Janus Flexible Device with Microcone Channels for Sampling and Analysis of Biological Microfluidics.

Controlling the spontaneous directional transport of droplets plays an important role in the application of microchemical reactions and microdroplet detection. Although the relevant technologies have been widely studied, the existing spontaneous droplet transport strategies still face problems of complex structure, single function, and poor flexibility. Inspired by the spontaneous droplet transport strategy in nature, an asymmetric wettability surface with microcone channels (AWS-MC) is prepared on a flexible fabric by combining surface modification and femtosecond laser manufacturing technology. On this surface, the capillary force and Laplace pressure induced by the wettability gradient and the geometric structure gradient drive the droplet transport from the hydrophobic surface to the hydrophilic surface. Notably, droplets in adjacent hydrophilic regions do not exchange substances even if the gap in the hydrophilic region is only 1 mm, which provides an ideal platform for numerous detections by a single drop. The droplet transport strategy does not require external energy and can adapt to the manipulation of various droplet types. Application of this surface in the blood of organisms is demonstrated. This work provides an effective method for microdroplet-directed self-transport and microdroplet detection.

Impact of undissociated volatile fatty acids on acidogenesis in a two-phase anaerobic system.

This study investigated the degradation and production of volatile fatty acids (VFAs) in the acidogenic phase reactor of a two-phase anaerobic system. 20 mmol/L bromoethanesulfonic acid (BESA) was used to inhibit acidogenic methanogens (which were present in the acidogenic phase reactor) from degrading VFAs. The impact of undissociated volatile fatty acids (unVFAs) on "net" VFAs production in the acidogenic phase reactor was then evaluated, with the exclusion of concurrent VFAs degradation. "Net" VFAs production from glucose degradation was partially inhibited at high unVFAs concentrations, with 59%, 37% and 60% reduction in production rates at 2190 mg chemical oxygen demand (COD)/L undissociated acetic acid (unHAc), 2130 mg COD/L undissociated propionic acid (unHPr) and 2280 mg COD/L undissociated n-butyric acid (unHBu), respectively. The profile of VFAs produced further indicated that while an unVFA can primarily affect its own formation, there were also unVFAs that affected the formation of other VFAs.

Determination of the archaeal and bacterial communities in two-phase and single-stage anaerobic systems by 454 pyrosequencing.

2-Phase anaerobic digestion (AD), where the acidogenic phase was operated at 2day hydraulic retention time (HRT) and the methanogenic phase at 10days HRT, had been evaluated to determine if it could provide higher organic reduction and methane production than the conventional single-stage AD (also operated at 12days HRT). 454 pyrosequencing was performed to determine and compare the microbial communities. The acidogenic reactor of the 2-phase system yielded a unique bacterial community of the lowest richness and diversity, while bacterial profiles of the methanogenic reactor closely followed the single-stage reactor. All reactors were predominated by hydrogenotrophic methanogens, mainly Methanolinea. Unusually, the acidogenic reactor contributed up to 24% of total methane production in the 2-phase system. This could be explained by the presence of Methanosarcina and Methanobrevibacter, and their activities could also help regulate reactor alkalinity during high loading conditions through carbon dioxide production. The enrichment of hydrolytic and acidogenic Porphyromonadaceae, Prevotellaceae, Ruminococcaceae and unclassified Bacteroidetes in the acidogenic reactor would have contributed to the improved sludge volatile solids degradation, and ultimately the overall 2-phase system's performance. Syntrophic acetogenic microorganisms were absent in the acidogenic reactor but present in the downstream methanogenic reactor, indicating the retention of various metabolic pathways also found in a single-stage system. The determination of key microorganisms further expands our understanding of the complex biological functions in AD process.

The role of methanogens in acetic acid production under different salinity conditions.

In this study, a fed-batch acidogenic reactor was operated at a 3 d hydraulic retention time (HRT) and fed with alkaline pre-treated sludge to investigate salinity effects on methanogens' abundance, activities and their consumption of produced acetic acid (HAc) and total volatile fatty acids (VFAs). The salinity concentration was increased step-wise by adding sodium chloride. At 3‰ (parts per thousand) salinity, the average produced volatile fatty acids (VFAs) concentration was 2410.16 ± 637.62 mg COD L(-1) and 2.70 ± 0.36 L methane was produced daily in the acidogenic reactor. Further batch tests indicated methanogens showed a HAc degradation rate of 3.81 mg COD g(-1) VSS h(-1) at initial HAc concentration of 1150 mg COD L(-1), and showed tolerance up to 16‰ salinity (3.76 g Na(+) L(-1)) as indicated by a constant HAc degradation rate. The microbiological study indicated this can be related to the predominance of acetate-utilizing Methanosarcinaceae and Methanomicrobiales in the reactor. However, with salinity increased to 20‰ and 40‰, increases in VFAs and HAc production and decreases in methane production, methanogens population, acidogenic bacteria population and acidification extent were observed. This study demonstrated presence of acetate-utilizing methanogens in an acidogenic reactor and their high tolerance to salinity, as well as their negative impacts on net VFAs production. The results would suggest the presence of methanogens in the acidogenic reactor should not be ignored and the recovery of methane from the acidogenic reactor needs to be considered to avoid carbon loss.

