Microbial network for waste activated sludge cascade utilization in an integrated system of microbial electrolysis and anaerobic fermentation

Characteristics and functional bacteria of an efficient benzocaine-mineralizing bacterial consortium

The extensive use of pharmaceutical and personal care products (PPCPs) has led to widespread residual pollution, which increases the risk of the development of drug resistance in pathogenic microorganisms. Benzocaine is a PPCP that is widely used medical anesthesia and in sunscreen. Microorganisms are essential for the degradation of residual PPCPs. However, no studies have reported the microbial degradation of benzocaine. In this study, through continuous enrichment of the initial consortium HJ1, the highly efficient benzocaine-degrading consortium HJ7 was obtained, HJ7 exhibited a degradation rate that was 1.92 times greater than that of HJ1. Methyl 4-aminobenzoate and 4-aminobenzoic acid were identified as major intermediate products during benzocaine biodegradation by consortium HJ1 or HJ7. Methylobacillus (57.8 % ± 0.9 %) and Pseudomonas (22.1 % ± 0.7 %), which are thought to harbor essential species for benzocaine degradation, were significantly enriched in consortium HJ7. Two benzocaine-degrading strains, Pseudomonas sp. A8 and Microbacterium sp. A741, and one methyl 4-aminobenzoate-degrading strain, Achromobacter sp. A5, were isolated from consortium HJ7, and they synergistically mineralized benzocaine. These findings not only provide new insights into the biotransformation of benzocaine but also provide strain resources for the bioremediation of residual benzocaine in the environment.

Effect of operational parameters on the performance of an anaerobic sequencing batch reactor (AnSBR) treating protein-rich wastewater

Treating protein-rich wastewater using cost-effective and simple-structured single-stage reactors presents several challenges. In this study, we applied an anaerobic sequencing batch reactor (AnSBR) to treat protein-rich wastewater from a slaughterhouse. We focused on identifying the key factors influencing the removal of chemical oxygen demand (COD) and the settling performance of the sludge. The AnSBR achieved a maximum total COD removal of 90%, a protein degradation efficiency exceeding 80%, and a COD to methane conversion efficiency of over 70% at organic loading rates of up to 6.2 g COD L-1 d-1. We found that the variations in both the organic loading rate within the reactor and the hydraulic retention time in the buffer tank had a significant effect on COD removal. The hydraulic retention time in the buffer tank and the reactor, which determined the ammonification efficiencies and the residual carbohydrate concentrations in the reactor liquid, affected the sludge settleability. Furthermore, the genus Clostridium sensu stricto 1, known as protein- and lipids-degraders, was predominant in the reactor. Statistical analysis showed a significant correlation between the core microbiome and ammonification efficiency, highlighting the importance of protein degradation as the governing process in the treatment. Our results will provide valuable insights to optimise the design and operation of AnSBR for efficient treatment of protein-rich wastewater.

Fundamentals and recent progress in bioelectrochemical system-assisted biohythane production

Biohythane, a balanced mixture of 10%-30% v/v of hydrogen and 70%-90% v/v of methane, could be the backbone of an all-purpose future energy supply. Recently, bioelectrochemical systems (BES) became a new sensation among environmental biotechnology processes with the potential to sustainably generate biohythane. Therefore, to unleash its full potential for scaling up, researchers are consistently improving microbial metabolic pathways, novel reactors, and electrode designs. This review presents a detailed analysis of recently discovered fundamental mechanisms and science and engineering intervention of different strategies to improve the biohythane composition and production rate from BES. However, several milestones are to be achieved, for instance, improving electrode kinetics using efficient catalysts, engineered microbial communities, and improved reactor configurations, for commercializing this sustainable technology. Thus, a future perspective section is included to recommend novel research lines, mainly focusing on the microbial communities and the efficient electrocatalysts, to enhance reactor performance.

Biochar enhances the biotransformation of organic micropollutants (OMPs) in an anaerobic membrane bioreactor treating sewage

The removal of emerging organic micropollutants (OMPs) in anaerobic membrane bioreactors (AnMBRs) has garnered considerable attention owing to the rapid development of AnMBR technology and the increased environmental risk caused by OMP discharge. We investigated the removal efficiency of 22 typical OMPs from sewage being treated in an AnMBR, and implemented and evaluated an upgrading strategy by adding biochar. The average removal efficiency of OMPs was only 76.8% due to hydrophilic OMPs containing electron-withdrawing groups (ketoprofen, ibuprofen, diclofenac, and carbamazepine) being poorly removed. Biochar addition (5.0 g/L) promoted the removal of recalcitrant OMPs by 45%, leading to an enhanced removal efficiency of 88.7%. Although biochar has a high adsorption capacity to different OMPs, the biotransformation rather than sorption removal efficiency of 13 of the 22 OMPs was largely enhanced, suggesting that adsorption-biotransformation was the main approach by which biochar enhances the OMP removal. Biotransformation test and microbial analysis revealed that the enrichment of species (Flavobacterium, Massilia, Acinetobacter, and Cloacibacterium) involved in OMP biotransformation on biochar contributed largely to the enhanced biotransformation removal efficiency of OMPs. In this way, the enhanced electron transfer activity and syntrophic metabolism between hydrogenotrophic methanogens and species that oxidize acetate to H₂/CO₂ on biochar jointly contributed to the stable CH₄ production and OMP biotransformation. This study provides a promising strategy to enhance the OMP removal in AnMBRs and improves our understanding of the underlying mechanism of biochar-amended OMP removal in anaerobic treatment systems.

Overlying water fluoride concentrations influence dissolved organic matter composition and migration from pore water in sediment via bacterial mechanisms

Fluoride (F-) is widespread in aquatic environments; however, it is not clear whether the fluctuation of F- concentrations in overlying lake water affects the composition and migration of dissolved organic matter (DOM) from sediment. A case study was presented in Sand Lake, China, and an experiment was conducted to analyze the influence of different F- concentrations in overlying water on DOM characteristics. Diffusion resulted in similarities in DOM components between overlying and pore waters, and bacterial activities and enzyme variation resulted in differences between them. Higher F- concentrations in overlying water resulted in a higher pH of pore water, which favored the enrichment of protein-like substances. Higher F- concentrations caused lower DOM concentrations and lower maximum fluorescence intensities (Fmax) of protein-like components in pore water. The F- concentrations had significantly negative correlations with Shannon indexes (P < 0.05). Thiobacillus influenced the migration of tyrosine-like substances by decreasing the pH of pore water. Trichococcus and Fusibacter altered the Fmax of protein-like, humic-like, and fulvic-like substances. The F- concentrations affected the DOM composition and migration due to the response of functional bacterial communities, which were positively correlated with the relative abundance of Thiobacillus and negatively correlated with the relative abundances of Trichococcus and Fusibacter. The high F- concentrations influenced the biosynthesis and degradation of protein-like substances by shifting the abundances of the relevant enzymes. The results of this study may provide ideas for investigating DOM cycling under the influence of F-, especially in lakes with fluctuations in F- concentrations.

