Kinetics of microbial bromate reduction in a hydrogen‐oxidizing, denitrifying biofilm reactor

Abstract

Bromate (BrO(3)(-)) is an oxidized contaminant produced from bromide (Br(-)) during ozonation and advanced oxidation of drinking water. Previous research shows that denitrifying bioreactors can reduce bromate to innocuous bromide. We studied a hydrogen-based, denitrifying membrane-biofilm reactor (MBfR) for bromate reduction, and report the first kinetics for a hydrogen-based bromate reduction process. A mixed-culture MBfR reduced up to 1,500 microg/L bromate to below 10 microg/L with a 50-min hydraulic residence time. Kinetics were determined using short-term tests on a completely mixed MBfR at steady state with an influent of 5 mg N/L nitrate plus 100 microg/L bromate. Short-term tests examined the impact of pH, nitrite, nitrate, and bromate on bromate reduction rates in the MBfR. Kinetic parameters for the process were estimated based on the short-term bromate tests. The q(max) for bromate reduction was 0.12 mg BrO(3)(-) x mg(x)(-1) x day(-1), and the K was 1.2 mg BrO(3)(-)/L. This q(max) is 2-3 times higher than reported for heterotrophic enrichments, and the K is the first reported in the literature. Nitrite and nitrate partially inhibited bromate reduction, with nitrite exerting a stronger inhibitory effect. Bromate was self-inhibitory at concentrations above 15 mg/L, but up to 50 mg/L of bromate had no inhibitory effect on denitrification. The optimum pH was approximately 7. We also examined the performance of an MBfR containing pure culture of the denitrifying bacterium Ralstonia eutropha. Under conditions similar to the mixed-culture tests, no bromate reduction was detected, showing that not all denitrifying bacteria are active in bromate reduction. Our results suggest the presence of specialized, dissimilatory bromate-reducing bacteria in the mixed-culture MBfR.

Biocatalytic membrane reactors for the removal of recalcitrant and emerging pollutants from wastewater

“…Therefore, the MBfR is an ideal tool for biological treatment using hydrogen since it allows effi cient bubble-free transfer of the gas to the biofi lm. The hydrogen-based MBfR has been investigated for a range of oxidized contaminants present in water, for example nitrate (Ergas and Reuss, 2001 ;Lee and Rittmann, 2000 ), perchlorate , trichloroethene (Edstrom et al ., 2005 ), selenate (Chung et al ., 2006c ), arsenate (Chung et al ., 2006a ), chromate (Chung et al ., 2006b ) and bromate (Downing and Nerenberg, 2007a ). It has also been combined with oxygen-based MBfRs for nitrifi cation followed by hydrogenotrophic denitrifi cation (Cowman et al ., 2005 ;Hwang et al ., 2009aHwang et al ., , 2010Shin et al ., 2005Shin et al ., , 2008Smith et al ., 2008 ).…”

Nitrogen Removal from Wastewater Using a Hybrid Membrane‐Biofilm Process: Pilot‐Scale Studies

“…Air-filled, hollow-fiber membranes are incorporated into a completely mixed activated sludge tank, and bulk aeration is suppressed. With a bulk-liquid SRT as low as three days, BOD concentrations as low as 1 mg/L can be achieved in the reactor, limiting BOD diffusion into the biofilm and minimizing attached heterotrophic biomass (Downing and Nerenberg, 2007). Oxygen from the membranes is consumed by ammonium and nitrite-oxidizing bacteria (AOB and NOB) forming the biofilm, which allows for anoxic bulk liquid conditions.…”

Evidence of specialized bromate-reducing bacteria in a hollow fiber membrane biofilm reactor

“…Significant bromate doi: 10.2166/wst.2009.216 reduction has been achieved using biologically activated carbon (Kirisits & Snoeyink 1999;Kirisits et al 2001Kirisits et al , 2002, a suspended growth bioreactor (Butler et al 2005b), a fixed-film bioreactor (Butler et al 2006), and a hollow fiber membrane biofilm reactor (Downing & Nerenberg 2007).…”