Culturable and inhalable airborne bacteria in a semiunderground municipal wastewater treatment plant: Distribution, transmission, and health risk assessment.

Airborne pathogens constitute a growing threat to global public health. Wastewater treatment plants (WWTPs) are important sources of airborne bacteria, which pose great health risks to the employee and nearby residents. In this study, the distribution, transmission and health risk of the airborne culturable and inhalable bacteria carried by PM2.5 in a semiunderground WWTP were evaluated. The concentrations of culturable bacteria in the air were 21.2-1431.1 CFU/m3, with the main contributions of primary and biological treatments. The relative abundances of culturable and total inhalable bacterial taxa were positively correlated (p < 0.05). However, certain bacteria, including Bacillus, Acinetobacter and Enterococcus, exhibited high reproductive capacity despite their low concentration in the air, suggesting that they can survive and regrow in suitable environments. Transmission modeling revealed that the concentrations of airborne bacteria exponentially decreased with distance from 18.67 to 24.12 copies /m3 at the source to 0.06-0.14 copies /m3 at 1000 m downwind. The risks of 8-h exposure in this WWTP except the outlet exceeded the reference value recommended by WHO, which were primarily dependent on P. aeruginosa, Salmonella, and E. coli. Management practices should consider improved controls for bioaerosols in order to reduce the risk of disease transmission.

Photocatalytic degradation of trihalomethanes and haloacetonitriles on graphitic carbon nitride under visible light irradiation.

Trihalomethanes (THMs) and haloacetonitriles (HANs), most common disinfection by-products in drinking water, pose adverse environmental impacts and potential risks to human health. There is a pressing need to develop innovative, economically feasible, and environmentally benign processes to control these persistent contaminants. In this paper, visible-light-responsive graphitic carbon nitride (g-C3N4) samples were synthesized to degrade the THMs and HANs and the photocatalytic degradation mechanism was explored. The results indicated that a carbon-doped g-C3N4 with an optimum dopant content (MCB0.07) displayed the best photocatalytic activity for the total trihalomethanes (TTHM) and total haloacetonitriles (THAN), with the reaction rate constant of 11.6 and 10.4 (10-3 min-1), respectively. MCB0.07 demonstrated a high THMs and HANs removal efficiency under visible light irradiation and could be reused. According to scavenger tests of the selected reactive species and X-ray photoelectron spectroscopy, holes play a dominant role for both THMs and HANs degradation on the MCB0.07. The degradation of HANs by holes proceeded mainly through breakage of the CC bond in the CCN group. The THMs degradation was achieved through hydrogen abstraction or/and dehalogenation. The brominated-THMs/HANs were more photosensitive than their chlorinated analogous and were less stable than bromo-chloro-THMs/HANs. This study sheds light on the mechanism of the photocatalytic degradation of THMs and HANs under visible light irradiation by carbon-doped g-C3N4. Furthermore, it could provide insights for engineering applications and contaminant control in drinking water purification.

Effect of carbon source on the denitrification in constructed wetlands.

The ability of constructed wetlands with different plants in nitrate removal were investigated. The factors promoting the rates of denitrification including organic carbon, nitrate load, plants in wetlands, pH and water temperature in field were systematically investigated. The results showed that the additional carbon source (glucose) can remarkably improve the nitrate removal ability of the constructed wetland. It demonstrated that the nitrate removal rate can increase from 20% to more than 50% in summer and from 10% to 30% in winter, when the nitrate concentration was 30-40 mg/L, the retention time was 24 h and 25 mg/L dissolved organic carbon (DOC) was ploughed into the constructed wetland. However, the nitrite in the constructed wetland accumulated a little with the supply of the additional carbon source in summer and winter, and it increased from 0.15 to 2 mg/L in the effluent. It was also found that the abilities of plant in adjusting pH and temperature can result in an increase of denitrification in wetlands. The seasonal change may also impact the denitrification.

[Study on the growth characteristics and root exudates of three wetlands plants at different culture conditions].

Wetland plants are the important component of constructed wetlands and their root exudates provide the interior hydrocarbon for denitrification. In this study, the growth characteristics and root exudates of Canna indica, Zizania caduciflora and Lythrum salicari in different culture conditions were researched. The results showed that the average biomass initial/biomass in 120 days growth of Canna indica, Zizania caduciflora and Lythrum salicari were 9.1, 3.7, and 4.7, respectively. There was a positive correlation between the root exudates and the biomass of plants, but the release rate of root exudates decreased with the biomass increase. The root exudates release rates of unit biomass were 0.92, 0.47, 0.43 mg x (g x d)(-1) for Lythrum salicari, Canna indica and Zizania caduciflora, respectively. And the root exudates of those three plants are mainly organic acids and arylprotein based on the three-dimensional fluorescence spectrum analysis. The results ofthis study also indicate that Canna indiea and Lythrum salicari are befitting wetlands plants.