Search

Hydrothermal liquefaction (HTL) has shown great potential to convert sewage sludge (SS) with high moisture into bio-crude. However, the disposal and reutilization of hydrothermal liquefaction wastewater (HTLWW) is a critical issue. Anaerobic digestion (AD) is proven to be an alternative to treat organic wastewater. Therefore, energy recovery from high ash-containing SS was studied by integrating AD with HTL. The effect of temperature on HTL efficiency was investigated and then methane production from HTLWW was conducted by AD with organic loading increasing from 2 g COD/L to 6 g COD/L. Results showed that the maximum bio-crude yield of 23.5 % was obtained at 350 °C. Methane yield of 309.4 mL CH4/g CODremoved was achieved at 2 g COD/L with COD removal rate of 72.5 %. Meanwhile, the microbial structure and abundance showed great shifts resulting from the adaptation to complex compounds. JGI-000079-D21, Aminicenantales, and Bacteroidetes_ vadinHA17 predominated in the bacterial community. Due to the presence of the toxic substances in HTLWW, such as phenolic and nitrogenous heterocyclic compounds, there was a decrease in methane yield when the organic loading was higher than 4 g COD/L. The organic matters in extracellular polymeric substances (EPS) were rich in fulvic acid-like and humic acid-like substances due to the attack and stimulation of toxicants. Under the condition of unstable fermentation, Advenella and Bacillus first appeared as phenol and pyridine degrading bacteria, respectively. The microbial diversity declined sharply to demonstrate the toxic effect of the refractory organics existing at high organic loading. The enrichment of Methanosaeta in methanogens meant that acetotrophic metabolism is the dominant pathway in methanogenesis. In this study, the profile of bio-fuel production from high ash-containing SS would provide an integrated reference to treat wet biomass and recover energy simultaneously.

The filamentous fungus strain Fusarium sp. ZW-21 was used for ethanol production with corncob hydrolysate. The fermentation conditions of ethanol production from corncob hydrolysate by the strain were investigated, and the effect of temperature, pH, nitrogen source, and surfactants on the ethanol production was investigated. The two factors yeast extract and polysorbate 80 were selected for further optimization by response surface methodology. The optimal conditions for ethanol production by the strain Fusarium sp. ZW-21 were 50 g/L sugar of corncob hydrolysate, 10.35 g/L yeast extract, 10 g/L KH2PO4, 0.5 g/L MgSO4·7H2O, 0.38 g/L polysorbate 80, pH 6.0, inoculum size of 1 mL/50 mL medium, and incubation temperature of 30 °C. The fermentation period was 5 d under oxygen-limited conditions, and the ethanol yield was 24.2 g/L.

Rose dregs were used for laccase production by the strain Pycnoporus sp. W-9 under liquid fermentation, and the obtained laccase was used for phenol degradation. The conditions for laccase production were optimized by Box-Behnken design, and the phenol degradation conditions using the crude laccase were optimized by central composite design. The optimal conditions for laccase production by the strain W-9 were as follows: rose dregs (40 g/L), KCl (0.144 g/L), KH2PO4 (1 g/L), K2HPO4 (0.699 g/L), NaCl (0.2 g/L), MgSO4·7H2O (0.3 g/L), CuSO4·5H2O (0.306 g/L), Tween 80 (0.2 g/L), and CaCO3 (1 g/L), at a pH of 6.0, incubated at 30 °C and 200 rpm for 7 d. The corresponding laccase yield reached 17.4 U/mL, which was approximately 1.8 times the original production. The optimal conditions for phenol removal by the crude laccase were as follows: laccase (12.2 U/mL), 0.1 mol/L citric acid-disodium hydrogen phosphate buffer (pH 3.5), phenol (100 μg/mL), and Triton X-100 (284 μg/mL), incubated at 45 °C for 2 h. The corresponding phenol degradation rate reached 86.6%. These results should be useful for utilization of rose dregs and bioremediation of soil and wastewater.

