Activiteit

This study attempted to shorten the time wasted at the startup of a complete autotrophic nitrogen removal over nitrite (CANON) process in a tidal flow constructed wetland (TFCW) to achieve higher nitrogen removal rates. Thus, the starting performance and the related microbiological characteristics of different kinds of filter media filling the TFCW were explored at an appropriate drainage rate. The results showed that the physicochemical properties of the filter medium could significantly affect the quantity and activity of the functional microbes (especially ANAMMOX bacteria) enriched in the TFCWs, leading to fluctuations of the starting time and nitrogen transformation rates of the systems filled with five different kinds of filter media. Compared with that of gravel, the quantity and activity of ANAMMOX bacteria in the bed could be enhanced to different degrees as the TFCW was filled with ceramsite, zeolite, broken bricks, and lobster shells. Correspondingly, the starting times of the TFCWs with the CANON process were shortened, and their nitrogen removal performances could also be optimized. When the hydraulic loading rate of the TFCW was 0.96 m3·(m2·d)-1, the initiation of the CANON process could be accomplished successfully in the system filled with lobster shells within 300 cycles, since AOB and ANAMMOX bacteria could become dominant quickly in the packing bed. Moreover, the TN and NH4+-N removal rates could reach up to (88.37±1.19)% and (91.03±0.66)%, respectively, followed by those of broken bricks, zeolite, ceramsite, and gravel.In order to study the performance and mechanisms of bioretention pond media (Enteromorpha prolifera biochar) for NH4+-N removal in rainfall runoff, three kinds of alkali modified biochars (marked as BC1, BC2, and BC3) were prepared with various concentrations of NaOH solution (1, 2, and 3 mol·L-1) to explore their adsorption performance for NH4+-N. The results showed that① Appropriate modifications of the NaOH concentration increased the specific surface area and surface microstructure of biochar, with the content of O and the surface functional groups being enriched. In addition, BC2 possessed the best adsorption performance. ② The adsorption capacity reached a maximum when the pH was 9.0 and the dosage of biochar was 0.5 g·L-1. Compared with BC, the adsorption capacity of BC1 and BC2 increased by 6.4% and 10.8%, respectively, while BC3 decreased by 13.7%. Moreover, BC2 had an optimal adsorption efficiency with a saturated adsorption capacity of 16.76mg·g-1. ③ The adsorption mechanism of biochar belonged to chemical adsorption with a monomolecular layer. The adsorption process was promoted by the high pH of biochar, the electrostatic attraction of biochar pores, the complexation and oxidization of the functional groups of hydroxyl (-OH), carboxyl (-COOH), and carbon-oxygen single bond (C-O). To sum up, the proper amount of NaOH to modify biochar can improve the adsorption performance of NH4+-N, and the modified biochar can be used as media of the bioretention pond to remove NH4+-N.Bioretention systems have become an optimal technology during the construction of the sponge city, but its nitrogen removal performance can be affected by antecedent dry days (ADD). This study was designed to investigate the effects of different lengths of ADD (1,2,3, 5, 7, 12, and 22 d) on nitrogen removal performance using a series of laboratory-scale bioretention systems to form seven constant alternate drying-rewetting regimes. The influence mechanism was further investigated by analyzing the spatial distribution of nitrogen reductase activity and microbial community structure under different drying-rewetting regimes. The results showed that the ammonium removal efficiency was not significantly affected by ADD, while exhibiting high variation depending on the hydraulic permeability of the filler and plant growth conditions. The nitrate and total nitrogen removal efficiency decreased as the length of ADD increased form 7 d to 22 d. In addition, the spatial distribution of nitrate reductase (NaR), nitrite reductase (NiR), and hydroxylamine reductase (HyR) were affected by ADD to some extent. It was found that the soil moisture of submerged layer (SL) regulated the nitrogen processes. selleck chemicals llc The nitrate dissimilatory reduction to ammonium (DNRA) can occur in the SL through secondary catalytic reduction by nitrogen reductases, thus affecting the removal of ammonium. The soil microbial community structure and its spatial distribution could be altered by ADD significantly, and the removal of multiple nitrogen species was partly affected. Thereinto, under shorter ADD values of 1, 2, 3, and 5 d, the dominant phylum was Firmicutes, a group of denitrifying microbes, and its dominant genus, Clostridium_sensu_stricto_1, also had the function of DNRA. The results of the study confirmed that ADD has a certain effect on the nitrogen removal capacity and nitrogen reductase activity, while resulting in spatial changes in the microbial community structure in the bioretention system under constant drying-rewetting conditions.In order to understand the characteristics of soil nitrogen and phosphorus loss under different land use patterns in the small watershed of the Three Gorges Reservoir area and provide a scientific basis for the prevention and control of agricultural non-point source pollution, a field test method was used to study the paddy fields and drought in the small Shipanqiu Watershed in the Three Gorges Reservoir area. The characteristics of different runoff concentrations and the fluxes of nitrogen and phosphorus in surface runoff under the five land use schemes of paddy filed, slope land, woodlands, citrus orchards, and vegetable land. The results show that the annual total nitrogen loss followed the order of paddy field[17.73 kg·(hm2·a)-1] > citrus orchards[4.86 kg·(hm2·a)-1] > dry slope land[4.33 kg·(hm2·a)-1] > vegetable field[4.00 kg·(hm2·a)-1] > woodland[2.41 kg·(hm2·a)-1]. The annual total phosphorous loss followed the order of vegetable fields[4.97 kg·(hm2·a)-1] > Citrus orchards[1.87 kg·(hm2·a)-1] > paddy fields[0.