The effect of nitrogen input on N2O emission depends on precipitation in a temperate desert steppe

Nitrous oxide (N2O) is the third most important greenhouse gas, and can damage the atmospheric ozone layer, with associated threats to terrestrial ecosystems. However, to date it is unclear how extreme precipitation and nitrogen (N) input will affect N2O emissions in temperate desert steppe ecosystems. Therefore, we conducted an in-situ in a temperate desert steppe in the northwest of Inner Mongolia, China between 2018 and 2021, in which N inputs were combined with natural extreme precipitation events, with the aim of better understanding the mechanism of any interactive effects on N2O emission. The study result showed that N2O emission in this desert steppe was relatively small and did not show significant seasonal change. The annual N2O emission increased in a non-linear trend with increasing N input, with a much greater effect of N input in a wet year (2019) than in a dry year (2021). This was mainly due to the fact that the boost effect of high N input (on June 17th 2019) on N2O emission was greatly amplified by nearly 17-46 times by an extreme precipitation event on June 24th 2019. In contrast, this greatly promoting effect of high N input on N2O emission was not observed on September 26th 2019 by a similar extreme precipitation event. Further analysis showed that soil NH4+-N content and the abundance of ammonia oxidizing bacteria (amoA (AOB)) were the most critical factors affecting N2O emission. Soil moisture played an important indirect role in regulating N2O emission, mainly by influencing the abundance of amoA (AOB) and de-nitrification functional microorganisms (nosZ gene). In conclusion, the effect of extreme precipitation events on N2O emission was greatly increased by high N input. Furthermore, in this desert steppe, annual N2O flux is co-managed through soil nitrification substrate concentration (NH4+-N), the abundance of soil N transformation functional microorganisms and soil moisture. Overall, it was worth noting that an increase in extreme precipitation coupled with increasing N input may significantly increase future N2O emissions from desert steppes.

Acclimation of electroactive biofilms under different operating conditions: comprehensive analysis from architecture, composition, and metabolic activity

Electroactive biofilms (EABs) have aroused wide concern in waste treatment due to their unique capability of extracellular electron transfer with solid materials. The combined effect of different operating conditions on the formation, microbial architecture, composition, and metabolic activity of EABs is still unknown. In this study, the impact of three different factors (anode electrode, substrate concentration, and resistance) on the acclimation and performance of EABs was investigated. The results showed that the shortest start-up time of 127.3 h and highest power density of 0.84 W m-2 were obtained with carbon brush as electrode, low concentration of substrate (1.0 g L-1), and 1000 Ω external resistance (denoted as N1). The EABs under N1 condition also represented strongest redox capacity, lowest internal resistance, and close arrangement of bacteria. Moreover, the EABs cultured under different conditions both showed similar results, with direct electron transfer (DET) dominated from EABs to anode. Microbial community compositions indicated that EABs under N1 condition have lowest diversity and highest abundance of electroactive bacteria (46.68%). Higher substrate concentration (3.0 g L-1) promoted the proliferation of some other bacteria without electroactivity, which was adverse to EABs. The metabolic analysis showed the difference of genes related to electron transfer (cytochrome C and pili) and biofilm formation (xap) of EABs under different conditions, which further demonstrated the higher electroactivity of EABs under N1. These results provided a comprehensive understanding of the effect of different operating conditions on EABs including biofilm formation and electrochemical activity.

Volatile fatty acid production in anaerobic fermentation of food waste saccharified residue: Effect of substrate concentration

In this study, food waste saccharified residue was used to produce volatile fatty acids (VFAs), and the effects of substrate concentration on VFA production, VFA composition, acidogenic efficiency, microbial community, and carbon transfer were investigated. Interestingly, chain elongation from acetate to n-butyrate played an important role with a substrate concentration of 200 g/L in the acidogenesis process. Results showed that 200 g/L was a suitable substrate concentration for both VFA and n-butyrate production, the highest VFA production, and n-butyrate composition were 280.87 mg COD/g vS and more than 90.00 %, respectively, and VFA/SCOD reached 82.39 %. Microbial analysis showed that Clostridium_Sensu_Stricto_12 promoted n-butyrate production by chain elongation. Carbon transfer analysis indicated that chain elongation made a contribution of 43.93 % to n-butyrate production. Totally 38.47 % of organic matter in food waste saccharified residue was further utilized. This study provides a new way for n-butyrate production with waste recycling and low cost.