Efficient methane production from waste activated sludge and Fenton-like pretreated rice straw in an integrated bio-electrochemical system

Integrated microbial electrolysis cell-anaerobic digestion (MEC-AD) systems have demonstrated potential advantages for methane production in the presence of small amounts of residual inhibitors. In this study, a series of tests were conducted to analyse the acidification and methanogenesis performance of pretreated rice straw (RS) in anaerobic digestion (AD) and MEC-AD systems after the addition of Fenton-like reagents. The results indicated that the short-chain acids (SCFAs) accumulations reached 2284.64 ± 21.57 mg COD/L with a dosage ratio of 1/4 (g RS/g VSS sludge) in the MEC-AD system and that methane production increased by 63.8% compared with that of an individual AD system. In the interim, the net energy output reached 1.09 × 10³ J/g TCOD, which was 1.23 times higher than that of the AD system. The residual Fe³⁺/Fe²⁺ in the pretreatment reagent was capable of promoting acidification and methanogenesis in sludge and RS fermentation. The RS hydrolysis products could constrain methanogenesis, which can be mitigated by introducing an MEC. The microbiological analyses revealed that the MEC strongly increased the enrichment of hydrogenotrophic methanogens, especially Methanobacterium (61.16%). Meanwhile, the Syntrophomonas and Acetobacterium abundances increased to 2.81% and 2.65%, respectively, which suggested the reinforcement of acetogenesis and methanogenesis. Therefore, the enhanced hydrogenotrophic methanogens might have served as the key for enhancing the efficiency of methanogenesis due to the introduction of an MEC.

Characterization of microbial communities and functions in shale gas wastewaters and sludge: Implications for pretreatment

As hydraulic fracturing (HF) practices keep expanding in China, a comparative understanding of biological characteristics of flowback and produced waters (FPW) and sludge in impoundments for FPW reserve will help propose appropriate treatment strategies. Therefore, in this study, the microbial communities and functions in impoundments that collected wastewaters from dozens of wells were characterized. The results showed that microbial richness and diversity were significantly increased in sludge compared with those in FPW. The vast majority of microorganisms found in FPW and sludge are organic degraders, providing the possibility of using these indigenous microorganisms to biodegrade organic compounds. Our laboratory findings first show that wastewater pretreatment using these microorganisms was effective, and organic compounds in FPW from different shale formations were removed by 35-68% within 72 h in a wide temperature range (8 - 30 ℃). Meanwhile, highly toxic compounds such as phthalate esters (PAEs), polycyclic aromatic hydrocarbons (PAHs), and petroleum hydrocarbons were effectively eliminated in reactors. The main microorganisms, key functional genes, and putative pathways for alkanes, PAHs, and PAEs degradation were also identified.

16S rRNA genes- and metagenome-based confirmation of syntrophic butyrate-oxidizing methanogenesis enriched in high butyrate loading

The understanding and enrichment of consortia formed by syntrophic butyrate-oxidizing bacteria and methanogens in the complex environment are crucial for effectively degrading butyrate and preventing acid inhibition. In this study, the better butyrate-tolerated and highly efficient microbial consortia were domesticated and enriched through adding butyric acid ranging from 0.2 to 4.4 g/(L·d). The volumetric biogas production continuously increased to 1.65 L/(L·d). Microbial community diversity showed that a dramatic shift of bacterial structure occurred at BAL of 1.6 g/(L·d) and the structure presented better stability at high BAL. The syntrophic consortia and the main metabolic pathways were revealed through combination of the 16S rDNA and metagenome sequencing analyses. Syntrophomonas was the major butyrate-oxidizing bacterium and oxidized butyrate mainly through β-oxidaiton. Synergistaceae and Mesotoga acted as the main acetate-oxidizing bacteria. IHT and methanogenesis pathways were strongly enhanced by DMER64 and Methanosarcina as the main H₂ carrier and dominant methanogen, respectively.

Enhancement of methane production from waste activated sludge using hybrid microbial electrolysis cells-anaerobic digestion (MEC-AD) process - A review

Hybrid microbial electrolysis cells-anaerobic digestion (MEC-AD) was proved to increase methane productivity and methane yield of waste activated sludge (WAS) by establishing direct interspecies electron transfer method and enriching functional microorganisms. This review first summarized the pretreatment methods of WAS for MEC-AD and then reviewed the reactor configurations, operation parameters, and the economic benefit of MEC-AD. Furthermore, the enhancement mechanisms of MEC-AD were reviewed based on the analysis of thermodynamics and microbial community. It was found that the decrease of hydrogen partial pressure due to the hydrogenotrophic methanogens enriched in cathodic biofilm and direct interspecies electron transfer between exoelectrogens and anode were the core mechanisms for improving acidogenesis, acetogenesis, and methanogenesis. Finally, the potentially technological issues that need to be addressed to increase energy efficiency in large-scale MEC-AD processes were discussed.

Insights into variations on dissolved organic matter of bauxite residue during soil-formation processes following 2-year column simulation

Bauxite residue, an industrial alkaline solid waste, has a low organic carbon content which hinders plant growth. Dissolved organic matter (DOM) drives many biogeochemical processes including carbon storage and soil formation in soils. Input of exogenous organic materials may provide organic carbon and accelerate soil formation processes in bauxite residue. However, the potential effects of ameliorants on the quantity and quality of DOM in bauxite residue are still poorly understood. Here, the integration of ultraviolet-visible (UV-Vis) spectra, fluorescence spectra, and parallel factor (PARAFAC) analysis were used to investigate the vertical characteristics of DOM in bauxite residue treated by PV (the combined addition of 2% phosphogypsum and 4% vermicompost, w/w) and BS (6% w/w including 4% bagasse and 2% bran) with 2-year column experiments. The content of DOM in untreated residues ranged from 0.064 to 0.096 g/kg, whilst higher contents of DOM were observed in PV (0.13 g/kg) and BS (0.26 g/kg) treatment. Meanwhile, with the increase of residue depth, the aromaticity and hydrophobic components of DOM in residue decreased, which indicated that the degree of humification of the treated residues in the upper layer was higher than that in the lower layer. Compared with BR, BS and PV treatment accumulated the related content of fulvic acid-like substance from 36.14% to 71.33% and 74.86%, respectively. The incorporation of vermicompost and biosolids increased the content of humic-like substances, whilst decreasing the content of protein-like substances in the surface layer, which may be due to the enrichment of the microbial community. During soil formation processes, the application of organic amendments reduced both salinity and alkalinity, enhanced microbial community diversity, and changed the quantity and quality of DOM in bauxite residue. These findings improve our understanding of the dynamics of DOM and response of DOM to soil formation processes in bauxite residue.

Stepwise alkaline treatment coupled with ammonia stripping to enhance short-chain fatty acids production from waste activated sludge

To recover resource from waste activated sludge (WAS) is of great significance. This study proposed a promising way, i.e., stepwise alkaline treatment coupled with ammonia stripping, to remarkably enhance short-chain fatty acids (SCFAs) production from WAS anaerobic digestion. The maximal production of SCFAs, with the value of 323 mg COD/g volatile suspended solid, was obtained with first initial pH = 10 adjustment followed by second initial pH = 10 adjustment on third day coupled with ammonia stripping. Mechanistic studies showed that solubilization of both extracellular polymeric substances and cells could be accelerated by stepwise initial pH = 10 adjustment. However, without ammonia stripping, the activities of either acidogens or methanogens could be inhibited by free ammonia formed under alkaline conditions; positively, anaerobes related to SCFAs production were enriched with ammonia stripping. Moreover, the proposed strategy can simultaneously achieve nitrogen and carbon recovery, providing some solutions for the carbon-neutral operation of wastewater treatment plants.

