Improved biohydrogen production by co-fermentation of corn straw and excess sludge: Insights into biochemical process, microbial community and metabolic genes.

The global climate change mainly caused by fossil fuels combustion promotes that zero-carbon hydrogen production through eco-friendly methods has attracted attention in recent years. This investigation explored the biohydrogen production by co-fermentation of corn straw (CS) and excess sludge (ES), as well as comprehensively analyzed the internal mechanism. The results showed that the optimal ratio of CS to ES was 9:1 (TS) with the biohydrogen yield of 101.8 mL/g VS, which was higher than that from the mono-fermentation of CS by 1.0-fold. The pattern of volatile fatty acids (VFAs) indicated that the acetate was the most preponderant by-product in all fermentation systems during the biohydrogen production process, and its yield was improved by adding appropriate dosage of ES. In addition, the content of soluble COD (SCOD) was reduced as increasing ES, while concentration of NH4+-N showed an opposite tendency. Microbial community analysis revealed that the microbial composition in different samples showed a significant divergence. Trichococcus was the most dominant bacterial genus in the optimal ratio of 9:1 (CS/ES) fermentation system and its abundance was as high as 41.8%. The functional genes prediction found that the dominant metabolic genes and hydrogen-producing related genes had not been significantly increased in co-fermentation system (CS/ES = 9:1) compared to that in the mono-fermentation of CS, implying that enhancement of biohydrogen production by adding ES mainly relied on balancing nutrients and adjusting microbial community in this study. Further redundancy analysis (RDA) confirmed that biohydrogen yield was closely correlated with the enrichment of Trichococcus.

An Energy-Efficient Flexible Multi-Modal Wireless Sweat Sensing System Based on Laser Induced Graphene.

Real-time sweat monitoring is vital for athletes in order to reflect their physical conditions, quantify their exercise loads, and evaluate their training results. Therefore, a multi-modal sweat sensing system with a patch-relay-host topology was developed, which consisted of a wireless sensor patch, a wireless data relay, and a host controller. The wireless sensor patch can monitor the lactate, glucose, K+, and Na+ concentrations in real-time. The data is forwarded via a wireless data relay through Near Field Communication (NFC) and Bluetooth Low Energy (BLE) technology and it is finally available on the host controller. Meanwhile, existing enzyme sensors in sweat-based wearable sports monitoring systems have limited sensitivities. To improve their sensitivities, this paper proposes a dual enzyme sensing optimization strategy and demonstrates Laser-Induced Graphene (LIG)-based sweat sensors decorated with Single-Walled Carbon Nanotubes (SWCNT). Manufacturing an entire LIG array takes less than one minute and costs about 0.11 yuan in materials, making it suitable for mass production. The in vitro test result showed sensitivities of 0.53 µA/mM and 3.9 µA/mM for lactate and glucose sensing, and 32.5 mV/decade and 33.2 mV/decade for K+ and Na+ sensing, respectively. To demonstrate the ability to characterize personal physical fitness, an ex vivo sweat analysis test was also performed. Overall, the high-sensitivity lactate enzyme sensor based on SWCNT/LIG can meet the requirements of sweat-based wearable sports monitoring systems.

Efficient butyrate production from rice straw in an optimized cathodic electro-fermentation process.

Butyrate production from renewable biomass shows great potential against climate change and over-consumption of fossil fuels. Herein, key operational parameters of a cathodic electro-fermentation (CEF) process were optimized for efficient butyrate production from rice straw by mixed culture. The cathode potential, controlled pH and initial substrate dosage were optimized at -1.0 V (vs Ag/AgCl), 7.0 and 30 g/L, respectively. Under the optimal conditions, 12.50 g/L butyrate with yield of 0.51 g/g-rice straw were obtained in batch-operated CEF system. In fed-batch mode, butyrate production significantly increased to 19.66 g/L with the yield of 0.33 g/g-rice straw, but 45.99% butyrate selectivity still needs to be improved in future. Enriched butyrate producing bacteria (Clostridium cluster XIVa and IV) with proportion of 58.75% on the 21st day of the fed-batch fermentation, contributed to the high-level butyrate production. The study provides a promising approach for efficient butyrate production from lignocellulosic biomass.

