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High-purity propionate production from glycerol in mixed culture fermentation (MCF) induced by high ammonium concentration was investigated. Fed-batch experiments revealed that higher ammonium concentration (>2.9g/L) had simultaneous negative effects on acetate and propionate degradation. Propionate production and yield was up to 22.6g/L and 0.45g COD/g COD glycerol, respectively, with a purity of 96%. Sequential batch experiments demonstrated that the yields of propionate were 0.3±0.05, 0.32±0.01, and 0.34±0.03g COD/g COD at a glycerol concentration of 2.78, 4.38, and 5.56g/L, respectively, and the purity of propionate was 91-100%. Microbial community analysis showed that the phylum Firmicutes dominated the bacterial community at different glycerol concentrations. However, the Methanosaeta population decreased from 46% to 6% when glycerol concentration increased from 2.78 to 5.56g/L, resulting in lower acetate degradation rate. Thus, the present study might provide an alternative option for the production of propionate from glycerol via MCF., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Abstract Syngas (CO/H 2) fermentation provides an alternative method for organics utilization. The hollow-fiber membrane biofilm reactor (HfMBR) offers a potential way to use CO and H 2 effectively. However, studies on syngas utilization by mixed culture fermentation (MCF) in HfMBR were seldom reported. This study is the first to demonstrate and compare the in-situ production of volatile fatty acids via syngas by mesophilic and thermophilic MCF, in which CO and H 2 utilization exceeded 95% and even reached 100%. Acetate (4.22 g/L), butyrate (1.35 g/L), caproate (0.88 g/L), and caprylate (0.52 g/L) were detected at 35 °C, whereas acetate was the main metabolite at 55 °C. The proportion of acetate ranged from 47.5% to 62.7% at 35 °C and exceeded 90% at 55 °C in the batch mode. Notably, the acetate concentration and the production rate could reach 24.6 g/L and 16.4 g/(L.d), respectively, at pH 6.5 in the continuous mode at 55 °C. Thus, thermophilic conditions are preferable for high-purity and high-concentration acetate production from syngas. As revealed by Illumina high-throughput sequencing, Clostridium (41.6%) and Thermoanaerobacterium (92.8%) were the dominant bacteria under mesophilic and thermophilic conditions, respectively. This study demonstrates a potential technique for syngas (CO/H 2) utilization and biochemicals production by MCF in HfMBR. Graphical abstract Image 1 Highlights • Syngas (H 2 /CO) fermentation was conducted in hollow-fiber membrane biofilm reactors. • The main metabolites contain acetate, butyrate, caproate and caprylate at 35 °C. • Acetate and minimal butyrate (less than 1 g/L) were detected at 55 °C. • Clostridium (41.6%) was the dominant bacterium at 35 °C. • The dominant bacterium was Thermoanaerobacterium (92.8%) at 55 °C. [ABSTRACT FROM AUTHOR]

This study examined the decolorization ability of Caldicellulosiruptor saccharolyticus isolated from a thermal spring at the optimum growth temperature of 70 °C. This study demonstrated, for the first time, C. saccharolyticus could effectively degrade methyl orange (MO) to 4-aminobenzenesulfonic acid (4-ABA) and N′ , N -dimethyl- p -phenylenediamine (DPD) with dissolved hydrogen (DH) as the reducing equivalent. The decolorization reaction was catalyzed by Ni–Fe hydrogenase and the reaction rate was correlated positively to the concentration of DH. At high concentrations of DH the decolorization rates were 6.65 and 7.08 mg/L/h, which decreased to 2.16 and 0.88 mg/L/h after purging with N 2 . Furthermore, the addition of MO decreased the yield of ethanol via glucose fermentation owing to the limited reducing equivalents. We suggest the competition for hydrogen between the reduction of azo dyes and hydrogenotrophic methanogenesis processes might exist in mixed culture fermentation. [ABSTRACT FROM AUTHOR]

Syngas fermentation is a promising route for resource recovery. Acetate is an important industrial chemical product and also an attractive precursor for liquid biofuels production. This study demonstrated high fraction acetate production from syngas (H 2 and CO 2) in a hollow-fiber membrane biofilm reactor, in which the hydrogen utilizing efficiency reached 100 % during the operational period. The maximum concentration of acetate in batch mode was 12.5 g/L, while the acetate concentration in continuous mode with a hydraulic retention time of 9 days was 3.6 ± 0.1 g/L. Since butyrate concentration was rather low and below 0.1 g/L, the acetate fraction was higher than 99 % in both batch and continuous modes. Microbial community analysis showed that the biofilm was dominated by Clostridium spp., such as Clostridium ljungdahlii and Clostridium drakei, the percentage of which was 70.5 %. This study demonstrates a potential technology for the in situ utilization of syngas and valuable chemical production. [ABSTRACT FROM AUTHOR]

