CARBON AND ENERGY FOOTPRINT ANALYSIS OF AN ADVANCED OXIDATION PROCESS FOR REMOVING NDMA IN INDIRECT POTABLE WATER REUSE OPERATIONS

摘要

The indirect potable reuse system operating in Orange County, CA is currently one of the largestrnwater reuse systems in the world, with average flow treated of 62 MGD, planned for futurernexpansion. The water reuse process is operated by the Orange County Water District (OCWD),rnusing the treated wastewater from the adjacent Orange County Sanitation District (OCSD) Plantrn1. The wastewater train includes primary and full secondary treatment with nutrient removal; thernwater reuse train includes microfiltration (MF), reverse osmosis (RO), a UV/H2O2 advancedrnoxidation process (AOP), and lime conditioning. N-Nitrosodimethylamine (NDMA), classifiedrnas probable human carcinogen by the US EPA, is a contaminant of concern for this system andrnits effluent concentration is regulated at 10 ng/L. The goal of this research is to show the weightrnof the AOP on the energy footprint of the water reuse process at OCWD, and on the combinedrnprocess at OCSD-OCWD. We also show the effects of varying NDMA removal on AOP’srncarbon and energy footprint for increasingly stringent effluent limits. The AOP’s carbonrnfootprint is dominated by the carbon equivalent of the energy footprint. This is amplified duringrnpeak periods in comparison to the nighttime, due to the reduced efficiency for power generationrnthat power utilities experience during peak power demand periods. Therefore, even though thernconsumed energy could be the same during different diurnal periods, carbon footprint could varyrnsignificantly. This suggests that flow equalization, when possible, would be a solution to mitigaterncarbon-equivalent emission, while leaving the energy-footprint and process throughputrnunaltered.