Long-term effective remediation of black-odorous water via regulating calcium nitrate sustained-release.

Nitrate addition is reported as a cost-effective method for remediating black-odorous water, which is mainly induced by the deficiency of electron acceptor. However, excessive release of nitrate and lack of long-term effectiveness significantly limited the application of direct nitrate dosing technology. Herein, for remediating black-odorous water, we constructed a nitrate sustained-release ecological concrete (ecoN-concrete), in which calcium nitrate (Ca(NO3)2) was dosed into concrete block to regulate the release of nitrate. The results showed that chemical oxygen demand (COD), turbidity, ammonia, phosphate, and sulfate were significantly removed in an ecoN-concrete-contained reactor fed with black-odorous water, and its removal efficiency was largely dependent on Ca(NO3)2 dosage. Meanwhile, the released nitrate was lower than 25% of its total dosage and nitrite was lower than 1.5 mg/L during 14 days remediation. After three recycles, the removal efficiencies of COD and turbidity by using ecoN-concrete were still more than 85%, indicating an excellent nitrate sustained-release performance of ecoN-concrete, which can be applied for preventing water re-blackening and re-stinking. Further investigation illustrated that the ecoN-concrete (1) decreased the abundance of Desulfovibrio, Desulfomonile, and Desulforhabdus in the phylum of Desulfobacterota to alleviate the odorous gas production and (2) significantly increased the abundance of Bacillus and Thermomonas, which utilized the released-nitrate for consuming organic matters and ammonia. This study provided an artful Ca(NO3)2 dosing strategy and long-term effective method for black-odorous water remediation.

A hormesis-like effect of FeS on heterotrophic denitrification and its mechanisms.

To alleviate the insufficiency of carbon source in sewage, many sulfur-containing inorganic electron donors were added into traditional heterotrophic denitrification process. However, the effects of extraneous inorganic electron donors on heterotrophic denitrification were still largely unknown. In this study, a hormesis-like effect of ferrous sulfide (FeS, a representative inorganic electron donors) on Paracoccus denitrificans was observed. Total nitrogen (TN) removal efficiency of P. denitrificans rose by 15% with the increase of FeS dosage from 0 to 0.3 g L-1 (low level), whereas the TN removal significantly decreased to 53% as the dosage of FeS mounted up to 5.0 g L-1 (high level). Furthermore, the impacts of FeS on glucose utilization and bacterial growth exhibited hormesis-like effects. A subsequent mechanistic study revealed that above influences were caused by its released ions (Fe2+, Fe3+, and S2-) rather than particle size. Further study illustrated that low dosage of FeS released a small amount of Fe2+ and Fe3+, which provided sufficient electrons via promoting glucose utilization, then improved denitrification. Conversely, FeS with high dosage inhibited denitrification via its released S2-, which suppressed the activity of key denitrifying enzymes rather than influenced glucose metabolism and electron provision. Our results provide an insight into improving denitrification efficiency of the mixotrophic process coexisting with autotrophic and heterotrophic denitrifiers.

Short- and long-term effects of decabromodiphenyl ether (BDE-209) on sediment denitrification using a semi-continuous microcosm.

The widespread use of decabromodiphenyl ether (BDE-209) resulted in its deposition in environmental media and biological matrices. However, to date, few studies focused on the effect of BDE-209 on microorganisms, and those available were investigated via an enclosed system completely cutting off the communication between testing system and its native environment. Herein, 4.0 mg/g BDE-209 acute exposure induced a 20% decline of NOX-N (the sum of NO3--N and NO2--N) removal efficiency and a significant accumulation of NO2--N and N2O. These inhibitory effects presented in a BDE-209 concentration-dependent manner. Using a semi-continuous microcosm, the inhibitory effects of BDE-209 on denitrification were observed to be significantly enhanced with the extending of exposure duration. Denitrifying genes assay illustrated that BDE-209 has an insignificant effect on the global abundance of denitrifying bacteria because of microbial exchange with its overlying water. But the utilization of electron donor (carbon substrate), the activity of electron transport system and denitrifying enzymes were significantly inhibited by BDE-209 exposure in a exposure-duration-dependent manner. Finally, insufficient electron donor and lower efficiency of electron transport and utilization on denitrifying enzymes deteriorated the denitrification performance. These results provided a new insight into BDE-209 influence on denitrification in the natural environment.

Identification of CO2 induces oxidative stress to change bacterial surface properties.

The surface properties of bacteria play an essential role in their abilities to perform transmembrane communication, adherence, immobilization, flocculation, etc. However, the responsiveness of bacterial surfaces to elevated atmospheric CO2 remains unknown. In this study, using the model bacteria, Paracoccus denitrificans, the effect of CO2 on the primary bacterial surface properties, specifically hydrophobicity and surface charge, has been explored. We found that hydrophilicity and negative surface charge both rose in conjunction with increased atmospheric CO2 concentrations. Studies of the potential mechanisms involved have illustrated that elevated CO2 significantly increases the production of polysaccharides in extracellular polymeric substances (EPS). Various hydrophilic groups and negative charges in these polysaccharides prompt hydrophilicity and surface charge variations in bacteria. Further research has identified that elevations in CO2 result in the accumulation of reactive species, specifically reactive nitrogen species (RNS). In this study, it was found that RNS damaged the permeability of bacterial membranes by inducing lipid peroxidation and then caused the leakage of intracellular substrate, which ultimately led to an increase in EPS polysaccharides. Our findings suggest that changes in bacterial surface properties due to atmospheric CO2 elevation, as well as the reactions these trigger, merit widespread attention.

Ionic copper strengthens the toxicity of tetrabromobisphenol A (TBBPA) to denitrification by decreasing substrate transport and electron transfer.

Increasing electrical and electronic waste have raised concerns about the potential toxicity of brominated flame retardants (BFRs) and heavy metals (HMs). However, few studies have focused on the combined effect of BFRs and HMs on microorganisms, especially denitrifying bacteria, which have an essential role in N cycles and N2O emission. Herein, we investigate the combined effect of tetrabromobisphenol A (TBBPA) and Cu on model denitrifying bacteria. A further 24.5% decline in N removal efficiency was observed when 0.05 mg/L Cu were added into a denitrifying system containing 0.75 mg/L TBBPA. Further study demonstrated that Cu heightened the toxicity of TBBPA to denitrification via following aspects: (1) Cu stimulated EPS secretion induced by TBBPA during denitrification, blocked the transmembrane transport of glucose, which caused insufficient carbon substrate for bacteria growth and electron provision; (2) Cu further suppressed key denitrifying enzymes' activity and down-regulated genes involving electron transport induced by TBBPA, led to the decrease of electron transport activity. Finally, the decrease of bacterial growth, insufficient electron donor, and lower electron transport activity caused the synergetic toxic effect of TBBPA and Cu on denitrification. Overall, the present study provides new insights into the combined effect of BFRs and HMs on microorganisms.