PILOT PLANT OBJECTIVES:

Pre-validation of UV reactors by manufacturers and on-site validation by some utilities reduces the need for separate pilot scale tests. The reader is referred to the validation section of this educational module for further information on the validation process. It is very doubtful that small water systems will run pilot plants, but since a variety of people may use this UV disinfection educational module, a discussion of pilot plants is included. For larger systems, there will be some cases where pilot tests are desired in order determine or corroborate design parameters, test system reliability, and evaluate operation and maintenance (USEPA, 2003). More specifically, USEPA’s draft Ultraviolet Disinfection Guidance Manual (2003) suggests that pilot and demonstration scale tests can be used to:

• Evaluate the impact of water quality that is out of the range of previous experience, e.g., high calcium or iron concentrations. (Based on work by Mackey, Cushing, and Wright as reported in USEPA’s draft Ultraviolet Disinfection Guidance Manual (2003), typical cleaning protocols and wiper frequencies were more than sufficient to clean lamp sleeves for waters with total and calcium hardness below 140 mg/L and iron less than 0.1 mg/L. Because their tests were limited to these concentration ranges, hardness, calcium and iron levels above these may require further evaluation of fouling potential, e.g., by pilot scale tests.)
• Better define design and safety factors in large systems for which optimizing the design of the UV reactor can be cost effective.
• Obtain experience in operating and maintaining a UV system in order to become more aware of the design, operation, maintenance, and training issues.
• Obtain information on a specific UV reactor or water treatment plant or both.

Typical pilot and demonstration scale test objectives include (USEPA, 2003):

• “The long-term performance and failure modes of the lamps
• The efficacy of cleaning mechanisms for lamp sleeves and UV intensity sensor windows
• The stability of UV intensity and UVT monitors
• The reliability of controls and alarm systems
• The ease of lamp and UV intensity sensor replacement, the use of reference sensors, and the maintenance of cleaning devices and solutions
• The rate of fouling on lamp sleeves and UV intensity sensor windows
• The most appropriate cleaning method
• The head loss across the reactor at various flow rates (demonstration-scale only)
• The impact on other unit operations at the WTP”

In scaling up from pilot to full scale facilities, several elements need to be kept identical including the intensity sensors, lamp and sleeve type, power system, cleaning system, cleaning frequency, and water quality (USEPA, 2003).