Results of a National Survey of POTWs Using UV Disinfection
Abstract:As part the Water Environment Research Foundation Project 04-HHE-4, the authors surveyed major publicly owned treatment works (POTWs) in the United States (US) with ultraviolet (UV) disinfection systems. The US Environmental Protection Agency (EPA) definition of major POTW was used: state or municipally owned wastewater treatment plants with an average dry weather design flow of greater than 0.95 million gallons per day (MGD). The two main goals of the survey were to examine the distribution of UV use across the country, and to understand issues in choosing, designing, installing, and operating UV units for wastewater treatment.
For the first goal, the total number of major POTWs in the US and the distribution of POTWs using UV was established from three databases: the EPA Clean Water Needs Survey (CWNS), the EPA Envirofacts (NPDES) database, and the US census. Based on this information, roughly 4,450 major POTWs operate in the US. UV usage was determined from the CWNS and vendor databases. These databases were cross-checked against the list of major POTWs, to ensure that only UV systems at major POTWs were included. The analysis indicated that as of 2005, 920 major POTWs used UV (with an error of ∼15%), although the methods used in this study may underestimate UV usage, because vendor data may be incomplete for new UV facilities and for vendors that went out of business, were acquired by other companies, or are very small.
Overall, the databases show a number of trends.
• Approximately 21% of all major POTWs use UV.
• Based on the sales of UV systems, UV use is growing, with approximately 40% of all UV systems sold between 2001 and 2005 (the last year for which information was available).
• UV use is distributed across the US, with all states except Delaware having at least one major POTW with UV disinfection.
• There are clusters of high UV use in the Pacific northwest, the middle of the country around Colorado, and near the Ohio River valley. Kansas has the highest adoption rate, with more than three quarters of the major POTWs using UV.
• The largest plants are less likely to use UV for disinfection, and of those that do, a lower percentage use the older low pressure low output (LPLO) lamps. This is likely due to slower adoption by large plants of this relatively new technology.
• As plant size increases, a higher percentage of plants use medium pressure (MP) lamps. MP lamps have higher energy output, and MP systems use a smaller footprint and require fewer lamps than LPLO or low pressure high output (LPHO) technologies. These characteristics are likely to be important in the dense, space-restricted urban areas where larger plants are located.
In the second part of this work, 103 POTWs were asked about their experiences with UV. All used at least secondary treatment, and almost half (47%) used tertiary treatment. The biggest driving forces for changing to UV disinfection were a safer work environment and elimination of gas chlorine and/or chlorination/dechlorination. Most respondents (62%) found the UV system to be more complex than their previous disinfection system, but 86% said their transition to UV was easier than expected or "not too bad." The most important factor for the success of a UV project was the consultant's skill and knowledge, followed by the vendor characteristics and visiting other facilities (both equally important), the skill and knowledge of staff at the POTW, and finally, other resources such as books and papers. The most important vendor characteristic was system design, followed by technical knowledge, responsiveness, and system features. The size of the company and sales staff were relatively unimportant.
For operations and maintenance, the median classroom training time across all plants was 6 hours, the median hands-on training time was 10 hours, and the median maintenance time was 4 hours/week; however, the answers varied by orders of magnitude, from 1 to 40 hours for classroom training, 1 to 80 hours for hands-on training, and 0.2 to 120 hours/week for maintenance. Median annual costs were $11,000 for lamps (ranging from $600 to $250,000), $2,000 for sleeves (ranging from $130 to $70,000), and $3,000 for ballasts (ranging from $110 to $200,000). Both costs and time requirements generally increased with increasing plant size, but variability was large; some small plants had very high costs/time requirements and vice versa. MP lamps had a median lifetime of 5,000 hours, half that of the LP lamps; MP lamps also had median annual costs for lamp components that were two to five times higher than those for LP lamps, although again, the reported values ranged over several orders of magnitude.
Finally, respondents gave advice to facilities considering a change to UV disinfection. The most common pieces of advice were
• Do thorough research to make sure that UV is applicable to the facility and to find out what costs and labor time requirements to expect, along with potential problems
• For easier and/or less maintenance:
○ Cover the UV system with a roof or building
○ Use automatic wipers
○ Use multiple flow channels or a bypass
• Beware of algae and animals (insects, fish) in and around the UV equipment
More information and results can be found in the WERF Report, Disinfection of Wastewater Effluent: Pros and Cons of Technologies (2007).
Document Type: Research Article
Publication date: October 1, 2007
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