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Dark fermentation (DF) is an eco-friendly process that simultaneously achieves organic matter degradation and obtains hydrogen (H 2 ). Nonetheless, low H 2 yield mainly caused by poor activity of key microbes, is still a problem that requires being resolved. In this work, MgFe 2 O 4 and Ca 0.5 Mg 0.5 Fe 2 O 4 nanoparticles (NPs) were synthetized and served as additives to boost H 2 form from DF. H 2 productivity gradually increased with the rise of NPs, and declined when NPs exceeded their optimal dosages. The highest H 2 yield was 183.6 ± 3.2 mL/g glucose at 100 mg/L of MgFe 2 O 4 NPs, being 35.2 % higher than that of the control yield (135.8 ± 3.1 mL/g glucose). However, the highest H 2 yield of 171.9 ± 2.5 mL/g glucose occurred at 400 mg/L of Ca 0.5 Mg 0.5 Fe 2 O 4 NPs, increasing by 26.6 % over the control. Interestingly, the two NPs favored the butyric acid pathway for H 2 synthesis. This provides guidance for multi-element oxide NPs used in DF., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Several reports have shown that pharmaceuticals and personal care products (PPCPs) have some negative effects on anaerobic digestion (AD), yet there are no convenient and efficient strategies for mitigating the adverse influences. The typical PPCPs of carbamazepine have a strong negative effect on lactic acid AD process. Therefore, in this work, novel lanthanum-iron oxide (LaFeO 3 ) nanoparticles (NPs) were used for adsorption and bioaugmentation to weak the negative effects of carbamazepine. The adsorption removal of carbamazepine increased from 0 to 44.30% as the dosage of LaFeO 3 NPs was increased from 0 to 200 mg/L, providing the necessary prerequisites for bioaugmentation. Adsorption reduced the probability of direct contact between carbamazepine and anaerobes, partly alleviating the inhibition of carbamazepine on microbes. The highest methane (CH 4 ) yield induced by LaFeO 3 NPs (25 mg/L) was 226.09 mL/g lactic acid, increasing by 30.06% compared to the control yield with a recovery to 89.09% of the normal CH 4 yield. Despite the ability of LaFeO 3 NPs to restore normal AD performance, the biodegradation rate of carbamazepine remained below 10% due to its anti-biodegradability. Bioaugmentation was primarily reflected in the enhanced bioavailability of dissolved organic matter, while the intracellular LaFeO 3 NPs promoted coenzyme F420 activity through binding to humic substances. Under the mediation of LaFeO 3 , a direct interspecies electron transfer system with Longilinea and Methanosaeta as functional bacteria was successfully constructed and the corresponding electron transfer rate was accelerated from 0.021 s -1 to 0.033 s -1 . LaFeO 3 NPs eventually recovered AD performance under carbamazepine stress in an adsorption and bioaugmentation manner., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Dark fermentation (DF) is a green hydrogen (H 2 ) production process, but it is far below the theoretical H 2 yield. In this study, calcium ferrite nanoparticles (CaFe 2 O 4 NPs) were produced to augment H 2 yield via DF. The highest H 2 yield of 250.1 ± 6.5 mL/g glucose was achieved at 100 mg/L CaFe 2 O 4 NPs. Furtherincreasein CaFe 2 O 4 NPs above 100 mg/L, such as 600 mg/L, would slightly lower H 2 yield to 208.6 ± 2.6 mL/g glucose. The CaFe 2 O 4 NPs in DF system released calcium and iron ions, promoting granular sludge formation andDF microbial activity. Soluble metabolites revealed that butyric acid was raised by CaFe 2 O 4 NPs, which indicated the improved metabolic pathway for more H 2 . Microbial structure composition further illustrated that CaFe 2 O 4 NPs could increase the abundance of dominant microbial populations, with the supremacy of Firmicutes up to 71.22 % in the bioH 2 evolution group augmented with 100 mg/L CaFe 2 O 4 