My bank has only had debit cards for about 6 months now. So far it has appeared to be an expense without any profit. I have always been told banks make money on debit card transactions. In what way should we be seeing income from debit card usage?

There is an income stream called interchange that the merchant side of the business pays to card issuers. In other words, it's a portion of the fee that businesses pay to accept the transctions that's called Merchant discount.