Product spectrum analysis and microbial insights of medium-chain fatty acids production from waste biomass during liquor fermentation process: Effects of substrate concentrations and fermentation modes

Substrate toxicity would limit the upgrading of waste biomass to medium-chain fatty acids (MCFAs). In this work, two fermentation modes of electro-fermentation (EF) and traditional fermentation (TF) with different concentration of liquor fermentation waste (20%, 40%, 60%) were used for MCFAs production as well as mechanism investigation. The highest caproate (4.04 g/L) and butyrate (13.96 g/L) concentrations were obtained by EF at 40% substrate concentration. TF experiments showed that the substrate concentration above 40% severely inhibited ethanol oxidation and products formation. Compared with TF mode, the total substrates consumption and product yields under EF mode were significantly increased by 2.6%-43.5% and 54.0%-83.0%, respectively. Microbial analysis indicated that EF effectively alleviated substrate toxicity and enriched chain elongation bacteria, particularly Clostridium_sensu_stricto 12, thereby promoting ethanol oxidation and products formation. Caproiciproducens tolerated high-concentration substrates to ensure normal lactate metabolism. This study provides a new way to produce MCFAs from high concentration wastewater.

Optimum relative frequency and fluctuating substrate selection in reinforcing anammox-mediated anabolic adaptation

Adaptation to substrate fluctuations is a life actuality of microbes in global municipal wastewater treatment plants (WWTPs). Yet there remains a lack of definite information on how influent changes with different alternation frequencies shape the stability of anammox consortia and the metabolic regulations they feedback. According to human rhythmic activity, day-fluctuant fed (every 6 h, alternating between 50 and 100 mg NH₄⁺-N/L) substantially diminished the robustness of nitrogen removal efficiency (NRE; 84.1 ± 7.0%, left-skewed distribution [R² = 0.87]) and shock-resistance ability (>30% effluent variability). Unexpectedly, the anammox ecosystem under week-fluctuant mode (every 6 d) displayed adapted growth (NRE 86.6 ± 3.1%, normal distribution [R² = 0.97]), higher extracellular polymeric substances (EPS) yields, and superior tolerance (juggling the shortest recovery time and highest NRE, tightest protein secondary structure facing long-term load shocks) than steady-state (75 mg NH₄⁺-N/L). 16S sequencing showed that the influent disturbance led to increased levels of bacterial diversity, however, a similar microbiota composition between week-fluctuant and steady systems was detected. Notably, K strategist Candidatus Kuenenia was more sensitive to substrate fluctuations, with the lower relative abundance at day-fluctuant (23.4 ± 5.1%) and week-fluctuant (39.5 ± 4.3%) than at steady-state community (47.5 ± 4.2%). Conversely, Candidatus Jettenia had higher relative abundance at day-fluctuant (i.e., 1.3 ± 0.1%) compared to that at week-fluctuant (0.2 ± 0.04%) and steady-state (0.05 ± 0.03%). Importantly, untargeted metabolomics revealed that week-fluctuant grown anammox microbiota increased protein synthesis and transporter expression while decreasing expression of catabolic pathways (citric acid cycle and bypass) as a strategy for efficient substrate uptake and utilization, which clearly different to day-fluctuant and steady-state survival ways. Overall, we predictively reported an "anabolic adaptation growth state" for the anammox consortia and put forward the associated reinforcement control strategy.

Effects of enzymatic hydrolysis and alkalization pretreatment on biohydrogen production by chlorella photosynthesis

The effects of alkalization pretreatment and enzymolysis on biohydrogen production with Chlorella vulgaris microalgae biomass by photosynthesis were studied, the alkalization pretreatment enzymolysis was to alkalize biomass raw materials before enzymolysis, the biohydrogen production kinetics equation of microalgae biomass was put forward by comparing the biohydrogen process of enzymatic hydrolysis with that of alkaline pretreatment enzymatic hydrolysis. The experimental results show: the optimum initial substrate concentration for biohydrogen production by enzymatic hydrolysis and alkaline pretreatment was 24 g/L, the maximum biohydrogen was 132.1 mL and 294.5 mL, the maximum specific biohydrogen production was 22.0 mL/g and 49.1 mL/g, and the maximum biohydrogen content was 43.9% and 56.8%. The effect of biohydrogen production by enzymatic hydrolysis after alkaline pretreatment of microalgae biomass is obviously better than that by direct enzymatic hydrolysis, which provides scientific reference and development of high efficiency and low cost biohydrogen production technology by photosynthesis of microalgae biomass.

