Simultaneous nitrate and sulfate biotransformation driven by different substrates: comparison of carbon sources and metabolic pathways at different C/N ratios.

Nitrate (NO3-) and sulfate (SO42-) often coexist in organic wastewater. The effects of different substrates on NO3- and SO42- biotransformation pathways at various C/N ratios were investigated in this study. This study used an activated sludge process for simultaneous desulfurization and denitrification in an integrated sequencing batch bioreactor. The results revealed that the most complete removals of NO3- and SO42- were achieved at a C/N ratio of 5 in integrated simultaneous desulfurization and denitrification (ISDD). Reactor Rb (sodium succinate) displayed a higher SO42- removal efficiency (93.79%) with lower chemical oxygen demand (COD) consumption (85.72%) than reactor Ra (sodium acetate) on account of almost 100% removal of NO3- in both Ra and Rb. Ra produced more S2- (5.96 mg L-1) and H2S (25 mg L-1) than Rb, which regulated the biotransformation of NO3- from denitrification to dissimilatory nitrate reduction to ammonium (DNRA), whereas almost no H2S accumulated in Rb which can avoid secondary pollution. Sodium acetate-supported systems were found to favor the growth of DNRA bacteria (Desulfovibrio); although denitrifying bacteria (DNB) and sulfate-reducing bacteria (SRB) were found to co-exist in both systems, Rb has a greater keystone taxa diversity. Furthermore, the potential carbon metabolic pathways of the two carbon sources have been predicted. Both succinate and acetate could be generated in reactor Rb through the citrate cycle and the acetyl-CoA pathway. The high prevalence of four-carbon metabolism in Ra suggests that the carbon metabolism of sodium acetate is significantly improved at a C/N ratio of 5. This study has clarified the biotransformation mechanisms of NO3- and SO42- in the presence of different substrates and the potential carbon metabolism pathway, which is expected to provide new ideas for the simultaneous removal of NO3- and SO42- from different media.

Effects of various COD/NO ratios on NOx removal performance and microbial communities in a BTF-ABR integrated system.

In this study, we investigated the removal performance of NOx and stability of the biotrickling filter-anaerobic baffled reactor (BTF-ABR) integrated system at various chemical oxygen demand (COD)/NO ratios (12.18, 6.71, and 4.63 in stages 1, 2, and 3, respectively) under 3.5% O2 and 50 ± 0.5 °C conditions for the first time. The results showed that the maximum elimination capacity of NOx was 4.46, 8.16, and 11.58 g/(m3·h) in stages 1, 2, and 3, respectively. The minimum operating cost in terms of glucose was 4.79 g of glucose/g of NO. However, a COD/NO ratio of 12.18 resulted in a wastage of carbon sources, while a COD/NO ratio of 4.63 led to about 20 mg/m3 N2O emission at the end of the study. Highly bacteria diversity and positive co-occurrence networks at the COD/NO ratio of 6.71 were the main reasons for no intermediate accumulation or N2O emission. Analysis of real-time polymerase chain reaction (PCR) indicated that nirS and norB were more sensitive to the changes in the COD/NO ratios than other denitrifying genes, and the denitrifiers with nirS filled more ecological niches as the NOx increased. Furthermore, although the decrease in COD/NO ratio significantly impacted the microbial community structure, the NOx RE was stabilized at over 90% because the micro-aerobic environment produced by ABR combined highly diverse microbes and functions in BTF, as well as the coordinated expression of denitrifying genes. Achieving efficient, stable, and low-cost denitrification is feasible in this BTF-ABR integrated system.

Effects of Air Pollution Exposure during Preconception and Pregnancy on Gestational Diabetes Mellitus.

This study aimed to investigate the association between air pollution and gestational diabetes mellitus (GDM) in small- and medium-sized cities, identify sensitive periods and major pollutants, and explore the effects of air pollution on different populations. A total of 9820 women who delivered in Handan Maternal and Child Health Hospital in the Hebei Province from February 2018 to July 2020 were included in the study. Logistic regression and principal component logistic regression models were used to assess the effects of air pollution exposure during preconception and pregnancy on GDM risk and the differences in the effects across populations. The results suggested that each 20 µg/m3 increase in PM2.5 and PM10 exposure during preconception and pregnancy significantly increased the risk of GDM, and a 10 µg/m3 increase in NO2 exposure during pregnancy was also associated with the risk of GDM. In a subgroup analysis, pregnant women aged 30-35 years, nulliparous women, and those with less than a bachelor's education were the most sensitive groups. This study provides evidence for an association between air pollution and the prevalence of GDM, with PM2.5, PM10, and NO2 as risk factors for GDM.