Bioelectrochemical systems with a cathode of stainless-steel electrode for treatment of refractory wastewater: Influence of electrode material on system performance and microbial community

The large-scale application of the bioelectrochemical system (BES) is limited by the cost-effective electrode materials. In this study, five kinds of stainless-steel materials were used as the cathode of the BES coupled with anaerobic digestion (BES-AD) for the treatment of diluted N, N-dimethylacetamide (DMAC) wastewater. Compared with a carbon-cloth cathode, BES-AD with a stainless-steel cathode had more engineering due to its low cost, although the operating efficiencies were slightly inferior. Stainless-steel mesh with a 100 µm aperture (SSM-100 μm) was the most cost-effective electrode and the implanted BES exhibited better COD removal efficiency, electrochemical performance and biodegradability. Analysis of microbial community revealed the synergetic effect between exoelectrogen and fermentative bacteria had been strengthened in the SSM-100 μm cathode biofilm. Function analysis of the microbial community based on PICRUSt predicted metagenomes revealed that the metabolic pathways of xenobiotics biodegradation and metabolism in the SSM-100 μm cathode were stimulated.

Thermophilic bacteria combined with alkyl polyglucose pretreated mariculture solid wastes using as denitrification carbon source for marine recirculating aquaculture wastewater treatment

In marine recirculating aquaculture systems (RAS), efficient nitrogen removal is challenging due to the high NO₃^--N concentration, low organic matters content, and high salinity. In this study, mariculture solid wastes (MSW) acidogenic liquid pretreated by thermophilic bacteria (TB) combined with alkyl polyglucose (APG) was first used as carbon source for denitrification to remove NO₃^--N. TB + APG pretreatment could accelerate the hydrolysis of MSW, and the highest volatile fatty acids (VFAs) yield (40.3%) was obtained with TB + 0.2 g/g VSS APG pretreatment. MSW acidogenic liquid pretreated by TB + 0.2 g/g VSS APG was a reliable carbon source for denitrification, and the optimum COD/NO₃^--N ratio (C/N) was 8 with no residue of NO_x^--N. VFAs were more effectively utilized by denitrifiers than carbohydrate and protein. The high denitrification potential (P_DN) and denitrification rate (V_DN) indicated the higher denitrification ability at C/N of 8 using MSW acidogenic liquid as carbon source. The outcomes of this work could provide useful information for promoting technological innovation in marine RAS wastewater treatment.

Alkaline thermal pretreatment of waste activated sludge for enhanced hydrogen production in microbial electrolysis cells

Resource utilization of waste activated sludge (WAS) has become a mainstream development direction. Alkaline thermal pretreatment (TPT) was found to greatly promote the bioaccessibility and biodegradability of the sludge. The organic matter including soluble chemical oxygen demand (SCOD), soluble carbohydrate, soluble protein and volatile fatty acids (VFAs) after low temperature (90 °C) pretreatment was 4.8%-65.9% higher than that after high temperature (180 °C) pretreatment. These increasements could be contributed by the alkaline treatment condition and the longer treatment time. The alkaline condition reduced the resistance of cell wall to the temperature. The pretreatment time at 90 °C was two times of that at 180 °C, allowing more organic matter to be released. But the total energy consumption of low temperature pretreatment (2580.7 kJ/L) was 30.5% lower than that of high temperature pretreatment (3711.8 kJ/L). The sludge fermentation liquid (SFL) was then employed as the substrate in microbial electrolysis cells (MECs), and the utilization efficiency of acetic acid was the highest (74.9%-83.2%). The hydrogen yield using low temperature pretreated sludge was 0.44 m³/(m³·d), which was higher than that of using high temperature pretreated sludge (0.31 m³/(m³·d)). These results suggested that alkaline TPT at 90 °C was an effective way to hydrolyze sludge and further enhance hydrogen production in MECs.

Anaerobic fermentation of hydrothermal liquefaction wastewater of dewatered sewage sludge for volatile fatty acids production with focuses on the degradation of organic components and microbial community compositions

Hydrothermal conversion (HTC) is a promising technology for the treatment of dewatered sewage sludge to produce bio-fuels including bio-oil and hydrochar. At the same time, a huge amount of wastewater (HTCWW) was produced. The present study investigated the organic compositions of HTCWW obtained at different HTC temperatures (170-320 °C) and volatile fatty acids (VFAs) yields through anaerobic fermentation. Results showed that the highest VFAs yield of 0.59 gCOD_VFA/gCOD was obtained from HTCWW obtained at 170 °C (HTCWW 170). Higher amount of easily biodegradable organics including proteins and carbohydrates were present in HTCWW 170 °C, which resulted in the highest VFAs yields. With the increase of HTC temperature, recalcitrant organic compounds were produced as revealed by 3D-EEM and GC-MS analysis, which resulted in lower VFAs yields. Furthermore, microbial analysis showed that different compositions in the HTCWW led to the enrichment of different microbial communities, which affected the VFAs yields.

Quorum sensing shaped microbial consortia and enhanced hydrogen recovery from waste activated sludge electro-fermentation on basis of free nitrous acid treatment

In this study, the feasibility of free nitrous acid (FNA) pretreatment coupled with quorum sensing (QS) was investigated to enhance hydrogen recovery from waste activated sludge (WAS) via electro-fermentation (EF). 3-oxo-hexanoyl-homoserine lactone (3OC6-HSL), as the signal molecule, was only added in the first three cycles of sludge inoculation at the phase of microbial electrolysis cells (MECs) startup. Results showed that QS combined FNA (AHL-FMEC) enabled highest hydrogen yield and current (4.3 mg/g VSS and 4.5 mA), while that generated from sole FNA/QS treated WAS (FMEC/AHL-RMEC) were only 3.5/3.0 mg/g VSS and 1.5/1.5 mA, respectively. Fourier transform infrared (FT-IR) spectra illustrated the effective conversion of organics in AHL-FMEC, the utilization efficiencies of proteins and carbohydrates achieved to 75.0% and 79.7%, respectively. Besides, the internal resistance decreased from 34.5 Ω (FMEC) to 22.9 Ω (AHL-RMEC), further to 18.0 Ω, indicating the promoted bioelectrochemical activity of electroactive bacteria (EAB) in AHL-FMEC. Correspondingly, both EAB (21.7%), e.g., Geobacter (9.3%) and Pseudomonas (3.2%) and anaerobic fermentation bacteria (AFB, 28.6%), e.g., Proteiniclasticum (14.2%) and Petrimonas (3.6%) enriched to peaks in AHL-FMEC. Moreover, molecular ecological network (MEN) analysis revealed the underling relationships among AFB, EAB and homo-acetogen in EF system, suggesting the possible cooperative QS has been constructed. The results obtained in this study may provide a new insight for efficient hydrogen recovery from electro-fermentation of WAS.

