Synthesis of amorphous-MnO2/Clinoptilolite and its utilization for NH4+-N oxidation in an anoxic environment.

Mediating the anoxic ammonia oxidation with manganese oxide (MnOx) can reduce the requirements of dissolved oxygen (DO) concentrations in constructed wetlands (CWs) and improve the removal of ammonium nitrogen (NH4+-N). Recent studies that employed natural manganese ore and/or mine waste as substrates in CWs may develop potentially negative environmental effects due to leachates. However, removing NH4+-N by anoxic ammonia oxidation is influenced by the crystal form of MnOx. In this study, a novel clinoptilolite-based amorphous-MnO2 (amorphous-MnO2/clinoptilolite) was synthesized by the sol-gel method as an alternative substrate to improve the efficiency of anoxic ammonia oxidation and reduce the impact of Mn ion leaching. According to the anoxic ammonia oxidation experiment of clinoptilolite, amorphous-MnO2/clinoptilolite, and manganese ore on NH4+-N, the amounts of NH4+-N removed were 24.55 mg/L/d, 44.55 mg/L/d, and 11.04 mg/L/d, respectively, and the initial NH4+-N concentration was 49.53 mg/L. These results indicated that the amorphous-MnO2/clinoptilolite had both the adsorption and the anoxic ammonia oxidation performance. The recycling experiment demonstrated that the effect of anoxic ammonia oxygen mediated by amorphous-MnO2 would not diminish with the gradual saturation of clinoptilolite for NH4+-N. Furthermore, the anoxic ammonia oxidation consumed NH4+-N in the clinoptilolite, which restored the adsorption capacity of the clinoptilolite and simultaneously decreased the leakage of manganese ions in the process, making it environmentally friendly. Therefore, the amorphous-MnO2/clinoptilolite provided an excellent substrate material for the constructed wetland under an anoxic environment, which greatly improved the nitrogen removal capacity compared to existing substrate materials.

Mn(VII) enhanced by CaSO3 to remove trace organic pollutants in high salt organic wastewater: Further enhancement of salinity.

The high concentration of salt in organic wastewater has a strong inhibitory effect on the removal of pollutants. A method for the efficient removal of trace pollutants in high-salinity organic wastewater was developed. This study investigated the effect of the combination of permanganate [Mn(VII)] and calcium sulfite [S(IV)] on pollutant removal in hypersaline wastewater. The Mn(VII)-CaSO3 system removed more pollutants from high-salinity organic wastewater than from normal-salinity wastewater. Chloride (increasing from 1 M to 5 M) and low concentration of sulfate (increasing from 0.05 M to 0.5 M) significantly enhanced the system's resistance to pollutants under neutral conditions. Despite the fact that Cl- can combine with the free radicals in the system and reduce their efficiency in removing pollutants, the presence of chloride ions greatly enhances the electron transfer rate in the system, promoting the conversion of Mn(VII) to Mn(III) and significantly increasing the reaction rate of Mn(III) as the primary active species. Therefore, chloride salts can greatly enhance the removal of organic pollutants by Mn(VII)-CaSO3. Although sulfate does not react with free radicals, a high concentration of sulfate (1 M) will affect the formation of Mn(III), which greatly weakens the removal effect of the entire system on pollutants. The system can still have a good pollutant removal effect with mixed salt. Altogether, this study demonstrates that the Mn(VII)-CaSO3 system offers new possibilities for the treatment of organic pollutants in hypersaline wastewater.

Spatiotemporal distribution and potential risk assessment of microcystins in the Yulin River, a tributary of the Three Gorges Reservoir, China.

Microcystins (MCs) pose potential threat for both aquatic organisms and humans, whereas their occurrence in response to hydrodynamic alterations are not clearly understood. Here, spatiotemporal variations of dissolved MC-RR and MC-LR were evaluated monthly in 2016 in the Yulin River, a tributary of the Three Gorges Reservoir (TGR). The environmental factors that linked to MCs concentration were discussed. The results revealed that MC-RR maximumly reached 3.55 µg/L, and the maximum MC-LR concentration exceeded the threshold value of 1.0 µg/L recommended by the WHO. MCs concentrations were higher during the flood season and decreased from the estuary to the upstream reach of the Yulin River. Ecological risk assessment confirmed that MC-LR had significant adverse effects on the benthonic invertebrates Potamopyrgus antipodarum. MCs content in the sediment was 1.70- to 20-fold higher than that in suspended particulate matter (SPM). The impacts of environmental factors on the MCs profile differed between flood and dry seasons and the longitudinal differences of MCs were determined by the longitudinal profile of water velocity and SPM content, which were affected by TGR operations. This study suggested that the occurrence of MCs in the Yulin River were influenced by hydrologic regime in TGR.