An Implantable Fiber Biosupercapacitor with High Power Density by Multi-Strand Twisting Functionalized Fibers.

Biosupercapacitors (BSCs) that can harvest and store chemical energy show great promise for power delivery of biological applications. However, low power density still limits their applications, especially as miniaturized implants. Here, we report an implantable fiber BSC with maximal power density of 22.6 mW cm-2 , superior to the previous reports. The fiber BSC was fabricated by integrating anode and cathode fibers of biofuel cell with supercapacitor fibers through multi-strand twisting. This twisting structure endowed many channels inside and high electrochemical active area for efficient mass diffusion and charge transfer among different fibers, benefiting high power output. The obtained thin and flexible fiber BSC operated stably under deformations and performed high biocompatibility after implantation. Eventually, the fiber BSC was implanted subcutaneously in rats and successfully realized electrical stimulation of sciatic nerve, showing promise as a power source in vivo.

Determining Factors for Nitrite Accumulation in an Acidic Nitrifying System: Influent Ammonium Concentration, Operational pH, and Ammonia-Oxidizing Community.

Acidic nitrification is attracting wide attention because it can enable robust suppression of nitrite-oxidizing bacteria (NOB) in wastewater treatment. This study reports a comprehensive assessment of the novel acidic nitrification process to identify the key factors that govern stable nitrite accumulation. A laboratory-scale moving-bed biofilm reactor receiving low-alkalinity wastewater was continuously operated under acidic conditions (pH < 6) for around two years, including nine stages varying influent and operational conditions. The results revealed that nitrite accumulation was related to three factors, i.e., influent ammonium concentration, operating pH, and ammonia-oxidizing microbial community. These three factors impact nitrite accumulation by altering the in situ concentration of free nitrous acid (FNA), which is a potent inhibitor of NOB. The critical FNA concentration is approximately one part per million (ppm, ∼1 mg HNO2-N/L), above which nitrite accumulation is stably maintained in an acidic nitrifying system. The findings of this study suggest that stable nitrite accumulation via acidic ammonia oxidation can be maintained under a range of influent and operational conditions, as long as a ppm-level of FNA is established. Taking low-strength mainstream wastewater (40-50 mg NH4+-N/L) with limited alkalinity as an example, stable nitrite accumulation was experimentally demonstrated at a pH of 4.35, under which an in situ FNA of 2.3 ± 0.6 mg HNO2-N/L was attained. Under these conditions, Candidatus Nitrosoglobus became the only ammonia oxidizer detectable by 16S rRNA gene sequencing. The results of this study deepen our understanding of acidic nitrifying systems, informing further development of novel wastewater treatment technologies.

An enhanced excess sludge fermentation process by anthraquinone-2-sulfonate as electron shuttles for the biorefinery of zero-carbon hydrogen.

Excess sludge (ES) largely produced in municipal wastewater treatment plants is known as a waste biomass and the traditional treatment processes such as landfill and incineration are considered as unsustainable due to the negative environmental impact. Fermentation process of ES for the biorefinery of zero-carbon hydrogen has attracted an increasing interesting and was extensively researched in the last decades. However, the technology is far from commercial application due to the insufficient effectivity. In the present study, anthraquinone-2-sulfonate (AQS) as electron shuttles was introduced into the fermentation process of ES for mediating the composition and activity of bacterial community to get an enhanced biohydrogen production. Inoculated with the same anaerobic activated sludge of 1.12 gVSS/L, a series of batch anaerobic fermentation systems with various dosage of AQS were conducted at the same ES load of 2.75 gVSS/L, initial pH 6.5 and 35 °C. The results showed that the fermentation process was remarkably enhanced by the introduction of 100 mg/L AQS, accompanying the lag phase was shortened to 1.35 h from 7.62. The obtained biohydrogen yield and the specific biohydrogen production rate were also remarkably enhanced to 24.9 mL/gVSS and 0.3 mL/(gVSS·h), respectively. Illumina Miseq sequencing showed that Longilinea and Guggenheimella as the dominant genera had been enriched from 9.2% to 0-12.0% and 4.7%, respectively, in the presence of 100 mg/L AQS. Function predicted analysis suggested that the presence of AQS had increased the abundance of genes involved in the transport and metabolism of carbohydrate, amino acid and energy production. Further redundancy analysis (RDA) revealed that the enhanced hydrogen production was highly positively correlated with the enrichment of genera such as Longilinea and Guggenheimella. The research work presents a novel potential biorefinery of ES for the effective production of zero-carbon hydrogen.

