Planktonic microbial community and biological metabolism in a subtropical drinking water river-reservoir system.

To understand the dynamics of planktonic microbial community and its metabolism processes in subtropical drinking water river-reservoir system with lower man-made pollution loading, this study selected Dongzhen river-reservoir system in Mulan Creek as object to investigate spatial-temporal characteristics of community profile and functional genes involved in biological metabolism, and to analyze the influence of environmental factors. The results indicated that Proteobacteria and Actinobacteria were the most diverse phyla with proportion ranges of 9%-80% in target system, and carbohydrate metabolism (5.76-7.12 × 10-2), amino acid metabolism (5.78-7.21 × 10-2) and energy metabolism (4.07-5.17 × 10-2) were found to be the dominant pathways of biological metabolism. Although there were variations in biological properties both spatially and temporally, seasonal variation had a greater influence on microbial community and biological metabolism, than locational differences. Regarding the role of environmental factors, this study revealed that microbial diversity could be affected by multiple abiotic factors, with total organic carbon, total phosphorus and temperature being more influential (absolute value of standardized regression weights >2.13). Stochastic processes dominated the microbial community assembly (R2 of neutral community model = 0.645), while niche-based processes differences represented by nutrients, temperature and pH level played secondary roles (R > 0.388, P < 0.01). Notably, the synergistic influences among the environmental factors accounted for the higher percentages of community variation (maximum proportion up to 17.6%). Additionally, pH level, temperature, and concentrations of dissolved oxygen, carbon and nitrogen were found to be the significant factors affecting carbon metabolism pathways (P < 0.05), yet only total organic carbon significantly affected on nitrogen transformation (P < 0.05). In summary, the microbial profile in reservoir is not completely dominated by that in feeding river, and planktonic microbial community and its metabolism in subtropical drinking water river-reservoir system are shaped by multiple abiotic and biotic factors with underlying interactions.

Boosting seawater denitrification in an electrochemical flow cell.

Nitrogen compounds in current seawater treatment processes typically are converted to nitrate, threatening seawater quality and marine ecology. Electrochemical denitrification is a promising technique, but its efficiency is severely limited by the presence of excess chloride ions. In this work, a flow-through cell went through an on-demand chlorine-mediated electrochemical-chemical tandem reaction process was designed for efficient seawater denitrification. Equipped with ultrathin cobalt-based nanosheets as the cathode catalyst and commercial IrO2-RuO2/Ti as the anode, the newly designed flow-through cell achieved nitrate removal efficiency that was about 50 times greater than the batch cell and nearly 100 % N2 selectivity. Moreover, nitrite and ammonia can also be removed with over 93 % efficiency in total nitrogen (TN) removal. Furthermore, the concentration of active chlorine in the effluent could be adjusted within two orders of magnitude, enabling on-demand release of active chlorine. Finally, this flow-through cell reduced the TN of actual mariculture tailwater (40.1 mg N L-1 nitrate) to only 5.7 mg N L-1, meeting the discharge standard for aquaculture tailwater of Fujian, China. This work demonstrates the paradigm of deep denitrification from ultra-concentrated chlorine ion wastewater using an on-demand active chlorine-mediated electrochemical-chemical tandem reaction process.

Ultrathin cobalt-based nanosheets containing surface oxygen promoted near-complete nitrate removal.

Electrocatalytic nitrate removal offers a sustainable approach to alleviate nitrate pollution and to boost the anthropogenic nitrogen cycle, but it still suffers from limited removal efficiency at high rates, especially at low levels of nitrate. Herein, we report the near-complete removal of low-level nitrate (10-200 ppm) within 2 h using ultrathin cobalt-based nanosheets (CoNS) containing surface oxygen, which was fabricated from in-situ electrochemical reconstruction of conventional nanosheets. The average nitrate removal of 99.7 % with ammonia selectivity of 98.2 % in 9 cyclic runs ranked in the best of reported catalysts. Powered by a solar cell under the winter sun, the full-cell nitrate electrolysis system, equipped with ultrathin CoNS, achieved 100 % nitrogen gas selectivity and 99.6 % total nitrogen removal. The in-situ Fourier Transform Infrared included experiments and theoretical computations revealed that in-situ electrochemical reconstruction not only increased electrochemical active surface area but also constructed surface oxygen in active sites, leading to enhanced stabilization of nitrate adsorption in a symmetry breaking configuration and charge transfer, contributing to near-complete nitrate removal on ultrathin CoNS. This work provides a strategy to design ultrathin nanocatalysts for nitrate removal.

