Teloon makes tennis balls and also runs a recycling programme for old balls. If you are a member of a club with tennis facilities, you might have seen one of their collection bins.
Alternatively, if you can contact them at their website to arrange for collection of old balls. You can also reach them on Carousell.
Like the ActiveSG running shoe collection, the tennis balls are sent to an NEA grinding plant. Then, the rubber in old balls is used for the construction of running tracks, fitness corners and children playgrounds.
Their recycling programme is endorsed by the Singapore Tennis Association, ActiveSG, and the NEA.