Bromate Reduction by Iron(II) during Managed Aquifer Recharge: A Laboratory-Scale Study

Critical Review on Bromate Formation during Ozonation and Control Options for Its Minimization

Ozone is a commonly applied disinfectant and oxidant in drinking water and has more recently been implemented for enhanced municipal wastewater treatment for potable reuse and ecosystem protection. One drawback is the potential formation of bromate, a possible human carcinogen with a strict drinking water standard of 10 μg/L. The formation of bromate from bromide during ozonation is complex and involves reactions with both ozone and secondary oxidants formed from ozone decomposition, i.e., hydroxyl radical. The underlying mechanism has been elucidated over the past several decades, and the extent of many parallel reactions occurring with either ozone or hydroxyl radicals depends strongly on the concentration, type of dissolved organic matter (DOM), and carbonate. On the basis of mechanistic considerations, several approaches minimizing bromate formation during ozonation can be applied. Removal of bromate after ozonation is less feasible. We recommend that bromate control strategies be prioritized in the following order: (1) control bromide discharge at the source and ensure optimal ozone mass-transfer design to minimize bromate formation, (2) minimize bromate formation during ozonation by chemical control strategies, such as ammonium with or without chlorine addition or hydrogen peroxide addition, which interfere with specific bromate formation steps and/or mask bromide, (3) implement a pretreatment strategy to reduce bromide and/or DOM prior to ozonation, and (4) assess the suitability of ozonation altogether or utilize a downstream treatment process that may already be in place, such as reverse osmosis, for post-ozone bromate abatement. A one-size-fits-all approach to bromate control does not exist, and treatment objectives, such as disinfection and micropollutant abatement, must also be considered.

Removal of bromate from drinking water using a heterogeneous photocatalytic mili-reactor: impact of the reactor material and water matrix

The main goal of this study was to evaluate the removal of bromate from drinking water using a heterogeneous photocatalytic mili-photoreactor, based on NETmix technology. The NETmix mili-reactor consists of a network of channels and chambers imprinted in a back slab made of acrylic (AS) or stainless steel (SSS) sealed, through mechanical compression and o-rings, with an UVA-transparent front borosilicate glass slab (BGS). A plate of UVA-LEDs was placed above the BGS window. TiO₂-P25 thin films were immobilized on the BGS (back-side illumination, BSI) or SSS (front-side illumination, FSI) by using a spray deposition method. The photoreduction rate of a 200 μg L^-1 (1.56 μM) BrO₃^- solution was assessed taking into account the following: (i) catalyst film thickness, (ii) catalyst coated surface and illumination mechanism (BSI or FSI), (iii) solution pH, (iv) type and dose of sacrificial agent (SA), (v) reactor material, and (vi) water matrix. In acidic conditions (pH 3.0) and in the absence of light/catalyst/SA, 28% and 36% of BrO₃^- was reduced into Br^- only by contacting with AS and SSS during 2-h, respectively. This effect prevailed during BSI experiments, but not for FSI ones since back SSS was coated with the photocatalyst. The results obtained have demonstrated that (i) the molar rate of disappearance of bromates was similar to the molar rate of formation of bromides; (ii) higher BrO₃^- reduction efficiencies were reached in the presence of an SA using the FSI at pH 3.0; (iii) formic acid ([BrO₃^-]:[CH₂O₂] molar ratio of 1:3) presented higher performance than humic acids (HA = 1 mg C L^-1) as SA; (iv) high amounts of HA impaired the BrO₃^- photoreduction reaction; (v) SSS coated catalyst surface revealed to be stable for at least 4 consecutive cycles, keeping its photonic efficiency. Under the best operating conditions (FSI, 18 mL of 2% wt. TiO₂-P25 suspension, pH 3.0), the use of freshwater matrices led to (i) equal or higher reaction rates, when compared with a synthetic water in the absence of SA, and (ii) lower reaction rates, when compared with a synthetic water containing formic acid with a [BrO₃^-]:[CH₂O₂] molar ratio of 1:3. Notwithstanding, heterogeneous TiO₂ photocatalysis, using the NETmix mili-reactor can be used to promote the reduction of BrO₃^- into Br^-, attaining concentrations below 10 μg L^-1 (guideline value) after 2-h reaction. Graphical Abstract .

Integrated control of CX3R-type DBP formation by coupling thermally activated persulfate pre-oxidation and chloramination

The alternative disinfectant chloramine can lower the formation of carbonaceous DBPs (C-DBPs) but promote the formation of nitrogenous DBPs (N-DBPs), which are more cytotoxic and genotoxic. In this study, the combination of thermally activated persulfate pre-oxidation and post-chloramination (TA/PS-NH₂Cl) was proposed to control the formation and reduce the toxicity of both C-DBPs and N-DBPs. The formation, speciation and toxicity of trihalomethanes, haloacetic acids, haloaldehydes, haloacetonitriles, halonitromethanes and haloacetamides, collectively defined as CX₃R-type DBPs, under TA/PS-NH₂Cl process were compared with processes of chlorination alone (Cl₂), chloramination alone (NH₂Cl) and coupled thermally activated persulfate pre-oxidation with post-chlorination (TA/PS-Cl₂). Results showed that chloramination could reduce formation of C-DBPs and total organic halogen (TOX) while increase N-DBP formation, and the introduction of TA/PS pretreatment process slightly increased the formation of C-DBPs and TOX but sharply reduced the formation of N-DBPs with higher toxicity as well as brominated CX₃R-type DBPs that are more toxic than their chlorinated analogues. By comprehensive toxicity calculation, an outright decline of both cytotoxicity and genotoxicity risk of CX₃R-type DBPs was observed during TA/PS-NH₂Cl process compared with Cl₂, NH₂Cl, and TA/PS-Cl₂ processes. In summary, TA/PS-NH₂Cl process was a potential effective method for integrally controlling the formation of CX₃R-type DBPs and their toxicity and is suggested to be used to treat raw waters containing no bromide or low levels of bromide considering bromate caused by TA/PS pre-oxidation. The study may provide a feasible and economical method for DBP control on the background of global warming.