Abstract
Sediment internal nitrogen release is a significant pollution source in the overlying water of aquatic ecosystems. This study aims to remove internal nitrogen in sediment-water microcosms by coupling sediment microbial fuel cells (SMFCs) with submerged aquatic plants. Twelve tanks including four treatments in triplicates were designed: open-circuit (SMFC-o), closed-circuit (SMFC-c), aquatic plants with open-circuit (P-SMFC-o) and aquatic plants with closed-circuit (P-SMFC-c). The changes in the bio-electrochemical characteristics of the nitrogen levels in overlying water, pore water, sediments, and aquatic plants were documented to explain the migration and transformation pathways of internal nitrogen. The results showed that both electrogenesis and aquatic plants could facilitate the mineralization of organic nitrogen in sediments. In SMFC, electrogenesis promoted the release of ammonium from the pore water, followed by the accumulation of ammonium and nitrate in the overlying water. The increased redox potential of sediments due to electrogenesis also contributed to higher levels of nitrate in overlying water when nitrification in pore water was facilitated and denitrification at the sediment-water interface was inhibited. When the aquatic plants were introduced into the closed-circuit SMFC, the internal ammonium assimilation by aquatic plants was advanced by electrogenesis; nitrification in pore water and denitrification in sediments were also promoted. These processes might result in the maximum decrease of internal nitrogen with low nitrogen levels in the overlying water despite the lower power production. The P-SMFC-c reduced 8.1%, 16.2%, 24.7%, and 25.3% of internal total nitrogen compared to SMFC-o on the 55th, 82th, 136th, and 190th days, respectively. The smaller number of Nitrospira and the larger number of Bacillus and Pseudomonas on the anodes via high throughput sequencing may account for strong mineralization and denitrification in the sediments under closed-circuit. The coupled P-SMFC system has shown good potential for the efficient removal of internal nitrogen.
Highlights
Nitrogen (N) is one of the essential nutrients for plant growth but excess amounts of N create toxic algal blooms that cause eutrophication and deterioration of aquatic ecosystems by depleting oxygen in water bodies [1,2]
Voltages of 54.9 mV and 56.9 mV were documented on the first day of the operation of sediment microbial fuel cells (SMFCs)-c and P-SMFC under closed circuit (SMFC-c), respectively
Phase, relatively lower voltage generation was observed for P-SMFC-c than SMFC-c when maximum voltages of 287 mV and 193 mV were documented, respectively
Summary
Nitrogen (N) is one of the essential nutrients for plant growth but excess amounts of N create toxic algal blooms that cause eutrophication and deterioration of aquatic ecosystems by depleting oxygen in water bodies [1,2]. Release from the sediments is generally regarded as the main source of N in the overlying water [3,4]. In addition to controlling the exogenous input, measures for decreasing internal N loading (sum of all forms of N in sediments and pore water) should be taken to control the eutrophication process. Sediment microbial fuel cells (SMFCs) have been used to harness bioelectricity from waterbased ecosystems, in which electro-chemically active microorganisms metabolize biodegradable organic matter (OM) in sediments and generate electrons. As the main source of N in overlying water, the influence of SMFC on the internal N is not well known. It is exigent to study the influence of SMFC on the migration and transformation of internal N to determine the potential of SMFC as a new technology for internal N removal
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