Adaptive shifts in plant traits associated with nitrogen removal driven by phytoremediation strategies in subtropical river restoration.

Phytoremediation, which is commonly carried out through hydroponics and substrate-based strategies, is essential for the effectiveness of nature-based engineered solutions aimed at addressing excess nitrogen in aquatic ecosystems. However, the performance and mechanisms of plants involving nitrogen removal between different strategies need to be deeply understood. Here, this study employed in-situ cultivation coupled with static nitrogen tracing experiments to elucidate the influence of both strategies on plant traits associated with nitrogen removal. The results indicated that removal efficiencies in plants with substrate-based strategies for ammonium nitrogen and nitrate nitrogen were 30.51-71.11 % and 16.82-99.95 %, respectively, which were significantly higher than those with hydroponics strategies (25.98-58.18 % and 7.29-79.19 %, respectively). Similarly, the plant nitrogen uptake rates in the substrate-based strategy also generally showed higher levels compared to hydroponics strategies (P < 0.05). Meanwhile, the microorganisms-mediated nitrous oxide emission rates in the substrate-based strategy during summer (unamended: 0.00-0.58 µg/g/d; potential: 3.35-7.65 µg/g/d) were obviously lower than those in the hydroponics strategy (unamended: 2.23-11.70 µg/g/d; potential: 9.72-43.09 µg/g/d) (P < 0.05). Notably, analysis of similarity tests indicated that the influences of strategy on the above parameters generally surpass the effects attributable to interspecies plant differences, particularly during summer (R > 0, P < 0.05). Based on statistical and metagenomic analyses, this study revealed that these differences were driven by the stabilizing influence of substrate-based strategy on plant roots and enhancing synergistic interplay among biochemical factors within plant-root systems. Even so, phytoremediation strategies did not significantly alter the characteristics of plants with regards to their tendency towards ammonium nitrogen uptake (up to 87.68 %) and dissimilatory nitrate reduction to ammonium as primary biological pathway for nitrogen transformation which accounted for 53.66-96.47 % nitrate removal. In summary, this study suggested that the substrate-based strategy should be a more effective strategy for enhancing the nitrogen removal ability of plants in subtropical river restoration practices.

Activating nickel foam with trace titanium oxide for enhanced water oxidation.

Nickel-based electrocatalysts for water oxidation suffer from low activity and poor stability. In this work, 0.015 mg cm-2 TiO2 nanosheets anchored on Ni foam addressed these problems after electrochemical activation. In situ investigations, including Raman spectra, corroborated the enhanced generation of highly active Ni(III)-O-O species on Ni foam in the presence of trace TiO2.

Re-evaluation and modification of dehydrogenase activity tests in assessing microbial activity for wastewater treatment plant operation.

Reliable and cost-effective methods for monitoring microbial activity are critical for process control in wastewater treatment plants. The dehydrogenase activity (DHA) test has been recognized as an efficient measure of biological activity due to its simplicity and broad applicability. Nevertheless, the existing DHA test methods suffer from imperfections and are difficult to implement as routine monitoring techniques. In this work, an accurate and cost-effective modified DHA approach was developed and the procedure for the DHA test was critically evaluated with respect to the standard construction, sample pretreatment, incubation and extraction conditions. The feasibility of the modified DHA test was demonstrated by comparison with the oxygen uptake rate and adenosine triphosphate in a sequencing batch reactor. The sensitivities of the two typical tetrazolium salts to toxicant inhibition by heavy metals and antibiotics were compared, revealing that 2,3,5-triphenyltetrazolium chloride (TTC) exhibited a higher sensitivity. Furthermore, the sensitivity mechanism of the two DHA tests was elucidated through electrochemical experiments, theoretical analysis and molecular simulations. Both tetrazolium salts were found to be effective artificial electron acceptors due to their low redox potentials. Molecular docking simulations revealed that TTC could outperform other tetrazolium salts in accepting electrons and hydrogens from dehydrogenase. Overall, the modified DHA approach presents an accurate and cost-effective way to measure microbial activity, making it a practical tool for wastewater treatment plants.

Enhancing sulfate reduction and hydrogen sulfide removal through gas stripping in the acidogenesis phase of a two-phase anaerobic process.

