Using the Checkpoint Bioassay To Increase UV System Energy Efficiency

Checkpoint Bioassay testing was conducted on the existing Ozonia Aquaray 40 HO VLS ultraviolet disinfection system (UV system) that is installed at the El Dorado Irrigation District (EID) (Placerville, California) Deer Creek Wastewater Treatment Plant. Based upon the prior testing of the Ozonia reactor, it must operate with an assumed UVT value of 55 or 65 percent, whichever is more conservative. The operation of the UV system is controlled by a programmable logic controller (PLC), that uses a step function consisting of two equations. The first equation controls system performance when the UVT is between 55 percent and 64.9 percent, while the second equation controls the UV system when the UVT is ≥ 65 percent. Operation is not allowed if the UVT drops below 55 percent. The purposes of this testing were 1) to characterize and document the performance of the UV system at high ultraviolet light transmittance (UVT) values (i.e., 77 percent) and 2) to utilize the results from the testing to generate a single equation that could be used for energy efficient system control. Because of this checkpoint bioassay testing, UV system performance at the higher UVT values was demonstrated. The results from this testing resulted in the developement of a single control equation that allowed the system to operate at UVT values ranging from 55 to 77 percent. Use of this newly developed equation will result in an estimated annual savings of almost 31,000 in energy and lamp costs to the EID.