Efficient advanced oxidation technologies against chemical threat in drinking water distribution systems

Abstract

Vulnerability of drinking water distribution systems (DWDS) is one of the main issues of concern to regulatory agencies and water utilities. Indeed, the threat of a deliberate (or even accidental) contamination of water supplies is real and is permanently under consideration. Although measures against such contamination events have been intensified in the last few years, major knowledge gaps still exist in what concerns the feasibility of the detection and remediation methods, especially those related with contamination by chemicals. This has been recently addressed in a European Project named SecurEau (www.secureau.eu) whose main objective was to launch an appropriate response for rapidly restoring the use of a DWDS after a contamination event. This chapter intends to present the developments made concerning the remediation methods, proposing several decontamination procedures, based on advanced oxidation processes (AOPs), for the treatment of waters/solids contaminated with key chemicals. Based on several criteria, three model compounds were selected: an organophosphate (chlorfenvinphos - CFVP), an herbicide (paraquat - PQ) and a brominated flame retardant (2,2', 4,4', 6-pentabromodiphenyl ether (BDE-100)). The treatment of waters contaminated with PQ was studied by both Fenton and photo-Fenton process under off-line conditions (batch reactor) and by Fenton's process under on-line conditions (i.e., in-situ of a pilot loop reactor, simulating a DWDS). Out of the pipelines, the photo-Fenton approach has great advantages over Fenton's process since it allows a significant increase on the PQ degradation rate and, particularly, on the mineralization degree (96% after 1 h of reaction). Concerning the in-situ treatment, the Fenton's reagent proved to be effective for the treatment of PQ-contaminated waters, and it was shown that some deposits and pipe materials could be used as catalysts, avoiding the addition of other chemicals inside the network. Water and deposits contaminated with CFVP can also be treated insitu by Fenton's reagent making use of the active iron available either on pipe materials, on deposits attached to them or on loose deposits as catalysts of the process. The direct photolysis methodology was successfully applied to the off-line remediation of BDE-100 contaminated waters. Batch experiments with pure water revealed a high BDE-100 degradation profile for the first five minutes of exposition to UV-light (1.6×10-6 Einstein/s). Therefore, it has been proved that several solutions exist using AOPs for the effective treatment of waters and deposits contaminated with various chemicals, with different properties; this might be an important step forward towards chemical threats in drinking water distribution systems.