Synergistic denitrification, partial nitrification - Anammox in a novel A2/O2 reactor for efficient nitrogen removal from low C/N wastewater.

A biofilm-based anaerobic-aerobic (A2O2) reactor was constructed to treat manure-free piggery wastewater. The reactor contained four compartments, among which the first two were anaerobic (A phase) and the last two were aerobic (O phase). Throughout around one-year operation, high-level nutrient removal was demonstrated. At an optimal reflux ratio of 100%, the average NH4+-N, TN, and COD removal efficiencies were high as 99.4%, 91.7%, and 79.4%, respectively, with the influent concentration of 220.6, 231.6 and 332 mg/L, respectively. The NH4+-N, TN, and COD concentrations in the final effluent were only 1.4, 18.5 and 65 mg/L, respectively. COD and nitrogen removal were mainly removed in the A phase and O phase, respectively. This result revolutionizes the previous perception that nitrogen is only removed in the A phase of conventional A-O configuration. Achievement of PN/A in the O phase was critical to the efficient nitrogen removal. Heterotrophic denitrification in the anaerobic compartments removed the nitrate produced by anammox, ensuring the high-level nitrogen removal. Anaerobic organic degradation was a major pathway for COD removal, as abundant methanogens detected in the A phase. This study provides a feasible technical scheme for the efficient nutrient removal from ammonium-rich wastewater.

Nutrient removal from high ammonium swine wastewater in upflow microaerobic biofilm reactor suffered high hydraulic load.

To understand the ability of an upflow microaerobic biofilm reactor (UMBR) to remove nutrient from manure-free swine wastewater rich in NH4+ with a COD/TN ratio less than 1.00, effect of hydraulic loading rate (HLR) on the microaerobic process was evaluated with a constant reflux ratio of 25 at 25 °C. The results showed that changes in HLR had a remarkable effect on the performance of the UMBR in nutrient removal from the wastewater. With the favorable HLR 3.0 m3/(m3·d) (Hydraulic Retention Time (HRT) 8 h), average removal of COD, NH4+ and TN in the microaerobic process reached 59.3%, 87.7% and 84.7%, respectively, though the COD/TN ratio was as low as 0.84. With an over HLR of 4.0 m3/(m3·d) (HRT decreased to 6 h), bad performance of the UMBR was observed with an average removal of COD, NH4+ and TN as low as 45.0%, 59.0% and 57.5%, respectively. Since the HLR was decreased to 2.4 m3/(m3·d) (HRT 10 h), the microaerobic process regained the efficiency in nutrient removal with a removal of COD, NH4+ and TN averaged 59.0%, 95.3% and 87.8%, respectively. The microaerobic condition allowed anammox bacteria, ammonia-oxidizing bacteria and archaea, nitrite-oxidizing bacteria and denitrifiers to all thrive in the UMBR, resulting in the efficient synchronous removal of organic carbon and nitrogen. As the dominant approach to nitrogen removal, anaerobic ammonium oxidation (anammox) pathway contributing to the TN removal in the microaerobic process exceeded 59.5% at HLR 3.0 m3/(m3·d). The results demonstrated that the UMBR can remove nitrogen and carbon from swine wastewater, with a suitable HLR.

Performance and microbial community analysis of an algal-activated sludge symbiotic system: Effect of activated sludge concentration.

It was focused on the effect of different sludge concentrations on the performances of an algal-activated sludge symbiotic system in terms of wastewater treatment, algal-activated sludge characteristics and community structure. The results showed that the highest nutrient removal efficiencies were obtained in the reactor R2 with soluble chemical oxygen demand (sCOD), ammonia nitrogen (NH4+-N) and phosphate (PO43- -P) removal efficiencies of (90.6±2.3)%, (97.69±2.6)% and (83.81±2.3)%, respectively. Further investigation exhibited that sludge concentration has a great effect on the dissolved oxygen (DO) concentration, the pH, the growth of algae and the extracellular polymeric substance (EPS) production, which resulted in influencing the settleability and the performance of symbiotic system. The denaturing gradient gel electrophoresis (DGGE) analysis demonstrated that the sludge concentration had a selective power for particular members of algae. Meantime, the stimulated algal population would selectively excite the members of bacteria benefited for the formation of algal-bacterial consortia. The variation of microbial compositions, which was influenced by the different sludge concentrations, might be ultimately responsible for the different treatment performances.

