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•Methane production were improved with addition of biochar, magnetic biochar and Fe3O4.•The cumulative methane yield was increased by 60.47% with 5 g/kg of Fe3O4.•The direct ...interspecies electron transfer (DIET) was enhanced by Fe3O4.•The strategy of recycling Fe3O4 additive has the best economic benefit.
The co-digestion of corn straw and sewage sludge with different additives (biochar, magnetic biochar, Fe3O4) were investigated. The highest cumulative methane yield of 245.15 mL/g VSadded was obtained with the Fe3O4 addition ratio of 5 g/kg, which was 60.47% higher than that of the control run (without additives). The lag phase time was shortened from 5.46 to 3.82 days with a biochar dosage of 5 g/kg. The performance of Fe3O4 on methane production from the co-digestion process was better than that of the biochar and magnetic biochar. The direct interspecies electron transfer (DIET) was enhanced with regard to the increased concentration of acetic acid and decreased concentration of propionic acid. Microbial community analysis showed that the Geobacter and Methanosarcina were selectively enriched on the surface of Fe3O4, promoting the DIET and acetoclastic methanogenesis pathway. The cost-benefit analysis proved that the strategy of recycling Fe3O4 additive has the best economic benefit.
In the present study, the simplex lattice mixture design method was adopted to design the artificial biomass with different ratios of three major components (cellulose, hemicellulose, lignin). The ...methane yield from the co-digestion of the artificial/ natural biomass (corn stover, wheat stover, rice straw, and peanut stalk) samples with the mixed sludge at the mixture ratio of 1:1 based on total solid (TS) content was recorded for 50 days. The original mathematical prediction models for estimating the cumulative methane production, maximum methane production rate, and lag phase time were established based on the experimental results from the co-digestion of artificial biomass with sludge. To investigate the influence of the structural features of biomass and interactions among the components of biomass which contributing to the inhibition of methane production, the macroscopic factor (MF) was proposed. The mathematical models which revealed the relationship between MF and the methane production parameters were developed by the combination of the prediction results from the original mathematical prediction model and experimental results from the co-digestion of natural biomass with sludge. Modification of the original mathematical prediction models was carried out by considering MF. After modification, the relative error (RE) and root mean square error (RMSE) of the prediction model for cumulative methane production were declined from 19.00 to 30.18% and 42.38 mL/g VS
added
to that of − 1.93~7.14% and 4.36 mL/g VS
added
, respectively.
The co-digestion of the individual component of biomass with sewage sludge was investigated, concerning the cumulative methane yield, variation of pH, chemical oxygen demand (COD), volatile fatty ...acids (VFAs), and total ammonia nitrogen (TAN) during 50-day digestion. The microbial community at the initial stage (stage I) and maximum methane production rate stage (stage II) of the digestion process were identified by Illumina MiSeq sequencing. The cumulative methane yield from co-digestion of cellulose and sludge was increased by 33.33% over the calculated value from that of mono-digestion of cellulose and sludge, while that from co-digestion of hemicellulose and sludge was achieved as 259.32% compared with the calculated value from that of mono-digestion of hemicellulose and sludge. The
Firmicutes
to
Bacteroidetes
(F/B) ratio at the stage II of co-digestion of hemicellulose and sludge was notably decreased from 46.53 to that of 1.39 for mono-digestion of hemicellulose. The percentage of
Methanosarcina
in acetoclastic methanogens at the stage II of mono-digestion of hemicellulose was largely increased from 1.06% to that of 97.03% for co-digestion of hemicellulose and sludge.