Denitrifying bio-cathodes developed from constructed wetland sediments exhibit electroactive nitrate reducing biofilms dominated by the genera Azoarcus and Pontibacter

To limit the nitrate contamination of ground and surface water, stimulation of denitrification by electrochemical approach is an innovative way to be explored. Two nitrate reducing bio-cathodes were developed under constant polarization (-0.5 V vs SCE) using sediments and water from a constructed wetland (Rampillon, Seine-et-Marne, France). The bio-cathodes responded to nitrate addition on chronoamperometry through an increase of the reductive current. The denitrification efficiency of the pilots increased by 47% compared to the negative controls without electrodes after polarization. 16S rRNA gene sequencing of the biofilms and sediments evidenced the significant and discriminating presence of the Azoarcus and Pontibacter genera in the biofilms from biocathodes active for nitrate reduction. Our study shows the possibility to promote the development of efficient Azoarcus-dominated biocathodes from freshwater sediment to enhance nitrate removal from surface waters.

Efficiency of integrated electrooxidation and anaerobic digestion of waste activated sludge

BACKGROUND

Most of the organic content of waste activated sludge (WAS) comprises microbial cells hard to degrade, which must be pre-treated for energy recovery by anaerobic digestion (AD). Electrooxidation pre-treatment (EOP) with boron-doped diamond (BDD) electrode have been considered a promising novel technology that increase hydrolysis rate, by the disintegrating cell walls from WAS. Although electrochemical oxidation could efficiently solubilize organic substances of macromolecules, limited reports are available on EOP of WAS for improving AD. In this endeavour, the mathematical optimization study and the energy analysis of the effects of initial total solids concentrations [TS] of WAS and current density (CD) during EOP on the methane production and removal of chemical oxygen demand (COD) and volatile solids (VS) were investigated. Because limited reports are available on EOP of WAS for improving biogas production, it is not well understood; however, it has started to attract interest of scientists and engineers.

RESULTS

In the present work, the energy recovery as biogas and WAS conversion were comprehensively affected by CD and [TS], in an integrated EOP and AD system. When working with WAS at 3% of [TS] pre-treated at current density of 24.1 mA/cm², the highest COD and VS removal were achieved, making it possible to obtain the maximum methane (CH₄) production of 305 N-L/kg VS and a positive energy balance of 1.67 kWh/kg VS. Therefore, the current densities used in BDD electrode are adequate to produce the strong oxidant (hydroxyl radical, ^·OH) on the electrode surface, allow the oxidation of organic compounds that favours the solubilization of particulate matter and VS from WAS.

CONCLUSIONS

The improvement of VS removal and COD solubilization were due to the effects of pre-treatments, which help to break down the microbial cells for faster subsequent degradation; this allows a decomposition reaction that leads to biodegrade more compounds during AD. The balance was positive, suggesting that even without any optimization the energy used as electricity could be recovered from the increased methane production. It is worth noting that this kind of analysis have not been sufficiently studied so far. It is therefore important to understand how operational parameters can influence the pre-treatment and AD performances. The current study highlights that the mathematical optimization and energy analysis can make the whole process more convenient and feasible.

Response of anaerobic digestion of waste activated sludge to residual ferric ions

This study was conducted to investigate the effects of residual ferric ions (FI), released from iron or its oxides for wastewater or waste activated sludge (WAS) treatment, on anaerobic digestion of WAS. Herein it was found that the anaerobic digestion process was greatly affected by FI dosages as well as FI distributions. The responses of performance and microorganism suggested that a low FI (e.g., 0.125 mmol/g volatile suspended solid (VSS)) enhanced methane production by 29.3%, and a medium FI (e.g., 0.3 mmol/g VSS) promoted short chain fatty acids accumulation to reach the maximum of 247 mg chemical oxygen demand /g VSS, conversely, a high FI (e.g., 0.9 mmol/g VSS) led to severe inhibition on acidogenesis and methanogenesis. The findings may provide some new insights for mechanism understanding on anaerobic digestion process influenced by iron or its oxides, as well as the disposal of WAS contained FI.

A network-based approach to deciphering a dynamic microbiome's response to a subtle perturbation

Over the past decades, one main issue that has emerged in ecological and environmental research is how losses in biodiversity influence ecosystem dynamics and functioning, and consequently human society. Although biodiversity is a common indicator of ecosystem functioning, it is difficult to measure biodiversity in microbial communities exposed to subtle or chronic environmental perturbations. Consequently, there is a need for alternative bioindicators to detect, measure, and monitor gradual changes in microbial communities against these slight, chronic, and continuous perturbations. In this study, microbial networks before and after subtle perturbations by adding S. acidaminiphila showed diverse topological niches and 4-node motifs in which microbes with co-occurrence patterns played the central roles in regulating and adjusting the intertwined relationships among microorganisms in response to the subtle environmental changes. This study demonstrates that microbial networks are a good bioindicator for chronic perturbation and should be applied in a variety of ecological investigations.

Alkaline aided thermophiles pretreatment of waste activated sludge to increase short chain fatty acids production: Microbial community evolution by alkaline on hydrolysis and fermentation

Adding alkaline into an anaerobic waste activated sludge (WAS) fermentation with thermophilic bacteria pretreatment could efficiently improve short-chain fatty acids (SCFAs) accumulation to 3550 ± 120 mg COD/L. The acidification rate in combined test was 21.2%, while that was 15.6% and 10.7% in sole thermophilic bacteria pretreatment and control tests respectively. Four distinct groups of microbes could be identified with noticeable shifts using the combined pretreatments, and tremendous effects were analyzed on organic content especially of the soluble proteins and SCFAs concentrations. Particularly, alkaline addition would significantly change the functional microbial structures, including the decrease of Caloramator with the function of thermophilic proteolytic and the increase of Acidobacteria TM7 and Petrimonas sp. The results above suggested that alkaline addition could decrease the hydrolytic substances consume by thermotolerance bacteria and final improve SCFAs accumulation in fermentation process.

Extracellular polymeric substance decomposition linked to hydrogen recovery from waste activated sludge: Role of peracetic acid and free nitrous acid co-pretreatment in a prefermentation-bioelectrolysis cascading system

Free nitrous acid (FNA) has been recently reported to be an effective and eco-friendly inactivator for waste activated sludge (WAS), while the limited decomposition of the extracellular polymeric substance (EPS) matrix hampers resource recovery from WAS. This work employed peracetic acid (PAA) to assist FNA and explored the contribution of co-pretreatment to hydrogen recovery in a prefermentation-bioelectrolysis cascading system. The results showed that co-pretreatment led to approximately 8.8% and 20.4% increases in the exfoliation of particulate proteins and carbohydrates, respectively, from tightly bound EPS (TB-EPS) over that of sole FNA pretreatment. Electron paramagnetic resonance analysis verified that the synergistic effect of FNA, PAA and various generated free radicals was the essential process. This effect further promoted the accumulation of volatile fatty acids (VFAs) after 96 h of prefermentation, and the peak concentration in co-pretreated WAS (AD-FPWAS) was approximately 2.5-fold that in sole FNA-pretreated WAS (AD-FWAS). Subsequently, the cascading utilization of organics in the bioelectrolysis step contributed to efficient hydrogen generation. A total of 10.8 ± 0.3 mg H₂/g VSS was harvested in microbial electrolysis cells (MECs) fed with AD-FPWAS, while 6.2 ± 0.1 mg H₂/g VSS was obtained from AD-FWAS. X-ray photoelectron spectroscopy (XPS) revealed the effective decomposition of the phospholipid bilayer in the cytomembrane and the transformation of macromolecular organics into VFAs and hydrogen in the cascading system. Further microbial community analysis demonstrated that co-pretreatment enhanced the accumulation of functional consortia, including anaerobic fermentative bacteria (AFB, 28.1%), e.g., Macellibacteroides (6.3%) and Sedimentibacter (6.9%), and electrochemically active bacteria (EAB, 57.0%), e.g., Geobacter (39.0%) and Pseudomonas (13.6%), in the prefermentation and MEC steps, respectively. The possible synergetic and competitive relationships among AFB, EAB, homo-acetogens, nitrate-reducing bacteria and methanogens were explored by molecular ecological network analysis. From an environmental and economic perspective, this promising FNA and PAA co-pretreatment approach provides new insight for energy recovery from WAS biorefineries.