NPs., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Some inhibition of biomethane (bioCH 4 ) production system can be observed, which is due to the propionic acid generation from lactic acid degradation. In this work, the three cobalt ferrate-based nanoparticles (NPs) such as CoFe 2 O 4 , CoAl 0.2 Fe 1.8 O 4 and CoCu 0.2 Fe 1.8 O 4 were synthesized to promote the bioCH 4 evolution from lactic acid. The CH 4 yields from the CoAl 0.2 Fe 1.8 O 4 , CoCu 0.2 Fe 1.8 O 4 and CoFe 2 O 4 groups at 300 mg/L of NPs were 431.52, 392.12 and 396.6 mL/g lactic acid, respectively. Moreover, the highest CH 4 yield was 34.15% higher than that of the control reactor (321.67 mL/g lactic acid) without NPs. The three NPs accelerated lactic acid biodegradation and propionic acid conversion, thus obtaining more CH 4 . Surprisingly, microbial structure revealed that CoAl 0.2 Fe 1.8 O 4 increased the abundance of Bacteroidetes_vadinHA17 to 16.6%, promoting the conversion from propionic acid to acetic acid. Meanwhile, the abundance of Methanobacterium in archaeal community from CoAl 0.2 Fe 1.8 O 4 group rose from 45.81% to 68.45%, which facilitated bioCH 4 production., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Two various materials, copper and aluminum doped cobalt ferrite nanoparticles (NPs) were fabricated for investigating their effects of addition amounts on hydrogen (H 2 ) synthesis and process stability. CoCu 0.2 Fe 1.8 O 4 NPs enhanced H 2 production more than CoAl 0.2 Fe 1.8 O 4 NPs under same condition. The highest H 2 yield of 212.25 ml/g glucose was found at optimal dosage of 300 mg/L CoCu 0.2 Fe 1.8 O 4 NPs, revealing the increases of 43.17% and 6.67% compared with the control without NPs and 300 mg/L CoAl 0.2 Fe 1.8 O 4 NPs groups, respectively. NPs level of more than 400 mg/L inhibited H 2 generation. Further investigations illustrated that CoCu 0.2 Fe 1.8 O 4 NPs were mainly distributed on extracellular polymer substance while CoAl 0.2 Fe 1.8 O 4 NPs were mostly enriched on cell membrane, which facilitated electron transfer behavior. Community structure composition demonstrated that CoCu 0.2 Fe 1.8 O 4 and CoAl 0.2 Fe 1.8 O 4 separately caused a 9.67% and 9.03% increase in Clostridium sensu stricto 1 compared with the control reactor without NPs exposure., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

In this work, nickel ferrite nanoparticles (NiFe 2 O 4 NPs) was prepared to improve hydrogen (H 2 ) production by dark fermentation. Moderate amounts (50-200 mg/L) promoted H 2 generation, while excess NiFe 2 O 4 NPs (over 400 mg/L) lowered H 2 productivity. The highest H 2 yields of 222 and 130 mL/g glucose were obtained in the 100 mg/L (37 °C) and 200 mg/L NiFe 2 O 4 NPs (55 °C) groups, respectively, and the values were 38.6% and 28.3% higher than those in the control groups (37 °C and 55 °C). Soluble metabolites showed that NiFe 2 O 4 NPs enhanced the butyrate pathway, corresponding to the increased abundance of Clostridium butyricum in mesophilic fermentation. The endocytosis of NiFe 2 O 4 NPs indicated that the released iron and nickel favored ferredoxin and hydrogenase synthesis and activity and that NiFe 2 O 4 NPs could act as carriers in intracellular electron transfer. The NPs also optimized microbial community structure and increased the levels of extracellular polymeric substances, leading to increased H 2 production., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Hydrogen (H 2 ) gas represents renewable resource candidate to traditional energy resource. Methods to promote the H 2 evolution rate attract increasing attentions. In the present research, ferric oxide/carbon nanoparticles (FOCNPs) were synthesized and evaluated the feasibility to enhance the production rate of H 2 gas from glucose through anaerobic fermentation by mixed bacteria. The results demonstrated that appropriate dose of FOCNPs