Journal
CHEMOSPHERE
Volume 287, Issue -, Pages -Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.chemosphere.2021.131993
Keywords
Nitrate reduction; Ammonium; Stoichiometry; Column study; Phosphate; Green rust
Categories
Funding
- North Sea Region Interreg project NuReDrain [8-2-17-16]
- University of Copenhagen
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The use of a ZVI-zeolite filter system can efficiently remove nitrate, convert a majority into ammonium, retain ammonium, and also adsorb phosphate from influent waters.
Nitrate reduction to ammonium followed by ammonium capture and reuse, represent a new pathway to recycle nitrogen, prevent eutrophication, and to save energy used for industrial ammonium production. The present study investigates the principle of nitrogen recycling to agricultural drainage water using a coupled zero-valent iron (ZVI) and zeolite-based filter column system tested in laboratory and field continuous-flow experiments. A 40-day laboratory test showed 82% nitrate removal, of which 70% was converted to ammonium. In the following pilot scale field test, a total of 59.2 m3 (1700 pore volumes) drainage water with a nitrate concentration of 2-8 mg L-1 NO3- -N was filtrated. An oxidizing unit inserted after the ZVI unit removed iron(II) and optimized ammonium retention in the zeolite unit. Nitrate removal efficiency was 94% for the entire 56-day period with a slight pH increase (pH 8.9). All ammonium produced was retained by the zeolite unit. Formation of green rust carbonate (layered FeII-FeIII-hydroxide) was observed on ZVI particle surfaces, which may increase the redox capacity of the filter system by up to 50% and contribute to its cost-efficiency. Moreover, all phosphate in the influent waters with concentrations between 0.1 and 0.5 mg L-1 was retained due to sorption by iron oxides in the system. Corrosion products formed cause partial filter clogging and should be removed by regular cleaning and backflushing. In conclusion, the ZVI - zeolite coupled filter system serves as a promising and cost-effective technology for nutrient removal and ammonium retention from agricultural drainage water.
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