Strategies for selecting indicator compounds to assess attenuation of emerging contaminants during UV advanced oxidation processes

A ranking system for monitoring-based process control was developed to select indicator compounds that can predict the attenuation of a broader range of trace organic compounds (TOrCs) in reclaimed water by low pressure (LP) and medium pressure (MP)-UV advanced oxidation processes (AOPs). The selected TOrCs were classified into three groups depending on their relative reactivity to UV direct photolysis and •OH oxidation. Group 1 includes the photolabile TOrCs, which are easily photodegraded with no additional oxidants by either LP or MP-UV light and include acesulfame, diclofenac, and sulfamethoxazole. Group 2 consists of the moderate photodegradable compounds with high reactivity of •OH oxidation, which include benzotriazole, fluoxetine, and hydrochlorothiazide as indicator compounds for assessing LP-UV AOP and propranolol, diltiazem, and diphenhydramine for MP-UV AOP. Group 3 is photo-resistant TOrCs, but highly reactive with •OH radicals and includes carbamazepine and DEET as appropriate indicator compounds. Therefore, the proposed ranking system is expected to provide a comprehensive monitoring tool to water reuse utilities for prioritizing a list of indicators to assess the treatment efficacy of UV AOPs that allows for subsequent operational control to achieve the treatment goal. This is the first strategic framework and guidelines for building a customizable tool of process control that depend on the site-specific occurrence profile of wastewater effluents and the UV system (UV lamp spectral output and power density).