No abstract

No abstract

No abstract

Anaerobic digestion foaming is a common operation problem in biogas plants with negative impacts on the biogas plants economy and environment. A survey of 16 Danish full-scale biogas plants on foaming problems revealed that most of them had experienced foaming in their processes up to three times per year. Foaming incidents often lasted from one day to three weeks, causing 20-50% biogas production loss. One foaming case at Lemvig biogas plant has been investigated and the results indicated that the combination of feedstock composition and mixing pattern of the reactor was the main cause of foaming in this case. Moreover, no difference in bacterial communities between the foaming and non-foaming reactors was observed, showing that filamentous bacteria were not the main reason for foaming in this case.

Acceleration of the anaerobic digestion (AD) process is crucial to achieving energy-efficient recycling of organic wastes. Hydrochar is produced by hydrothermal liquefaction of biomass, yet its application in the AD process is rarely reported. The present study showed that sewage sludge-derived hydrochar (SH) enhanced the methane production rate of glucose by 37%. SH increased the methane production rate from acetate but did not affect acidification and the methane production rate from H 2 /CO 2 . SH enhanced hydrogenotrophic methanogenesis, which could be due to direct interspecies electron transfer (DIET) by converting H + , e − , and CO 2 to methane. Trichococcus and Methanosaeta were dominant in the AD process with SH. Label-free proteomic analysis showed Methanosaeta was involved in DIET as reflected by the up-regulation of proteins involved in hydrogenotrophic methanogenesis. Hydrochars derived from corn straw (CH), Enteromorpha algae (EH), and poplar wood (PH), as well as activated carbon (AC), were also tested in the AD process. SH, CH, and EH obviously increased the methane production rates, which were 39%, 15%, and 20% higher than the control experiment, respectively. It was neither electrical conductivity nor the total redox property of hydrochars and AC but the abundances of surface oxygen-containing functional groups that correlated to the methane production rates.

No abstract

No abstract

Hydrolysate was tested as substrate for hydrogen production by extreme thermophilic mixed culture (70 degrees C) in both batch and continuously fed reactors. Hydrogen was produced at hydrolysate concentrations up to 25% (v/v), while no hydrogen was produced at hydrolysate concentration of 30% (v/v), indicating that hydrolysate at high concentrations was inhibiting the hydrogen fermentation process. In addition, the lag phase for hydrogen production was strongly influenced by the hydrolysate concentration, and was prolonged from approximately 11 h at the hydrolysate concentrations below 20% (v/v) to 38 h at the hydrolysate concentration of 25% (v/v). The maximum hydrogen yield as determined in batch assays was 318.4 +/- 5.2 mL-H(2)/g-sugars (14.2 +/- 0.2 mmol-H(2)/g-sugars) at the hydrolysate concentration of 5% (v/v). Continuously fed, and the continuously stirred tank reactor (CSTR), operating at 3 day hydraulic retention time (HRT) and fed with 20% (v/v) hydrolysate could successfully produce hydrogen. The hydrogen yield and production rate were 178.0 +/- 10.1 mL-H(2)/g-sugars (7.9 +/- 0.4 mmol H(2)/g-sugars) and 184.0 +/- 10.7 mL-H(2)/day L(reactor) (8.2 +/- 0.5 mmol-H(2)/day L(reactor)), respectively, corresponding to 12% of the chemical oxygen demand (COD) from sugars. Additionally, it was found that toxic compounds, furfural and hydroxymethylfurfural (HMF), contained in the hydrolysate were effectively degraded in the CSTR, and their concentrations were reduced from 50 and 28 mg/L, respectively, to undetectable concentrations in the effluent. Phylogenetic analysis of the mixed culture revealed that members involved hydrogen producers in both batch and CSTR reactors were phylogenetically related to the Caldanaerobacter subteraneus, Thermoanaerobacter subteraneus, and Thermoanaerobacterium thermosaccharolyticum.