Impaired Sphingolipid Hydrolase Activities in Dementia with Lewy Bodies and Multiple System Atrophy

The synucleinopathies are a group of neurodegenerative diseases characterized by the oligomerization of alpha-synuclein protein in neurons or glial cells. Recent studies provide data that ceramide metabolism impairment may play a role in the pathogenesis of synucleinopathies due to its influence on alpha-synuclein accumulation. The aim of the current study was to assess changes in activities of enzymes involved in ceramide metabolism in patients with different synucleinopathies (Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA)). The study enrolled 163 PD, 44 DLB, and 30 MSA patients as well as 159 controls. Glucocerebrosidase, alpha-galactosidase, acid sphingomyelinase enzyme activities, and concentrations of the corresponding substrates (hexosylsphingosine, globotriaosylsphingosine, lysosphingomyelin) were measured by liquid chromatography tandem-mass spectrometry in blood. Expression levels of GBA, GLA, and SMPD1 genes encoding glucoceresobridase, alpha-galactosidase, and acid sphingomyelinase enzymes, correspondently, were analyzed by real-time PCR with TaqMan assay in CD45 + blood cells. Increased hexosylsphingosine concentration was observed in DLB and MSA patients in comparison to PD and controls (p < 0.001) and it was associated with earlier age at onset (AAO) of DLB (p = 0.0008). SMPD1 expression was decreased in MSA compared to controls (p = 0.015). Acid sphingomyelinase activity was decreased in DLB, MSA patients compared to PD patients (p < 0.0001, p < 0.0001, respectively), and in MSA compared to controls (p < 0.0001). Lower acid sphingomyelinase activity was associated with earlier AAO of PD (p = 0.012). Our data support the role of lysosomal dysfunction in the pathogenesis of synucleinopathies, namely, the pronounced alterations of lysosomal activities involved in ceramide metabolism in patients with MSA and DLB.

Enhancing sensitivity of microbial fuel cell sensors for low concentration biodegradable organic matter detection: Regulation of substrate concentration, anode area and external resistance

The relatively low sensitivity is an important reason for restricting the microbial fuel cell (MFC) sensors' application in low concentration biodegradable organic matter (BOM) detection. The startup parameters, including substrate concentration, anode area and external resistance, were regulated to enhance the sensitivity of MFC sensors. The results demonstrated that both the substrate concentration and anode area were positively correlated with the sensitivity of MFC sensors, and an external resistance of 210 Ω was found to be optimal in terms of sensitivity of MFC sensors. Optimized MFC sensors had lower detection limit (1 mg/L) and higher sensitivity (Slope value of the linear regression curve was 1.02), which effectively overcome the limitation of low concentration BOM detection. The essential reason is that optimized MFC sensors had higher coulombic efficiency, which was beneficial to improve the sensitivity of MFC sensors. The main impact of the substrate concentration and anode area was to regulate the proportion between electrogens and nonelectrogens, biomass and living cells of the anode biofilm. The external resistance mainly affected the morphology structure and the proportion of living cells of the anode. This study demonstrated an effective way to improve the sensitivity of MFC sensors for low concentration BOM detection.

Deciphering the succession dynamics of dominant and rare genera in biofilm development process

Deciphering the succession dynamics of dominant and rare taxa is crucial to understand the stability and ecosystem functions of biofilm communities. However, the essential laws of the succession dynamics based on dominant and rare taxa were still unenlightened. Herein, we investigated the succession dynamics of dominant and rare genera in multi-species biofilms developed in flow cells fed with 10 and 40 mg-TOC/L LB broth. The relative abundance of dominant genera (Enterobacteria and Acinetobacter) decreased remarkably (from 94.63% to 73.22%) in 10 mg-TOC/L LB broth, whereas they kept relatively steady (93.75 ± 4.23%) along with the cultivation time in 40 mg-TOC/L LB broth. Fluorescence in situ hybridization showed that rare genera tended to form clusters at both concentrations, while weaker dispersal of dominant genera caused patchier biofilm structures in 10 mg-TOC/L LB broth compared to that in 40 mg-TOC/L LB broth. Null model analyses further demonstrated that the stochastic ecological drift was more pronounced in the community assembly of biofilms in 10 mg-TOC/L LB broth (73.33%) than those in 40 mg-TOC/L LB broth (60.95%), weakening the competitive superiority of dominant taxa in the patchier biofilms. In addition, the co-occurrence network reflected that the positive interactions among rare genera contributed to exclude dominant genera in 10 mg-TOC/L LB broth, whereas negative interactions only occurred between the dominant Enterobacter and Acinetobacter or rare Comamonas in 40 mg-TOC/L LB broth. This study highlighted the distinctive succession dynamics of dominant and rare genera in biofilms at different substrate concentrations, which would advance our understanding of the biofilm communities in biofilm-related process.

