Call order_id in customer email

In the email sent to the customer directly after completing checking, I need to display the order_id in a section of the email.

The module that I am editing is the bank deposit payment module which I want to send the order number as part of the banking information to be displayed in the memo when wiring the payment.

Here is the language define:

 
 
   define('MODULE_PAYMENT_WIRETRANSFER_TEXT_EMAIL_FOOTER', 
   "Please use the following banking information to deposit or wire transfer payment for your order:\n\n" .
   "\nAccount No.:  " . MODULE_PAYMENT_WIRETRANSFER_ACCNUM .
   "\nBSB Number:   " . MODULE_PAYMENT_WIRETRANSFER_BSB . 
   "\nAccount Name: " . MODULE_PAYMENT_WIRETRANSFER_ACCNAM . 
   "\nBank Name:    " . MODULE_PAYMENT_WIRETRANSFER_BANKNAM .
   "\nMemo:         " . "Order No." . $order_id .
   "\n\nYour order will be shipped once payment has been verified as cleared in the above account.\n");
  }

I need a function to call the correct order_id from the database and give $order_id this value.