Abstract: The ratio of H2/acetate in glucose fermentation shall be equal or less than 2. However, the ratio over 2 is found in the literature. Two possible reasons were proposed in this study: acetate oxidation or biomass growth via acetyl-CoA. In order to find out the right reason, glucose fermentation by Caldicellulosiruptor saccharolyticus was investigated. Under different glucose concentrations (1.0 g/L, 2.0 g/L, 3.5 g/L and 7.5 g/L), the Optical Density (OD) reached a maximum value of 0.35, 0.48, 0.53 and 0.55, respectively. It was found that the ratios of H2/acetate under different glucose concentrations were all greater than 2. When CH3-13COOH was added to the system, 60% of CH3-13COOH was converted to isotope ethanol. About the same amount of 13CO2 (0.01 mmol) was detected in both the control and isotopic experiments, illustrating acetate oxidation didn't occur in this study. The corrected ratio of H2/acetate after the compensation from biomass growth was around 2, demonstrating the biomass growth from acetyl-CoA was the right reason for the abnormal high ratio. [Copyright &y& Elsevier]

Graphical abstract Highlights • 95% of phosphorus from wastewater was concentrated into Fe-sludge at 25 mg/L FeCl 3. • Phosphorus release and recovery from alkaline Fe-sludge fermentation was studied. • 69.35% of phosphorus was released at pH 11 with 20.57 mg/L. • 90% of the released phosphorus in the fermented liquid can be precipitated as MAP. Abstract Phosphorus release and recovery from Fe-based chemically enhanced primary sedimentation (CEPS) sludge via alkaline fermentation was investigated. The coagulation results showed that 78% of organic matter and 95% of phosphorus were concentrated from sewage into sludge with the optimum dosages of 25 mg/L FeCl 3. The batch fermentation results revealed that 69.35% of the phosphorus in the Fe-sludge can be released and the maximum phosphorus concentration was 20.57 mg/L at pH 11. In the recovery stage, 90% of the P released in the fermented sludge supernatant was precipitated at a 2:1 ratio of magnesium to phosphorus and pH 11. The result of X-ray diffraction indicated that magnesium ammonium phosphate (MAP) was the major component of the precipitated solids. Thus, the present study provides an alternative option for phosphorus release and recovery as MAP from CEPS sludge via alkaline fermentation. [ABSTRACT FROM AUTHOR]

• VFAs and P production via Al-WAS fermentation with stepwise pH increase was studied. • The maximum yield of VFAs was 358.03 mg-COD/g VS at pH 11. • VFAs yield was enhanced from Al-WAS with step-wise pH operation. • P was also released and the maximum concentration was 186 mg/L at pH 11. • IP release at pH 11 fermentation was originated from NAIP dissolution. In this study, the performance of volatile fatty acids (VFAs) production and phosphorus (P) release during Al-waste activated sludge (Al-WAS) anaerobic fermentation with stepwise pH increases from 8 to 11 was investigated via a long-term acclimation strategy. As results, VFAs concentration increased with increasing pH and the maximum yield of VFAs was 358.03 mg-COD/g VS at pH 11, which was much higher than at pH 8. P was also released during the process, and the P concentration increased gradually from 26 mg/L at pH 8 to 186 mg/L at pH 11, accounting for 35.8% of the total P in the Al-WAS. The P distribution results demonstrated the dissolution of non-apatite inorganic phosphorus (NAIP) and organic P in the sludge contributed to release P into the liquid at pH 8, 9, and 10, while inorganic P release originated from the dissolution of NAIP at pH 11. [ABSTRACT FROM AUTHOR]

• Effects of different pH control treatments on WAS fermentation were studied. • The purity of VFAs were enhanced by initial pH 10 fermentation (RIA). • P removal efficiency and fermented sludge dewaterability was also improved in RIA. • VFAs via RIA was a better way to applied as carbon resource into the WWTP. Volatile fatty acids (VFAs) from waste activated sludge (WAS) via alkaline fermentation have been shown to provide an effective alternative carbon source for biological nutrient removal in wastewater treatment plants (WWTPs) that promotes the subsequent release of phosphorus (P) and refractory dissolved organic matter. The dewatering ability of fermented sludge is known to decrease during alkaline fermentation. Here, a novel strategy of initiating fermentation at a pH of 10 was developed to improve VFA purity, P removal efficiency, and fermented sludge dewaterability during WAS fermentation. Although VFAs concentration was lower (1.69 ± 0.09 g COD/L) when the pH was only initially adjusted to pH 10 (R IA) relative to when the pH was maintained at 10 on a daily basis (R DC), the purity of VFAs in the fermented liquid was improved (58.48%). Furthermore, the release of total phosphorous (TP) in R IA was 5.90 times lower than that in R DC (139.37 mg/L). The normalized capillary suction time and specific resistance to filtration in R IA decreased to 42.23% and 40.70%, respectively, suggesting that the dewaterability of fermented sludge also improved. The amount of alkali needed was 17.44 kg for each ton of total solid (TS) in R IA , which was 5.49 times lower than that in R DC. Thus, approximately 45.44 USD was saved in operational costs for each ton of TS processed in R IA. These results indicated that VFAs production via initial pH 10 fermentation was a robust and cost-efficient way for providing carbon resources in WWTPs. [ABSTRACT FROM AUTHOR]

