Successional dynamics of low C/N activated sludge system under salinity shock: Performance, nitrogen removal pathways, microbial community, and assembly

Unveiling significant roles of phytohormone 6-benzylaminopurine in empowering Phaeodactylum tricornutum for high-salinity wastewater treatment and bioresource recovery

High-salinity presents significant challenges in microalgal wastewater treatment and bioresource recovery due to salinity stress. This study explored the use of salt-tolerant microalgae in conjunction with phytohormone regulation. 1 µM 6-benzylaminopurine increased the biomass of Phaeodactylum tricornutum by 38.3 % and enhanced lipid production by 36.8 %. 6-benzylaminopurine significantly improved the removal of inorganic carbon, total nitrogen, and total phosphorus by 85.2 %, 27.4 %, and 31.9 %. Specifically, 6-benzylaminopurine improved K+ transportation by 71.0 %, increased the activity of Ca2+ transport ATPase and Ca2+ sensors by 49.0 %-83.0 %, optimized osmotic balance, and alleviated salt-induced damage. The contents of proline and extracellular polymers increased by 34.8 % and 35.5 %. A 38.4 % reduction in reactive oxygen species indicated that high-salinity stress was mitigated. The analysis of Sustainable Development Goals showed a 56.2 % improvement in Affordable and Clean Energy. Overall, these findings further highlighted the promising application of the phytohormone 6-benzylaminopurine in microalgal high-salinity wastewater treatment and lipid production.

Ammonia oxidizing bacteria (AOB) denitrification and bacterial denitrification as the main culprit of high N2O emission in SBR with low C/N ratio wastewater

A large amount of greenhouse gas nitrous oxide (N2O) will be produced during the biological nitrogen removal process for organic wastewater of low C/N ratio. One of the effective methods to solve this problem is to incorporate inexpensive carbon source. In this study, raw wastewater (RW) from pig farm, that was not anaerobically digested, was utilized as exogenous carbon in both A/O and SBR aerobic reactor to treat liquid digestate with high ammonia nitrogen and low C/N ratio. The results showed that N2O emission in SBR was higher than that of A/O process under the same nitrogen load. The N2O conversion in the biological nitrogen removal process was investigated by the strategy of integrating stable isotope method and metagenomics. The δO18-N2O, δN15-N2O, and SP values of the SBR were closer to the denitrification values of Ammonia-Oxidizing Bacteria (AOB) than those of A/O. The abundance of AOB in the SBR reactor was higher than that in the A/O reactor, while the abundance of denitrifying bacteria was lower. The amoA/B/C gene abundance in the SBR was greater than that in the A/O, and the NOS gene abundance was the opposite. The results indicated that both AOB denitrification and bacterial denitrification led to the increase of N2O emissions of the SBR.

Regulatory of salinity on assembly of activated sludge microbial communities and nitrogen transformation potential in industrial plants of the lower Yangtze River basin

This study aims to thoroughly investigate the impact mode of salinity carried by industrial wastewater on the anaerobic-anoxic-oxic (A2O) sludge in wastewater treatment plants (WWTPs). Through comprehensive investigation of the A2O stage activated sludge (AS) from 19 industrial WWTPs in the downstream area of the Yangtze River, China, A total of 38 samples of anaerobic sludge and oxic sludge were collected and analyzed. We found that salinity stress significantly inhibits the growth of the AS community, particularly evident in the anaerobic sludge community. Furthermore, the high-saline environment induces changes in the structure and functional patterns of the AS community, leading to intensive interactions and resource exchanges among microorganisms. Halophilic microorganisms may play a crucial role in this process, significantly impacting the overall community structure, especially in the oxic sludge community. Additionally, salinity stress not only suppresses the nitrogen transformation potential of the AS but also leads to the accumulation of nitrite, thereby increasing the emission potential of both NO and N2O, exacerbating the greenhouse effect of the A2O process in industrial WWTPs. The findings of this study provide necessary theoretical support for maintaining the long-term stable operation of the A2O sludge system in industrial WWTPs, reducing carbon footprint, and improving nitrogen removal efficiency.

The ecology of the sewer systems: Microbial composition, function, assembly, and network in different spatial locations

Microbial induced concrete corrosion (MICC) is the primary deterioration affecting global sewers. Disentangling ecological mechanisms in the sewer system is meaningful for implementing policies to protect sewer pipes using trenchless technology. It is necessary to understand microbial compositions, interaction networks, functions, alongside assembly processes in sewer microbial communities. In this study, sewer wastewater samples and microbial samples from the upper part (UP), middle part (MP) and bottom part (BP) of different pipes were collected for 16S rRNA gene amplicon analysis. It was found that BP harbored distinct microbial communities and the largest proportion of unique species (1141) compared to UP and MP. The community in BP tended to be more clustered. Furthermore, significant differences in microbial functions existed in different spatial locations, including the carbon cycle, nitrogen cycle and sulfur cycle. Active microbial sulfur cycling indicated the corrosion risk of MICC. Among the environmental factors, the oxidation‒reduction potential drove changes in BP, while sulfate managed changes in UP and BP. Stochasticity dominated community assembly in the sewer system. Additionally, the sewer microbial community exhibited numerous positive links. BP possessed a more complex, modular network with higher modularity. These deep insights into microbial ecology in the sewer system may guide engineering safety and disaster prevention in sewer infrastructure.

Soil microbial community structure, function and network along a mangrove forest restoration chronosequence

Mangrove forests have high ecological, social and economic values, but due to environmental changes and human activities, natural mangrove forests have experienced serious degradations and reductions in distribution area worldwide. In the coastal zones of southern China, an introduced mangrove species, Sonneratia apetala, has been extensively used for mangrove restoration because of its rapid growth and strong environmental adaptability. However, little is known about how soil microorganisms vary with the restoration stages of the afforested mangrove forests. Here, we examined the changes in soil physicochemical properties and microbial biomass, community structure and function, and network in three afforested S. apetala forests with restoration time of 7, 12, and 18 years and compared them with a bare flat and a 60-year-old natural Kandelia obovata forest in a mangrove nature reserve. Our results showed that the contents of soil salinity, organic carbon, total nitrogen, ammonium nitrogen, and microbial biomass increased, while soil pH and bacterial alpha diversity decreased with afforestation age. Soil microbial community structure was significantly affected by soil salinity, organic carbon, pH, total nitrogen, ammonium nitrogen, available phosphorus, and available kalium, and susceptibility to environmental factors was more pronounced in bacterial than fungal community structure. The relative abundances of aerobic chemoheterotrophy were significantly higher in 12- and 18-year-old S. apetala than in K. obovata forest, while that of sulfate-reducing bacteria showed a decreasing trend with afforestation age. The abundance of dung saprotroph was significantly higher in 12- and 18-year-old S. apetala forests than in the natural forest. With the increasing afforestation age, the modularity of microbial networks increased, while stability and robustness decreased. Our results suggest that planting S. apetala contributes to improving soil fertility and microbial biomass but may make soil microbial networks more vulnerable.