This study aims at evaluating two-phase and single-phase reactors for treating sulfate wastewater with low COD/SO42- ratios. Additionally, a new process of gas stripping in an acidogenesis phase is proposed to reduce hydrogen sulfide (H2S) inhibition and enhance biomethanation. The two-phase performed better than the single-phase in terms of COD removal, CH4 production and H2S resistance. After 30 days of stripping, the COD and sulfate degradation rates increased from 85.16% to 91.09% and from 49.39% to 63.07% in the two-phase, respectively. In contrast, without stripping, they were from 79.21% to 64.37% and from 50.26% to 53.15% in the single-phase, respectively. The microbial biodiversity was augmented via stripping, including norank_f__Spirochaetaceae, Petrimonas, Desulfurella and Blvii28_wastewater-sludge_group. Stripping operation enhanced the dissimilatory sulfate reduction, amino acid metabolism and possibly sulfate-dependent anaerobic ammonia oxidation (S-ANAMMOX). This study provides a promising strategy to improve sulfate reduction and reduce H2S inhibition under a low COD/SO42- ratio.

Antibiotic resistant genes profile in the surface water of subtropical drinking water river-reservoir system.

To comprehensively understand antibiotic resistant genes (ARGs) profile in the subtropical drinking water river-reservoir system, this study selected Dongzhen river-reservoir system in Mulan Creek as object to investigate the spatial-temporal characteristics of ARGs diversity, bacterial host and resistance mechanism, and to analyze the key environmental factors driving ARGs profile variation. The results indicated that a total of 440 ARGs were detected in the target system, and the ARGs distribution pattern in the reservoir was attributed to autologous evolution or the comprehensive influence of feeding river system. The predominant bacterial host at different sites showed similar variations to dominated ARGs, and Proteobacteria, Actinobacteria and Bacteroidetes harbored most ARGs at phylum level, which showed the highest proportions of 74%, 37% and 35%, respectively. Antibiotic efflux was the primary resistance mechanism in all samples from wet season (45%-60%), yet the samples from dry season exhibited multiple resistance mechanisms, including inactivation (37%-52%), efflux (44%), and target alteration (43%). The total relative abundances of ARGs in the target system ranged from 0.89 × 10-2 to 1.71 × 10-2, and seasonal variation had a more significant influence on ARGs abundance than spatial variation (R = 0.68, P < 0.01). Environmental factors analysis indicated that the concentrations of nitrite nitrogen and total organic carbon were significant factors explaining ARGs number and various resistance mechanism proportions (P < 0.01), accounting for 48.7% and 61.1% of the variation, respectively; ammonia nitrogen concentration, total organic carbon concentration, temperature and pH were the significant influence factors on the relative abundance of ARGs (P < 0.05), with standardized regression weights of 0.700, 1.414, 1.447, and 1.727, respectively. In summary, in the surface water of the target system, ARGs diversity was primarily driven by ARGs horizontal transfer and antibiotics biosynthesis. Nutrients mainly promoted ARGs abundance by providing abundant energy, rather than increasing bacterial reproductive capacity.

Fish scale-based biochar with defined pore size and ultrahigh specific surface area for highly efficient adsorption of ciprofloxacin.

A fish scale-based porous activated biochar with defined pore size (DPBC) was fabricated by a one-step calcination and activation method. The DPBC possessed an ultrahigh specific surface area of 3370 m2 g-1 and its pore diameter centered at 1.49 nm which fits into the ciprofloxacin (CIP) molecular dimension, making it an ideal adsorbent for CIP adsorption due to the molecular pore-filling effect. The maximum Langmuir monolayer adsorption capacity of DPBC for CIP was higher than 1000 mg g-1 and the equilibrium time was less than 4 h, superior to most adsorbents reported in literature. Thermodynamic analysis indicated the adsorption process was spontaneous and endothermic. Notably, fixed-bed experiments showed an encouraging adsorption performance towards CIP, with a high saturated dynamic adsorption capacity of 880.3 mg g-1. Both Thomas and Yoon-Nelson models predict the fixed-bed column adsorption performance well. Hydrophobic effect, π-π interaction, π-π EDA, cation exchange, hydrogen bonding formation, pore filling effect, electrostatic and cation-π interaction involved in the CIP adsorption on the DPBC.

Novel online monitoring and alert system for anaerobic digestion reactors.

