Nitrate-induced mobilization of trace elements in reduced groundwater environments.

Groundwater is an essential source for drinking water production. Nitrate infiltration into groundwater due to over-fertilization can cause a potential risk for groundwater quality. Pyrite and other geogenic minerals can be oxidized and trace metals consequently released into water, e.g., nickel and uranium. To achieve a better understanding of the nitrate-induced mobilization of metals, this study investigated the release of antimony, arsenic, chromium, cobalt, molybdenum, uranium, and vanadium from three different reduced sediments after nitrate addition. The experiments were conducted as batch and soil column tests under oxygen-free conditions. In addition to the ORP, the pH value was a relevant driver for the metal mobilization due to pH dependent adsorption and ion exchange processes. Uranium concentrations in the water increased with increasing redox potential. Also, antimony and, to a lesser extent, molybdenum showed higher mobilization at higher ORP as well as at higher pH values. On the contrary, arsenic and cobalt was immobilized with increasing redox potential. Pourbaix diagrams demonstrated very complex species distributions even in synthetic water. The mobilization of trace metals is expected to be also influenced by the type of surrounding rocks and water quality parameters such as dissolved organic carbon.

Pool water disinfection by ozone-bromine treatment: Assessing the disinfectant efficacy and the occurrence and in vitro toxicity of brominated disinfection by-products.

Pool water is continuously circulated and reused after an extensive treatment including disinfection by chlorination, ozonation or UV treatment. In Germany, these methods are regulated by DIN standard 19643. Recently, the DIN standard has been extended by a new disinfection method using hypobromous acid as disinfectant formed by introducing ozone into water with naturally or artificially high bromide content during water treatment. In this study, we tested the disinfection efficacy of the ozone-bromine treatment in comparison to hypochlorous acid in a flow-through test rig using the bacterial indicator strains Escherichia coli, Enterococcus faecium, Pseudomonas aeruginosa, and Staphylococcus aureus and the viral indicators phage MS2 and phage PRD1. Furthermore, the formation of disinfection by-products and their potential toxic effects were investigated in eight pool water samples using different disinfection methods including the ozone-bromine treatment. Our results show that the efficacy of hypobromous acid, depending on its concentration and the tested organism, is comparable to that of hypochlorous acid. Hypobromous acid was effective against five of six tested indicator organisms. However, using Pseudomonas aeruginosa and drinking water as test water, both tested disinfectants (0.6 mg L-1 as Cl2 hypobromous acid as well as 0.3 mg L-1 as Cl2 hypochlorous acid) did not achieve a reduction of four log10 levels within 30 s, as required by DIN 19643. The formation of brominated disinfection by-products depends primarily on the bromide concentration of the filling water, with the treatment method having a smaller effect. The eight pool water samples did not show critical values in vitro for acute cytotoxicity or genotoxicity in the applied assays. In real pool water samples, the acute toxicological potential was not higher than for conventional disinfection methods. However, for a final assessment of toxicity, all single substance toxicities of known DBPs present in pool water treated by the ozone-bromine treatment have to be analyzed additionally.