Effects of microplastics on the properties of different types of sewage sludge and strategies to overcome the inhibition: A review.

Microplastics have been identified as an emerging pollutant. When microplastics enter wastewater treatment plants, the plant traps most of the microplastics in the sludge during sewage treatment. Therefore, the effects of microplastics on sludge removal performance, and on the physical and chemical properties and microbial communities in sludge, have attracted extensive attention. This review mainly describes the presence of microplastics in wastewater treatment plants, and the effects of microplastics on the decontamination efficiency and physicochemical properties of activated sludge, aerobic granular sludge, anaerobic granular sludge and anaerobic ammonium oxidation sludge. Further, the review summarizes the effects of microplastics on microbial activity and microbial community dynamics in various sludges in terms of type, concentration, and contact time. The mechanisms used to strengthen the reduction of microplastics, such as biochar and hydrochar, are also discussed. This review summarizes the mechanism by which microplastics influence the performance of different types of sludge, and proposes effective strategies to mitigate the inhibitive effect of microplastics on sludge and discusses removal technologies of microplastics in sewage. Biochar and hydrochar are one of the effective measures to overcome the inhibition of microplastics on sludge. Meanwhile, constructed wetland may be one of the important choice for the future removal of microplastics from sewage. The goal is to provide theoretical support and insights for ensuring the stable operation of wastewater treatment plants and reducing the impact of microplastics on the environment.

Fe(III) enhances Cr(VI) bioreduction in a MFC-granular sludge coupling system: Experimental evidence and metagenomics analysis.

The influence of Fe(III) on the bioreduction efficiency of Cr(VI) in a microbial fuel cell (MFC)-granular sludge coupling system using dissolved methane as an electron donor and carbon source was explored, and the mechanism of Fe(III) mediating enhancement in the bioreduction process of Cr(VI) in the coupling system was also investigated. Results showed that the presence of Fe(III) enhanced the ability of the coupling system to reduce Cr(VI). The average removal efficiencies of Cr(VI) in the anaerobic zone in response to 0, 5, and 20 mg/L of Fe(III) were 16.53±2.12%, 24.17±2.10%, and 46.33±4.41%, respectively. Fe(III) improved the reducing ability and output power of the system. In addition, Fe(III) enhanced the electron transport systems activity of the sludge, the polysaccharide and protein content in the anaerobic sludge. Meanwhile, X-ray photoelectron spectrometer (XPS) spectra demonstrated that Cr(VI) was reduced to Cr(III), while Fe2p participated in reducing Cr(VI) in the form of Fe(III) and Fe(II). Proteobacteria, Chloroflexi, and Bacteroidetes were the dominant phylum in the Fe(III)-enhanced MFC-granular sludge coupling system, accounting for 49.7%-81.83% of the microbial community. The relative abundance of Syntrophobacter and Geobacter increased after adding Fe(III), indicating that Fe(III) contributed to the microbial mediated anaerobic oxidation of methane (AOM) and bioreduction of Cr(VI). The genes mcr, hdr, and mtr were highly expressed in the coupling system after the Fe(III) concentration increased. Meanwhile, the relative abundances of coo and aacs genes were up-regulated by 0.014% and 0.075%, respectively. Overall, these findings deepen understanding of the mechanism of the Cr(VI) bioreduction in the MFC-granular sludge coupling system driven by methane under the influence of Fe(III).

Use of iron-loaded biochar to alleviate anammox performance inhibition under PFOA stress conditions: Integrated analysis of sludge characteristics and metagenomics.

The negative effects of perfluorooctanoic acid (PFOA) on biological nitrogen removal performance in wastewater treatment plants, are receiving increasing attention due to the widespread reporting of this issue. In this study, pomelo peel iron-loaded biochar (Fe-PBC) was added to an anammox bioreactor to alleviate the negative effects of PFOA. Results showed that the addition of Fe-PBC increased the ammonia and nitrite removal efficiencies from 77.7 ± 9.6 % and 79.5 ± 5.6 % to 94.45 ± 5.1 % and 95.9 ± 5.0 %, respectively. In addition, Fe-PBC promoted the removal of PFOA from wastewater, increasing the PFOA removal efficiency from 5.2 % to 29.2 ± 4.3 % from 100 to 200 days. The introduction of iron-loaded biochar into the anammox bioreactor increased the CO ratio by 13.64 % by 150 days. In addition, a CO fitting peak was detected in the Fe-PBC, indicating that the Fe-PBC was loaded with microorganisms. Microbial community analysis showed a decrease in the relative abundances of Proteobacteria and Nitrospirae from 31 % and 3.4 % to 16.8 % and 0.9 %, respectively, while the relative abundance of Planctomycetes increased from 26.8 % to 44.1 %. Metagenomic analysis found that the functional genes hzsB and hdh increased from 98,666 ± 11,400 and 3190 ± 460 to 119,333 ± 15,534 and 138,650 ± 11,233 copy numbers/MLSS. The increase in anammox biomass may be attributed to the presence of iron, an essential element for the synthesis of key anammox enzyme. Furthermore, iron was also associated with the enhanced extracellular electron transfer in the anammox system induced by Fe-PBC.

Influence of biodegradable polybutylene succinate and non-biodegradable polyvinyl chloride microplastics on anammox sludge: Performance evaluation, suppression effect and metagenomic analysis.

Microplastics (MPs) has been widely detected in wastewater treatment plants. However, there is a lack of research on its influence on anaerobic ammonia oxidation (anammox) process. Therefore, the effects of polybutylene succinate (PBS) and polyvinyl chloride (PVC) MPs on the nitrogen removal performance, microbial community and metabolites of anammox sludge were investigated. Results showed that PBS and PVC MPs reduced the nitrite removal efficiency of the anammox sludge, and PVC1 (0.1 g/L PVC) group was the most significant at 19.2 %. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) spectra showed that PBS2 (0.5 g/L PBS) group increased the polysaccharide content in the anammox sludge. This may be because of the byproduct, which was produce during the biodegradation of PBS MPs, and decrease the agglomeration capacity of sludge, so as to increase the mass transfer. PBS2 group reduced the relative abundance of Methanosaeta (10.18 %) and the methane modules, and stimulated the anammox bacteria Ca. Brocadia (1.17 %) and the relative nitrogen metabolism modules. PVC2 group reduced the relative abundance of Ca. Brocadia (3.02 %), while was enriched Methanosaeta (2.1 %). Non-biodegradable PVC MPs was more harmful to anammox sludge, which would draw attention to the entry of PVC MPs into the anammox system.