Effective monitoring and diagnosis of anaerobic digestion processes is a great challenge for anaerobic digestion reactors, which limits their stable operation. In this work, an online monitoring and alert system for upflow anaerobic sludge blanket (UASB) reactors is developed on the basis of a set of novel evaluating indexes. The two indexes, i.e., stability index S and auxiliary index a, which incorporate both gas- and liquid-phase parameters for UASB, enable a quantitative and comprehensive evaluation of reactor status. A series of shock tests is conducted to evaluate the response of the monitoring and alert system to organic overloading, hydraulic, temperature, and toxicant shocks. The results show that this system enables an accurate and rapid monitoring and diagnosis of the reactor status, and offers reliable early warnings on the potential risks. As the core of this system, the evaluating indexes are demonstrated to be of high accuracy and sensitivity in process evaluation and good adaptability to the artificial intelligence and automated control apparatus. This online monitoring and alert system presents a valuable effort to promote the automated monitoring and control of anaerobic digestion process, and holds a high promise for application.

[Analysis of the EEM fluorescence spectra of effluent from anaerobic methane reactor during the inhibition process].

The effluents from the anaerobic methane reactor were characterized by the EEM fluorescence spectra. The EEM fluorescence spectra and relative concentration of the main components were acquired by PARAFAC models. Results show that the main components of the effluents from the uninhibited reactor were protein, coenzyme NADH and F420. When the methane-producing reaction was inhibited, the production rate of methane decreased rapidly. Correspondingly, the fluorescence of F420 disappeared and the main components of the reactor were protein and NADH. The fluorescence intensity scores of protein from the diluted sample were remarkably correlated to the protein determination by chemical analysis and the correlation efficient was 0.93. The fluorescence intensity scores of F420 were correlated to the production rate of methane, which implicated that coenzyme F420 could be used to reflect the activity of methane production in a certain bioreactor. This work provides a new method to monitor the operation status of anaerobic methane-producing reactor.

Alleviation of Reverse Salt Leakage across Nanofiber Supported Thin-Film Composite Forward Osmosis Membrane via Heat-Curing in Hot Water.

Electrospun nanofiber with interconnected porous structure has been studied as a promising support layer of polyamide (PA) thin-film composite (TFC) forward osmosis (FO) membrane. However, its rough surface with irregular pores is prone to the formation of a defective PA active layer after interfacial polymerization, which shows high reverse salt leakage in FO desalination. Heat-curing is beneficial for crosslinking and stabilization of the PA layer. In this work, a nanofiber-supported PA TFC membrane was conceived to be cured on a hot water surface with preserved phase interface for potential "defect repair", which could be realized by supplementary interfacial polymerization of residual monomers during heat-curing. The resultant hot-water-curing FO membrane with a more uniform superhydrophilic and highly crosslinked PA layer exhibited much lower reverse salt flux (FO: 0.3 gMH, PRO: 0.8 gMH) than that of oven-curing FO membrane (FO: 2.3 gMH, PRO: 2.2 gMH) and achieved ∼4 times higher separation efficiency. It showed superior stability owing to mitigated reverse salt leakage and osmotic pressure loss, with its water flux decline lower than a quarter that of the oven-curing membrane. This study could provide new insight into the fine-tuning of nanofiber-supported TFC FO membrane for high-quality desalination via a proper selection of heat-curing methods.

Catalytic degradation of ciprofloxacin by a visible-light-assisted peroxymonosulfate activation system: Performance and mechanism.

Peroxymonosulfate (PMS) is extensively used as an oxidant to develop the sulfate radical-based advanced oxidation processes in the decontamination of organic pollutants and various PMS activation methods have been explored. Visible-light-assisted PMS activation to construct a Fenton-like process has shown a great potential for pollution control. In our work, BiVO4 nanosheets were prepared using a hydrothermal process and used to activate PMS under visible light. A rapid degradation of ciprofloxacin (CIP) was achieved by dosing PMS (0.96 g/L), BiVO4 (0.32 g/L) under visible light with a reaction rate constant of 77.72-fold higher than that in the BiVO4/visible light process. The electron spin resonance and free radical quenching experiments indicate that reactive species of •O2-, h+, •OH and SO4•- all worked, where h+, •OH and SO4•- were found as the dominant contributors to the CIP degradation. The spectroscopic analyses further demonstrate that the photoinduced electrons were directly involved in the PMS activation process. The generated •O2- was partially utilized to activate PMS and more •OH was produced because of the chain reactions between SO4•- and H2O/OH-. In this process, PMS acted as an electron acceptor to transfer the photo-induced charges from the conduction band of BiVO4 and PMS was successfully activated to yield the high-powered oxidative species. From the degradation intermediates of CIP detected by a liquid-chromatography-mass spectrometer, the possible degradation pathways were proposed. The substantially decreased toxicity of CIP after the reaction was also observed. This work might provide new insights into the visible-light-assisted PMS activation mechanisms and is useful to construct environmentally-friendly catalytic processes for the efficient degradation of organic pollutants.

