Abstract
Nitrification-denitrification is the most widely used nitrogen removal process in wastewater treatment. However, this process can lead to undesirable nitrite accumulation and subsequent ammonium production. Biogenic Fe(II-III) hydroxycarbonate green rust has recently emerged as a candidate to reduce nitrite without ammonium production under abiotic conditions. The present study investigated whether biogenic iron(II-III) hydroxycarbonate green rust could also reduce nitrite to gaseous nitrogen during bacterial nitrate reduction. Our results showed that biogenic iron(II-III) hydroxycarbonate green rust could efficiently decrease the selectivity of the reaction towards ammonium during heterotrophic nitrate reduction by native wastewater-denitrifying bacteria and by three different species of Shewanella: S. putrefaciens ATCC 12099, S. putrefaciens ATCC 8071 and S. oneidensis MR-1. Indeed, in the absence of biogenic hydroxycarbonate green rust, bacterial reduction of nitrate converted 11–42% of the initial nitrate into ammonium, but this value dropped to 1–28% in the presence of biogenic hydroxycarbonate green rust. Additionally, nitrite accumulation did not exceed the 2–13% in the presence of biogenic hydroxycarbonate green rust, versus 0–28% in its absence. Based on those results that enhance the extent of denitrification of about 60%, the study proposes a water treatment process that couples the bacterial nitrite production with the abiotic nitrite reduction by biogenic green rust.
Highlights
Nitrogen is present in the environment as organicand inorganic forms, including soluble and gaseous compounds
The current study shows that biogenic mixed-valent iron(II-III) hydroxycarbonate green rust can efficiently reduce nitrite and decrease ammonium selectivity during bacterial nitrate reduction by three different strains of Shewanella, and by a native bacterial consortium from wastewater
The biogenic hydroxycarbonate green rusts were produced from the bioreduction of ferric oxyhydroxycarbonate or of lepidocrocite by Shewanella putrefaciens ATCC 12099 at neutral pH in the presence of sodium methanoate as an electron donor, and of anthraquinone-2,6-disulfonate (AQDS) as an electron shuttle under anoxic conditions
Summary
Inorganic forms, including soluble (ammonium ‘NH4 + ’, nitrate ‘NO3 − ’, nitrite ‘NO2 − ’) and gaseous (nitric oxide ‘NO’, nitrous oxide ‘N2 O’, di-nitrogen ‘N2 0 ) compounds. Numerous fermenting and non-fermenting microorganisms are capable of converting nitrate into ammonium by dissimilatory nitrate reduction to ammonium (DNRA) [7] (Figure 1). Minerals 2020, 10, x FOR PEER REVIEW numerous fermenting and non-fermenting microorganisms are capable of converting nitrate into. Minerals 2020, 10, 818 ammonium by dissimilatory nitrate reduction to ammonium (DNRA) [7] (Figure 1). As a result of nitrification and denitrification processes, nitrite accumulation can be observed in oxic and anoxic environments, in sensitive zones [1,8,9]. Can be in transformed into nitrification and denitrification processes, nitrite accumulation cannitrite be observed oxic and anoxic carcinogenic
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