TREATMENT PERFORMANCE:

The purpose of installing a UV disinfection system is to provide a method of disinfection that meets treatment requirements without producing known DPBs. Minimum treatment requirements for the Surface Water Treatment Rule requires 3 log removal and inactivation of Giardia and 4 log removal and inactivation of viruses. The proposed LT2ESWTR requires that filtered water systems have between 0-2.5 log additional treatment for Cryptosporidium, depending on the source water Cryptosporidium concentration, and unfiltered systems have 2-3 log treatment. In order to achieve the desired inactivation performance goals, certain steps should be followed. The following information is summarized from the USEPA draft Ultraviolet Disinfection Guidance Manual (2003).

Each facility considering the addition of UV disinfection should begin with a plan for the facility. This plan should specify exactly what the goals are in terms of the microorganism to be targeted and the desired inactivation to meet requirements of the LT2ESWTR. Details of the LT2ESWTR requirements are given in the Design Criteria section of this module.

Once disinfection goals have been determined the next step is to select the proper equipment. The facility should take time to evaluate the UV equipment available. Each manufacturer offers different designs with their own special features. The decision to purchase equipment should not be completely based on the cost of the equipment itself. Maintenance and operational costs need to be factored into the decision too.

Upon selection of the UV equipment the facility must validate the equipment to ensure delivery of the target dose. The validation process is composed of many steps which are described in detail in the Design Criteria section of this module. Additional information can also be obtained from the USEPA draft Ultraviolet Disinfection Guidance Manual (2003).

The final step in this process is the on-going monitoring of the equipment to ensure that the unit is operating under the validated conditions. The UV system is equipped with alarms and control systems to alert the facility when off-specification conditions occur. The parameters monitored are dependent on the control strategy involved. A more detailed discussion is presented in the Operation and Maintenance section of this module.