Evaluation of hydrogen yield potential from Chlorella by photo-fermentation under diverse substrate concentration and enzyme loading

Chlorella is widely distributed, can be cultured in waste water and had short growth cycle. The high carbohydrate composition shows great potential for bioenergy output. In this work, concentrated Chlorella solution was adopted as raw material. Reducing sugar concentration, pH, and cumulative bio-hydrogen yield were taken as indexes, the effects of substrate concentration and enzyme (cellulase or neutral protease) load on photo-fermentation bio-hydrogen production process from microalgae biomass were investigated. Results showed that highest cumulative hydrogen yield was obtained at the optimal substrate concentration of 25 g/L, when the load of cellulase and protease are both 15%, the effect is the best which were 16.65 mL, 29.44 mL, and 43.62 mL, respectively. Results fitted well to the Gompertz model, indicating the feasibility of photo-fermentative bio-hydrogen production from concentrated Chlorella.

Effect of substrate concentration on hydrogen production by photo-fermentation in the pilot-scale baffled bioreactor

Effect of substrate concentration on photo-fermentative hydrogen production was studied with a self-designed 4m³ pilot-scale baffled photo-fermentative hydrogen production reactor (BPHR). The relationships between parameters, such as hydrogen production rate (HPR, mol H₂/m³/d), hydrogen concentration, pH value, oxidation-reduction potential, biomass concentration (volatile suspended solids, VSS) and reducing sugar concentration, during the photo-fermentative hydrogen production process were investigated. The highest HPR of 202.64±8.83mol/m³/d was achieved in chamber #3 at a substrate concentration of 20g/L. Hydrogen contents were in the range of 42.19±0.94%-49.71±0.27%. HPR increased when organic loading rate was increased from 3.3 to 20g/L/d, then decreased when organic loading rate was further increased to 25g/L/d. A maximum HPR of 148.65±4.19mol/m³/d was obtained when organic loading rate was maintained at 20g/L/d during continuous bio-hydrogen production.

Impact of substrate concentration on anammox-UBF reactors start-up

Two up-flow blanket filter (UBF) reactors were employed to treat synthetic wastewater with different substrate concentrations and nitrogen load rates (NLR) for 178days. During days 0-60, higher influent NLR of R₂ (0.21-0.58kg·m³·d) slowed down the formation of anammox sludge compared with the lower NLR of R₁ (0.18-0.31kg·m³·d). Difference in sludge color and nitrogen conversion rate indicated greater anammox activity of R₂ than R₁. During days 61-178, R₁ and R₂ achieved the maximum nitrogen removal rates (NRR) of 1.213 and 1.684kg/(m³·d) under the NLRs of 1.924 and 2.502kg/(m³·d), respectively. Furthermore, high-throughput sequencing showed that R₂ (43.5%) had a higher proportion of anammox bacteria than R₁ (37.8%) and less species. These results showed that after going through a higher NLR acclimation process during start-up period, stronger resistant capability against high impact nitrogen load and greater anammox activity were obtained by R₂.

Nitrate removal and bioenergy production in constructed wetland coupled with microbial fuel cell: Establishment of electrochemically active bacteria community on anode

The constructed wetland coupled with microbial fuel cell (CW-MFC) systems operated at different substrate concentration and pH influents were evaluated for bioelectricity generation, contaminant removal and microbial community structure. Performance of CW-MFC was evaluated at organic loading rate of 75.3gCODm^-3d^-1 and pH gradients of (5.18±0.14, 7.31±0.13, and 8.75±0.12) using carbon fiber felt as electrodes. Peak power density was observed at slightly neutral influent condition. Compared with the open circuit CW-MFC, average COD and NO₃-N removal efficiency in CW-MFC increased by 8.3% and 40.2% respectively under slightly neutral pH of influents. However, the removal efficiency and bioenergy production have been inhibited with acidic influents. The relative abundance of beta-Proteobacteria, nitrobacteria and denitrifying bacteria was significantly promoted in closed-circuit CW-MFC. Using of CW-MFC as a biochemical method for nitrate removal and bioelectricity generation under slightly neutral and alkaline influent conditions was a promising technology.

