In a content supply system, content data is supplied from a content supply apparatus to a content playback apparatus via a network. The method includes the steps of providing a thin film with a thickness of 5 micrometers or less; providing a bonding layer of oxide with a thickness that is equal to or greater than the thickness of the thin film with the bonding layer formed by low pressure chemical vapor deposition. Disposed on a first side is a stud that is connectable to a bracket. The sludge included in effluent which flows from the biological steps is separated in a sedimentation tank 41.