Salt stress altered anaerobic microbial community and carbon metabolism characteristics: The trade-off between methanogenesis and chain elongation

Selective removal of organic matters from high-salinity chemical industrial wastewater: Ultrafiltration or nanofiltration?

The effective separation and treatment of high-salinity chemical industrial wastewater has become a critical issue for the chemical industry. Membrane separation technology, including ultrafiltration (UF) and nanofiltration (NF) membranes, are potential candidates for selectively separating inorganic salts and organic compounds. In this study, we investigated the selective separation performance of real high-salinity chemical industrial wastewater by a series of commercial UF (UF10k, UF5k, UF3k, and UF1k) and NF (NF270, NF90, BSY90, BSY60, BSY30) membranes. UF1k exhibited the best separation performance among the various UF membranes, owing to its lowest molecular weight cut-off (MWCO) of 1 kDa. Further two-pass UF and coagulation-UF cannot effectively improve the separation performance of UF as the presence of low molecule weight organics in the wastewater. Among the NF membranes, we surprisingly found that some NF membranes, despite having smaller pore sizes theoretically, exhibited even lower rejection of organic matters than UF1k in high-salinity environments. Mechanistic investigation revealed that increased salt concentrations led to pore swelling, pore-wall dehydration and charge shielding effects in NF membranes, which resulted in a substantially enlarged MWCO. BSY90, the tightest NF membrane, exhibited the best performance in the rejection of organic compounds from the high-salinity chemical industrial wastewater, owing to its smallest pore size and highest zeta potential. Our findings offer guidance for the proper selection of UF and NF in the precise selective separation of substances in high-salinity chemical industrial wastewater.

Anaerobic membrane distillation bioreactors for saline organic wastewater treatment: Impacts of salt accumulation on methanogenesis and microbial community

Anaerobic membrane distillation bioreactor (AnMDBR), which possesses several distinctive advantages such as high-quality water production, desalination and methanogenesis, shows enormous potential in saline organic wastewater (SAOW) treatment. However, salt accumulation in the reactor may deactivate anaerobic organisms and impede methanogenesis. In this work, effects of salt accumulation were comprehensively investigated regarding pollutant removal performance and methanogenesis in AnMDBRs over a 30-d operation. The investigative influent salinity was in the range of 0.0-2.0 %. The results demonstrated that AnMDBR achieved excellent chemical oxygen demand (COD) rejection (> 97 %) in the stabilization phase regardless of influent salinity. Moreover, the methane production was as high as 267 mL/gCOD, when the influent salinity did not exceed 1.0 %. When the influent salinity increased to 2.0 %, the methane production was significantly restricted, because salt stress altered the microbial community, resulting in a more sensitive and fragile ecosystem. Thermophilic and halophilic bacteria genera (Bacillus and Caproiciproducens) were selectively enriched in AnMDBR, promoting short-chain fatty acids generation. Meanwhile, these bacteria severely suppressed methanogenic archaea Methanosarcina, leading to an 80 % reduction in species abundance compared to a robust reactor. Furthermore, the salt stress inactivated key enzymes (mtr and mcr), disrupting methanogenic metabolism.

Resilience and response of anaerobic digestion systems to short-term hydraulic loading shocks: Focusing on total and active microbial community dynamics

Anaerobic digestion is known to be sensitive to operational changes, such as hydraulic loading shock, yet the impact on the microbiome, particularly the active RNA-based community, has not been fully understood. This study aimed to investigate the performance of anaerobic reactors and their microbial communities under short-term hydraulic loading shocks. Using synthetic wastewater, the reactor was subjected to 24-h shocks at three-fold and seven-fold the baseline loading rate, followed by DNA and RNA analyses to assess the system's resiliency and microbial responses. The research focused on shifts in major microbial groups and their functions, paying close attention to the active RNA community during loading shock events to better reflect the system's immediate condition. Findings indicated that although the microbial community structure, particularly among the archaea, was altered, the reactor quickly regained its balance. Differences were observed between DNA and RNA profiles and between regular and shock loadings; however, the alpha diversity and functions of the overall community were sustained. This study offers important insights for the design and operation of wastewater treatment plants, with the goal of achieving stable and efficient anaerobic digestion systems.

Temperature-Driven Activated Sludge Bacterial Community Assembly and Carbon Transformation Potential: A Case Study of Industrial Plants in the Yangtze River Delta

Temperature plays a critical role in the efficiency and stability of industrial wastewater treatment plants (WWTPs). This study focuses on the effects of temperature on activated sludge (AS) communities within the A2O process of 19 industrial WWTPs in the Yangtze River Delta, a key industrial region in China. The investigation aims to understand how temperature influences AS community composition, functional assembly, and carbon transformation processes, including CO2 emission potential. Our findings reveal that increased operating temperatures lead to a decrease in alpha diversity, simplifying community structure and increasing modularity. Dominant species become more prevalent, with significant decreases in the relative abundance of Chloroflexi and Actinobacteria, and increases in Bacteroidetes and Firmicutes. Moreover, higher temperatures enhance the overall carbon conversion potential of AS, particularly boosting CO2 absorption in anaerobic conditions as the potential for CO2 emission during glycolysis and TCA cycles grows and diminishes, respectively. The study highlights that temperature is a major factor affecting microbial community characteristics and CO2 fluxes, with more pronounced effects observed in anaerobic sludge. This study provides valuable insights for maintaining stable A2O system operations, understanding carbon footprints, and improving COD removal efficiency in industrial WWTPs.

Evaluation of the effect of a novel substrate that is composed of landfill-mined-soil-like-fractions on plant growth and heavy metal accumulation

In the pursuit of a safe, low-cost, and sustainable method for the reuse of landfill-mined-soil-like-fractions (LFMSFs), pot experiments were conducted using seven growth substrates consisting of LFMSFs, tea residue, and peat for the cultivation of Photinia × fraseri. Six of the substrates had 40 %:60 %, 60 %:40 %, and 80 %:20 % volume ratios of LFMSFs to tea residue or peat, and one substrate consisted entirely of LFMSFs. The physicochemical properties of the substrate, growth parameters of the plants, and heavy metal content in the different pots were determined after one year of growth. The results indicated that the physicochemical properties of the substrate, that was composed of a mixture of LFMSFs and tea residue showed a significant improvement in organic matter, nitrogen, phosphorus, and potassium. However, there was also an increase in the salt and heavy metal contents when compared with those of peat. The plant growth in the LFMSF and tea residue substrate was slightly lower than that in the LFMSF and peat mixture. Notably, the best plant growth and environmentally friendly effects were observed when LFMSFs were added at 40 %. Additionally, most of the heavy metals were primarily removed from the substrate through the leaves of the seedlings, with the heavy metal contents being relatively low. In conclusion, LFMSFs as a cultivation substrate, represent a practical approach for reutilization, which could contribute to the reduction of reliance on traditional resources.