Ordering Information:
ORDER NUMBER:  91202
DATE AVAILABLE: Spring 2008

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PRINCIPAL INVESTIGATORS:
Lina Boulos, Hélène Baribeau, Brian Carrico, Gil Crozes, David Kimbrough, and Mel Suffet.

OBJECTIVES:
The objectives of the study were to (1) determine operational conditions under which electrolysis removes bromide and decreases the formation of halogenated disinfection by-products (DBPs); (2) investigate the effect of electrolysis on ozonation DBPs (bromate), bacterial regrowth, and taste andor; (3) evaluate the impact of electrolysis on conventional coagulation/flocculation/sedimentation and ozonation; (4) evaluate scalability and conceptual design issues; (5) determine preliminary capital and operational costs; and (6) determine future needs for demonstrating the technology.

BACKGROUND:
The presence of bromide in drinking water typically leads to the formation of brominated DBPs upon chlorination. Bromide is not removed by conventional water treatment processes. Ion-exchange and high-pressure membrane filtration remove bromide but produce a concentrated brine waste stream. One emerging technology for bromide removal is electrolysis. Limited design data on bromide removal by electrolysis are available in the literature. However, design parameters, operational constraints, and costs need to be defined.

HIGHLIGHTS:

• Aqueous bromide removal was directly proportional to applied current. The higher the current, the higher the removal.
• Total bromide removal (i.e., sum of aqueous bromide and bromine) was limited by the accumulation of bromine in the water.
• Too high of a direct current resulted in an increase in DBP formation potentials.
• An optimal range of current was identified for DBP decrease for various residence time conditions.
• Higher bromide removal was achieved under longer residence times and low mixing conditions.
• Electrolyzed water samples exhibited lower bacterial re-growth potential as compared to un-electrolyzed samples.

APPROACH:
A four phased-approach was undertaken to conduct this project. During the first phase, the electrolytic reactor was designed, constructed, and activated. During the second phase, the electrolytic reactor was operated under several conditions of hydraulic residence time, current level, and influent bromide level. Key analytical parameters were measured, including bromide, bromine, chlorine, and THM and HAA concentrations. During the third phase, conventional treatment consisting of coagulation/flocculation/sedimentation and/or ozonation was tested downstream of electrolysis to investigate whether electrolysis is feasible in a conventional treatment plant context. During the fourth phase, scale up, safety, and conceptual design issues were identified and preliminary costs estimated. A workshop was held towards the end of the study to identify future needs.

RESULTS/FINDINGS:

Bromide and Bromine
Aqueous bromide oxidation to bromine was a direct function of the current. Bromine accumulation was observed when too high of a current was applied, limiting the total bromide removal. Optimal power ranges were defined for various hydraulic residence times (HRT). Under low HRT and high mixing conditions, a higher power was required. However, limited data show that the majority of beneficial bromide oxidation was actually occurring over the first 10 cm of the anode plates depth (equivalent to 1-min HRT).

Disinfection By-Product Formation Potential (DBPFP)
Under ambient and spiked bromide conditions, a 10–30 percent decrease in THM and HAA formation potentials was observed when the optimal power range was used. Above that optimal power level, DBPs were observed to increase.

Bacterial Regrowth
Significantly lower bacterial counts were measured in samples electrolyzed with currents 25 amps and higher, as compared to un-electrolyzed samples.

Synergy Testing
Conventional treatment (coagulation/flocculation/sedimentation and/or ozonation) increased bromide removals by 14 to 18 percent. A significant decrease in the fraction of residual bromine was observed. A decrease in THMFP in electrolyzed samples from 165 to 110 µg/L was measured. Bromate concentrations in the conventionally treated un-electrolyzed waters were 2 to 10 µg/L higher than those in the treated electrolyzed waters.

IMPACT:
Bromide in drinking water can lead to brominated disinfection by-products, which are associated with harmful health effects. Under optimal conditions of current, electrolysis was capable of removing 50 to 60 percent of the total influent bromide, which led to the decrease in halogenated DBPs, and somewhat led to a decrease in bromate. In addition, another beneficial effect was the inhibition of bacterial regrowth. The cost of treatment was within the ranges of other bromide removal technologies. However, unlike these technologies, no waste was generated with electrolysis.

RESEARCH PARTNER:
Castaic Lake Water Agency, Calif.