UV DISINFECTION LEADS TO REGULATORY APPROVAL OF HIGHER FILTRATION RATES AND INCREASED PLANT CAPACITY

Water utilities throughout the country are faced with increasingly stringent regulations, a public that is more educated on water quality issues than ever before and increasingly tight budgets for capital and operational expenses. Optimizing existing facilities is perhaps more important than ever, especially when faced with the need to increase plant capacity. The Frederick County (Maryland) Department of Utilities and Solid Waste Management (DUSWM) is currently facing this challenge at its New Design Road Water Treatment Plant (NDRWTP). The DUSWM has entered into a supply agreement with the City of Frederick, Maryland to provide up to 8 mgd of finished drinking water as early as 2008, which requires that the capacity of the NDRWTP must be more than doubled in the next two years while simultaneously complying with the recently promulgated Stage 2 DBP and Long Term 2 Enhanced Surface Water Treatment Rules. One possible means of achieving both the water quantity and water quality goals was to re-rate the existing filters and install ultraviolet light disinfection.An innovative use of UV disinfection to allow an increase in the plant's filtration rate from 4 gpm/sf to 5 gpm/sf was negotiated with the Maryland Department of the Environment (MDE). The use of high rating existing filters is a cost effective means of increasing plant capacity when upstream treatment processes have already been designed with the higher capacity. The addition of UV disinfection downstream of filtration can assist with the high-rating of filters by providing another barrier to passage of pathogenic organisms into the finished water supply, since filtered water quality is far more susceptible to variations in pretreatment process operation than the unit flow rate through dual media filters. Furthermore, the installation of UV disinfection will provide superior protection against pathogenic microorganisms than filtration alone, even at higher filtration rates.By incorporating UV disinfection into their plants, many utilities may have the opportunity to increase plant capacity without construction of new conventional treatment processes.