Magnesium (120 mmol/L) was dosed to investigate the effects of different methods and times on performance of waste activated sludge (WAS) alkaline fermentation. The investigation revealed that maximum soluble chemical oxygen demand (SCOD) was achieved without magnesium addition, indicating magnesium addition, regardless of dosing method or time, could constrain the sludge hydrolysis process. Fermented sludge dewaterability was improved with magnesium addition, as based on results of capillary suction time (CST) and bound water. The optimal magnesium dosage was reached following WAS alkaline fermentation, in which little volatile fatty acids (VFAs) reduction (67 mg COD/L), higher PO 4 3--P removal efficiency (95.41%), and lower alkali consumption were achieved. Further, 682.19 mg chemical oxygen demand (COD)/L of the released protein was precipitated, suggesting that soluble protein was effectively recovered from sludge with magnesium addition after fermentation. In conclusion, dosing magnesium after WAS alkaline fermentation has multiple merits and warrants further study. Image 10020 • Effects of different Mg dosing strategies on WAS alkaline fermentation were studied. • Mg addition was able to improve alkaline fermented sludge dewaterability. • Dosing magnesium after WAS alkaline fermentation has plurality merits. • Little VFAs reduction and higher P removal efficiency were achieved. • 37.33% of release protein was recovered and lower alkali was consumed. [ABSTRACT FROM AUTHOR]

• Multiple uses of MgCl 2 addition in WAS alkaline fermentation was investigated. • Higher MgCl 2 concentration inhibited acidogenesis, while it improved the VFAs purity. • Phosphorus removal efficiency was higher than 80% with MgCl 2 addition. • Sludge dewaterability was enhanced with increased MgCl 2 addition. Multiple uses of magnesium chloride during waste activated sludge (WAS) alkaline fermentation was investigated. The results revealed that a higher MgCl 2 concentration inhibited acidogenesis, while the purity of volatile fatty acids (VFAs) improved and the maximum percentage of VFAs accounted for 52.92% (w/w) of soluble chemical oxygen demand (SCOD) at 120 mmol/L Mg2+. A phosphate removal efficiency of 81.22% was obtained at 15 mmol/L MgCl 2 concentration, while only a 14.77% increase was observed when further MgCl 2 was added (120 mmol/L MgCl 2). Capillary suction time (CST) values decreased sharply from 4410.20 s to 207.30 s with the increase of MgCl 2. A similar trend was observed in bound water and the minimum value was 85.56 ± 0.06%. The distribution of extracellular polymeric substances (EPS) and rheological profiles of the fermented sludge were also analyzed and the results confirmed that a high MgCl 2 concentration had a positive effect on sludge dewatering. [ABSTRACT FROM AUTHOR]

This study examined the microbial reduction of hexavalent chromium [Cr(VI)] by an extremely thermophilic bacterium, Caldicellulosiruptor saccharolyticus , under glucose fermentation conditions at 70 °C. Experimentation with different initial Cr(VI) concentrations confirmed that C. saccharolyticus had the ability to reduce Cr(VI) and immobilize Cr(III). At a concentration of 40 mg/L, Cr(VI) was completely reduced within 12 h, and 97% of the reduction product Cr(III) precipitated on the cell surface. Cr(VI) reduction was accelerated by the addition of neutral red (NR, an electron mediator), resulting in the reduction time shortened to 1 h. The addition of CuCl 2 , a Ni-Fe hydrogenase inhibitor, also enhanced Cr(VI) reduction. Additionally, analysis of the relationship between Cr(VI) reduction and glucose fermentation suggested that different electron sources acted during CuCl 2 and NR conditions. Hydrogen served as an electron donor under normal fermentation and NR conditions with the catalysis of Ni-Fe hydrogenase. However, when the activity of Ni-Fe hydrogenase was inhibited by CuCl 2 , C. saccharolyticus directly used reduction equivalents during glucose fermentation for intracellular Cr(VI) reduction. Therefore, our findings demonstrated high Cr(VI) reduction ability and different electron transfer pathways during Cr(VI) reduction by C. saccharolyticus . [ABSTRACT FROM AUTHOR]