Florfenicol restructured the microbial interaction network for wastewater treatment by microbial electrolysis cells

To investigate the influence of antibiotics on microbial interactions in a biofilm community, we set up eight replicate reactors of microbial electrolysis cell (MEC) and applied a broad-spectrum antibiotic florfenical (FLO) as an environmental disturbance. According to the results, exposure to FLO resulted in degradation of reactor performance. The MEC could also rebound back to the comparably stable state at a certain time which exhibited a great resilience ability in response to antibiotic disturbance. The FLO perturbation showed a significant influence on the electroactive biofilms (EABs) with a distinct reformation of the community structure. Network analysis revealed that microbial interactions in the biofilms after full recovery became much closer, with a rapid increase in the positive interactions between the predominant genus Geobacter and other microorganisms as compared to the stage before FLO disturbance. Moreover, the keystone species in the networks after full recovery possessed more connections between Geobacter and potential synergistic species. Our results demonstrated that FLO, with broad-spectrum antibacterial ability, could restructure the EABs with more positive interactions for hydrogen production. This study demonstrated the response mechanisms of the MECs to the antibiotic disturbance, providing a scientific reference for the rapid development of this biotechnology to treat wastewater containing antibiotics.

Combined freezing-thawing pretreatment and microbial electrolysis cell for enhancement of highly concentrated organics degradation from dewatered sludge

The influence of freezing-thawing (F/T) pretreatment on the degradation of highly concentrated organic matters from dewatered sludge (DS) in microbial electrolysis cell (MEC) was investigated in this study. Extended freezing disintegrated the DS matrix and resulted in accelerated hydrolysis rate. The biogas production and stabilization were increased due to the pretreatment by 25–70% of H₂ production rate and 17.8–33.8% of COD reduction rate, respectively. Fourier transform infrared spectroscopy analysis indicated that the pretreatment was unable to alter the bioelectrochemical reactions except for accelerating degradation rate. Excitation and emission matrix (EEM) spectra showed that aromatic protein and soluble microbial products (SMPs)-like materials in DS were increasingly solubilized by the pretreatment and significantly removed during electrogenesis. The F/T-pretreated DS favored the enrichment of exoelectrogens in MEC.

Enrichment of specific microbial communities by optimum applied voltages for enhanced methane production by microbial electrosynthesis in anaerobic digestion

This study investigates the distribution of microbiome in microbial electrosynthesis systems at different applied voltages (0.5, 1.0, and 1.5 V) for methane production. Results revealed that more favorable conditions for methane production were observed with 1.0 V applied voltage. In Venn plots, the bioelectrodes at 1.0 V had higher numbers of unique operational taxonomic units compared to those at 0.5 and 1.5 V. Hierarchical cluster, non-metric multidimensional scaling, and principal component ordinate analyses revealed that the biocathode at 1.0 V clustered separately from the rest of the biofilms mainly because of the quantitative differences in the microbial distribution. Taxonomically, exoelectrogens (Geobacter spp.) dominated the bioanode at 1.0 V, while the syntrophic assemblages of hydrogen-producing bacteria (i.e., Bacteroidetes and Firmicutes) and hydrogen-consuming methanogens (i.e., Methanobacterium sp.) existed in the biocathode. These results suggest that the optimum applied voltage enriched specific microbial communities on the anode and cathode for enhanced methane production.

Improving methane productivity of waste activated sludge by ultrasound and alkali pretreatment in microbial electrolysis cell and anaerobic digestion coupled system

In order to enhance the productivity of methane from the waste activated sludge (WAS), a coupled system of microbial electrolysis cell (MEC) and anaerobic digestion (AD) was proposed. In this study, alkali, ultrasound-alkali, high-temperature coupled microaeration (TM) were applied as pretreatment methods to disintegrate the WAS flocs and break bacterial cell. After ultrasound-alkali pretreatment, the maximum accumulated concentration of VFAs and SCOD increased by 6.4 and 13.8 times compared with the initial concentration, which were 2.8 and 2.6 times of alkali pretreatment, and 2.1 and 2.1 times of TM pretreatment. Then, the pretreated sludge was transferred into MEC-AD coupled reactors and control group of AD reactors. The results showed that, methane production rate was enhanced to 0.15 m³ CH₄/m³ reactor/d in the coupled reactors, which was improved by 3 times compared with control AD (0.05 m³ CH₄/m³ reactor/d). The methane yield of MEC-AD coupled reactors achieved 808 ± 8 mL, which were increased by 97.0% ± 1.85% compared to control AD (410 mL). Using MEC can promote the rate of organics degradation and methane yield. The MEC-AD coupled system realized a good performance on the treatment of WAS and improved the efficiency of methane production.

Contribution of electrodes and electric current to process stability and methane production during the electro-fermentation of food waste

Electro-fermentation is used as an alternative to conventional anaerobic digestion to enhance system stability and methane production from food waste. In particular, the contributions of electrode materials and an electric current are analyzed separately. The results showed that the introduction of electrodes (conductive carbon brushes without applied voltage) rapidly decreased the average concentration of volatile fatty acids (VFAs) from 6617 mg/L to 174 mg/L quickly, accelerated stabilization of digestion system, and improved methane production by 13.5%. When low voltage was supplied, the VFAs concentration declined to 129 mg/L, and methane production increased by 26.3%. Electric current stimulated the growth of hydrogenotrophic methanogens, but acetotrophic Methanosaeta still made up 27.6-61.9% of archaeal community. Geobacter occurred at the cathode with a low abundance. The energy contained in incremental methane was 4.55 times the consumption of electric energy, indicating the enhanced methanogenesis was mainly attributed to the improved digestion environment.

Electro-driven methanogenic microbial community diversity and variability in the electron abundant niche

The underlying dynamics of microbial (bacteria and archaea) communities ecologically responding to an applied potential are critical to achieving the goal of enhancing bioenergy recovery but are not sufficiently understood. We built a MEC-AD mode that increased methane production rate by several times (max. 3.8 times) during the startup period compared to control AD, changed the absence or presence of external voltage to provide the pre-, dur-, and post- samples for microbial analysis. From a time and spatially dependent community analysis of electrode-respiring bacteria and methanogens, the corresponding Geobacter developed under the influence of external voltage, pairing with methanogens in the anodic and cathodic biofilm to generate methane. Additionally, at the cathode, the Alkaliphilus (basophilic bacteria) also correspondingly shifted alongside the change of external voltage. The mcrA sequencing confirmed a change in the dominant microbe from acetoclastic (mostly Methanosarcina mazei LYC) to hydrogenotrophic methanogens (mostly basophilic Methanobacterium alcaliphilum) at the cathode with 0.8 V voltage. Overall, the external voltage not only enriched the functional microbes including electrogens and methanogens but also indirectly shifted the composition of the bacterial and archaeal community via disturbing the pH condition. The predictive functional profiling indicated that the cathodic methanogenesis principally followed the metabolism pathway of the hydrogenotrophic methanogens, suggesting the F420 co-enzyme could be the key mediate for electron transfer. All data suggested that the electric stimulation would change and maintain the micro-environmental conditions to shift the bacterial/archaeal community.