Bioaugmentation with Mixed Hydrogen-Producing Acetogen Cultures Enhances Methane Production in Molasses Wastewater Treatment.

Hydrogen-producing acetogens (HPA) have a transitional role in anaerobic wastewater treatment. Thus, bioaugmentation with HPA cultures can enhance the chemical oxygen demand (COD) removal efficiency and CH4 yield of anaerobic wastewater treatment. Cultures with high degradation capacities for propionic acid and butyric acid were obtained through continuous subculture in enrichment medium and were designated as Z08 and Z12. Bioaugmentation with Z08 and Z12 increased CH4 production by glucose removal to 1.58. Bioaugmentation with Z08 and Z12 increased the COD removal rate in molasses wastewater from 71.60% to 85.84%. The specific H2 and CH4 yields from COD removal increased by factors of 1.54 and 1.63, respectively. Results show that bioaugmentation with HPA-dominated cultures can improve CH4 production from COD removal. Furthermore, hydrogen-producing acetogenesis was identified as the rate-limiting step in anaerobic wastewater treatment.

The role of COD/N ratio on the start-up performance and microbial mechanism of an upflow microaerobic reactor treating piggery wastewater.

This study investigated the role of COD/N ratio on the start-up and performance of an upflow microaerobic sludge reactor (UMSR) treating piggery wastewater at 0.5 mgO2/L. At high COD/N ratio (6.24 and 4.52), results showed that the competition for oxygen between ammonia-oxidizing bacteria, nitrite-oxidizing bacteria and heterotrophic bacteria limited the removal of nitrogen. Nitrogen removal efficiency was below 40% in both scenarios. Decreasing the influent COD/N ratio to 0.88 allowed achieving high removal efficiencies for COD (∼75%) and nitrogen (∼85%) due to the lower oxygen consumption for COD mineralization. Molecular biology techniques showed that nitrogen conversion at a COD/N ratio 0.88 was dominated by the anammox pathway and that Candidatus Brocadia sp. was the most important anammox bacteria in the reactor with a relative abundance of 58.5% among the anammox bacteria. Molecular techniques also showed that Nitrosomonas spp. was the major ammonia-oxidiser bacteria (relative abundance of 86.3%) and that denitrification via NO3- and NO2- also contributed to remove nitrogen from the system.

An innovative wood-chip-framework substrate used as slow-release carbon source to treat high-strength nitrogen wastewater.

Removal of nitrogen in wastewater before discharge into receiving water courses is an important consideration in treatment systems. However, nitrogen removal efficiency is usually limited due to the low carbon/nitrogen (C/N) ratio. A common solution is to add external carbon sources, but amount of liquid is difficult to determine. Therefore, a combined wood-chip-framework substrate (with wood, slag and gravel) as a slow-release carbon source was constructed in baffled subsurface-flow constructed wetlands to overcome the problem. Results show that the removal rate of ammonia nitrogen (NH4+-N), total nitrogen (TN) and chemical oxygen demand (COD) could reach 37.5%-85%, 57.4%-86%, 32.4%-78%, respectively, indicating the combined substrate could diffuse sufficient oxygen for the nitrification process (slag and gravel zone) and provide carbon source for denitrification process (wood-chip zone). The nitrification and denitrification were determined according to the location of slag/gravel and wood-chip, respectively. Nitrogen removal was efficient at the steady phase before a shock loading using slag-wood-gravel combined substrate because of nitrification-denitrification process, while nitrogen removal was efficient under a shock loading with wood-slag-gravel combined substrate because of ANAMMOX process. This study provides a new idea for wetland treatment of high-strength nitrogen wastewater.

Effects of metal ions on biomass and 5-aminolevulinic acid production in Rhodopseudomonas palustris wastewater treatment.

