Insights into high-solids anaerobic digestion of food waste concomitant with sorbate: Performance and mechanisms.

High-solids anaerobic digestion (HS-AD) of food waste is increasingly applied commercially. Sorbate, a food preservative extensively used in the food industry, induces potential environmental risks. Results indicated sorbate at 0-10 mg/g volatile solids (VS) slightly inhibited methane production, and the cumulative methane yield suggested a negative correlation with 25 mg/g VS sorbate, with a reduction of 15.0% compared to the control (from 285.7 to 253.6 mL CH4/g VS). The reduction in methane yield could be ascribed to the promotion of solubilization and inhibition of acidogenesis and methanogenesis with sorbate addition. Excessive sorbate (25 mg/g VS) resulted in the inhibition of aceticlastic metabolism and the key enzymes activities (e.g., acetate kinase and coenzyme F420). This study deeply elucidated the response mechanism of HS-AD to sorbate, supplemented the potential ecological risk assessment of sorbate, and could provide insights to further prevent the potential risk of sorbate in anaerobic digestion of food waste.

Visualization of mass transfer in mixing processes in high solid anaerobic digestion using Laser Induced Fluorescence (LIF) technique.

High solid anaerobic digestion (HSAD) is a promising technology for the treatment of organic waste. Mixing process in HSAD is quite difficult with long mixing time, poor homogenization, significant short-circuiting and stagnant zones. However, the mass transfer in mixing process in HSAD has not been visualized due to the lack of a proper method. In this study, a novel approach for experimentally quantifying the mass transfer in HSAD's mixing process was proposed in a mixing tank equipped with multistage impellers by means of the Laser Induced Fluorescence (LIF) technique. Flow field was investigated for better illustrating the mass transfer, thus Particle Image Velocimetry (PIV) and Computational Fluid Dynamics (CFD) technique were conducted for flow field measurement. The obtained results revealed that the feedstock tended to accumulate around the impeller in the HSAD system, especially near the 1st stage. The tracer diffused rapidly around the 1st impeller in t = 10 s, but the diffusion around the 2nd impeller was quite tough even after 4 h 08 min 23 s. And prolonging mixing time could not significantly improve the flow pattern along with the mixing. In this study, new insight was thrown into the visualization of the mass transfer in mixing process within a HSAD reactor. The visualization of mass transfer in the mixing process in HSAD could offer reference information to the study of the mixing process of HSAD even in full-scale.

Transitions of microbial communities in the solid and liquid phases during high-solids anaerobic digestion of organic fraction of municipal solid waste.

This study presents a microbiological diagnosis of a mesophilic high-solids anaerobic digestion (HSAD) system with percolate recirculation. The results demonstrated a significant decrease in microbial diversity in both the solid digestate and the liquid percolate. Also, the digestate from the top and middle sections of the digester had similar diversity, whereas the digestate from the bottom of the tank had a slightly lower diversity. These results suggest that despite percolate recirculation, substrate gradients might have developed across the system. Archaeal communities showed shifts towards known hydrogenotrophic and ammonia-tolerant methanogens (genera Methanocelleus, Methanolinea, Methanosarcina, vadin CA11, etc.), which was a consequence of decreased volatile fatty acids and increased ammonia-nitrogen levels over time. Compared to initial solid and liquid inoculum, the relative abundances of some bacteria (phyla Proteobacteria and Firmicutes) and archaea of the genus Methanosarcina changed between two phases in the opposite direction, indicating a shift of microbes between two phases.

Efficient acetogenesis of anaerobic co-digestion of food waste and maize straw in a HSAD reactor.

In this study, food waste and maize straw were used as feedstock, and the two-phase high-solid anaerobic digestion (TP-HSAD) technology was used to optimize the process parameters of leachate reflux in acid-production stage. Results indicated that compared with other waste activated sludge, pig manure digestate (PM) as leachate can achieve better hydrolysis and acidification effect. The increase of leachate reflux ratio can shorten the fermentation time of the acid-producing stage and increase the fermentation efficiency. When the reflux ratio was 32:1, peak concentration of volatile fatty acids (VFAs) was 45.4 g/L and the volatile solids (VS) removal rate was 61.7%. Reflux frequency has minimal effect on the concentration of VFAs and the degree of degradation of VS, but a higher reflux frequency will prolong the reaction time of acid-production stage. When PM is used as reflux leachate, the HSAD reactor can improve the hydrolysis and acidification of the anaerobic fermentation.

Flow field investigation of high solid anaerobic digestion by Particle Image Velocimetry (PIV).

High solid anaerobic digestion (HSAD) is a promising anaerobic digestion technology. Homogenization and mixing mechanism are essential for HSAD's performance, but relative knowledge still remains poor. In order to investigate HSAD's mixing behavior, a novel flow field measuring approach was proposed as following. Firstly, laponite suspension was selected as the model fluid of HSAD digestate, because the rheological properties and material structure they displayed were highly similar. Then, water and polyacrylamide (PAAm) solution were chosen as basic reference fluid and another non-Newtonian fluid respectively. Flow fields of the three fluids under different rotation speeds were measured via Particle Image Velocimetry (PIV). The evolution of working fluids did induce consecutively the significant flow and mixing behavior of HSAD, because their rheological properties and complexity were getting progressively closer to the real HSAD digestate. Results indicated that the flow field of simulated HSAD fluid was quite different from those of water and PAAm solution, i.e. only the fluid around the impeller could be mixed in HSAD. Besides, increasing rotation speed could not significantly enhance the mixing area of HSAD. Thus, multilayer impellers arranged abreast were recommended for HSAD's mixing. Considering that HSAD's flow field had never been measured before, this study proposed a novel flow field measuring method for such opaque non-Newtonian fluid for the first time. The visualization of HSAD's complex hydrodynamic conditions was also firstly achieved in this study, and thus could further help improve the homogenization of HSAD.

