Aquatic plant root exudates: A source of disinfection byproduct precursors in constructed wetlands.

Aquatic plant-derived dissolved organic matter (DOM) in water bodies is an important source of disinfection byproduct (DBP) precursors. It is therefore very important to investigate DBP formation, and the main DBP precursors that enter drinking water during treatment processes. In this study, Lythrum salicaria root extract (LSRE) and Acorus calamus root extract (ACRE) were analyzed. The LSRE and ACRE were chlorinated and disinfected to generate trihalomethanes, haloacetic acids, haloketones, and haloacetaldehydes. The DBP formation potential of LSRE, dominated by humus, was higher than that of Suwannee River natural organic matter (SRNOM), and trichloroacetic acid was the main DBP. It was calculated that 2.09 % of the increased DOC brought by the surface flow wetland planted with emergent aquatic plants, and the contribution rates of TCMFP, DCAAFP and TCAAFP in effluent were 3.34 %, 3.23 % and 3.05 %, respectively. A total of 706 chlorinated-formula were detected by FTICR-MS, among which mono- and di-chlorinated formulae were the most abundant. Macromolecular hydrophobic organics and tannins were the main precursors for LSRE. Unlike LSRE, the DOM composition of ACRE was dominated by protein or aliphatic compounds; therefore, the risk of DBP formation was not as high as that for LSRE. This study is the first to determine the risk of DBP formation associated with aquatic plant root extracts, and confirmed that tannins in plant-derived DOM are more important DBP precursors than lignins.

Long-term electricity generation and denitrification performance of MFCs with different exchange membranes and electrode materials.

Different biocathode electrode materials (graphite felt and carbon brush, GF and CB) and exchange membranes (proton exchange membrane and cation exchange membrane, PEM and CEM) were used in three microbial fuel cell (MFC) configurations operated for 300-days to investigate the power generation and the COD and N removal performance. Results showed no effect on the COD removal (all above 96%); however, the power generation (46.11 mW·h) and denitrification performance (68.0 ± 1.6%) of the MFC-B (GF + PEM) system were higher than those of the other systems (MFC-A: CB + PEM; MFC-C: CB + CEM) (P < 0.01), and the power generation and denitrification performance of all three systems decreased with time (P < 0.01). By analyzing the physicochemical properties of the exchange membrane and cathode electrode materials, the reasons that affect the power generation performance of the system were clarified. Furthermore, the increase in bioelectricity enhanced the electricity-related nitrification and denitrification reactions. The average 300-day unit denitrification cost of MFC-A was 4.2 and 6.3 times that of MFC-B and MFC-C, respectively. Comprehensive consideration of electricity generation, denitrification, and service life, combined with cost analysis and better selection of construction materials, provides a theoretical basis for the long-term stable operation and sustainable application of MFCs.

Low-cost magnetic herbal biochar: characterization and application for antibiotic removal.

Magnetic biochar (M-BC) was derived from herbal medicine waste, Astragalus membranaceus residue, and was used as an adsorbent for ciprofloxacin removal from aqueous solutions. The M-BC was characterized by Brunauer-Emmett-Teller surface area analyses, Fourier transform infrared spectrometry, X-ray diffraction analysis, hysteresis loops, scanning electron microscopy energy-dispersive spectrometry, and X-ray photoelectron spectroscopy. The BET surface area increased from 4.40 to 203.70 m2/g after pyrolysis/magnetic modification. Batch experiments were performed at different dosages, initial concentrations, contact times, and solution pHs. Adsorption performances were evaluated using Langmuir and Freundlich isotherm models, and the results indicated that the Langmuir model appropriately described the adsorption process. The kinetic data were better fitted by a pseudo-second-order kinetic model. The maximum ciprofloxacin removal was observed at pH 6 (adsorption capacity of 68.9 ± 3.23 mg/g). Studies demonstrated that magnetically modified biochar might be an attractive, cost-effective, and easily separated adsorbent for contaminated water. Graphical abstract.