i would be tempted to add a numeric or alphanumeric string to the beginning of your order number rather than a random number, as you would want to ensure the id is unique.
in this case, you could add the characters you desire in front of the php statement...
eg <?php echo($row_WADAtblorders['orderID']); ?>
becomes
123<?php echo($row_WADAtblorders['orderID']); ?>
or alternatively, concatenate the returned php value
<?php echo('123'.$row_WADAtblorders['orderID']); ?>