Improved efficiency and stability using a novel elemental sulfur-based moving-bed denitrification process

Elemental sulfur-based denitrification (ESDeN) technology is known as a cost-saving alternative to its heterotrophic counterpart for nutrient removal from organic-deficient water. However, the traditional fixed-bed reactor (FixBR), as an extensively used process, suffers from a low denitrification rate and even performance deterioration during long-term operation. Herein, we proposed a novel elemental sulfur-based denitrifying moving-bed reactor (ESDeN-MovBR), in which a screw rotator was employed to drive the filled sulfur particles to be microfluidized vertically (a state of vertical-loop movement). Our results showed that the ESDeN-MovBR realized much superior and more stable denitrification performance compared to the ESDeN-FixBR, as indicated by 3.09-fold higher denitrification rate and over one order of magnitude lower intermediates (NO2- and N2O) yield, which could last for over 100 days. Further research revealed that the microfluidization of sulfur particles facilitated the expelling of nitrogen bubbles and excessive biomass, resulting in the prolongation of actual hydraulic retention time by over 80 % and could partially explain the higher denitrification rate in ESDeN-MovBR. The remaining contribution to the improvement of denitrification rate was suggested to be result from changes in biofilm properties, in which the biofilm thickness of ESDeN-MovBR was found to be 3.29 times thinner yet enriched with 2.52 times more autotrophic denitrifiers. This study offered a completely new solution to boost up the denitrification performance of ESDeN technology and provided in-depth evidence for the necessity of biofilm thickness control in such technology.

Long-distance responses of ginger to soil sulfamethoxazole and chromium: Growth, co-occurrence with antibiotic resistance genes, and consumption risk

The coexistence of antibiotics and heavy metals in agroecosystems is nonnegligible, which permits the promotion of antibiotic resistance genes (ARGs) in crops, thus posing a potential threat to humans along the food chain. In this study, we investigated the bottom-up (rhizosphere→rhizome→root→leaf) long-distance responses and bio-enrichment characteristics of ginger to different sulfamethoxazole (SMX) and chromium (Cr) contamination patterns. The results showed that ginger root systems adapted to SMX- and/or Cr-stress by increasing humic-like exudates, which may help to maintain the rhizosphere indigenous bacterial phyla (i.e., Proteobacteria, Chloroflexi, Acidobacteria and Actinobacteria). The root activity, leaf photosynthesis and fluorescence, and antioxidant enzymes (SOD, POD, CAT) of ginger were significantly decreased under high-dose Cr and SMX co-contamination, while a "hormesis effect" was observed under single low-dose SMX contamination. For example, CS100 (co-contamination of 100 mg/L SMX and 100 mg/L Cr) caused the most severe inhibition to leaf photosynthetic function by reducing photochemical efficiency (reflected on PAR-ETR, φPSII and qP). Meanwhile, CS100 induced the highest ROS production, in which H2O2 and O2·- increased by 328.82% and 238.00% compared with CK (the blank control without contamination). Moreover, co-selective stress by Cr and SMX induced the increase of ARG bacterial hosts and bacterial phenotypes containing mobile elements, contributing to the high detected abundance of target ARGs (sul1, sul2) up to 10-2∼10-1 copies/16S rRNA in rhizomes intended for consumption.