The fate of nitrification and urease inhibitors in simulated bank filtration

Fates of potentially persistent and mobile organic substances in embedded outdoor columns for artificial groundwater recharge simulation

Persistent and mobile organic micropollutants (OMP) are ubiquitously found in the aquatic environment and have a high propensity to distribute in water resources and are difficult to remediate. Managed aquifer recharge systems such as artificial groundwater recharge, produce high-quality drinking water by removing numerous OMP from the source water. In this study, the fates of selected emerging and potentially persistent and mobile OMP were investigated in outdoor columns for artificial groundwater recharge simulation. Breakthrough curves of OMP were modeled to differentiate between sorption and bio-transformation. The study showed that selected OMP were persistent in the surface water and no photo-degradation was observed, except for diclofenac. The trends of dissolved organic carbon concentrations and UV light absorption at 254 nm wavelength suggest elevated biological activity in the first 0.3 m of the columns. The study revealed that the bio-transformation of cyanoguanidine, valsartan acid and diclofenac correlated with the biological activity in the sand columns. Benzyltrimethylammonium, n-(3-(dimethylamino)-propyl)methacrylamide, 1,3-di-o-tolylguanidine, 1,3-diphenylguanidine and melamine were completely eliminated within the first 0.3 m, likely due to sorption. Less mobile compounds such as carbamazepine and adamantan-1-amine also showed sorption. Sorption was also observed for diclofenac, likely due to decreased pH along the column depth. Retardation factors of several OMP were higher in the first 0.3 m of the columns, likely due to higher organic carbon contents compared to the remaining depth. Six organic substances (for example 2-acrylamido-2-methylpropane sulfonate and dimethylbenzene sulfonate) were persistent and mobile throughout the experiment. Overall, this study reveals the vital role of pH and sand organic carbon for sorption and residence time and biological activity for OMP elimination.

Insight into the functional mechanisms of nitrogen-cycling inhibitors in decreasing yield-scaled ammonia volatilization and nitrous oxide emission: A global meta-analysis

Soil ammonia (NH3) volatilization and nitrous oxide (N2O) emission decrease nitrogen (N) utilization efficiency and cause some environmental problems. The N-cycling inhibitors are suggested to apply to enhance N utilization efficiency. Quantifying effects of N-cycling inhibitors on yield-scaled NH3 volatilization and N2O emission and functional genes could provide support for the optimal selection and application of N-cycling inhibitor. We conducted a meta-analysis to reveal the effects of N-cycling inhibitors on soil abiotic properties, functional genes and yield-scaled NH3 volatilization and N2O emission by extracting data from 166 published articles and linked their comprehensive relationships. The N-cycling inhibitors in this meta-analysis mainly includes nitrification inhibitors 3, 4-dimethyl pyrazole phosphate, dicyandiamide and 2-chloro-6-trichloromethylpyridine, urease inhibitor N-(n-butyl) thiophosphoric triamide and biological nitrification inhibitors methyl 4-hydroxybenzoate and 1, 9-decanediol. The N-cycling inhibitor applications significantly increased alkaline soil pH but significantly decreased acidic soil pH. The N-cycling inhibitors decreased soil AOB amoA gene abundances mostly under the condition of pH 4.5-6 (mean: 212%, 95% confidence intervals (CI): 249% and -176%) and significantly decreased nirS gene (mean: 39%; 95% CI: 72% and -6%). The yield-scaled NH3 volatilization was significantly decreased by the N-cycling inhibitors under the condition of soil pH = 7-8.5 (mean: 45%; 95% CI: 59% and -31%). The yield-scaled N2O emission was also significantly reduced by all N-cycling inhibitors and had negative correlations with the soil nirK and nirS gene abundances. The effects of N-cycling inhibitors on soil pH, ammonium-N, nitrate-N and nitrifying and denitrifying genes and yield-scaled NH3 volatilization and N2O emission were dominated by the inhibitor types, soil textures, crop species and environmental pH. Our study could provide technical support for the optimal selection and application of N-cycling inhibitor under different environmental conditions.

Transformation of potentially persistent and mobile organic micropollutants in column experiments

The occurrence of potentially persistent and mobile (PM) organic micropollutants (OMP) in the aquatic environment is recognized as a severe threat to water resources and drinking water suppliers. The current study investigated long-term fate (persistency and bio-transformation) of several emerging contaminants in a simulated bank filtration (BF) for the first time. In parallel, four sand column systems were operated with groundwater and continuously spiked with an average concentration of 1 μg/L for 24 OMP. Each column system consisted of two sand columns connected in series. Presumably, biological activities in the first column were higher than in the second column, as dissolved oxygen utilization, dissolved organic matter (DOM) and UV absorbance at 254 nm (UV₂₅₄) reduction rates were high in the first column. This study revealed that 9 out of 24 OMP were persistent and mobile throughout the study under oxic conditions and within a hydraulic retention time (HRT) of 12 days. However, 2 (out of 9) OMP were persistent but showed sorption behavior. 15 (out of 24) OMP displayed bio-transformation, 4 were eliminated entirely within 4.5 days of HRT. Others showed constant or improved degradation with the adaptation (or operation) time. Improved degradation with adaption was high in the bioactive sand columns. However, 8 OMP showed improved elimination at high HRT, even in low biologically active columns. In addition, no significant effect of the DOM on the eliminations of OMP was found except for 4-hydroxy-1-(2-hydroxyethyl)-2,2,6,6,-tetramethylpiperidine (HHTMP), 2-methyl-2-propene-1-sulfonic acid (MPSA) and sulfamethoxazole (SMX). The eliminations of HHTMP (Pearson's r > 0.80, p < 0.05), MPSA (Pearson's r > 0.70) and SMX (Pearson's r > 0.80) correlated with the removals of humic substances in the sand columns. Overall, adaptation time and HRT play a crucial role in the elimination of emerging OMP through BF, yet at the same time several OMP exhibit persistent behavior.