promoted, while excessive concentration of FOCNPs suppressed the production of H 2 . Addition of 200 mg/L FOCNPs resulted in the highest yield of 218.63 ml H 2 /g glucose, 33.7% higher than 163 ml H 2 /g glucose of the control test without addition of FOCNPs. However, 400 mg/L of FOCNPs inhibited the H 2 evolution to 154 ml/g glucose, 5.5% lower than the control. It was revealed that the H 2 evolution followed the acetic pathways. The FOCNPs had a specific surface area of 27.63 m 2 /g, and thus addition of FOCNPs could provide more attachment sites for the growth of anaerobes. Moreover, FOCNPs could promote the activity of hydrogenase and electron transfer efficiency, beneficial for the bio-H 2 evolution. However, excessive addition of FOCNPs could be toxic to microbes, and further suppressing the H 2 production. The present research provided an effective method to promote the evolution rate of H 2 gas. [ABSTRACT FROM AUTHOR]

In this work, the cobalt ferrate nanoparticles were prepared by a sol-gel method for investigating their influence on hydrogen production from dark fermentation. A moderate amounts (0.1–0.4 g/L) of these nanoparticles effectively enhanced the fermentation process. The highest hydrogen yield of 205.24 mL/g glucose was achieved at a dosing level of 0.4 g/L, which was a 31.8% enhancement compared to the control, while excess (0.5 g/L) nanoparticles decreased the hydrogen production by 9.7% compared to the control group. The mechanism analysis exhibited that the nanoparticles could either attach to the microbial surface or enter the cell interior without destroying the cell integrity, which promoted the electron transfer to anaerobes and stimulated the activities of hydrogen-producing enzymes such as enzymes and coenzymes. The microbial community revealed that a moderate amount of cobalt ferrate nanoparticles increased the abundance of Clostridium sensu stricto 1 from 14.49% to 18.84%, which was dominant and favored the sustainable conversion of glucose wastewater into clean hydrogen. [Display omitted] • Cobalt ferrate nanoparticles (CoFe 2 O 4 NPs) were synthesized to increase H 2 yield. • BioH 2 production was enhanced by 31.8% with 0.4 g/L CoFe 2 O 4 NPs. • CoFe 2 O 4 NPs changed the type of fermentation to butyric acid fermentation. • CoFe 2 O 4 NPs promoted microbial activity by acting on the microbial interface. • CoFe 2 O 4 NPs improved the abundance of Clostridium_sensu_stricto_1. [ABSTRACT FROM AUTHOR]

[Display omitted] • BioH 2 yield via dark fermentation increased by 47% with LaFeO 3 NPs. • Butyrate fermentation pathway was strengthened using LaFeO 3 NPs. • Gene copy number of hydrogenase was elevated adding LaFeO 3 NPs. • Firmicutes was selectively enriched and colonized by LaFeO 3 supplementation. • Glycolysis was promoted with LaFeO 3 addition by PICRUSt2 analysis. Low hydrogen (H 2) yield via dark fermentation often occurs, being mainly due to H 2 generation pathway shift. In this study, lanthanum-iron oxide nanoparticles (LaFeO 3 NPs) were prepared to investigate their effects on bioH 2 production. The highest H 2 yield of 289.8 mL/g glucose was found at 100 mg/L of LaFeO 3 , being 47.6% higher than that from the control (196.3 mL/g glucose). The relative abundance of Firmicutes increased from 54.2% to 67.5%. The large specific surface area of LaFeO 3 provided sufficient sites for the colonization of Firmicutes and increased the bacterial access to nutrients. Additionally, the La3+ gradually released from LaFeO 3 NPs raised microbial transmembrane transport capacity, promoting glycolytic efficiency and Fe availability, thereby increasing hydrogenase content, and shifting the bioH 2 evolution to butyrate pathway for more H 2. This provides the novelty for biochemical utilization of La and new insights into the improved H 2 yield amended with LaFeO 3. [ABSTRACT FROM AUTHOR]