Manipulating Head Loss to Improve Disinfection Efficiency of UV Reactors

The ideal hydraulic behavior for UV reactors is generally considered to be near plug-flow with effective lateral or transverse mixing. Typically, head loss increases as the transverse mixing increases and vice versa. Accordingly, head loss is a critical factor in determining a UV disinfection system's design application. Head loss is typically caused by friction and turbulence created as water flows through the reactor channel or is redirected or affected by reactor components such as lamps and deflectors. Extremely high head loss in a UV system can result in a loss of disinfection or in an upset of upstream processes such as clarification and/or filtration. Therefore, head loss through a UV reactor is most frequently associated with negative connotations. Seldom considered is the beneficial effect on disinfection efficiency due to head loss gain associated with increased transverse mixing. This paper illustrates the ability to increase the disinfection performance of UV reactors by manipulating the head loss associated with cross-flow lamp arrays.Examination of head loss and Reynolds number on an open-channel vertical lamp system indicates that turbulent hydraulic conditions are created under typical operating conditions, which provides for effective mixing and subsequent high reactor performance. Dose-flow curves generated during bioassay validation testing of the same type of reactor revealed that disinfection efficiency improved with increasing flow. In a separate evaluation focusing on the impact of the side deflectors, results indicate that the vertical deflectors increase the disinfection efficiency of the reactor by adding turbulent hydraulics while concurrently increase the head loss. Past research is reviewed to access the sensitivity of reactor performance to approach.The paper will demonstrate that head loss “payments”, while certainly an important design parameter, can generate a “return on investment” via the opportunity to lower O&M costs due to the gain in disinfection performance resulting from the efficient design of UV reactors employing cross-flow lamp arrays.