Bioelectrochemical CO2 Reduction to Methane: MES Integration in Biogas Production Processes

Anaerobic digestion (AD) is a widely used technique to treat organic waste and produce biogas. This article presents a practical approach to increase biogas yield of an AD system using a microbial electrosynthesis system (MES). The biocathode in MES reduces carbon dioxide with the supplied electrons and protons (H+) to form methane. We demonstrate that the MES is able to produce biogas with over 90% methane when fed with reject water obtained from a local wastewater treatment plant. The optimised cathode potential was observed in the range of −0.70 V to −0.60 V and optimised feed pH was around 7.0. With autoclaved feed, these conditions allowed methane yields of about 9.05 mmol/L(reactor)-day. A control experiment was then carried out to make a comparison between open circuit and MES methanogenesis. The highest methane yield of about 22.1 mmol/L(reactor)-day was obtained during MES operation that performed 10–15% better than the open circuit mode of operation. We suggest and describe an integrated AD-MES system, by installing MES in the reject water loop, as a novel approach to improve the efficiency and productivity of existing waste/wastewater treatment plants.

Enhanced Degradation of Waste Activated Sludge in Microbial Electrolysis Cell by Ultrasonic Treatment

This study investigates the feasibility of ultrasonic pretreatment for improving treatment efficiency of waste activated sludge (WAS) in microbial electrolysis cell (MEC). Results showed that at applied voltage of 0.5 V, biogas production and cathodic hydrogen recovery enhanced 3.68-fold and 2.56-fold, respectively. Due to the transformation of soluble COD accelerated by the pretreatment, the removal rates of suspended solids and volatile suspended solids were significantly enhanced by 1.38-fold and 1.48-fold, respectively. Various kinds of organics, including VFAs (volatile fatty acids), proteins and carbohydrates, could be utilized in sequence. The primary biodegradable substance in MEC was hydrophilic fraction from sludge organics and the pretreatment effectively resulted in an elevated concentration of this fraction. The 16S rRNA pyrosequencing analysis demonstrated multiple syntrophic interactions between fermentative bacteria, exoelectrogenes, and methanogenic archaea in MEC for WAS.

Reduction of Gibbs free energy and enhancement of Methanosaeta by bicarbonate to promote anaerobic syntrophic butyrate oxidation

Bicarbonate (HCO₃^-) has been extensively researched as a buffer in anaerobic digestion. The effect of HCO₃^- concentration on syntrophic butyrate oxidation process was evaluated by batch culturing of anaerobic activated sludge, and the mechanism was further revealed by the changes of Gibbs free energy (ΔG) and the interspecies transfers of electron and proton. The results showed that butyrate degradation rate was enhanced by 32.07% when the supplement of HCO₃^- increased from 0 to 0.20 mol/L. However, methane production and acetate degradation were strongly inhibited by HCO₃^- more than 0.10 mol/L. More function of HCO₃^- was found as 1) decreasing the ΔG of syntrophic methanogenesis of butyrate while increasing the ΔG of methanogenesis of acetate, 2) enriching M. harundinacea and M. concilii, 3) increasing the diffusion rate of protons between the syntrophic consortia. This work would increase the anaerobic digestion efficiency by enhancing the interaction of the syntrophic consortia.

Enhancing Anaerobic Digestion: The Effect of Carbon Conductive Materials

Anaerobic digestion is a well-known technology which has been extensively studied to improve its performance and yield biogas from substrates. The application of different types of pre-treatments has led to an increase in biogas production but also in global energy demand. However, in recent years the use of carbon conductive materials as supplement for this process has been studied resulting in an interesting way for improving the performance of anaerobic digestion without greatly affecting its energy demand. This review offers an introduction to this interesting approach and covers the different experiences performed on the use of carbon conductive materials proposing it as a feasible alternative for the production of energy from biomass, considering also the integration of anaerobic digestion and thermal valorisation.

Prospects in bioelectrochemical technologies for wastewater treatment

Bioelectrochemical technologies are emerging as innovative solutions for waste treatment, offering flexible platforms for both oxidation and reduction reaction processes. A great variety of applications have been developed by utilizing the energy produced in bioelectrochemical systems, such as direct electric power generation, chemical production or water desalination. This manuscript provides a literature review on the prospects in bioelectrochemical technologies for wastewater treatment, including organic, nutrients and metals removal, production of chemical compounds and desalination. The challenges and perspectives for scale-up were discussed. A technological strategy to improve the process monitoring and control based on big data platforms is also presented. To translate the viability of wastewater treatment based on bioelectrochemical technologies into commercial application, it is necessary to exploit interdisciplinary areas by combining the water/wastewater sector, energy and data analytics technologies.

A comprehensive comparison of five different carbon-based cathode materials in CO2 electromethanogenesis: Long-term performance, cell-electrode contact behaviors and extracellular electron transfer pathways

Each carbon-based material, due to the discrepancy in critical properties, has distinct capability to enrich electroactive microbes able to electrosynthesize methane from CO₂. To optimize electromethanogenesis process, this study physically prepared and examined several carbon-based cathode materials: carbon stick (CS), CS twined by Ti wire (CS-Ti) or covered with carbon fiber (CS-CF), graphite felt (CS-GF) and carbon cloth (CS-CC). CS-GF electrode had constantly stable methane production (75.8 mL/L/d at -0.9 V vs. Ag/AgCl) while CS-CC showed a suppressed performance over time caused by the desposition of inorganic shell. Electrode material properties affected biofilms growth, cell-electrode contact behaviors and electron exchange. Methane formation with CS-CC biocathode was H₂-concnetration dependent; CS-GF cathode possessed high antifouling properties and extensive space, enriching the microorganisms capable of catalyzing electromethanogenesis through more efficient non-H₂ route. This study re-interpreted the application potentials of carbon-based materials in CO₂ electroreduction and electrofuel recovery, providing valuable guidance for materials' selection.

Bioelectrochemically assisted anaerobic digestion system for biogas upgrading and enhanced methane production

The objective of this study was to evaluate the effect of biofilm and external voltage on the performance and microbial community composition of batch-fed, combined anaerobic digestion-bioelectrochemical cell (AD-BEC) systems under different operational conditions. A dextrin/peptone mixture was fed at a range of organic loading rates (0.34 to 1.37g COD/L-d). The hybrid system with both suspended biomass and biofilm without any external potential application achieved a substantially higher initial soluble COD consumption (53.7±2.3% vs. 39.7±3.7) and methane (CH₄) production (331 vs. 225mL) within one day of feeding than the conventional AD system (suspended biomass only). Compared to the conventional AD system, the hybrid systems had higher resilience to shock organic loadings. A range of external potential (0.5 to 2.0V vs. Ag/AgCl) was applied to AD-BEC reactors, developed with two different start-up procedures. A potential of 2.0V resulted in water electrolysis leading to a higher CH₄ production rate (105 vs. 84mL/L-d) and biogas CH₄ content (88.5±1.4 vs. 64.5±1.9%) in the AD-BEC reactor (closed vs. open circuit condition, respectively). Application of external potential enriched putative exoelectrogens at the anode biofilm and hydrogenotrophic methanogens at the cathode biofilm, which may have contributed to the observed enhanced CH₄ production in the AD-BEC system. A phylotype related to Methanobacterium formicicum, a hydrogenotrophic methanogen, dominated the archaeal community in the AD-BEC cathode biofilm.