This work investigated the effects of eight metal ions on Rhodopseudomonas palustris growth and 5-aminolevulinic acid (ALA) yield in wastewater treatment. Results show that metal ions (Mg(2+) of 15 mmol/L, Fe(2+) of 400 µmol/L, Co(2+) of 4 µmol/L, Ni(2+) of 8 µmol/L and Zn(2+) of 4 µmol/L) could effectively improve the chemical oxygen demand (COD) removal, Rp. palustris biomass and ALA yield. The highest ALA yield of 13.1 mg/g-biomass was achieved with Fe(2+) of 400 µmol/L. ALA yields were differentially increased under different metal ions in the following order: Fe(2+) group > Mg(2+) group > Co(2+) group = Ni(2+) group > Zn(2+) group = Mo(2+) group > control. Cu(2+) and Mn(2+) inhibited Rp. palustris growth and ALA production. Mechanism analysis revealed that metal ions changed ALA yields by influencing the activities of ALA synthetase and ALA dehydratase.

Influence of glucose fermentation on CO2 assimilation to acetate in homoacetogen Blautia coccoides GA-1.

Fermentation of glucose influences CO2 assimilation to acetate in homoacetogens. Blautia coccoides was investigated for a better understanding of the metabolic characteristics of homoacetogens in mixotrophic cultures. Batch cultures of the strain with H2/CO2 as a sole carbon source reached an acetate yield of 5.32 g/g dry cell weight after 240 h of incubation. Autotrophic metabolism was inhibited as glucose was added into the culture: the higher the glucose concentration the lower the autotrophic ability of the bacterium. Autotrophy was inhibited by high glucose concentration, probably due to the competition for coenzyme A between the Embden-Meyerhof-Parnas pathway and the Wood-Ljungdahl carbon fixation pathway, the energy (adenosine triphosphate) allocation for synthesis of cell carbon and reduction of CO2, in combination with the low pH caused by the accumulation of acetate.

Improving the growth of Rubrivivax gelatinosus cultivated in sewage environment.

Rubrivivax gelatinosus cultivated in wastewater environment can combine the biomass resource recycling for generating chemicals with sewage purification. However, low biomass accumulation restricts the exertion of this advantage. Thus, this paper investigated Fe(3+) advancement for biomass production in starch wastewater under light-anaerobic condition. Results showed that addition of Fe(3+) was successful in enhancing biomass production, which certainly improved the feasibility of biomass recycling in R. gelatinosus starch wastewater treatment. With optimal Fe(3+) dosage (20 mg/L), biomass production reached 4,060 mg/L, which was 1.63 times that of control group. Amylase activity was improved by 48 %. Both COD removal and starch removal reached 90 %. Hydraulic retention time was shortened by 25 %. Proper Fe(3+) dosage enhanced biomass production, but excess Fe(3+) was harmful for biomass accumulation.

Magnesium ions improving the growth and organics reduction of Rhodospirillum rubrum cultivated in sewage through regulating energy metabolism pathways.

Rhodospirillum rubrum has the potential for biomass resource recycling combined with sewage purification. However, low biomass production and yield restricts the potential for sewage purification. This research investigated the improvement of biomass production, yield and organics reduction by Mg²âº in R. rubrum wastewater treatment. Results showed that with optimal dosage (120 mg/L), biomass production reached 4,000 mg/L, which was 1.5 times of that of the control group. Biomass yield was improved by 43.3%. Chemical oxygen demand (COD) removal reached over 90%. Hydraulic retention time was shortened by 25%. Mechanism analysis indicated that Mg²âº enhanced the isocitrate dehydrogenase and Ca²âº/Mg²âº-ATPase activities, bacteriochlorophyll content on respiration and photophosphorylation. These effects then enhanced ATP production, which led to more biomass accumulation and COD removal. With 120 mg/L Mg²âº dosage, the isocitrate dehydrogenase and Ca²âº/Mg²âº-ATPase activities, bacteriochlorophyll content, ATP production were improved, respectively, by 33.3%, 50%, 67%, 41.3% compared to those of the control group.

Mg2+ improves biomass production from soybean wastewater using purple non-sulfur bacteria.

