Environmental life cycle comparison of conventional and biological filtration alternatives for drinking water treatment

Abstract

Drinking water utilities face challenges with meeting increasingly stringent regulations, often at higher costs and operational complexity, and all are expected to increase, especially with deteriorating source water quality. Biofiltration, which enables organic matter biodegradation, may be used as an alternative to conventional filtration to reduce chemical coagulant requirements while maintaining equivalent treatment. However, the advantages and disadvantages of filtration options depend on many factors, including source water, complex water chemistry interactions, and other site-specific conditions, such as the use of pre-ozonation to improve biofiltration performance and different types of chemicals for coagulation and disinfection. To identify and quantify the environmental and performance trade-offs between conventional and biological filtration, with and without pre-ozonation, a comprehensive modeling and systems approach is needed. To this end, life cycle assessment methodology was used to develop a new model in order to compare the environmental impacts of drinking water treatment trains that used conventional filtration, nonozonated biofiltration, and ozonated biofiltration. All were designed to produce the same water quality, in terms of total organic carbon (TOC), turbidity, Giardia, Cryptosporidium, and virus reductions. To account for different treatment targets, 4 treatment scenarios (summarized by differences in TOC removal requirements: 30%, 40%, 50%, and enhanced coagulation requirements based on U.S. regulation) were evaluated. The relative environmental impacts of all three treatment train alternatives, under each treatment scenario, were evaluated for 60 000 unique source waters. Generally, ozonated biofiltration had the worst environmental performance while nonozonated biofiltration had the lowest environmental impacts. However, the comparison of nonozonated biofiltration to conventional filtration depended on the treatment scenario and source water quality. For example, under the 50% TOC removal treatment scenario, nonozonated biofiltration had better relative environmental performance when the source water had high alkalinity (>50 mg L⁻¹ CaCO₃), low specific ultraviolet absorbance (SUVA) (<2.75 L mg⁻¹ m⁻¹), high pH (>7), and high temperature (especially >20 °C). Under the enhanced coagulation treatment scenario, both conventional filtration and nonozonated biofiltration had similar environmental impacts for most source waters. This new model and comprehensive water quality analysis can help utilities decide which filtration alternative best meets their needs, especially by reducing environmental impacts while improving drinking water quality.