Aircraft never had problems with air filtration - they never bothered. The major change since aircraft banned smoking is that the air is actually staler and stuffier on board.

When you're going several hundred miles an hour through clean air, diverting some through the cabin is never a problem. The actual expense is in warming it to a sane temperature. As it's that warming that takes energy, now they don't have the smoke, they don't refresh the air so much.