Evaluation the impact of polystyrene micro and nanoplastics on the methane generation by anaerobic digestion.

The widespread existence of microplastics in wastewater has caused great concern. As the exposure time of microplastics in the environment increases, the microplastic leaching solution (i.e.,chemical additives) may be released into the environment causing toxic effects. In this study, the effect of polystyrene (PS) microplastics on the anaerobic digestion system was investigated. The results showed that the exposure to 80 nm and 5 µm polystyrene microplastics with the concentrations of 0.2 g/L or lower did not significantly affect the cumulative methane production (P ≥ 0.05). On the other hand, 80 nm and 5 µm PS microplastic level of 0.25 g/L led to a decrease in methane production by 19.3% (P = 2 × 10-5) and 17.9% (P = 4 × 10-5), respectively. The 80 nm PS nanoplastics therefore had slightly higher inhibition capacity on methane production than 5 µm PS microplastics. The pH of all groups remained stable at 6.7-7.5. Volatile fatty acids (VFAs) concentration and ammonium-nitrogen concentration had no obvious relationship to PS micro and nanoplastics addition. Further investigation showed that PS micro and nanoplastics concentration of 0.25 g/L or higher could inhibit acidification and methanation stage of anaerobic digestion. However, the main negative influence of PS micro and nanoplastics on methane production was due to the severe inhibition on the methanization stage.

Enriching ruminal polysaccharide-degrading consortia via co-inoculation with methanogenic sludge and microbial mechanisms of acidification across lignocellulose loading gradients.

Using lignocellulosic materials as substrates, ruminal microbiota were co-inoculated with anaerobic sludge at different loading rates (LR) to study the microbial community in the semi-continuous mode. The results indicated that the highest CH4 yield reached 0.22 L/g volatile solid at LR of 4 g/L/day, which obtained 56-58% of the theoretical value. In the steady stage with LR of 2-4 g/L/day and slurry recirculation, copies of total archaea increased. Especially the Methanobacteriales increased significantly (p < 0.05) to 3.30 × 108 copies/mL. The microbial communities were examined by MiSeq 16S rRNA sequencing. Enriched hydrolytic bacteria mainly belonged to Clostridiales, including Ruminococcus, Ruminiclostridium, and Ruminofilibacter settled in the rumen. High-active cellulase and xylanase were excreted in the co-inoculated system. Acid-producing bacteria by fermentation were affiliated with Lachnospiraceae and Bacteroidales. The acidogen members were mainly Spirochaetaceae and Clostridiales. Syntrophic oxidation bacteria mainly consisted of Synergistetes, propionate oxidizers (Syntrophobacter and Pelotomaculum), and butyrate oxidizers (Syntrophus and Syntrophomonas). There had no volatile fatty acid (VFA) accumulation and the pH values varied between 6.94 and 7.35. At LR of 6 g/L/day and a recirculation ratio of 1:1, the hardly degradable components and total VFA concentrations obviously increased. The total archaea and Methanobacteriales then deceased significantly to 8.56 × 105 copies/mL and 4.14 × 103 copies/mL respectively (p < 0.05), which resulted in the inhibition of methanogenic activities. Subsequently, microbial diversity dropped, and the hydrolytic bacteria and syntrophic oxidizers obviously decreased. In contrast, the abundances of Bacteroidales increased significantly (p < 0.05). Acetate, propionate, and butyrate concentrations reached 2.02, 6.54, and 0.53 g/L, respectively, which indicated "acidification" in the anaerobic reactor. Our study illustrated that co-inoculated anaerobic sludge enriched the ruminal function consortia and hydrogenotrophic methanogens played an important role in anaerobic digestion of lignocelluloses.

[Construction of a High Efficiency Anaerobic Digestion System for Vinegar Residue].

The model of high solid anaerobic digestion was used by improving the degree of homogeneity of the reaction system and biogas slurry reflux to gradually increase the material load. The vinegar residue-efficient anaerobic digestion system was successfully constructed without pretreatment.The optimum anaerobic digestibility was observed when the material loading of the reaction system reached 6.15 g·(L·d)-1, when the amount of biogas produced per unit of dry material was 396 mL·g-1, and the amount of methane produced per unit of dry material was 211 mL·g-1. The degradation rate of hemicellulose reached 63.66%, which was the main reason for the improvement of anaerobic digestion performance. The degradation rates of cellulose and lignin were 21.46% and 24.43%, respectively. The lower degradation efficiency was mainly due to the complicated degradation of the benzene ring structure in lignin and hindered hydrolysis of cellulose, which had a shielding effect on cellulose degradation.

Evaluation and characterization during the anaerobic digestion of high-strength kitchen waste slurry via a pilot-scale anaerobic membrane bioreactor.

The anaerobic digestion of high-strength kitchen waste slurry via a pilot-scale anaerobic membrane bioreactor (AnMBR) was investigated at two different operational modes, including no sludge discharge and daily sludge discharge of 20 L. The AnMBR provided excellent and reliable permeate quality with high COD removal efficiencies over 99%. The obvious accumulations of long chain fatty acids (LCFAs) and Ca(2+) were found in the anaerobic digester by precipitation and agglomeration. Though the physicochemical process contributed to attenuating the free LCFAs toxicity on anaerobic digestion, the digestion efficiency was partly influenced for the low bioavailability of those precipitates. Moreover, higher organic loading rate (OLR) of 5.8 kg COD/(m(3) d) and digestion efficiency of 78% were achieved as the AnMBR was stably operated with sludge discharge, where the membrane fouling propensity was also alleviated, indicating the crucial significance of SRT control on the treatment of high-strength kitchen waste slurry via AnMBRs.