Understanding and mitigating the distinctive stresses induced by diverse microplastics on anaerobic hydrogen-producing granular sludge

Contribution of chemical toxicity to the overall toxicity of microplastic particles: A review

Nanoplastics and microplastics are of growing research interest due to their persistence in the environment and potential harm to organisms through physical damage, such as abrasions or blockages, and chemical harm from leached additives and contaminants. Despite extensive research, a clear distinction between the physical and chemical toxicity of plastic particles has been lacking. This study addresses this gap by reviewing studies examining both toxicity types, focusing on environmentally relevant leachates. The chemicals used in plastics manufacturing, which number over 16,000, include additives, processing aids, and monomers, many of which pose potential hazards due to their toxicity, persistence, and bioaccumulation. Studies typically use extraction or leaching methods to assess chemical toxicity, with leaching more closely mimicking environmental conditions. Factors influencing leaching include plastic type, particle size, and environmental conditions. A systematic literature search identified 35 relevant studies that assessed the toxicity of plastic particle suspensions and their leachates. Analysis revealed that, in 52 % of the cases, both the suspension and leachate had toxic effects, while in 35 % of the cases, toxicity was attributed to the suspension alone. At 13 %, only the leachate was toxic. This suggests that leachates contribute significantly to overall toxicity. However, the results vary widely depending on the experimental conditions and plastic type, highlighting the complexity of microplastic toxicity. The preparation methods used for leachates significantly influence toxicity results. Factors such as leaching time, particle size, and separation techniques affect the concentration and presence of toxic chemicals. Additionally, washed particles-those subjected to procedures for removing leachable chemicals-often showed reduced toxicity, although the results varied. This underscores the need for standardized methods to compare studies better and understand the relative contributions of physical and chemical toxicity to microplastic pollution.

An in-depth analysis of microbial response to exposure to high concentrations of microplastics in anaerobic wastewater fermentation

The impact of microplastics (MPs) in anaerobic wastewater treatment on microbial metabolism is significant. Anaerobic granular sludge (AS) and biofilm (BF) are two common ways, and their responses to microplastics will have a direct impact on their application potential. This study investigated the microbial reactions of AS and BF to three types of MPs: polyethylene (PE), polyvinyl chloride (PVC), and a mixture of both (MIX). Results exhibited that MPs reduced methane output by 44.65 %, 55.89 %, and 53.18 %, elevated short-chain fatty acid (SCFA) levels by 95.93 %, 124.49 %, and 110.78 %, and lowered chemical oxygen demand (COD) removal by 28.77 %, 36.78 %, and 33.99 % for PE-MP, PVC-MP, and MIX-MP, respectively, with PVC-MP showing the greatest inhibition. Meanwhile, microplastics also facilitated the relative production of reactive oxygen species (ROS, 40.29 %-96.99 %), lactate dehydrogenase (LDH, 20.01 %-75.02 %), and adenosine triphosphate (ATP, 26.64 %-43.80 %), while reducing cytochrome c (cyt c, 23.60 %-49.02 %) and extracellular polymeric substances (EPS, 17.44 %-26.58 %). AS and BF displayed distinct enzymatic activities under MPs exposure. Correspondingly, 16S-rRNA sequencing indicated that AS was mainly involved in acetate generation by Firmicutes, while BF performed polysaccharide degradation by Bacteroidota. Metatranscriptomic analysis showed AS to be rich in acetogens (Bacillus, Syntrophobacter) and methanogens (Methanothrix, Methanobacterium), while BF contained more fermentation bacteria (Mesotoga, Lentimicrobium) and electroactive microorganisms (Clostridium, Desulfuromonas) under MIX-MP. Moreover, BF exhibited higher glycolysis gene expression, whereas AS was more active in methane metabolism, primarily through the acetoclastic methanogenic pathway's direct acetate conversion. This study provides new insights into understanding the microbial response produced by microplastics during anaerobic wastewater digestion.

Insight into furfural-tolerant and hydrogen-producing microbial consortia: Mechanism of furfural tolerance and hydrogen production

Furfural-tolerant and hydrogen-producing microbial consortia were enriched from soil, with hydrogen production of 259.84 mL/g-xylose under 1 g/L furfural stress. The consortia could degrade 2.5 g/L furfural within 24 h in the xylose system, more efficient than in the sugar-free system. Despite degradation of furfural to furfuryl alcohol, the release of reactive oxygen species and lactate dehydrogenase was also detected, suggesting that furfuryl alcohol is also a potential inhibitor of hydrogen production. The butyrate/acetate ratio was observed to decrease with increasing furfural concentration, leading to decreased hydrogen production. Furthermore, microbial community analysis suggested that dominated Clostridium butyricum was responsible for furfural degradation, while Clostridium beijerinckii reduction led to hydrogen production decrease. Overall, the enriched consortia in this study could efficiently degrade furfural and produce hydrogen, providing new insights into hydrogen-producing microbial consortia with furfural tolerance.