[Mechanism on Enhanced Nitrogen Removal in Municipal Secondary Effluent via Internal-Electrolysis Constructed Wetlands at Low Temperature in Winter]

Aiming at the low pollutant removal efficiency of constructed wetlands (CWs) at low temperature in winter, three laboratory-scale vertical-flow CWs, namely unplanted CWs, ordinary CWs, and internal-electrolysis CWs, were used to investigate the nitrogen removal efficiency of municipal secondary effluent when the water temperature was 3-12℃. Moreover, the mechanism of enhanced denitrification of the new wetland was revealed through analysis of the microbial community diversity and community structure. The results showed that the internal-electrolysis CWs could make better use of the carbon sources in the municipal secondary effluent and had a higher removal rate. The effluent TN concentration was maintained at about (9±0.29) mg·L^-1. The average TN removal rate was 42.27%, which was 17.91% and 17.33% higher than those of the unplanted CWs and ordinary CWs, respectively. The microbial activity was detected using fluorescein diacetate (FDA), and the result revealed that the microbial activity of the internal-electrolysis CWs could reach 0.224 mg·g^-1, which was 2.6 times and 3.4 times of that of the unplanted CWs and ordinary CWs, respectively. The microbial denitrification intensity of the internal-electrolysis CWs was 2.8 times and 3.3 times of that of the unplanted and ordinary CWs, respectively. The results of high-throughput sequencing showed that the microbial community diversity of the internal electrolysis CWs was higher than those of the unplanted and ordinary CWs. Denitrification microorganisms were detected, mainly Dechloromonas, Rhizobium, Hyphomicrobium, and Rhodobacter, as well as Thiobacillus, which is an autotrophic denitrifying bacterium. There were obvious advantages in the total amount of denitrifying microorganisms in the internal-electrolysis CWs, as the denitrification microorganisms accounted for 7.13% of the total microbial biomass, which was 3.8 times and 8.7 times of that of the unplanted CWs and ordinary CWs, respectively.

Adsorption of selected emerging contaminants onto PAC and GAC: Equilibrium isotherms, kinetics, and effect of the water matrix

The removal of three emerging contaminants (ECs) (amitriptyline hydrochloride (AH), methyl salicylate (MS) and 2-phenoxyethanol (PE)) dissolved in several water matrices by means of their adsorption onto powdered activated carbon (PAC) and granular activated carbon (GAC) has been investigated. When dissolved in ultrapure water, adsorption of the ECs followed the trend of AH > MS > PE, with a positive effect of the adsorbent dose. According to the analysis of the adsorption isotherms and adsorption kinetics, PAC showed strongly higher adsorption efficiency in both capacity and velocity of the adsorption, in agreement with its higher mesoporosity. Equilibrium isotherm data were fitted by Langmuir and Freundlich models. Pseudo-second order kinetics modeled very successfully the adsorption process. Finally, the effect of the presence of dissolved organic matter (DOM) in the water matrices (ultrapure water, surface water and two effluents from wastewater treatment plants) on the adsorption of the selected ECs onto PAC was established, as well as its performance on the removal of water quality parameters. Results show a negative effect of the DOM content on the adsorption efficiency. Over 50% of organic matter was removed with high PAC doses, revealing that adsorption onto PAC is an effective technology to remove both micro-pollutants and DOM from water matrices.

[Removal of Nitrogen in Municipal Secondary Effluent by a Vertical Flow Constructed Wetland Associated with Iron-carbon Internal Electrolysis]

Aiming at the problem of high concentration of total nitrogen (TN) and low available carbon source for microorganisms in municipal secondary effluent, the vertical flow constructed wetland associated with iron-carbon internal electrolysis (ICIE-VFCW) was applied to investigate the removal efficiencies of pollutants in municipal secondary effluent. Moreover, the mechanism for enhanced nitrogen removal was primarily discussed by the applications of UV visible spectrum (UV-VIS) and gel filtration chromatography (GFC). The results showed that the ICIE-VFCW could improve the COD removal efficiencies and the effluent COD of less than 30 mg·L^-1could be stably obtained. The average COD removal efficiencies of the whole year, warm months, and cold months could be increased by 10.16%, 9.81%, 11.22%, respectively, compared to the control group. The effluent TN of the ICIE-VFCW could be maintained below 10 mg·L^-1, and the average TN removal efficiencies of the whole year, warm months and cold months could be increased by 13.72%,12.90%,16.17%, respectively. Besides, compared to the influent, the humification, aromaticity and average relative molecular weight (M_r) in the effluent obviously decreased, and the M_r decreased more significantly in the ICIE-VFCW. The ICIE-VFCW could promote the conversion of refractory organics in municipal secondary effluent to the small and readily biodegradable molecules, which could enhance the utilization of organic compounds by microorganisms, thus improving the removal efficiency of nitrogen.