Disinfection of Sewage Effluents: The Jersey Experience

Abstract

About 35 years ago the island of Jersey in the Channel Islands set about rationalizing and modernizing its sewage‐treatment operations. Treatment was carried out in one central, advanced sewagetreatment works producing a Royal Commission effluent which received nominal dilution in a small stream before discharging into the sea in one of the foremost bathing areas on the island. In 1989, a thorough investigation was carried out on the options to secure an environmentally acceptable solution to effluent disposal. The investigation concluded that disinfection, in combination with a change to the outfall discharge point, offered the most cost‐effective solution. Alternative disinfection techniques were identified, which recognized the nature and sensitivity of the receiving waters and the limited space available on the site. Only ultraviolet disinfection was suitable. An ultraviolet disinfection system depends on the exposure of the micro‐organisms causing disease to their germicidal wavelength. Light of this wavelength (about 253.7 nanometres) is absorbed by the nucleic acids in the cell which damages or rearranges the genetic information, effectively rendering the cell unable to replicate and resulting in the death of the cell. In over 300 installations in North America the system has proven to be reliable, simple, economic and, above all, environmentally acceptable. An ultraviolet disinfection system is currently being installed at Bellozanne, Jersey.