PROGRESS OF WASTEWATER UV SYSTEMS – A SURVEY OF LARGE SYSTEMS

One of the most popular means used today for disinfection of wastewater worldwide is ultraviolet light (UV). As part of a recent study funded by AwwaRF, 19 wastewater treatment facilities, all of which having design flows more than 100 mgd and different water quality requirements and discharge limits, were surveyed. In the wastewater industry, compliance with discharge limits is the key factor in the success or failure of the UV system.The purpose of the survey was to examine issues such as level control, the relationships between low flow and treatment effectiveness, and the use of backup power. Each facility was contacted to validate information and to collect performance information. As more than 30 percent of these facilities were located outside the US, the survey provided a worldwide assessment of use of UV technology.Level control was established using a control device and then adjusted to reflect the flow discharged from the plant. The most frequently used flow control devices were found to be gates, weirs, and penstocks.Performance impacts attributable to low flow were difficult to quantify because, in many cases, plant operators indicated that they did not review data unless the system was in noncompliance. Average daily flows at the 19 plants were found to be one-third to one-half the design flow, which provides sufficient capacity at low flow conditions.Backup power supply was provided either through dual power feeds or by backup generators. None of the facilities surveyed indicated the use of an uninterruptible power supply for backup power.The survey found that large UV systems can be successfully used at facilities with design flows greater than 100 mgd. Any difficulties with scale-up have been successfully addressed by the UV system manufacturers. The systems appear to be meeting their discharge limits regardless of the discharge, influent water quality, or geographic location of the facility.One of the facilities surveyed had installed an LP system in the 1990s and is now converting to an LP-HI system. This indicates that the wastewater industry will continue to use UV and that its use at large wastewater facilities will increase. This paper discusses the results of the survey and the implications of UV use to wastewater facilities being constructed today.