Performance and mechanism of chromium reduction in denitrification biofilm system with different carbon sources

Chromium dynamics in soil and detoxification of chromite belts using rhizospheric soil-plant interface

The chromium-contaminated soil expresses its severe eco-toxicity on living organisms of the locality and adjoining regions. This review has focused on the chemical interactions of chromium variants in soil and the sequestration of chromium using the soil-plant interface in the rhizosphere. The application of plant hyper-accumulators on chromium-contaminated soil for chromium sequestration is an attempt to minimize chromium toxicity of mining and industrial belts. This review utilized the PRISMA 2009 systematic review methodology. The literature screening was conducted by searching databases such as Scopus, Google Scholar, and Web of Science up to 2025 using specific keywords. In countries like Kazakhstan, South Africa, and India, more than 90% of world shipping-grade mine reserves of chromium are present. The mining and metallurgy of chromium can threaten the environmental quality and the region's public health. The Sukinda chromite mines in India are globally known for their rich chromite mining, metallurgy, and eco-toxicity. The present article analyzes the ecological challenges and searches for possible interactions of chromium variants in soil. The solution to mitigate chromium toxicity is possible using the rhizospheric soil-plant interface. This article's findings and discussion section help solve ecological challenges and strive for healthy soil at chromium-polluted sites. This review article can contribute to sustainable soil quality improvement at mining and industrial belts. Further research on the isotopic tracer technique is recommended to enhance the understanding of chromium dynamics in soil.

3D-printed controllable bio-accelerators with sustained release property to boost chromium (VI) inhibited denitrification recovery

Although soluble bio-accelerators have proven effective in mitigating Cr(VI) inhibition within denitrification system, issues persist in immobilizing bio-accelerators and making them slow-release for sustained regulation. In this study, a novel strategy was proposed to fabricate immobilized bio-accelerators with controlled structure, sustained release property by 3D printing technology. Notably, the sustained release of bio-accelerators from 3D-printed bio-accelerators (3DP-B) lasted for at least 144 h. Compared to control group, 3DP-B with basic components (3DP-BB) shortened the recovery time by 1.4 folds, and the COD and NO3--N removal efficiency was 36.5 % and 38.0 % higher than that of natural recovery. Correspondingly, the activity of key enzymes (nitrate reductase, nitrite reductase, nitric oxide reductase, and nitrous oxide reductase), electron transfer system activity and extracellular polymer substances of denitrification biofilm maintained at relatively high levels. Furthermore, introducing 60 mg·L-1 anthraquinone-2,6-disulfonate (AQDS) into the ink showed noticeable superiority on the bio-inhibition release over 1000 mg·L-1 AQDS. The released AQDS facilitated the electron transport capacity by 1.25 times compared with control group. The groundbreaking findings of this study could advance the development of 3D printing technology and utilization of bio-accelerators in the field of wastewater treatment.

Exploratory study on the metabolic similarity of denitrifying carbon sources

Mixed carbon sources have been developed for denitrification to eliminate the "carbon dependency" problem of single carbon. The metabolic correlation between different carbon sources is significant as guidance for the development of novel mixed carbon sources. In this study, to explore the metabolic similarity of denitrifying carbon sources, we selected alcohols (methanol, ethanol, and glycerol) and saccharide carbon sources (glucose, sucrose, and starch). Batch denitrification experiments revealed that methanol-acclimated sludge improved the denitrification rate of both methanol (14.42 mg-N/gMLVSS*h) and ethanol (9.65 mg-N/gMLVSS*h), whereas ethanol-acclimated sludge improved the denitrification rate of both methanol (7.80 mg-N/gMLVSS*h) and ethanol (22.23 mg-N/gMLVSS*h). In addition, the glucose-acclimated sludge and sucrose-acclimated sludge possibly improved the denitrification rate of glucose and sucrose, and the glycerol-acclimated sludge improved the denitrification rate of volatile fatty acids (VFAs), alcohols, and saccharide carbon sources. Functional gene analysis revealed that methanol, ethanol, and glycerol exhibited active alcohol oxidation and glyoxylate metabolism, and glycerol, glucose, and sucrose exhibited active glycolysis metabolism. This indicated that the similarity in the denitrification metabolism of these carbon sources was based on functional gene similarity, and glycerol-acclimated sludge exhibited the most diverse metabolism, which ensured its good denitrification effect with other carbon sources.