Long-term, selective production of caproate in an anaerobic membrane bioreactor.

Fermentative caproate production from wastewater is attractive but is currently limited by the low product purity and concentration. In this work, continuous, selective production of caproate from acetate and ethanol, the common products of wastewater anaerobic fermentation, was achieved in an anaerobic membrane bioreactor (AnMBR). The reactor was continuously operated for over 522 days without need for chemical cleaning. With an ethanol-to-acetate ratio of 3.0, the effluent caproate concentration was 2.62 g/L on average and the caproate ratio in liquid products reached 74%. Further raising the influent ethanol content slightly increased the effluent caproate level but lowered the product selectivity and resulted in microbial inhibition. The Clostridia (the major caproate-producing bacteria) and Methanobacterium species (which consume hydrogen to alleviate microbial inhibition) was significantly enriched in the acclimated sludge. Our results imply a great potential of utilizing AnMBR to recover caproate from the effluent of wastewater acidogenic fermentation process.

Fermentative H2 production in an upflow anaerobic sludge blanket reactor at various pH values.

Fermentative H(2) production in an upflow anaerobic sludge blanket reactor (UASB) at various pH values was investigated in this study. Experimental results show that the H(2) partial pressure in biogas, H(2) production rate and H(2) yield were all pH-dependent, in the range of 0.25-0.52 atm, 42-145 ml-H(2) l(-1) h(-1) and 0.47 to 1.61 mol-H(2)mol-glucose(-1), respectively. The maximum pH for the H(2) partial pressure was observed at pH 7.50. However, the optimum H(2) production rate and H(2) yield were observed at pH 6.50-7.50. In this UASB reactor, acetate, propionate, butyrate, i-butyrate, valerate, caporate and ethanol were present in the effluent as main aqueous products, and the dominant fermentation was butyrate-type at various pHs. The metabolic pathways and thermodynamics of H(2) production were also analyzed. Both H(2) production performance and fermentation pathways in this H(2)-producing UASB reactor were significantly affected by the pH value.

Response of a biohydrogen-producing reactor to the substrate shift from sucrose to lactose.

The response of an upflow acidogenic granule-based reactor to the substrate shift from sucrose to lactose was investigated in this study. Experimental results show that it took 60h for the reactor to completely degrade the new substrate. Hydrogen production performance, in terms of H2 partial pressure, H2 production rate and H2 yield, was affected. Acetate, propionate, butyrate, valerate, caporate, ethanol and propanol were present in the reactor effluent, and their distribution changed significantly after the substrate shift. As the substrate was changed, the caproate- and ethanol-type fermentation was weakened, while the propionate-type fermentation was strengthened. Throughout the experiment, the butyrate-type fermentation played an important role. The H2 yield had a close correlation with both propionate and B/A (butyrate/acetate) in this substrate shift process.

Modeling of acetate-type fermentation of sugar-containing wastewater under acidic pH conditions.

In this study, a kinetic model was developed based on Anaerobic Digestion Model No. 1 to provide insights into the directed production of acetate and methane from sugar-containing wastewater under low pH conditions. The model sufficiently described the dynamics of liquid-phase and gaseous products in an anaerobic membrane bioreactor by comprehensively considering the syntrophic bioconversion steps of sucrose hydrolysis, acidogenesis, acetogenesis and methanogenesis under acidic pH conditions. The modeling results revealed a significant pH-dependency of hydrogenotrophic methanogenesis and ethanol-producing processes that govern the sucrose fermentative pathway through changing the hydrogen yield. The reaction thermodynamics of such acetate-type fermentation were evaluated, and the implications for process optimization by adjusting the hydraulic retention time were discussed. This work sheds light on the acid-stimulated acetate-type fermentation process and may lay a foundation for optimization of resource-oriented processes for treatment of food wastewater.

Synthesis of Fe3O4/Polyacrylonitrile Composite Electrospun Nanofiber Mat for Effective Adsorption of Tetracycline.

