Nutrients removal and bacterial community structure for low C/N municipal wastewater using a modified anaerobic/anoxic/oxic (mA2/O) process in North China.

A modified anaerobic/anoxic/oxic (mA2/O) process based on utilizing the internal carbon source and adding polypropylene carriers was operated for 90d to investigate the nutrients removal performance and bacterial community. This system exhibited a stable and efficient performance, particularly, in removing the NH4+-N and total phosphorus. The results of high-throughput sequencing showed that the 13 dominant genera containing Pseudomonas, Comamonas, Arcobacter, Nitrobacteria, Nitrosospira, Nitrosomonas, Bacteroides, Flavobacterium, Rhizobium, Acinetobacter, Zoogloea, Rhodocyclus and Moraxella were shared by five zones, inferring that they were the essential players in treating low C/N (below 5.0) municipal wastewater around 10°C. The average abundance of Nitrosospira (4.21%) was higher than that of Nitrosomonas (2.93%), suggested that Nitrosospira performed well under low temperature for nitrification. Additionally, both known Rhodocyclus-related PAOs and GAOs Competibacter were not detected possibly due to low temperature. Redundancy analysis (RDA) indicated that DO played more important roles in regulating bacterial community composition than HRT.

Effects of chemically induced hypoxia on in vitro expression of hypoxia inducible factor-lα, vascular endothelial growth factor, aggrecanase-1, and tissue inhibitor of metalloproteinase-3 in rat mandibular condylar chondrocytes.

AIMS: To examine the expression of hypoxia inducible factor-lα (HIF-1α), vascular endothelial growth factor (VEGF), aggrecanase-1 (ADAMTS-4), and tissue inhibitor of metalloproteinase-3 (TIMP-3) in rat mandibular condylar chondrocytes under hypoxic conditions and examine the relationship of these expressed factors in early condylar cartilage growth. METHODS: CoCl2 was used to mimic a hypoxic microenvironment by chemically inducing hypoxia. Chondrocytes, which were obtained from the mandibular condyles of 3-week-old female Sprague-Dawley rats, were treated with 125 µmol/L CoCl2 for 48 hours. The HIF-1α, VEGF, ADAMTS-4, and TIMP-3 mRNA levels in chondrocytes were detected using a semiquantitativepolymerase chain reaction (PCR) at 12, 24, and 48 hours after the initiation of hypoxia and normoxia conditions. A univariate variance analysis (pairwise least significant difference t test) using a SPSS 13.0 software package was performed to test for differences between different groups. RESULTS: PCR analysis of the chondrocytes showed that the expression of HIF-1α and VEGF mRNA increased at 12, 24, and 48 hours after induction of hypoxia. HIF-1α expression gradually increased throughout the study duration, while VEGF expression peaked at 12 hours. Compared to normoxia conditions, hypoxia resulted in constantly elevated expression levels of both. On the other hand, there was no significant difference in the ADAMTS-4 and TIMP-3 mRNA expression between hypoxic and normoxic conditions throughout the study (P > .05). CONCLUSION: An upregulated HIF-1α and VEGF mRNA expression indicates their important roles in cartilage vascularization and development in newly hypoxic microenvironments. Additionally, chemically induced hypoxia has little effect on the expressions of ADAMTS-4 and TIMP-3.