Thermochemical process of biomass is one of the promising renewable energy technologies; however, the by-product (wood vinegar wastewater) is rich in refractory organics, which is harmful to the environment and inhibits the conversion efficiency of microorganisms. Consequently, the dominant functional microbial communities corresponding to the various substrate were obtained through the continuous domestication, and the relationship between the dominant functional communities and the degradation of organic compounds was comprehensively analyzed. The bacterial community was absolutely dominant (approximately 85%), while archaea and fungi had similar relative abundance. The diversity showed that glucose was not conducive to the development of microbial diversity, while the substrate containing wood vinegar wastewater showed the opposite trend. The functional analysis revealed that the enrichment of bacteria associated with the hydrolysis and acidification of organics increased in the domestication process. Glucose facilitated hydrogen-trophic methanogenesis as the main methanogenic pathway in the methanogenic stage.

Anaerobic digestion (AD) of wood vinegar wastewater (WVWW) has considerable potential in energy recovery and sustainable development. WVWW contains abundant acetic acid and some refractory organics. Therefore, the batch and continuous AD of WVWW were investigated. The threshold value of the inhibitory concentration was obtained at a chemical oxygen demand (COD) of 4 g/L in batch AD. Three-dimensional electrolysis was adopted to improve the biodegradability of WVWW, and a reduction in the inhibitory rate from 38.2% to 4.9% and an increase in methane production by 53.8% were observed. The up-flow anaerobic sludge blanket reactor achieved an efficient conversion of methane at an organic loading rate (OLR) of8.58 g COD/L·d. However, the OLR of 10.01 g COD/L·d decreased the methane production from 350.6 to 42.5 mL CH

The effects of various microaeration strategies and process parameters on anaerobic digestion (AD) of lignocellulosic substrates have received increased attention; however, different results have been reported. To determine optimal conditions and clarify the mechanisms influencing this process, the effect of pretreatment of microaerobic microbial on corn stover decomposition and AD was investigated with real-time pH control. Fresh cow manure was chosen as the inoculum, as it has the strongest cellulose hydrolysis capacity under microaeration conditions. Microaeration microbial pretreatment effectively promoted the hydrolysis and acidogenesis of corn stover, and pH considerably affected total solid reduction, volatile fatty acid (VFA), and accumulation of soluble chemical oxygen demand (sCOD) patterns by shifting microbial communities. Different pH levels and pretreatment times led to positive and negative effects on methane yield. A 12-h pretreatment of substrate at pH 8 prior to AD increased the methane yield by 16.6% in comparison with the un-pretreated sample.

Corn straw silage (CSS) is one of the organic solid residues available for biogas production. The aim of this study was to investigate the possibility and optimal controlling strategy for anaerobic digestion (AD) of CSS. Four leaching bed reactors (LBR) were operated at different pH. Maximum volatile fatty acids (VFAs) concentration of 19.34 g/L was reached at pH 8.0 with acetic and propionic acids as dominant VFAs. The subsequent microbial analysis indicated that abundant bacteria were Firmicutes, Bacteroidetes and Proteobacteria. UASB as methanogenic reactor was integrated with the LBR. The organic loading rate (OLR) could reach 8 g COD/L·d with effective conversion of VFAs. Acetotrophic Methanosaeta and hydrogenotrophic Methanobacterium played major roles in methanogenic process. In the whole process, the results showed that methane yield of 143.4 mL CH4/g volatile solid (VS) was obtained. pH and OLR controls in two-phase AD were feasible for methane production from CSS.

In this work, black liquor as a waste from paper industry was used to pretreat corn stover before anaerobic digestion. The batch mode anaerobic digestion achieved a methane production up to 260.5 mL/g VS when the corn stover was pretreated the black liquor of 12 g NaOH/L alkalinity for 24 h, which was 59.1% higher than the control. In the semi-continuous mode anaerobic digestion, black liquor pretreatment increased the buffering capacity of the digestate to maintain suitable pH and total VFA/alkalinity ratio with no adverse effect resulted from the presence of ions. The structural and chemical changes of corn stover after the pretreatment were investigated to rationalize the enhanced performance of anaerobic digestion.

