BROMIDE REMOVAL IN SOURCE WATER BY ELECTROLYSIS – A PROCESS FOR REDUCTION OF DBPs IN DRINKING WATER

摘要

Brominated THM specie is seventy five percent of the four regulated TTHM and has significantly greater implications, especially DCBM, as drinking water contaminant than chlorinated THM regarding human health. Of the four individual trihalomethanes, only high DCBM exposure was associated with spontaneous abortion both alone and after adjustment for the other THMs [1]. This project explored the use of electrolysis with silver electrodes, coated Ti electrodes (DSA)* and combination of both to remove bromide from California SWP at Palmdale Water District Treatment Plant, CA, USA. Herbert Henry Dow used electrolysis coupled with air stripping of brine that has high proportion of bromide to manufacture bromine [2]. In surface water treatment, bromide occurs at very low levels and may form very low levels of hypobromous acid (HOBr), hypobromic acid (HBr) and hypobromite (Obr-) ions during electrolysis especially if the energy provided is below the ionization energy for bromide. These byproducts are difficult to remove by air or gas stripping and make bromine available to form TTHM downstream. With silver electrodes at ambient temperature, silver ions released from the anode immediately bond directly with all halogens to various degrees depending on their concentrations, current applied, contact time, and electrode spacing. Minimal amount of oxyhalides are formed and power requirement is low. Varying current density and bromide concentration, positioning the electrolytic cell before coagulation and after sedimentation, and changing electrode combinations (Silver/Silver, DSA/DSA, and Silver/DSA as cathode/anode respectively), bromide removal was achieved to varying degrees. This process in combination with enhanced coagulation can be used to substantially extend the life of biologically active GAC filter and ensure compliance with the USEPA Stage 2 DBPR, LRAA of 80μg/L TTHM.