Three different types of urban sewage sludges (the mixed sludge, the dewatered secondary sludge and the sludge filtered by screens) were used for individual anaerobic digestion and co-digestion with ...agricultural biomass. The initial TS level (4%) and substrate to inoculum ratio (3:1) were maintained into all runs at mesophilic conditions, and the co-substrates was mixed at the recommended VS ratio of 1:1 (sludge: straw under the co-digestion conditions. It was found that the mixed sludge exhibited prominent anaerobic digestion performance, selected as a potential reagent for the co-digestion with biomass. The total volume of the produced methane from co-digestion of the mixed sludge and wheat stalk reached to 187.01 ± 3.27 mL g
−1
VS
added
, which was about 1.52 times higher than that from the individual digestion of the sludge. The experimental value of methane yield from co-digestion of the mixed sludge with wheat stalk is about 9.46% more than that of the estimated value, imply the enhanced interactions between the sludge and biomass during the co-digestion process. The pH of the co-digestion system of the mixed sludge and the wheat stalk was maintained at a relevant stable value around 6.50. It indicated that the buffering capacity of the digestion system could improved by adding the mixed sludge. The modified Gompertz model and the first-order kinetic model were proposed to simulate the co-digestion process between the mixed sludge and agricultural straw. The estimated kinetic parameters indicated that the maximum releasing rate of methane was significantly increased during the co-digestion process.
Graphic Abstract
Anaerobic digestion (AD) is an attractive straw resource treatment technology as it can improve the utilization efficiency of straw resource. Raw straw materials contain complex polymers, so some ...enhancements are needed to achieve better biodegradability. The addition of various additives has become an effective method to improve the AD efficiency, among which the effect of nano zero-valent iron (NZVI) and biochar (BC) on AD has become a research hot spot. In this paper, the powder of NZVI and BC (mixing ratio 1:1) was used as additives to study the effect of different addition amount (3%, 6%, 9%, 12% and 15%) on the AD of corn straw for methane production. The cycle of AD was 28 days, the fermentation temperature was 35 ℃, and the total solid (TS) concentration was 4%. The combined addition of NZVI and BC enhanced the pH stability of the digestion process and the degradation of organic acids. The greatest enhancement of methane production was obtained when the combined addition amount of NZVI and BC was 9%, and the cumulative methane production was 151.06 mL/g VS, which is 20.73% higher than the control group. The combined addition of NZVI and BC could increase the methane content within a certain range, but an inhibitory effect was observed when exceeded 9%. When the addition amount reached 12% and 15%, the cumulative gas production and cumulative methane production of corn straw AD were inhibited to varying degrees. The VS removal efficiency was the highest in the group with the addition amount of 9%, which was 20.41% higher than the control. The modified Gompertz equation fitted well with the maximum methane production rate (Rm) and lag time (
λ
) when the addition amount was 9%, with high correlation coefficients. Considering that NZVI could be recovered by magnetic separation to further reduce the cost of additives, while the cost of biochar was relatively low, it was believed that the crop straw AD technology had certain commercial application value.
Graphic abstract
Featuring high caloric value, clean-burning, and renewability, hydrogen is a fuel believed to be able to change energy structure worldwide. Biohydrogen production technologies effectively utilize ...waste biomass resources and produce high-purity hydrogen. Improvements have been made in the biohydrogen production process in recent years. However, there is a lack of operational data and sustainability analysis from pilot plants to provide a reference for commercial operations. In this report, based on spectrum coupling, thermal effect, and multiphase flow properties of hydrogen production, continuous pilot-scale biohydrogen production systems (dark and photo-fermentation) are established as a research subject. Then, pilot-scale hydrogen production systems are assessed in terms of sustainability. The system being evaluated, consumes 171,530 MJ of energy and emits 9.37 t of CO
eq when producing 1 t H
, and has a payback period of 6.86 years. Our analysis also suggests future pathways towards effective biohydrogen production technology development and real-world implementation.
5-Ethoxymethylfurfural (EMF) can be considered as a potential biofuel because of its excellent combustion properties, such as high energy density and low carbon smoke emissions. In this study, ...Ultra-stable Y (USY) zeolite was modified with NH4H2PO4 and then used as an efficient solid catalyst for the catalytic synthesis of EMF via ethanolysis of glucose First, the NH4H2PO4-modified USY was characterized by FT-IR, XRD, BET, and NH3-TPD. The effect of reaction temperature, reaction time, substrate concentration, and catalyst loading on the yield of EMF was investigated. The P0.2-USY optimal EMF yield was 39.6 mol%, which increased by 20.7% compared to USY, and still had better activity after being reused for 5 cycles. Moreover, the pseudo-homogeneous first-order kinetics model was developed to elucidate the kinetics of EMF formation from glucose, and the kinetics results showed that the activation energy of EMF formation (64.2 kJ⋅mol-1) was lower than that of humins formation (73.2 kJ⋅mol-1). Finally, the ethanolysis pathway was proposed based on the product distribution.
