Hengfeng Miao

Coupling of the hydrogen and polyhydroxyalkanoates (PHA) production through anaerobic digestion from Taihu blue algae

Coupling bio-production of hydrogen and polyhydroxyalkanoates (PHA) from Taihu blue algae through metabolites circulation was investigated. It was found that the pH adjustment, especially basification was more practical and efficient than other methods for the pretreatment of blue algae before anaerobic digestion. On this occasion, SCOD, biogas accumulation and hydrogen content reached 26 mg/gTS, 500 mL and 37.2%, and which were 4.3, 1.3 and 14.4 times of those of the control group, respectively. Secondly, amounts of both butyric acid and hydrogen could be further increased when blue algae was alkali pretreated at pH 13, as the accumulation of butyric acid, acetic acid and hydrogen reached 1.7, 1.4 and 3.8 times compared to those of the control, respectively. Finally, the coupling bio-production of hydrogen and PHA was conducted through pumping organic residues into PHA fermenter from anaerobic digester. Remarkably, it was found that the larger the pumping rate of carbon and nitrogen sources supply, the higher the yield of DCW and PHA could be expected by Bacillus cereus.

In situ volatile fatty acids influence biogas generation from kitchen wastes by anaerobic digestion.

Anaerobic digestion is considered to be an efficient way of disposing kitchen wastes, which can not only reduce waste amounts, but also produce biogas. However, the excessive accumulation of volatile fatty acids (VFA) caused by high organic loads will inhibit anaerobic digestion intensively. Effects of the VFA composition on biogas generation and microbial community are still required for the investigation under various organic loads of kitchen wastes. Our results showed that the maximum specific methane production was 328.3 ml g TS(-1), and acetic acid was the main inhibitor in methanogenesis. With the increase of organic load, aceticlastic methanogenesis was more sensitive to acetic acid than hydrogenotrophic methanogenesis. Meanwhile, methanogenic microbial community changed significantly, and few species grew well under excessive organic loads. This study provides an attempt to reveal the mechanism of VFA inhibition in anaerobic digestion of kitchen wastes.

Enhancement of Taihu blue algae anaerobic digestion efficiency by natural storage

Taihu blue algae after different storage time from 0 to 60 d were anaerobic fermented to evaluate their digestibility and process stability. Results showed that anaerobic digestion (AD) of blue algae under 15 d natural storage led to the highest CH4 production of 287.6 mL g(-1) VS at inoculum substrate ratio 2.0, demonstrating 36.69% improvement comparing with that from fresh algae. Storage of blue algae led to cell death, microcystins (MCs) release and VS reduction by spontaneous fermentation. However, it also played an important role in removing algal cell wall barrier, pre-hydrolysis and pre-acidification, leading to the improvement in CH4 yield. Closer examination of volatile fatty acids (VFA) variation, VS removal rates and key enzymes change during AD proved short storage time (≤ 15 d) of blue algae had higher efficiencies in biodegradation and methanation. Furthermore, AD presented significant biodegradation potential for MCs released from Taihu blue algae.

Degradation of phenazone in aqueous solution with ozone: influencing factors and degradation pathways.

Oxidation kinetics and degradation pathways of phenazone (an analgesic and antipyretic drug) upon reaction with O3 were investigated. Kinetic studies on degradation of phenazone were carried out under different operating conditions such as temperature, pH, anions and H2O2 addition. Results showed that the degradation followed the pseudo-first-order kinetic model. The reaction rate constant (kobs) of phenazone reached the maximum at 20 °C (9.653×10(-3) s(-1)). The presence of NO3(-) could enhance the degradation rate, while the addition of HCO3(-), SO4(2)(-), Cl(-) and the rise of pH showed negative effects on the ozonation of phenazone. H2O2 addition increased the phenazone degradation efficiency by 45.9% with the optimal concentration of 0.135 mM. Reaction by-products were evaluated by UPLC-Q-TOF-MS, which allowed the identification of a total of 10 by-products. The transformation pathways of phenazone ozonation consisted mainly of electrophilic addition and substitution, pyrazole ring opening, hydroxylation, dephenylization and coupling. The toxicity of these intermediate products showed that they are expected not to be more toxic than phenazone, with the exception of P7 (aniline) and P10 (1,5-dimethyl-4-((1-methyl-2-phenylhydrazinyl)methoxy)-2-phenyl-1H-pyrazol-3(2H)-one).