Enhanced degradation of phenol by Sphingomonas sp. GY2B with resistance towards suboptimal environment through adsorption on kaolinite

The effects of clay minerals on microbial degradation of phenol under unfavorable environmental conditions were investigated. Degradation of phenol by Sphingomonas sp. GY2B adsorbed on kaolinite, montmorillonite, and vermiculite were evaluated in comparison with free bacteria under optimal conditions. Kaolinite was found to be the most effective in accelerating degradation rate (reducing the degradation time) as well as improving degradation efficiency (increasing the percentage of phenol degraded), with GY2B/kaolinite complex achieving a degradation efficiency of 96% within 6 h. GY2B adsorbed on kaolinite was more competent than free GY2B in degradation under conditions with high phenol concentrations and at alkaline pH. Kaolinite reduced the time required for degradation by 8-12 h and improved the degradation efficiency by as much as 82% at high phenol concentrations. Meanwhile, the GY2B/kaolinite complex reduced the degradation time by 24 h and improved the degradation efficiency by 46% at pH 12. The improvement was partially due to the buffering effects of kaolinite. It was also shown that Cr(VI) and kaolinite synergistically enhanced the degradation by GY2B, with Cr(VI) and kaolinite both increasing the degradation rate and kaolinite being primarily responsible for enhanced degradation efficiency. These results showed one of the common clay minerals, kaolinite, is able to significantly improve the microbial degradation performance, and protect microorganisms against unfavorable environment. Kaolinite can collaborate with Cr(VI) to further improve the microbial degradation performance. It is implied that clay minerals have great potential to be applied in enhancing the biodegradation of phenol.

Improvement of hydrogen production via ethanol-type fermentation in an anaerobic down-flow structured bed reactor

Although a novel anaerobic down-flow structured bed reactor has shown feasibility and stable performance for a long-term compared to other anaerobic fixed bed systems for continuous hydrogen production, the volumetric rates and yields have so far been too low. In order to improve the performance, an operation strategy was applied by organic loading rate (OLR) variation (12-96 g COD L(-1) d(-1)). Different volumetric hydrogen rates, and yields at the same OLR indicated that the system was mainly driven by the specific organic load (SOL). When SOL was kept between 3.8 and 6.2 g sucrose g(-1) VSS d(-1), the volumetric rates raised from 0.1 to 8.9 L H2 L(-1) d(-1), and the yields were stable around 2.0 mol H2 mol(-1) converted sucrose. Furthermore, hydrogen was produced mainly via ethanol-type fermentation, reaching a total energy conversion rate of 23.40 kJ h(-1) L(-1) based on both hydrogen and ethanol production.

An experimental study on fermentative H₂ production from food waste as affected by pH

Batch dark fermentation experiments were performed on food waste and mixtures of food waste and wastewater activated sludge to evaluate the influence of pH on biological H2 production and compare the process performance with and without inoculum addition. The effect of a preliminary thermal shock treatment of the inoculum was also investigated as a means to harvest the hydrogenogenic biomass. The best performance in terms of both H2 generation potential and process kinetics was observed at pH=6.5 under all experimental conditions (no inoculum, and untreated or thermally treated inoculum added). H2 production from food waste was found to be feasible even without inoculum addition, although thermal pre-treatment of the inoculum notably increased the maximum production and reduced the lag phase duration. The analysis of the fermentation products indicated that the biological hydrogen production could be mainly ascribed to a mixed acetate/butyrate-type fermentation. However, the presence of additional metabolites in the digestate, including propionate and ethanol, also indicated that other metabolic pathways were active during the process, reducing substrate conversion into hydrogen. The plateau in H2 generation was found to mirror the condition at which soluble carbohydrates were depleted. Beyond this condition, homoacetogenesis probably started to play a role in the degradation process.

Kinetics of substrate degradation and electricity generation in anodic denitrification microbial fuel cell (AD-MFC)

Effect of substrate concentration on substrate degradation and electricity generation in anodic denitrification microbial fuel cell (AD-MFC) was investigated over a broad range of substrate concentrations. Substrate degradation rates and power generation could be promoted with increasing substrate concentration in a certain range, but both of them would be inhibited at high substrate concentrations. Maximum denitrification rate of 1.26 ± 0.01 kg NO(-)-N/m(3)d and maximum output voltage of 1016.75 ± 4.74 mV could be achieved when initial NO3(-)-N concentration was 1999.95 ± 2.86 mg/L. Based on Han-Levenspiel model, kinetics of substrate degradation and power generation in the AD-MFC were established. According to the kinetic model, the half-saturation coefficient and the critical inhibitory concentration for nitrate were more than 200 and 4300 mg/L, respectively. The results demonstrated that AD-MFC was capable of treating nitrate-containing wastewater and generating electricity simultaneously, and tolerant to high strength nitrate-containing wastewater.