Long-term exposure of polytetrafluoroethylene-nanoplastics on the nitrogen removal and extracellular polymeric substances in sequencing batch reactor

Insight into the mechanisms of combined toxicity of cadmium and flotation agents in luminescent bacteria: Role of micro/nano particles

Currently, risk assessment and pollution management in mines primarily focus on toxic metals, with the flotation agents being overlooked. However, the combined effects of metals and flotation agents in mines remain largely unknown. Therefore, this study aimed to evaluate the combined effects of Cd and two organic flotation agents (ethyl xanthate (EX) and diethyldithiocarbamate (DDTC)), and the associated mechanisms. The results showed that Cd + EX and Cd + DDTC exhibited synergistic toxicity. The EC50 values for luminescent bacteria were 1.6 mg/L and 1.0 mg/L at toxicity unit ratios of 0.3 and 1, respectively. The synergistic effects were closely related with the formation of Cd(EX)2 and Cd(DDTC)2 micro/nano particles, with nano-particles exhibiting higher toxicity. We observed severe cell membrane damage and cell shrinkage of the luminescent bacteria, which were probably caused by secondary harm to cells through the released CS2 during their decomposition inside cells. In addition, these particles induced toxicity by altering cellular levels of biochemical markers and the transcriptional levels of transport proteins and lipoproteins, leading to cell membrane impairment and DNA damage. This study has demonstrated that particulates formed by Cd and flotation agents contribute to the majority of the toxicity of the binary mixture. This study helps to better understand the complex ecological risk of inorganic metals and organic flotation agents in realistic mining environments.

Insights into the response mechanisms of activated sludge system under long-term dexamethasone stress

Dexamethasone (DEX) is a hormone drug that is often detected in wastewater treatment plants, but its impact on activated sludge systems is unknown. This study explored the long-term effects of DEX on nutrient removal, microbial activities, microbial assembly, and microbial interactions in the activated sludge system. During the 90-day DEX exposure experiment, both chemical oxygen demand and total nitrogen removal efficiencies were initially inhibited and then recovered. Microbial activities, i.e., specific oxygen uptake rate and denitrification, did not differ significantly from that of the control reactor (p > 0.05), possibly due to the secretion of extracellular polymers that act as a protective barrier against excess reactive oxygen species induced by DEX. This barrier protects cell membrane integrity and ensures stable treatment performance. Analysis of microbial assembly identified the drift of stochastic processes (from 92.7 % to 51.8 %) and homogeneous selection of deterministic processes (from 1.6 % to 38.7 %) as the main driving forces of microbial community structure succession under long-term DEX stress. Although long-term exposure to 1000 μg/L DEX did not significantly increase the abundance levels of functional bacteria (Nitrosomonas and 996-1) and key genes (AmoCAB and Hao), the ammonia oxidation capacity of the activated sludge system was enhanced. Analysis of microbial interactions indicated that streamlining of functional subnetworks and increased cooperation were the primary reasons. This is the first study to explore the long-term effects of DEX on activated sludge and provide insights into microbial interaction and assembly. Moreover, the findings of this study broaden our knowledge and lay an experimental foundation for reducing risks associated with hormone drugs.

Innovation for continuous aerobic granular sludge process in actual municipal sewage treatment: Self-circulating up-flow fluidized bed process

Aerobic granular sludge (AGS) capable of nitrogen and phosphorus removal is mainly limited to the applications in sequencing batch reactors. This study introduced an innovative continuous self-circulating up-flow fluidized bed process (Zier process) using separate aeration. The process was composed of an anoxic column (Zier-A), aeration column (Zier-OO) and aerobic column (Zier-O), and was used to treat actual municipal sewage continuously for 170 days. The process achieved self-circulation of 20-32 times and an up-flow velocity within the reactor of 7-16 m/h which were accurately controlled with only separate aeration. The larger proportion of self-circulating multiple times contributed to particle formation and stability, providing hydraulic shear conditions, and screened the precipitation performance of the granular sludge (GS). Meanwhile, the dissolved oxygen (DO) of Zier-O was controlled at 0.1-0.3 mg/L, and the DO of Zier-A input water was zero. The accurate oxygen supply enhanced simultaneous nitrification and denitrification (SND) as well as short-cut nitrification and denitrification in Zier-O and improved the COD utilization rate and the nitrogen removal rate in Zier-A. The COD treatment capacity reached 2.46 kg-COD/(m³·d). With a hydraulic retention time of 10 h, the process consistently ensured that the average concentrations of ammonia nitrogen and total nitrogen in the effluent were maintained below 5 and 15 mg/L, respectively. Moreover, the process maintained the shape and stability of GS, the median diameter of GS ranged between 300-1210 μm, the percentage of mass with particle size distribution < 200 μm at a height of 150 cm within Zier-A and Zier-O accounted for as low as 0.04%-0.05%, and showed good settling performance. The suspended solids in effluent can be maintained at 50-80 mg/L. Overall, the unique structural setting and control method of the Zier process provide another approach for the application of continuous AGS treatment for municipal sewage.

Predictive metabolomic signatures for safety assessment of three plastic nanoparticles using intestinal organoids

Nanoplastic particles are pervasive environmental contaminants with potential health risks, while mouse intestinal organoids provide accurate in vitro models for studying these interactions. Metabolomics, especially through LC-MS, enables detailed cellular response studies, and there's a novel interest in comparing metabolic changes across nanoparticle species using gut organoids. This study used a mouse intestinal organoid combined with cell model to explore the differences in metabolites and toxicity mechanisms induced by exposure to three nanoplastics (PS, PTFE, and PMMA). The results showed that PS, PTFE, and PMMA exposure reduced mitochondrial membrane potential, intracellular ROS accumulation and oxidative stress, and inhibited the AKT/mTOR signaling pathway. Non-targeted metabolomics results confirmed that three types of nanoplastic particles regulate cellular status by regulating fatty acid metabolism, nucleotide metabolism, necroptosis and autophagy pathways. More importantly, these representative metabolites were further validated in model groups after mouse intestinal organoids and HCT116 cells were exposed to the respective NPs, indicating that organoid metabolomics results can be used to effectively predict toxicity. Untargeted metabolomics is sensitive enough to detect subtle metabolomic changes when functional cellular analysis shows no significant differences. Overall, our study reveals the underlying metabolic mechanism of NPs-induced intestinal organoid toxicity and provides new insights into the possible adverse consequences of NPs.

Thermoplastic starch (TPS) bioplastic, the green solution for single-use petroleum plastic food packaging - A review

Plastic throughout the years is now one of the biggest world commodities and also the largest pollution to have an environmental impact, accumulating in landfills and also leaching into water systems and oceans. Especially with the shift to single-use disposable plastic, evermore positions plastics as the number one novel entity that pollutes the earth. This shift is also consistent in the food packaging industry. Managing plastic waste is still an issue at large, while the process of pyrolysis incineration still requires an obscene amount of energy that also does not resolve the problems with its environmental impact, the cost of mechanical-chemical degradation even outweighs the cost of producing the materials, and biodegradation process is a very slow and long process. Converting to bioplastics is one of the potential solutions to the global plastic issue. This review covers the potentials, limitations, challenges, progress and advancements of bioplastics, especially thermoplastic starch (starch-based bioplastic) in their efforts to replace petroleum plastics in food packaging and smart food packaging, especially for single-use (disposable) food packaging.