Evaluation and characterization during the anaerobic digestion of high-strength kitchen waste slurry via a pilot-scale anaerobic membrane bioreactor

The anaerobic digestion of high-strength kitchen waste slurry via a pilot-scale anaerobic membrane bioreactor (AnMBR) was investigated at two different operational modes, including no sludge discharge and daily sludge discharge of 20 L. The AnMBR provided excellent and reliable permeate quality with high COD removal efficiencies over 99%. The obvious accumulations of long chain fatty acids (LCFAs) and Ca(2+) were found in the anaerobic digester by precipitation and agglomeration. Though the physicochemical process contributed to attenuating the free LCFAs toxicity on anaerobic digestion, the digestion efficiency was partly influenced for the low bioavailability of those precipitates. Moreover, higher organic loading rate (OLR) of 5.8 kg COD/(m(3) d) and digestion efficiency of 78% were achieved as the AnMBR was stably operated with sludge discharge, where the membrane fouling propensity was also alleviated, indicating the crucial significance of SRT control on the treatment of high-strength kitchen waste slurry via AnMBRs.

Enhancement of substrate solubilization and hydrogen production from kitchen wastes by pH pretreatment

Pretreatment at different pHs was adopted in this study to enhance the substance solubilization and hydrogen production from kitchen wastes through anaerobic digestion. After a pretreatment set at pH = 13, solubilization of kitchen wastes improved substantially as the concentration of soluble carbohydrate, soluble protein, lipids and soluble chemical oxygen demand increased by 283.1%, 203.2%, 259.1% and 108.2%, respectively, as compared with those of the control. The maximum hydrogen production potential reached 105.38 mL/g VS after the pretreatment, which was 2.66 times that of the control. Furthermore, butyric acid and acetic acid were the major components in the total metabolites after fermentation, while propionic acid had a relatively low concentration. Finally, the concentration of exoprotein and exopolysaccharide within extracellular polymeric substances (EPS) kept increasing during the initial 14 and 9 hours, respectively, then decreased afterwards. However, the concentration of DNA increased throughout the whole stage. The total EPS might indirectly indicate the anaerobic digestion process. These findings may represent a feasible method for high‐quality treatment of kitchen wastes.

Identical full-scale biogas-lift reactors (Blrs) with anaerobic granular sludge and residual activated sludge for brewery wastewater treatment and kinetic modeling.

Two identical full-scale biogas-lift reactors treating brewery wastewater were inoculated with different types of sludge to compare their operational conditions, sludge characteristics, and kinetic models at a mesophilic temperature. One reactor (R1) started up with anaerobic granular sludge in 12 weeks and obtained a continuously average organic loading rate (OLR) of 7.4 kg chemical oxygen demand (COD)/(m3 x day), COD removal efficiency of 80%, and effluent COD of 450 mg/L. The other reactor (R2) started up with residual activated sludge in 30 weeks and granulation accomplished when the reactor reached an average OLR of 8.3 kg COD/(m3 x day), COD removal efficiency of 90%, and effluent COD of 240 mg/L. Differences in sludge characteristics, biogas compositions, and biogas-lift processes may be accounted for the superior efficiency of the treatment performance of R2 over R1. Grau second-order and modified StoverKincannon models based on influent and effluent concentrations as well as hydraulic retention time were successfully used to develop kinetic parameters of the experimental data with high correlation coefficients (R2 > 0.95), which further showed that R2 had higher treatment performance than R1. These results demonstrated that residual activated sludge could be used effectively instead of anaerobic granular sludge despite the need for a longer time.