This work evaluated the methane potential and methane production rate of the stem bark (SB), stem pith (SP), and leaves (LV) of corn stover from batch anaerobic digestion. The obtained cumulative methane potential and the hydrolysis kinetics constant were 0.201, 0.214, and 0.199 L g−1 VS (volatile solids) and 0.090, 0.149, and 0.227 d−1 for SB, SP, and LV, respectively. The chemical composition and the crystalline structure of the substrates as well as their changes during the anaerobic digestion were inspected, and their impacts on the characteristics of methane production were assessed. The methane production rate correlated positively with the hemicellulose and soluble compounds content and negatively with the cellulose and lignin content, but the degradation rates of hemicellulose and cellulose in the specific substrate were complex and comparable. The methane production has limit correlation with the crystalline structure of the substrates. Microbial community structure was analyzed to elucidate functional microorganism contributing to methane production of different substrate. The abundance of Bacteroidetes and Firmicutes was most affected by the substrate, and positively related to methane yields.

The effects of carbohydrate/protein ratio (CH/Pr) and pH on hydrogen production from waste activated sludge (WAS) were investigated. Firstly, the optimal pH value for hydrogen production was influenced by the CH/Pr ratio, which was pH 10, 9, 8, 8, 8 and 6 at the CH/Pr ratio (COD based) of 0.2 (sole sludge), 1, 2.4, 3.8, 5 and 6.6, respectively. The maximal hydrogen production (100.6 mL/g-COD) was achieved at CH/Pr of 5 and pH 8, which was due to the synergistic effect of carbohydrate addition on hydrogen production, the enhancement of sludge protein degradation and protease and amylase activities, and the suitable fermentation pathway for hydrogen production. As hydrogen consumption was observed at pH 8, in order to further increase hydrogen production a two-step pH control strategy (pH 8 + pH 10) was developed and the hydrogen production was further improved by 17.6%.

A new method to identify flow regime in two-phase flow was presented, based on signal processing of differential pressure using Hilbert Huang transform (HHT). Signals obtained from a Venturi meter were decomposed into different intrinsic mode functions (IMFs) with HHT, then the energy fraction of each intrinsic mode and the mean value of residual function were calculated, from which the rules of flow regime identification were summarized. Experiments were carried out on two-phase flow in the horizontal tubes with 50mm and 40mm inner diameter, while water flowrate was in the range of 1.3m 3 ·h −1 to 10.5m 3 ·h −1 , oil flowrate was from 4.2m 3 ·h −1 to 7.0m 3 ·h −1 and gas flowrate from 0 to 15m 3 ·h −1 . The results show that the proposed rules have high precision for single phase, bubbly, and slug, plug flow regime identification, which are independent of not only properties of two-phase fluid. In addition, the method can meet the need of industrial application because of its simple calculation.

In this study an efficient strategy, i.e., controlling the fermentation pH at constant pH 10, for significantly increasing hydrogen yield from waste activated sludge (WAS) via the improvement of anaerobic process (sludge solubilization, hydrolysis, and acidification) and inhibition of hydrogen consumption by acetobacteria was reported. Without addition of pure hydrogen producer and nutrient source, the effect of different constant pH in the range of pH 4-11 on hydrogen production from WAS was compared with that of different initial pH. The maximal hydrogen yield was observed respectively at constant pH 10 and initial pH 10, but the former was 47.8% higher than the latter (26.9 versus 18.2 mL per gram volatile suspended solids) and much greater than that reported in literature. Then, the mechanisms for constant pH 10 resulting in remarkably higher hydrogen production than initial pH 10 were investigated. It was observed that constant pH 10 fermentation showed much higher solubilization of sludge main particulate organic matters, hydrolysis of solubilized organic materials and acidification of hydrolyzed products, which were of benefit to the hydrogen production. Also, there was more acetic but less propionic acid in the constant pH 10 test, which was in correspondence with the theory of fermentation type affecting hydrogen production. Moreover, in the reactor of initial pH 10 the produced hydrogen was readily converted to acetic acid, but no obvious hydrogen consumption was observed in constant pH 10 reactor. Further investigation of microorganisms with enzymes analysis and fluorescence in situ hybridization (FISH) indicated that the activity and growth of acetobacteria in the reactor of constant pH 10 was much lower than those in initial pH 10 reactor.