Once. According to the information of official website of Bengbu University, the borrowing regulations of the library are as follows: readers can borrow up to 4 books at a time for 60 days, and can renew them again before the expiration for 30 days. If they return it on time, they won't incur any expenses. If it is overdue, it will be charged as a penalty of 0. 1 yuan per day.