In this paper, three bio-reactors were designed to determine the effects of different zero-valent iron (ZVI) powder dosages on anammox. Initially, a high ZVI dosage inhibited the anammox process, while anammox adopted the habitat after long-term culture. The continuous experiment indicated that R2 (100 mg ZVI/L) had no notable effect on shortening the anammox start-up time, while R3 (1000 mg ZVI/L) reduced the start-up time from 96 to 87 days. The stable nitrogen isotope test suggested that the anammox activity of R3 was higher than that of R1 (without ZVI powder) during the stabilisation stage. The anammox growth rate increased by 20% in R3, which was verified by the real-time quantitative PCR results. In comparison to the control, the anammox quantity increased by approximately 44.5% and 54% at 100 and 1000 mg/L on day 120, respectively, which is likely due to lower dissolved oxygen and oxide-reduce potential created by the ZVI powder. The addition of ZVI may release iron ions, reduce the DO and ORP, and regulate the habitat pH conditions, which are beneficial for promoting anammox bacteria. Moreover, ZVI may directly partake in the anammox reaction pathway and improve the total nitrogen removal.
Chaoyang Gong,Yuan Gong,Maung Kyaw Khaing Oo,Yu Wu,Yunjiang Rao,Xiaotian Tan,Xudong Fan
We report an optofluidic catalytic laser for sensitive sulfide ion detection. In the catalytic reaction , horseradish peroxidase (HRP) enzyme is used for catalyzing the non-fluorescent substrate, 10-Acetyl-3,7-dihydroxyphenox-azine (ADHP), to produce highly fluorescent resorufin , which was used as gain medium for lasing. Using sulfide ions as inhibitors, the catalytic reaction slows down, resulting in a delay in the lasing onset time, which is used as the sensing signal. The sensing mechanism of the catalytic laser is theoretically analyzed and the performance is experimentally characterized. Sulfide anion is chosen as a model ion because of its broad adverse impacts on both environment and human health. Due to the optical feedback provided by the laser, the small difference in the sulfide ion concentration can be amplified. Consequently, a detection limit of 10 nM is achieved with a dynamic range as large as three orders of magnitude, representing significant improvement over the traditional fluorescence and colorimetric methods. This work will open a door to a new catalytic-laser-based chemical sensing platform for detecting a wide range of species that could inhibit the catalytic reaction.
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