Changes in the microbial consortium during dark hydrogen fermentation in a bioelectrochemical system increases methane production during a two-stage process

BACKGROUND

Bioelectrochemical systems (BESs) are an innovative technology developed to influence conventional anaerobic digestion. We examined the feasibility of applying a BES to dark hydrogen fermentation and its effects on a two-stage fermentation process comprising hydrogen and methane production. The BES used low-cost, low-reactivity carbon sheets as the cathode and anode, and the cathodic potential was controlled at - 1.0 V (vs. Ag/AgCl) with a potentiostat. The operation used 10 g/L glucose as the major carbon source.

RESULTS

The electric current density was low throughout (0.30-0.88 A/m² per electrode corresponding to 0.5-1.5 mM/day of hydrogen production) and water electrolysis was prevented. At a hydraulic retention time of 2 days with a substrate pH of 6.5, the BES decreased gas production (hydrogen and carbon dioxide contents: 52.1 and 47.1%, respectively), compared to the non-bioelectrochemical system (NBES), although they had similar gas compositions. In addition, a methane fermenter (MF) was applied after the BES, which increased gas production (methane and carbon dioxide contents: 85.1 and 14.9%, respectively) compared to the case when the MF was applied after the NBES. Meta 16S rRNA sequencing revealed that the BES accelerated the growth of Ruminococcus sp. and Veillonellaceae sp. and decreased Clostridium sp. and Thermoanaerobacterium sp., resulting in increased propionate and ethanol generation and decreased butyrate generation; however, unknowingly, acetate generation was increased in the BES.

CONCLUSIONS

The altered redox potential in the BES likely transformed the structure of the microbial consortium and metabolic pattern to increase methane production and decrease carbon dioxide production in the two-stage process. This study showed the utility of the BES to act on the microbial consortium, resulting in improved gas production from carbohydrate compounds.

Enhanced carbon-sulfur cycling in the sediments of Arabian Sea oxygen minimum zone center

Biogeochemistry of oxygen minimum zone (OMZ) sediments, which are characterized by high input of labile organic matter, have crucial bearings on the benthic biota, gas and metal fluxes across the sediment-water interface, and carbon-sulfur cycling. Here we couple pore-fluid chemistry and comprehensive microbial diversity data to reveal the sedimentary carbon-sulfur cycle across a water-depth transect covering the entire thickness of eastern Arabian Sea OMZ, off the west coast of India. Geochemical data show remarkable increase in average total organic carbon content and aerial sulfate reduction rate (JSO42-) in the sediments of the OMZ center coupled with shallowing of sulfate methane transition zone and hydrogen sulfide and ammonium build-up. Total bacterial diversity, including those of complex organic matter degraders, fermentative and exoelectrogenic bacteria, and sulfate-reducers (that utilize only simple carbon compounds) were also found to be highest in the same region. The above findings indicate that higher organic carbon sequestration from the water-columns (apparently due to lower benthic consumption, biodegradation and biotransformation) and greater bioavailability of simple organic carbon compounds (apparently produced by fermetative microflora of the sediments) are instrumental in intensifying the carbon-sulfur cycle in the sediments of the OMZ center.

mcrA sequencing reveals the role of basophilic methanogens in a cathodic methanogenic community

Cathodic methanogenesis is a promising method for accelerating and stabilising bioenergy recovery in anaerobic processes. The change in composition of microbial (especially methanogenic) communities in response to an applied potential-and especially the associated pH gradient-is critical for achieving this goal, but is not well understood in cathodic biofilms. We found here that the pH-polarised region in the 2 mm surrounding the cathode ranged from 6.9 to 10.1, as determined using a pH microsensor; this substantially affected methane production rate as well as microbial community structure. Miseq sequencing data of a highly conserved region of the mcrA gene revealed a dramatic variation in alpha diversity of methanogens concentrated in electrode biofilms under the applied potential, and confirmed that the dominant microbes at the cathode were hydrogenotrophic methanogens (mostly basophilic Methanobacterium alcaliphilum). These results indicate that regional pH variation in the microenvironment surrounding the electrode is an ecological niche enriched with Methanobacterium.

Potassium ferrate addition as an alternative pre-treatment to enhance short-chain fatty acids production from waste activated sludge

A potentially practical technology based on ferrate (VI), i.e. potassium ferrate (PF), pretreatment integrated into waste activated sludge (WAS) anaerobic fermentation has been presented to greatly enhance short-chain fatty acids (SCFAs) production with a shortened fermentation time. The maximum production of SCFAs, 343mg chemical oxygen demand/g volatile suspended solid with acetic acid proportion of 48.2%, was obtained with PF dosage of 56mg Fe(VI)/g total suspended solid within 5days, which was increased to 5.72times compared to that of control. The mechanism study showed that PF accelerated the release rate of both intracellular and extracellular constituents. And the activities of key hydrolytic enzymes were much improved with PF addition. Moreover, PF positively enriched the abundance of microorganisms responsible for WAS hydrolysis and SCFAs production, especially acetic acid-forming characteristic genera such as Petrimonas, Fusibacter and Acetoanaerobium. Besides, the incubation time of acidogenesis and methanogenesis were separated by PF.

A review on the bioenergetics of anaerobic microbial metabolism close to the thermodynamic limits and its implications for digestion applications

The exploration of the energetics of anaerobic digestion systems can reveal how microorganisms cooperate efficiently for cell growth and methane production, especially under low-substrate conditions. The establishment of a thermodynamically interdependent partnership, called anaerobic syntrophy, allows unfavorable reactions to proceed. Interspecies electron transfer and the concentrations of electron carriers are crucial for maintaining this mutualistic activity. This critical review summarizes the functional microorganisms and syntroph partners, particularly in the metabolic pathways and energy conservation of syntrophs. The kinetics and thermodynamics of propionate degradation to methane, reversibility of the acetate oxidation process, and estimation of microbial growth are summarized. The various routes of interspecies electron transfer, reverse electron transfer, and Poly-β-hydroxyalkanoate formation in the syntrophic community are also reviewed. Finally, promising and critical directions of future research are proposed. Fundamental insight in the activities and interactions involved in AD systems could serve as a guidance for engineered systems optimization and upgrade.

