My son (who is now 4 1/2) was a biter, and I worried all the time he would get kicked out of daycare or that it would never stop. He would bite at school sometimes, but not every day, and he would also bite us and his twin sister which was making me crazy. He also got bitten himself at school by other kids, so it's totally normal, but it's hard when you are told about it and you feel bad for the other kid and their parents.
We told him all the time "no biting", and the daycare teachers were good about that too. We (and the teachers) tried to give him things to bite on if he had the urge to do so. We would tell him to bite "this" not people. It seemed like it would never end, and then it was only happening once in a while, but it finally ended. I think he was around 3 1/2.
I think he was biting out of frustration at not being able to express his feelings about something or get the words out that he wanted to say. He would also do it if he wanted something that another child had or if another child got in the way of what he was doing.
It's hard for kids your son's age to be around other kids and share toys, etc. The key is that the teacher needs to be on top of it. Maybe you can have a talk with her about your concerns. I wish you lots of luck. I know how frustrating it is.