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Medium Preparation for the Cultivation of Microorganisms under Strictly Anaerobic/Anoxic Conditions
Published on: August 15, 2019
An in-depth analysis of microbial response to exposure to high concentrations of microplastics in anaerobic
Hui Wang1, Wenbo Liao2, Qixing Zhou3
1College of Life Science, China West Normal University, Nanchong 637009, China; MOE Key Laboratory of Pollution Processes and Environmental Criteria, Tianjin Key Laboratory of Environmental Remediation and Pollution Control, Carbon Neutrality Science Center, College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China.
Abstract:
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.
Insights
Microplastics significantly inhibit anaerobic wastewater treatment, reducing methane production and COD removal while increasing short-chain fatty acids. Different microbial communities in sludge and biofilm respond distinctly to microplastic pollution.
Area of Science:
- Environmental Microbiology
- Environmental Chemistry
- Biotechnology
Background:
- Microplastics (MPs) pose a growing threat to aquatic ecosystems and wastewater treatment processes.
- Anaerobic digestion, a key wastewater treatment method, relies on microbial communities within granular sludge (AS) and biofilms (BF).
- Understanding the impact of MPs on these microbial systems is crucial for effective wastewater management.
Purpose of the Study:
- To investigate the effects of different microplastic types (polyethylene, polyvinyl chloride, and a mixture) on anaerobic granular sludge and biofilm.
- To analyze the impact of microplastics on microbial metabolism, including methane production, short-chain fatty acid generation, and chemical oxygen demand removal.
- To elucidate the distinct microbial responses and metabolic pathways in AS and BF exposed to microplastics.
Main Methods:
- Exposure of anaerobic granular sludge (AS) and biofilm (BF) to polyethylene (PE), polyvinyl chloride (PVC), and mixed (MIX) microplastics.
- Measurement of key performance indicators: methane output, short-chain fatty acid (SCFA) levels, and chemical oxygen demand (COD) removal.
- Analysis of cellular stress markers (ROS, LDH, ATP, cyt c, EPS) and enzymatic activities.
- Microbial community structure analysis using 16S rRNA sequencing and functional gene expression profiling via metatranscriptomics.
Main Results:
- Microplastics significantly reduced methane output (44.65%-55.89%) and COD removal (28.77%-36.78%), while increasing SCFA levels (95.93%-124.49%). PVC microplastics exhibited the strongest inhibitory effect.
- Microplastic exposure increased reactive oxygen species (ROS), lactate dehydrogenase (LDH), and adenosine triphosphate (ATP) production, while decreasing cytochrome c (cyt c) and extracellular polymeric substances (EPS).
- AS and BF showed distinct microbial community compositions and metabolic activities; AS favored acetate generation (Firmicutes) and methane metabolism, while BF excelled in polysaccharide degradation (Bacteroidota) and glycolysis.
Conclusions:
- Microplastics disrupt anaerobic wastewater treatment processes, impacting microbial metabolism and overall efficiency.
- Anaerobic granular sludge and biofilm exhibit differential responses to microplastic contamination, influencing their respective roles in wastewater treatment.
- The findings highlight the need to consider microplastic pollution in the design and operation of anaerobic wastewater treatment systems.
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