A Comparative Study of Sequential Hydrogen-methane and Independent Methane Production from Kitchen Wastes

Abstract Analysis of sequential hydrogen-methane and independent methane production were carried out in this study to investigate the optimal bio-energy production from kitchen wastes. The study indicated that production of hydrogen and the sequential methane achieved 75.0 and 287.4 mL/gVS, respectively, during the sequential hydrogen-methane process. Specifically, the sequential methane increased by 34.0% compared to independent methane production. Additionally, the measured concentration of total organic acids increased to 13,599.8 mg/L at the end of hydrogen fermentation, then decreased to 4,284.9 mg/L at the end of the sequential methane process. The major acid component was butyric acid in the sequential methane process as opposed to acetic acid in an independent process. Remarkably, it was found that the major component of extracellular polymeric substances in hydrogen producing sludge was exopolysaccharide, while in both methane producing processes it was exoprotein. The maximum measured concentration of exoprotein and exopolysaccharide reached to 84.3, 36.3 mg/gVS and 63.4, 30.4 mg/gVS, while DNA increased throughout the stages of the two methane processes. These findings may represent a feasible method for high energy achievement from kitchen wastes.

Insights into sludge granulation during anaerobic treatment of high-strength leachate via a full-scale IC reactor with external circulation system

In this study, a full-scale internal circulation (IC) reactor coupled with an external circulation system was developed to treat high-strength leachate from a municipal solid waste (MSW) incineration plant, in which anaerobic sludge granulation was intensively investigated. Results showed that the IC reactor achieved excellent treatment performance under high organic loading rates (OLR) of 21.06-25.16kg chemical oxygen demand (COD)/(m3∙day). The COD removal efficiency and biogas yield respectively reached 89.4%-93.4% and 0.42-0.50m3/kgCOD. The formation of extracellular polymeric substances (EPS) was closely associated with sludge granulation. Protein was the dominant component in sludge EPS, and its content was remarkably increased from 21.6 to 99.7mg/g Volatile Suspended Solid (VSS) during the reactor operation. The sludge Zeta potential and hydrophobicity positively correlated with the protein/polysaccharide ratio in EPS, and they were respectively increased from -26.2mV and 30.35% to -10.6mV and 78.67%, which was beneficial to microbial aggregation. Three-dimensional fluorescence spectroscopy (3D-EEM) and Fourier transform infrared spectroscopy (FT-IR) analysis further indicated the importance of protein-like EPS substances in the sludge granulation. Moreover, it was also found that the secondary structures of EPS proteins varied during the reactor operation.

Performance and dynamic characteristics of microbial communities in an internal circulation reactor for treating brewery wastewater

A laboratory-scale internal circulation (IC) anaerobic reactor fed with brewery wastewater was operated at 35°C±1°C. The influent was pumped into the bottom of the IC reactor by a pulse pump, whereas the effluent was drawn from the upper outlet and allowed to flow into the effluent tank. The biogas volume was recorded using a gas container connected to a biogas metre. The results indicated that the maximum organic loading rate (OLR) of the IC reactor was 19.5 kg chemical oxygen demand (COD)/m 3/day; at which point, the dominant archaeal populations found in the sludge using the polymerase chain reaction with denaturing gradient gel electrophoresis were Methanosaeta species. The COD removal efficiencies of the reactor exceeded 85%, with a maximum specific methane production rate of 210 mL CH4/g volatile suspended solids (VSS)/day and a coenzyme F420 content of 0.16 μmol/g VSS, respectively. The main archaeal species in the sludge samples at different OLRs varied greatly, as compared with the organisms in the inoculated sludge. The dominant archaeal species in the treated sludge at low OLRs were Methanosarcina species, whereas those at high OLRs were Methanosaeta species.