soon became my favorites. Metal knitting needles have become my absolutely, avoided-whenever-possible, last choice, and plastic needles are hardly any better.
Sadly, I've now discovered, the points will eventually show some wear. The erosion is visible, as the points are now misshapen, but even worse, the new irregular shape creates an inaudible click at every stitch. ("Inaudible click" might be an oxymoron, but you knitters know what I mean.)
On a website about recycling I once read that any clever person could find a new use for the chopsticks they received at an oriental restaurant by converting them into knitting needles. Shaping the points was the hardest part, it was admitted, and the resulting needles might be a tad shorter, but after all, the motivation was recycling, not knitting.
The next question is, how does one recycle used bamboo knitting needles? Put them aside for the moment. Sooner or later someone, perhaps a child, will express an interest in learning to knit. Start them out with the the less-than-perfect bamboo needles, but point out that they will want to get a new pair of their own as soon as they get the hang of the craft.