PCR-DGGE Analysis on Microbial Community Structure of Rural Household Biogas Digesters in Qinghai Plateau

To investigate contribution of environmental factor(s) to microbial community structure(s) involved in rural household biogas fermentation at Qinghai Plateau, we collected slurry samples from 15 digesters, with low-temperature working conditions (11.1-15.7 °C) and evenly distributed at three counties (Datong, Huangyuan, and Ledu) with cold plateau climate, to perform polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and further sequencing. The bacterial communities in the total 15 digesters were classified into 38 genera with Mangroviflexus (12.1%) as the first dominant, and the archaeal communities into ten genera with Methanogenium (38.5%) as the most dominant. For each county, the digesters with higher biogas production, designated as HP digesters, exclusively had 1.6-3.1 °C higher fermentation temperature and the unique bacterial structure composition related, i.e., unclassified Clostridiales for all the HP digesters and unclassified Marinilabiliaceae and Proteiniclasticum for Ledu HP digesters. Regarding archaeal structure composition, Methanogenium exhibited significantly higher abundances at all the HP digesters and Thermogymnomonas was the unique species only identified at Ledu HP digesters with higher-temperature conditions. Redundancy analysis also confirmed the most important contribution of temperature to the microbial community structures investigated. This report emphasized the correlation between temperature and specific microbial community structure(s) that would benefit biogas production of rural household digesters at Qinghai Plateau.

Microbial network of the carbonate precipitation process induced by microbial consortia and the potential application to crack healing in concrete

Current studies have employed various pure-cultures for improving concrete durability based on microbially induced carbonate precipitation (MICP). However, there have been very few reports concerned with microbial consortia, which could perform more complex tasks and be more robust in their resistance to environmental fluctuations. In this study, we constructed three microbial consortia that are capable of MICP under aerobic (AE), anaerobic (AN) and facultative anaerobic (FA) conditions. The results showed that AE consortia showed more positive effects on inorganic carbon conversion than AN and FA consortia. Pyrosequencing analysis showed that clear distinctions appeared in the community structure between different microbial consortia systems. Further investigation on microbial community networks revealed that the species in the three microbial consortia built thorough energetic and metabolic interaction networks regarding MICP, nitrate-reduction, bacterial endospores and fermentation communities. Crack-healing experiments showed that the selected cracks of the three consortia-based concrete specimens were almost completely healed in 28 days, which was consistent with the studies using pure cultures. Although the economic advantage might not be clear yet, this study highlights the potential implementation of microbial consortia on crack healing in concrete.

Microbial community shift in a suspended stuffing biological reactor with pre-attached aerobic denitrifier

Bioaugmentation is substantially determined by pre-attached communities in biological stuffing systems. However, the inevitable changes of microbial community shift occurred between pre-attached microorganisms on stuffing material and other existing communities in wastewater. Targeting at nitrogen removal in aerobic denitrification reactors, biological augmentation was built by polyurethane supporting material and aerobic denitrification bacteria of Pseudomonas stutzeri strains were primarily colonized. The total nitrogen removal reached a high efficiency of 77 ± 6%, resulting from a relative high nitrate removal (90%) and a low nitrite production of 24 mg l^-1. The nitrate removal was kept 10% higher using preattached strains than that using wastewater communities. During the bioaugmentation process, abundant bacteria related to nitrogen removal were evolutively enriched to compete with preattached Pseudomonas stutzeri. The most abundant bacteria growing up in the biofilm belonged to various Classes of Proteobacteria Phylum. A noticeable nitrite production with a relative low TN removal efficiency occurred when Brucella sp. and Brevundimonas sp. were simultaneously enriched in place of Pseudomonas, because Brevundimonas also accumulated nitrite during denitrification under an aerobic condition. The results indicated that pre-attached denitrifiers in comprehensive communities on stuffing material can be established for the efficient nitrogen and COD removal in aerobic denitrification reactors.

Impact of Ferrous Iron on Microbial Community of the Biofilm in Microbial Fuel Cells

The performance of microbial electrochemical cells depends upon microbial community structure and metabolic activity of the electrode biofilms. Iron as a signal affects biofilm development and enrichment of exoelectrogenic bacteria. In this study, the effect of ferrous iron on microbial communities of the electrode biofilms in microbial fuel cells (MFCs) was investigated. Voltage production showed that ferrous iron of 100 μM facilitated MFC start-up compared to 150 μM, 200 μM, and without supplement of ferrous iron. However, higher concentration of ferrous iron had an inhibitive influence on current generation after 30 days of operation. Illumina Hiseq sequencing of 16S rRNA gene amplicons indicated that ferrous iron substantially changed microbial community structures of both anode and cathode biofilms. Principal component analysis showed that the response of microbial communities of the anode biofilms to higher concentration of ferrous iron was more sensitive. The majority of predominant populations of the anode biofilms in MFCs belonged to Geobacter, which was different from the populations of the cathode biofilms. An obvious shift of community structures of the cathode biofilms occurred after ferrous iron addition. This study implied that ferrous iron influenced the power output and microbial community of MFCs.

Nitrogen removal and microbial community shift in an aerobic denitrification reactor bioaugmented with a Pseudomonas strain for coal-based ethylene glycol industry wastewater treatment

An aerobic denitrification system, initially bioaugmented with Pseudomonas strain T13, was established to treat coal-based ethylene glycol industry wastewater, which contained 3219 ± 86 mg/L total nitrogen (TN) and 1978 ± 14 mg/L NO₃^--N. In the current study, a stable denitrification efficiency of 53.7 ± 4.7% and nitrite removal efficiency of 40.1 ± 2.7% were achieved at different diluted influent concentrations. Toxicity evaluation showed that a lower toxicity of effluent was achieved when industry wastewater was treated by stuffing biofilm communities compared to suspended communities. Relatively high TN removal (~50%) and chemical oxygen demand removal percentages (>65%) were obtained when the influent concentration was controlled at below 50% of the raw industry wastewater. However, a further increased concentration led to a 20-30% decrease in nitrate and nitrite removal. Microbial network evaluation showed that a reduction in Pseudomonas abundance was induced during the succession of the microbial community. The napA gene analysis indicated that the decrease in nitrate and nitrite removal happened when abundance of Pseudomonas was reduced to less than 10% of the overall stuffing biofilm communities. Meanwhile, other denitrifying bacteria, such as Paracoccus, Brevundimonas, and Brucella, were subsequently enriched through symbiosis in the whole microbial network.

Characterization of biocarbon-source recovery and microbial community shifts from waste activated sludge by conditioning with cornstover: Assessment of cellulosic compositions

Most studies on the production of volatile fatty acids (VFAs) from waste activated sludge (WAS) digestion have focused on operating conditions, pretreatments and characteristic adjustments. Conditioning by extra carbon sources (ECS), normally added in a solid form, has been reported to be an efficient approach. However, this has caused considerable waste of monomeric sugars in the hydrolysate. In this study, the effects of two added forms (pretreated straw (S) and hydrolyzed liquid (L)) of cornstover (CS) on WAS acidification were investigated. To obtain different cellulosic compositions of CS, low-thermal or autoclaved assisted alkaline (TA or AA) pretreatments were conducted. The results showed that AA-L test achieved the highest VFAs value (653 mg COD/g VSS), followed by AA-S (613 mg COD/g VSS). These values were 12% and 28% higher, respectively, than that obtained in the TA-L and TA-S tests. Meanwhile, higher percentages of acetic acid were observed after AA pretreatment (~62% versus ~53% in TA). The added forms of CS played an important role in structuring the innate microbial community in the WAS, as shown by high-throughput sequencing and canonical correspondence analysis. The findings obtained in this work may provide a scientific basis for the potential implementation of co-digesting WAS with ECS simultaneously obtaining energy and high value-added products.