Acetic acid effects on methanogens in the second stage of a two-stage anaerobic system.

This study reports on biomass tolerance towards high concentrations of acetic acid (HAc) within the system. Biomass from the second stage of a two-stage anaerobic sludge digestion system was used for this study. Microbial community analysis by 454 pyrosequencing highlighted hydrogenotrophic Methanomicrobiales was the predominant archaeal population in the second stage (>99% of the total archaeal community). Second stage biomass degraded HAc up to 4200 mg HAc L(-1) without observable lag phase. However, at HAc-shock loading of 7400 mg HAc L(-1), it showed a one day lag phase associated with decreased biomass activity. After stepwise HAc-acclimation over 27 d, the biomass degraded HAc of up to 8200 mg HAc L(-1) without observable lag phase. The dominance of Methanomicrobiales had remained unchanged in proportion - while the total archaeal population increased during acclimation. This study showed stepwise acclimation could be an approach to accommodate HAc accumulation and hence higher concentrations resulting from an enhanced first stage.

Comparison of single-stage and two-phase anaerobic sludge digestion systems - Performance and microbial community dynamics.

This study compared reactor performance and the respective microbial community dynamics in the conventional single-stage and 2-phase anaerobic digestion (AD) systems, treating municipal sludge to generate methane. The 2-phase system's COD and VS reduction, and methane production could be maintained throughout the three HRTs tested (p=0.05), which was associated with an increase in organic loading (30d=1.5gCODL(-1)d(-1), 20d=2.2gCODL(-1)d(-1) and 10d=3.5gCODL(-1)d(-1)); but this was not so in the single-stage system where it deteriorated at HRT of 10d (p=0.05) due to impairment of particulate COD reduction. qPCR, DGGE and the subsequent phylogenetic analysis revealed that microbial adaptation occurred as the seed sludge formed a different community in each reactor at 30d HRT; however, no further significant microbial shift occurred at lower HRTs. The presence of specific hydrolytic and acidogenic Flavobacteriales and Clostriales in the acidogenic reactor may have allowed for enhanced hydrolysis and acidogenesis, leading to higher organic loading tolerance at 10d HRT. Methanogenic activity in the acidogenic reactor may have been performed by Methanobacteriales and Methanosarcinaceae. Operation of the acidogenic reactor at neutral pH may have to be considered to ensure the cultivation of propionate oxidising bacteria, which could in turn, prevent reactor "souring" during high load conditions.

Dynamics of propionic acid degradation in a two-phase anaerobic system.

This paper reports on propionic acid (HPr) degradation in a laboratory scale two-phase anaerobic system, where HPr was accumulated in the acidogenic reactor and degraded in the methanogenic reactor. Batch tests using biomass from the two-phase anaerobic system showed HPr degradation was rarely detectable in the acidogenic reactor when HPr concentration ranged from 639 to 4531mgHPrL(-1) and at pH 4.50 to 6.50. Biomass from the methanogenic reactor could, however, successfully degrade HPr at its initial concentration of up to 4585mgHPrL(-1) at pH 6.40-7.30. ATP results showed that differences in the degradation ability of HPr by the acidogenic and methanogenic biomass may be related with their respective different biomass activities. Results from pyrosequencing showed that the predominant propionic acid oxidizing bacteria (POB) in the methanogenic reactor were Smithella (2.68%) and Syntrophobacter (0.35%); while poor degradation of HPr in the acidogenic reactor may be associated with the low abundance of POB (0.02% Desulfacinum and 0.08% Desulfobulbus). This might have been induced by the long-term unfavorable environment for POB growth in the acidogenic reactor.

The effect of pH on solubilization of organic matter and microbial community structures in sludge fermentation.

Sludge fermentation between pH 4 and 11 was investigated to generate volatile fatty acids (VFA). Despite the highest sludge solubilization of 25.9% at pH 11, VFA accumulation was optimized at pH 8 (12.5% out of 13.1% sludge solubilization). 454 pyrosequencing identified wide diversity of acidogens in bioreactors operated at the various pHs, with Tissierella, Petrimonas, Proteiniphilum, Levilinea, Proteiniborus and Sedimentibacter enriched and contributing to the enhanced fermentation at pH 8. Hydrolytic enzymatic assays determined abiotic effect to be the leading cause for improved solubilization under high alkaline condition but the environmental stress at pH 9 and above might lead to disrupt biological activities and eventually VFA production. Furthermore, molecular weight (MW) characterization of the soluble fractions found large MW aromatic substances at pH 9 and above, that is normally associated with poor biodegradability, making them disadvantageous for subsequent bioprocesses. The findings provided information to better understand and control sludge fermentation.