Novel Fe3O4/polyacrylonitrile (PAN) composite nanofibers (NFs) were prepared by a simple two-step process, an electrospinning and solvothermal method. Characterization by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) demonstrated formation of a uniform nanoparticles coating (about 20 nm in thickness) on the PAN nanofiber backbone. The coating was constructed by well-crystallized cubic phase Fe3O4 nanoparticles as examined by X-ray diffraction spectroscopy (XRD). The coating doubled the specific surface area of NFs, from 8.4 to 17.8 m2 g(-1), as confirmed by nitrogen sorption isotherm analysis. To evaluate the feasibility of Fe3O4/PAN composite NFs as a potential adsorbent for antibiotic removal, batch adsorption experiments were conducted using tetracycline (TC) as the model antibiotic molecule. The results showed that Fe3O4/PAN composite NFs were effective in removing TC with no impactful loss of Fe in the pH regime of environmental interest (5-8). The adsorption of TC onto Fe3O4/PAN composite NFs better fitted the pseudo-second-order kinetics model, and the maximum adsorption capacity calculated from Langmuir isotherm model was 257.07 mg g(-1) at pH 6. The composite NFs also exhibited good regenerability over repeated adsorption/desorption cycles. Surface complexation between TC and the composite NFs contributed most to the adsorption as elucidated by X-ray photoelectron spectroscopy (XPS). This highly effective and novel adsorbent can be easily modularized and separated, promising its huge potential in drinking and wastewater treatment for antibiotic removal.

Mechanism, kinetics and microbiology of inhibition caused by long-chain fatty acids in anaerobic digestion of algal biomass.

BACKGROUND: Oleaginous microalgae contain a high level of lipids, which can be extracted and converted to biofuel. The lipid-extracted residue can then be further utilized through anaerobic digestion to produce biogas. However, long-chain fatty acids (LCFAs) have been identified as the main inhibitory factor on microbial activity of anaerobic consortium. In this study, the mechanism of LCFA inhibition on anaerobic digestion of whole and lipid-extracted algal biomass was investigated with a range of calcium concentrations against various inoculum to substrate ratios as a means to alleviate the LCFA inhibition. RESULTS: Whole algal biomass of Nannochloropsis salina represents high lipid content algal biomass while lipid-extracted residue represents its low lipid counterpart. The anaerobic digestion experiments were conducted in a series of serum bottles at 35 °C for 20 days. A kinetic model, considering LCFA inhibition on hydrolysis, acidogenesis as well as methanogenesis steps, was developed from the observed phenomenon of inhibition factors as a function of the LCFA concentration and specific biomass content or calcium concentration. The results showed that inoculum to substrate ratio had a stronger effect on biogas production than calcium, and calcium had no effect on biogas production when inoculum concentration was extremely low. The microbial community analysis by high-throughput Illumina Miseq sequencing indicated that diversity of both bacterial and methanogenic communities decreased with elevation of lipid concentration. Hydrolytic bacteria and aceticlastic methanogens dominated bacterial and archaea communities, respectively, in both high and low LCFA concentration digesters. CONCLUSIONS: This study demonstrated that inoculum concentration has a more significant effect on alleviating LCFA inhibition than calcium concentration, while calcium only played a role when inoculum concentration met a threshold level. The model revealed that each functional microbial group was subject to different levels of LCFA inhibition. Although methanogens were the most susceptible microbes to LCFA inhibition, the inhibition factor for hydrolytic bacteria was more highly affected by inoculum concentration. The microbial community analysis indicated that the bacterial community was affected more than the methanogenic community by high LCFAs concentration. Syntrophic acetogens were sensitive to high LCFA concentrations and thus showed a decreased abundance in such an environment. Graphical abstractProposed mechanism of calcium mitigated LCFA inhibition.

The maximum specific hydrogen-producing activity of anaerobic mixed cultures: definition and determination.

Fermentative hydrogen production from wastes has many advantages compared to various chemical methods. Methodology for characterizing the hydrogen-producing activity of anaerobic mixed cultures is essential for monitoring reactor operation in fermentative hydrogen production, however there is lack of such kind of standardized methodologies. In the present study, a new index, i.e., the maximum specific hydrogen-producing activity (SHAm) of anaerobic mixed cultures, was proposed, and consequently a reliable and simple method, named SHAm test, was developed to determine it. Furthermore, the influences of various parameters on the SHAm value determination of anaerobic mixed cultures were evaluated. Additionally, this SHAm assay was tested for different types of substrates and bacterial inocula. Our results demonstrate that this novel SHAm assay was a rapid, accurate and simple methodology for determining the hydrogen-producing activity of anaerobic mixed cultures. Thus, application of this approach is beneficial to establishing a stable anaerobic hydrogen-producing system.