Acetate is an important industrial chemical and its production from wastes via mixed culture fermentation (MCF) is economic. In this work, the effect of hydraulic retention time (HRT) on acetate production from tofu processing wastewater (TPW) in extreme-thermophilic (70 °C) MCF was first investigated. It was found that long HRT (>3 days) could lead to less acetate production while stable acetate production was achieved at short HRT (3 days) with the yield of 0.57 g-COD/g-COD TPW . The microbial community analysis showed that hydrogenotrophic methanogens (mainly Methanothermobacter ) occupied up to 90% of archaea at both HRTs of 3 and 5 days. However, Coprothermobacter , the main acetate-degraders, decreased from 35.74% to 10.58% of bacteria when HRT decreased from 5 to 3 days, supporting the aggravation of syntrophic acetate oxidation in long HRT. This work demonstrated that HRT was a crucial factor to maintain stable acetate production from TPW in extreme-thermophilic MCF. [ABSTRACT FROM AUTHOR]

Thermophilic (55 °C) mixed culture fermentation (MCF) is a promising technology for converting organic wastes into bioproducts including hydrogen and chemicals. In this study, the effect of pH, hydrogen partial pressure ( P H 2 ) and influent glucose concentration on the metabolic distribution in thermophilic chemostat was investigated. The results showed that the metabolite composition was changed from acetate, butyrate and hydrogen to acetate, ethanol, propionate and format when pH increased from 4.0 to 7.0. The conversion of hydrogen to formate was found to be thermodynamically controlled. Reducing P H 2 did not significantly increase the hydrogen yield and consequently the metabolites did not change much. Lactate accumulation was observed only at high influent glucose concentration. The maximum hydrogen yield was 2.2 ± 0.16 mol/mol-glucose at P H 2 0.05 atm, while the maximum hydrogen production rate was 7.9 ± 0.1 L/(L-reactor·Day) at influent glucose concentration of 76.3 mmol/L. Thus, considering the operating cost, increasing influent glucose concentration to 76.3 mmol/L in this work could be a more practical approach to produce hydrogen in thermophilic MCF. Meanwhile, the impacts of precedent pH and influent glucose concentration on the metabolites distribution were negligible in thermophilic chemostat. The thermodynamic analysis illustrated that a mixture of acetate, butyrate, ethanol, propionate and/or lactate was essential for thermophilic hydrogen producing MCF. [ABSTRACT FROM AUTHOR]

• Anaerobic acidic and alkaline fermentation in WAS was comprehensively compared. • VFAs yield from alkaline fermentation was 2.7 times higher than acidic fermentation. • Better sludge dewaterability was achieved at acidic fermentation. • Acidic fermentation produced less organics (PN, PS), nutrients (P, N) and metals. • VFAs via acidic fermentation may be a suitable way as carbon source for BNR process. This study conducted a comprehensive comparison of acidic (R 5.0) and alkaline (R 10.0) anaerobic fermentations of waste activated sludge (WAS). The results showed that alkaline fermentation was able to increase biopolymer release and benefitted the production of volatile fatty acids (VFAs). However, large amounts of the released organic matter in the R 10.0 fermented liquid had low biodegradability unsuitable for the biological nutrient removal (BNR) process, resulting in increased C, nitrogen, and phosphorus loads in BNR effluent. Further, Al was more readily released than other metals and its maximum concentration reached 134.52 mg/L in R 10.0 , 2.99 times higher than in R 5.0. The fermented sludge filterability was severely deteriorated at R 10.0 , as indicated by the normalized capillary suction time and specific resistance to filtration. Considering these findings, VFAs from WAS via acidic fermentation may represent a suitable carbon source for direct use in the BNR process. [ABSTRACT FROM AUTHOR]

• Organics and P recovery from PACl-sludge via alkaline fermentation was studied. • 43.3% of organics and 36.49% of P can be released to fermentation liquid at pH 11. • 24.9% of organics and 27.9% of P from wastewater can be formed to valuable product. • Alkaline fermentation promotes organics and phosphorus recovery from PACl sludge. In this study, alkaline fermentation was applied to promote organics and P recovery from polyaluminum chloride (PACl)-enhanced primary sedimentation sludge. Coagulant results demonstrated that the optimum PACl dosage of 100 mg/L resulted in the effective concentration of 73% of organic matter and 90% of P from wastewater into sludge. Batch fermentation results highlighted the ability of alkaline fermentation in improving the biodegradability of PACl sludge. More specifically, at pH 11, 43.3% of soluble organics and 36.49% of P were released to the fermentation supernatant. Furthermore, P fractionation fermented sludge results revealed that partial Al-P dissolution and organic phosphorus hydrolysis were the main drivers of the released P. Finally, at pH 11, 85% of P was recovered as magnesium ammonium phosphate from the fermentation supernatant at the 2:1 Mg/P molar ratio. In conclusion, 24.9% of organics and 27.9% of P from raw wastewater were converted to valuable products via alkaline fermentation. [ABSTRACT FROM AUTHOR]