I'll post the answers here, in case anyone else is wondering.
From my very green neighbor Mary:
1. Paint – we did some painting and I found paint for our old paint colors that is still good – can I donate that somewhere or do I just let it dry out and put it out in the garbage?
2. Dirty kitty litter – I am buying the Feline Pine stuff now – should I put that in the industrial composting?
Here's what I found:
1. You can bring the paint to the South Hennepin Dropoff Center in Bloomington. There's a paint swap section where you can leave paint and people can take it.
From their site: "Reuse center
Residents may pick up free of charge items designated by the County for reuse. The County does not guarantee these products and items selected are used at their own risk. The following are available: oil-based paint, adhesives and glues, motor oil, household cleaners, latex paint, automobile products."
2. Cat litter can't go in the Linden Hills composting program because of the risk of parasites. I found some online sites, though, that talk about composting cat litter; one site said you have to compost it for 18 months to kill any parasites.