Pilot and full-scale studies of UV disinfection of wastewater have demonstrated that the process could consistently meet an effluent fecal coliform standard of 200/100 mL or less, depending on suspended solids and UV transmission. Since 1984 over three hundred systems have been installed at municipal wastewater treatment plants in North America. The majority of these are in treatment plants which have been using chlorination. The UV systems have been retrofitted into the existing chlorine contact tanks or existing channels. The capital costs of retrofitting compare favourably to the costs of upgrading chlorination systems, especially when de-chlorination equipment is required. As experience is gained in the operation of these UV systems, their performance has been monitored for their disinfection efficiency and cost of operation. Several installations are examined and their performance and costs analyzed. The evidence to date supports the premise that UV disinfection can meet demands for reliable effluent disinfection in a cost effective manner.
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.
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