Soybean wastewater was used to generate biomass resource by use of purple non-sulfur bacteria (PNSB). This study investigated the enhancement of PNSB cell accumulation in wastewater by Mg2+ under the light-anaerobic condition. Results showed that with the optimal Mg2+ dosage of 10 mg/L, biomass production was improved by 70% to 3630 mg/L, and biomass yield also was improved by 60%. Chemical Oxygen Demand (COD) removal reached above 86% and hydraulic retention time was shortened from 96 to 72 hr. The mechanism analysis indicated that Mg2+ could promote the content of bacteriochlorophyll in photosynthesis because Mg2+ is the bacteriochlorophyll active center, and thus improved adenosine triphosphate (ATP) production. An increase of ATP production enhanced the conversion of organic matter in wastewater into PNSB cell materials (biomass yield) and COD removal, leading to more biomass production. With 10 mg/L Mg2+, bacteriochlorophyll content and ATP production were improved by 60% and 33% respectively.

A study on inorganic phase-change resist Ge2Sb2(1-x)Bi2xTe5 and its mechanism.

The inorganic phase-change photoresist Ge2Sb1.5Bi0.5Te5 has a lot of advantages such as the two-sides of the photoresist, a large difference in the etching rate between it and Si, and so on, making it a promising candidate for use in the full-vacuum manufacture of the next generation ultra-large scale integrated circuits (ULSI). However, the physical origin of its excellent properties is still unclear, hindering its improvement and the optimization of its performance. In this work, we extended the Ge2Sb1.5Bi0.5Te5 to Ge2Sb2(1-x)Bi2xTe5 (GSBT, x = 0.1, 0.25, 0.35) and further investigated their properties. Using X-ray diffraction and X-ray absorption fine structure (XAFS) analyses, we built the structures of crystalline and amorphous GSBT, and attributed the excellent physical and chemical properties of crystalline GBST to the different atomic structures compared to amorphous GBST. Moreover, we clarified that the performance of GSBT was enhanced by the increase of Bi, accompanied by a decrease of the phase-change temperature, and gave a criterion for improving GSBT.

Strengthening the growth of Rubrivivax gelatinosus in sewage purification through ferric ion regulated photophosphorylation and respiration.

Rubrivivax gelatinosus has the potential of biomass resource recycling combined with sewage purification. However, low biomass production and yield restricts the potential for sewage purification. Thus, this research investigated the improvement of biomass production and yield and organics reduction by Fe(3+) in R. gelatinosus wastewater treatment. Results showed that 10-30 mg/L Fe(3+) improved biomass yield in wastewater to a level found in culture medium. With optimal dosage (20 mg/L), biomass production reached 4,300 mg/L, which was 1.67 times that of the control group. Biomass yield was improved by 43.3%. Chemical oxygen demand (COD) removal reached above 91%. Hydraulic retention time was shortened by 25%. Mechanism analysis indicated that Fe(3+) enhanced the succinate and NADH dehydrogenase activities and, bacteriochlorophyll content in three energy metabolism pathways. These effects then enhanced adenosine triphosphate (ATP) production, which led to more biomass accumulation and COD removal. With 20 mg/L Fe(2+) dosage, succinate and NADH dehydrogenase, coproporphyrinogen III oxidase activities, bacteriochlorophyll content and ATP production were improved, respectively, by 48.4, 50.8, 50, 67 and 56% compared to those of the control group.

Acetone-butanol-ethanol fermentation of corn stover by Clostridium species: present status and future perspectives.

Sustainable vehicle fuel is indispensable in future due to worldwide depletion of fossil fuel reserve, oil price fluctuation and environmental degradation. Microbial production of butanol from renewable biomass could be one of the possible options. Renewable biomass such as corn stover has no food deficiency issues and is also cheaper in most of the agricultural based countries. Thus it can effectively solve the existing issue of substrate cost. In the last 30 years, a few of Clostridium strains have been successfully implemented for biobutanol fermentation. However, the commercial production is hindered due to their poor tolerance to butanol and inhibitors. Metabolic engineering of Clostridia strains is essential to solve above problems and ultimately enhance the solvent production. An effective and efficient pretreatment of raw material as well as optimization of fermentation condition could be another option. Furthermore, biological approaches may be useful to optimize both the host and pathways to maximize butanol production. In this context, this paper reviews the existing Clostridium strains and their ability to produce butanol particularly from corn stover. This study also highlights possible fermentation pathways and biological approaches that may be useful to optimize fermentation pathways. Moreover, challenges and future perspectives are also discussed.