Utility of 99mTc-human serum albumin diethylenetriamine pentaacetic acid SPECT for evaluating endoleak after endovascular abdominal aortic aneurysm repair.

OBJECTIVE: The purpose of this study was to assess the utility of (99m)Tc-human serum albumin diethylenetriamine pentaacetic acid ((99m)Tc-HSAD) SPECT in the detection of endoleaks after endovascular abdominal aortic aneurysm repair. SUBJECTS AND METHODS: Fifteen patients (11 men, four women) with aneurysm sac expansion of 5 mm or greater after endovascular abdominal aortic aneurysm repair underwent three-phase CT, (99m)Tc-HSAD SPECT, and CT during aortography. Sensitivity calculations for three-phase CT and (99m)Tc-HSAD SPECT were performed with CT during aortography as the reference standard. The volume of each endoleak was measured with CT during aortography. Seven subjects underwent embolization with N-butyl cyanoacrylate (NBCA)-Lipiodol (ethiodized oil, Guerbet and metallic coils. Three-phase CT and (99m)Tc-HSAD SPECT were repeated after embolization to assess their efficacy. RESULTS: Endoleaks were interpreted as perigraft radioisotope accumulation in 12 patients (80.0%) on (99m)Tc-HSAD SPECT images, in 13 patients (86.7%) on three-phase CT images, and in 15 patients (100%) on CT during aortography. The mean endoleak volume visualized with (99m)Tc-HSAD SPECT was 8.37 cm(3) (range, 5.2-15.1 cm(3)), and the volume not visualized was 3.47 cm(3) (2.5-4.6 cm(3)), a statistically significant difference (p = 0.019). In two patients, (99m)Tc-HSAD SPECT depicted endoleaks evident at delayed phase CT during aortography but not at three-phase CT, suggesting they were slow-filling endoleaks. Accumulation of (99m)Tc-HSAD corresponding to endoleaks disappeared after embolization, but CT evaluation of embolization was impeded by artifacts of NBCA-Lipiodol and metallic coils. CONCLUSION: Technetium-99m-labeled HSAD SPECT proved less sensitive than three-phase CT but depicted endoleaks with volumes 5.2 cm(3) or greater as perigraft radioisotope accumulation. Slow-filling endoleaks can be visualized with (99m)Tc-HSAD SPECT, which can be used to evaluate the efficacy of embolization.

Mechanism-based inhibition of HsaD: a C-C bond hydrolase essential for survival of Mycobacterium tuberculosis in macrophage.

Mycobacterium tuberculosis remains the leading cause of death by a bacterial pathogen worldwide. Increasing prevalence of multidrug-resistant organisms means prioritizing identification of targets for antituberculars. 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoate hydrolase (HsaD), part of the cholesterol metabolism operon, is vital for survival within macrophage. The C-C bond hydrolase, HsaD, has a serine protease-like catalytic triad. We tested a range of serine protease and esterase inhibitors for their effects on HsaD activity. As well as providing a potential starting point for drug development, the data provides evidence for the mechanism of C-C bond hydrolysis. This screen also provides a route to initiate development of fragment-based inhibitors.

Comparative analysis of genes encoding key steroid core oxidation enzymes in fast-growing Mycobacterium spp. strains.

A comparative genome analysis of Mycobacterium spp. VKM Ac-1815D, 1816D and 1817D strains used for efficient production of key steroid intermediates (androst-4-ene-3,17-dione, AD, androsta-1,4-diene-3,17-dione, ADD, 9α-hydroxy androst-4-ene-3,17-dione, 9-OH-AD) from phytosterol has been carried out by deep sequencing. The assembled contig sequences were analyzed for the presence putative genes of steroid catabolism pathways. Since 3-ketosteroid-9α-hydroxylases (KSH) and 3-ketosteroid-Δ(1)-dehydrogenase (Δ(1) KSTD) play key role in steroid core oxidation, special attention was paid to the genes encoding these enzymes. At least three genes of Δ(1) KSTD (kstD), five genes of KSH subunit A (kshA), and one gene of KSH subunit B of 3-ketosteroid-9α-hydroxylases (kshB) have been found in Mycobacterium sp. VKM Ac-1817D. Strains of Mycobacterium spp. VKM Ac-1815D and 1816D were found to possess at least one kstD, one kshB and two kshA genes. The assembled genome sequence of Mycobacterium sp. VKM Ac-1817D differs from those of 1815D and 1816D strains, whereas these last two are nearly identical, differing by 13 single nucleotide substitutions (SNPs). One of these SNPs is located in the coding region of a kstD gene and corresponds to an amino acid substitution Lys (135) in 1816D for Ser (135) in 1815D. The findings may be useful for targeted genetic engineering of the biocatalysts for biotechnological application.