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Highlights • Combined ultrasound-acid pretreatment improved H 2 yield of grass by 311.7%. • The combined pretreatment improved the substrate utilization efficiency. • The combined pretreatment induced a more efficient fermentation pathway. • More enrichment of Clostridium contributed to the improvement in H 2 production. Abstract In this study, the dilute acid pretreatment combined with ultrasound was applied to improve fermentative hydrogen production from grass. The experimental results indicated that SCOD and soluble carbohydrate contents of grass was improved by 98.6% and 236.9% after the combined treatment, respectively. Surface morphology (SEM and AFM) and crystallinity analysis revealed that the combined pretreatment process could effectively destroyed the biomass structure and increased their surface area. Owing to the increased soluble organics proportion and better enzymatic accessibility of residual solids, the hydrogen yield reached 42.2 mL/g-dry grass after the combined treatment, which was 311.7%, 190.0% and 35.0% higher in comparison with the control, individual ultrasound and acid pretreated groups, respectively. Meanwhile, the combined treatment also increased the substrate utilization efficiency and induced a more efficient fermentation pathway. Bacterial community analysis revealed that more enrichment of Clostridium and less enrichment of Enterococcus contributed to the improved hydrogen production. [ABSTRACT FROM AUTHOR]

In this study, the combined ionizing radiation-acid pretreatment process was firstly applied to enhance hydrogen fermentation of grass waste. Results showed that the combined pretreatment synergistically enhanced hydrogen fermentation of grass waste. The SCOD and soluble polysaccharide contents of grass waste increased by 1.6 and 2.91 times after the combined pretreatment, respectively. SEM observation and crystallinity test showed the combined pretreatment effectively disrupted the grass structure. Owing to the more favorable substrate conditions, the hydrogen yield achieved 68 mL/g-dry grass added after the combined pretreatment, which was 161.5%, 112.5% and 28.3% higher than those from raw, ionizing radiation pretreated and acid pretreated grass waste, respectively. The VS removal also increased from 13.9% to 25.6% by the combined pretreatment. Microbial community analysis showed that the abundance of dominant hydrogen producing genus Clostridium sensu stricto 1 increased from 37.9% to 69.4% after the combined pretreatment, which contributed to more efficient hydrogen fermentation. [ABSTRACT FROM AUTHOR]

The synergetic effect of ultrafine grinding coupled with the incorporation of an appropriate amount of nanomaterials (NMs) on biohydrogen (bioH 2) production from corn stover (CS) was studied. The changes in the physicochemical and optical characteristics of CS pretreated with various ultrafine grinding times were comprehensively studied. High-quality SnO 2 NMs with high defect concentrations (e.g., oxygen vacancies (OVs)) were successfully synthesised. The physio-optical structures of pretreated CS and synthesised NMs were analysed using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy, and diffuse reflectance spectroscopy. SEM measurements confirmed that the morphology of the CS changed with the increase in grinding time and the particle size was reduced to the submicron range with increased surface roughness. The biomass particle size changed considerably from micron to submicron with an increase in grinding time. The intensities of the diffracted peak 22° decreased and the full width at half maximum increased with the increase in grinding time, which confirmed the considerable modification of biomass crystalline structure. The SEM analysis revealed that the synthesised SnO 2 NMs were spherical in nature with a uniform size distribution. XRD analysis confirmed that the synthesised NMs had a stable rutile structure without any secondary phases. Hydrogen production tests were performed by utilising a mixed consortium of photosynthetic bacteria HAU-M1 as the inoculum. Hydrogen production rates of 120, 123, and 145 mL/h were observed for samples pretreated with 2, 4, and 6 h of ultrafine grinding, respectively. Owing to the synergetic effect of ultrafine grinding and nanomaterial loading, the hydrogen production rate increased considerably to 143, 144, and 163 mL/h after 2, 4, and 6 h of ultrafine grinding and nanomaterial loadings of 200, 150, and 150 mg/L, respectively. The highest cumulative bioH 2 production of 425 mL was recorded after ultrafine grinding for 6 h and nanomaterial loading of 150 mg/L, 49% higher than that achieved with the standard sample (285 mL). Furthermore, the synergetic effect reduced not only the lag time (from 36 to 24 h) but also the amount of SnO 2 NMs loading required to achieve the highest hydrogen production rate (150 mg/L) as compared with the standard sample (200 mg/L). Our results highlight that an appropriate combination of pretreatments can present a potential roadmap to enhance bioH 2 production from lignocellulosic biomass, which can be a prospective sustainable energy supply. [Display omitted] • SEM images showed 6 h ultrafine grinding has particle size in the range of micron. • High quality SnO 2 NMs with size variation of 5–15 nm were fabricated. • Highest HPR of 163 mL/h was observed at 6 h of ultrafine grinding and 150 mg/L NMs. • In comparison to SS, the total bioH 2 yield is 49% higher with synergetic effect. • The synergetic effect helped to reduce the lag time (24 h from 36 h). [ABSTRACT FROM AUTHOR]

Biohydrogen production from sewage sludge through anaerobic fermentation is a cleaner production process. However, the complex sludge structure, especially the outer-layer extracellular polymeric substances, significantly restricts the utilization of available organics in the inner-layer sludge cells for hydrogen production. In view of this, this study firstly adopted a cation-binding agent, sodium citrate (SC), to strip the outer-layer extracellular polymeric substances from the sludge floc, followed by thermal disintegration of microbial cells, which aimed to promote the disintegration performance and biohydrogen productivity. The results showed that the sludge with the combined SC-Thermal pretreatment (0.3 g SC/g-SS + 121 °C for 30 min) achieved the maximum biohydrogen yield of 28.6 mL/g-VS added , which was 346.9%, 73.3% and 148.7% higher that of the control, sole SC pretreated system, and sole thermal pretreated system, respectively. The mechanism study revealed that the combined SC-Thermal pretreatment synergistically disintegrated the sludge floc and promoted the soluble organics content by 107.5 times. Meanwhile, the combined pretreatment also shortened the lag time of hydrogen formation, accelerated the hydrolysis, and improved the organics utilization, thus contributing to the improvement of hydrogen yield. The bacterial community analysis demonstrated that the combined pretreatment promoted the abundances of hydrolytic genera (Bacteroides , Proteocatella and Proteiniclasticum) and hydrogen-producing genera (Clostridium sensu stricto , Citrobacter , Paraclostridium and Escherichia-Shigella), which might be fundamentally responsible for the improvement of biohydrogen productivity. [Display omitted] • Combined sodium citrate-thermal pretreatment evidently disrupted the sludge flocs • Pretreatment promoted the SCOD content by 107.5 times and accelerated the hydrolysis • Pretreatment improved the bioH 2 yield by 346.9% and shortened the lag phase • Pretreated sludge exhibited the mixed acid type fermentation • Pretreatment improved the abundance of hydrogen-producing bacteria in the reactor [ABSTRACT FROM AUTHOR]