(NH4)2Mo3S13/MnFe2O4 hybrid with multiple active sites boosted activation of peroxymonosulfate for removal of tetracycline.

Advanced oxidation processes (AOPs) based on peroxymonosulfate (PMS) activation have attracted much attention in wastewater treatment. Here, a series of (NH4)2Mo3S13/MnFe2O4 (MSMF) composites were prepared and used as PMS activators to remove tetracycline (TC) for the first time. When the mass ratio of (NH4)2Mo3S13 to MnFe2O4 was 4.0 (MSMF4.0), the composite showed remarkable catalytic efficiency for activating PMS to remove TC. Over 93% of TC was removed in MSMF4.0/PMS system in 20 min. The aqueous •OH as well as the surface SO4•- and •OH were the primary reactive species for TC degradation in MSMF4.0/PMS system, and the comprehensive experimental results excluded the contributions of aqueous SO4•-, O2•-, and 1O2, high-valent metal-oxo species, and surface-bound PMS. The Mn(II)/Mn(III), Fe(II)/Fe(III), Mo(IV)/Mo(VI), and S2-/SOx2- all contributed to the catalytic process. MSMF4.0 also showed excellent activity and stability after five cycles and significant degradation efficiency for a variety of pollutants. This work will provide theoretical basis for applying MnFe2O4-based composites in PMS-based AOPs.

Modeling the effects of temperature on the migration and transformation of nitrate during riverbank filtration using HYDRUS-2D.

Riverbank filtration is a natural aquifer-based process. The nitrogen dynamics in a riverbank filtration system are affected by many factors, including temperature, water quality, and travel time, which cannot be quantified easily. In this study, a field experiment was conducted to investigate nitrogen transport during riverbank filtration. The HYDRUS-2D software package was used to investigate and quantify the factors that affect the fate of nitrogen. The effects of temperature, water quality, and travel time on nitrate transport were considered. The model was calibrated and validated using field experimental data from the river water and groundwater during riverbank filtration at different periods. The results showed that HYDRUS-2D adequately simulated nitrate transport during riverbank filtration. The denitrification rate constant exhibited a positive exponential relationship with temperature. An empirical formula describing this relationship in riverbank filtration was developed and validated. In addition, the denitrification rate can be quantified within a specified temperature data range under field conditions. Compared with indoor experimental conditions, for the same temperature, there was a 10-fold increase in the denitrification rate constant under field conditions. The results showed that most of the nitrate removal occurred in the riparian zone at high temperatures during riverbank filtration. We concluded that the fate of nitrate in the riparian zone is strongly controlled by groundwater temperature. Travel time also plays an important role in nitrate removal during riverbank filtration.

Experimental investigation and simulation of nitrogen transport in a subsurface infiltration system under saturated and unsaturated conditions.

The nitrogen dynamics in a subsurface infiltration system (SIS) are affected by many factors, including temperature, system design, and feed water quality, which are not easily quantified. In this study, a column experiment was conducted to simulate an SIS. The HYDRUS-1D software package was used to investigate and quantify the factors that affect nitrate transport in an SIS. Three treatments were carried out based on different hydraulic conditions, including continuous wetting (CW), wetting/drying (WD), and a specific hydraulic loading rate (SH). The effects of hydraulic conditions and temperature on nitrate transformation were investigated. The model was calibrated and validated using two-year experimental data. Simulations of cumulative outflow volume and nitrate concentration fitted well with the observations. Among the three SISs, the denitrification rate was greatest under unsaturated conditions at high water temperature. The denitrification rate constant had an exponential relationship with temperature. An empirical formula describing this relationship was developed and validated in the SIS. The results showed that the SH column attained the greatest nitrate removal efficiency, mainly due to its low hydraulic loading and long retention time. Overall, the results showed that HYDRUS-1D adequately simulated nitrate transport through the soil column under different temperature and hydraulic conditions in an SIS. The fate of nitrate was directly controlled by the water temperature and hydraulic conditions.