Fe
4
O
3
has shown great potential as an enhancer of batch anaerobic digestion performance. In this study, the effect of two types of Fe
3
O
4
additive utilization strategies (magnetic separation ...recycling strategy and replenishment without recycling strategy) on semi-continuous anaerobic co-digestion of sludge and corn straw were investigated. A maximum methane yield of 163.88 ± 12.18 mL/g·VS·d was obtained at the dosage of 10 g/kg Fe
3
O
4
with magnetic separation recycling strategy compared to the control without the addition of Fe
3
O
4
. As compared to the replenishment strategy, the recycling strategy improved specific daily methane yields by 38.45% and 45.75% for Fe
3
O
4
addition amounts of 5 g/kg and 10 g/kg, respectively. The results show that the recycling of Fe
3
O
4
additives can further optimize the composition of VFAs. Although the total VFAs were not elevated, the proportion of acetic acid increased and the proportion of propionic acid as well as butyric acid decreased. The present research supports the magnetic recycling of Fe
3
O
4
as a new strategy to solve the problem of additive loss in semi-continuous anaerobic digestion process.
A coproduction tests of quaternary (Q) phase(6CaO·4Al2O3·MgO·SiO2) -3CaO·3Al2O3·CaSO4 cement clinker and an experimental study on the relationship between the mineral production capability and the ...physiochemical properties are conducted in a two-stage multiphase reaction test bed with Changguang coal. X-ray diffractometer (XRD) analyses are performed on the coproduction clinker samples. The results demonstrate that, with the reduction in particle sizes of the coal powder and the additives and expanded screening level differences between them, both the proportion of Q phase and the mass of 3CaO·3Al2O3·CaSO4 in the clinker increase accordingly. When mixed coal powder particles are prepared through reducing particle sizes and expanding screening level differences between coal powder and additives, the additives CaO and MgO are more likely to be enclosed by coal powder to form globular polymerized particles. In addition, this preparation aids in polymerization and promotes even distribution of CaO, MgO and coal minerals, thus facilitating clinker mineral formation reactions of inorganic substances in the mixed coal powder. Target minerals, such as 2CaO·SiO2 and Q phase, are found in both industrial high-calcium limestone and low-calcium limestone coproduction clinker samples. A diffraction peak of free CaO is also evident in both samples. Compared with a coproduction clinker sample of high-calcium limestone, that of low-calcium limestone exhibits higher diffraction peaks for 2CaO·SiO2 and Q phase. With the current state of the art, it is not yet the optimum choice to substitute CaCO3 for CaO in Q-phase cement clinker coproduction. Before the technology matures and gains practical application, further study on the form and the mixing process of calcium-based additives for cement clinker coproduction will be required.
Biological pretreatment can promote the degradation of biomass and enhance methane production via the subsequent anaerobic digestion. In addition, a large amount of bio-heat can be generated during ...the pretreatment process to provide heat for the anaerobic digestion process. In this study, composite microorganisms were employed for pretreating corn straw. The impact of different pretreatment times and the heat generated by the pretreatment process on subsequent anaerobic digestion were studied. The results show that the maximum temperature of the pretreatment process was 56.2 °C, obtained on day 6. After 14 days of pretreatment, the degradation rate of the pretreatment group increased by 41% compared with the control group. As a consequence, straws with different pretreatment times were used for anaerobic digestion. The group that underwent 6 days of pretreatment and utilized bio-heat generated from pretreatment achieved the highest cumulative methane production of 401.58 mL/g VS, which was 60.13% higher than in the control group without pretreatment. After 6 days of composite microorganism pretreatment, the group that utilized bio-heat achieved a 29.08% increase in cumulative methane production compared to the group that did not utilize bio-heat. In conclusion, this study highlights the potential of biological pretreatment with composite microorganisms followed by anaerobic digestion using bio-heat as an effective method for treating corn straw.
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