Abstract
Selenate removal in drinking water is being vigorously debated due to the various health issues concerned. As a viable treatment option, this study investigated a fixed-bed biofilm reactor (FBBR) with internal recycling. The experimental design tested how hydraulic loading rate and electron donor affect selenate reduction together with other oxyanions. The tested accompanying oxyanions were nitrate and perchlorate and experiments were designed to test how an FBBR responded to the limited electron donor condition. The results showed that the reactor achieved almost complete selenate reduction with the initial hydraulic loading rate of 12 m3/m2/day (influent concentration of 1416 µg SeO42−/L). Increasing the hydraulic loading rates to 16.24 and 48 m3/m2/day led to a gradual decline in selenate removal efficiency. A sufficient external carbon source (C:N of 3.3:1) achieved an almost complete reduction of nitrate as well as selenate. The FBBR acclimated to selenate instantaneously and reduced nitrate via synergistic denitrification. An experiment with another oxyanion addition, perchlorate (459 µg ClO4−/L), revealed that perchlorate-reducing bacteria were more strongly associated with carbon limitation than selenate-reducing bacteria, which can help us to understand parallel reactions in FBBRs. This research provides a framework to further study the use of electron donor-controlled FBBRs for simultaneous reduction of selenate and other oxyanions threatening the drinking water-related environment and public health.
Highlights
Selenium (Se) is an essential element for human and animal nutrition but exposure to an excess amount of Se is toxic to living organisms and can cause adverse health effects in humans, such as hair loss, nail discoloration, damage to the kidney, liver congestion and problems with the nervous and circulatory systems [1,2]
Summarizes the average fixed-bed biofilm reactor (FBBR) performance for effluent selenate concentration and selenate reduction summarizes the average FBBR performance for effluent selenate concentration and selenate efficiency according to the selenate loading rate and empty bed contact time (EBCT) during phases 1 to 4
Only perchlorate reduction was significantly inhibited in the FBBR under dissolved organic carbon (DOC)-limited conditions. This result demonstrates that the cessation of perchlorate reduction in the presence of other oxyanions may be linked to the difference in electron donor affinity between heterotrophic selenate- and perchlorate-reducing bacteria [21,22]
Summary
Selenium (Se) is an essential element for human and animal nutrition but exposure to an excess amount of Se is toxic to living organisms and can cause adverse health effects in humans, such as hair loss, nail discoloration, damage to the kidney, liver congestion and problems with the nervous and circulatory systems [1,2]. Various physicochemical methods, such as membranes, ion exchange, reducing oxyanions, problematic byproducts generation, slow reaction kinetics, low pH, etc., make the process agents, metal powders, green rusts, etc., may be applicable to selenate reduction, the existence of costly [9,10]. Thesystem potential microbial washout while biocatalysts, i.e.,inselenate reducing bacteria, in the of biofilm reactors can be extended via a long acclimation period [12], which can simultaneously longer. The potential of biofilm reactors can be extended via a long acclimation period reduce and other anions,reduce such selenate as nitrate and perchlorate, even in diluted agricultural or [12],selenate which can simultaneously and other anions, such as nitrate and perchlorate, coal-mining drainage [13].
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