Study of an enhanced dry anaerobic digestion of swine manure: Performance and microbial community property.

Anaerobic digestion could treat organic wastes and recovery energy. Dry anaerobic digestion had advantages of low heating energy, small digester and less digestate, but its methane production was poor. In this study, an enhanced dry anaerobic digestion of swine manure (thermal treatment + dry anaerobic digestion) was proposed, and its feasibility was investigated via semi-continuous experiment. Results showed that methane production rates were 314.6, 416.0, 298.0 and 69.9 mL CH4/g VS at solid retention time (SRT) of 41 d, 35 d, 29 d and 23 d. Volatile solids (VS) removal rate and methane production rate could reached 71.4% and 416.0 mL CH4/g VS respectively at SRT of 35 d. Methane production rate of the enhanced dry anaerobic digestion was 390% higher than that of dry anaerobic digestion. Microbial study indicated that hydrogenotrophic methanogens predominated with the abundance of 90.2%, while acetoclastic methanogens were not detected. This process was feasible, and was of great practical importance.

Novel insight into high solid anaerobic digestion of swine manure after thermal treatment: Kinetics and microbial community properties.

Compared to traditional anaerobic digestion (AD), high solid anaerobic digestion (HSAD) had the advantages of small digester, low heating energy and less digestate. However, the methane production was poor. In our previous study, thermal treatment (70 ±â€¯1 °C, 3 days) without any dilution could satisfactorily enhance the methane production rate of HSAD by up to 39.5%. However, effects of solid content on HSAD after thermal treatment were not yet studied. In this study, HSAD was conducted at 11.7-17.6% solid content, and the control experiment was conducted at low solid content (4.4% solid content). Results showed that HSAD's methane production rate was the highest at 11.7% solid content (158 mL CH4/g VS), and could reach up to 89.2% of that at 4.4% solid content. The utilization of organics was revealed by kinetics analysis that the readily biodegradable organics could be utilized at increasing solid content with decreasing hydrolysis rate. Furthermore, it was notable that methylotrophic methanogens predominated in HSAD with the abundance of 82.6%. This was quite unique from the general belief that AD system was usually dominated by acetoclastic or hydrogenotrophic methanogenic pathways. In this study, the microbial community structure of HSAD after thermal treatment was firstly studied, its unique specific methanogenic pathways was firstly revealed.

Room temperature precipitated dual phase CsPbBr3-CsPb2Br5 nanocrystals for stable perovskite light emitting diodes.

Although the efficiency of metal halide perovskite light emitting diodes (PeLEDs) has been improved to an attractive level, the poor stability of perovskite emitting layers is a major concern for the application of PeLEDs. Herein, we report a facile ligand-assisted precipitation synthesis of stable dual-phase CsPbBr3-CsPb2Br5 nanocrystals (NCs) for improving the stability of PeLEDs. In our synthetic process, the bromide-rich circumstance is beneficial to generate high quality dual-phase perovskite NCs with PLQY as high as 92% and a narrow emission linewidth (19 nm). More importantly, as-synthesized dual phase perovskite NCs exhibit extremely high thermal stability in heating tests in air with a considerable humidity of 30%-55% in comparison with previously reported single phase CsPbBr3 NCs. The aforementioned advantages of our synthesized dual-phase CsPbBr3-CsPb2Br5 NCs allow for the fabrication of light emitting layers of PeLEDs under ambient conditions. The fabricated green PeLED based on CsPbBr3-CsPb2Br5 NCs shows a low turn-on voltage of 2.5 V and a high brightness of 8383 cd m-2 at 8 V. Owing to the high stability of dual-phase CsPbBr3-CsPb2Br5 NCs, the fabricated PeLED also exhibits better operational stability in comparison with those PeLEDs based on single phase CsPbBr3 NCs. Our work presents a new route to fabricate stable perovskite light-emitting diodes using room temperature precipitated dual-phase CsPbBr3-CsPb2Br5 NCs as emitting layer materials.

Effects of thermal treatment on high solid anaerobic digestion of swine manure: Enhancement assessment and kinetic analysis.

Anaerobic digestion (AD), which is a process for generating biogas, can be applied to the treatment of organic wastes. Owing to its smaller footprint, lower energy consumption, and less digestate, high solid anaerobic digestion (HSAD) has attracted increasing attention. However, its biogas production is poor. In order to improve biogas production and decrease energy consumption, an improved thermal treatment process was proposed. Raw swine manure (>20% solid content) without any dilution was thermally treated at 70±1°C for different retention times, and then its effect on HSAD was investigated via batch AD experiments at 8.9% solid content. Results showed that the main organic components of swine manure hydrolyzed significantly during the thermal treatment, and HSAD's methane production rate was improved by up to 39.5%. Analysis using two kinetic models confirmed that the treatment could increase biodegradable organics (especially the readily biodegradable organics) in swine manure rather than upgrading its hydrolysis rate. It is worth noting that the superimposed first-order kinetics model was firstly applied in AD, and was a good tool to reveal the AD kinetics mechanism of substrates with complex components.

Size effect of anaerobic granular sludge on biogas production: A micro scale study.

This study investigated the influence of anaerobic granular sludge size on its bioactivity at COD concentration of 1000, 3000 and 6000 mg/L. Based on size, granules were categorized as large (3-3.5 mm), medium (1.5-2 mm) and small (0.5-1 mm). A positive relationship was obtained between granule size and biogas production rate. For instance, at COD 6000 mg/L, large granules had highest biogas production rate of 0.031 m(3)/kgVSS/d while medium and small granules had 0.016 and 0.006 m(3)/kgVSS/d respectively. The results were reaffirmed by applying modified Fick's law of diffusion. Diffusion rates of substrate for large, medium and small granules were 1.67×10(-3), 6.1×10(-4)and 1.8×10(-4) mg/s respectively at that COD. Large granules were highly bio-active due to their internal structure, i.e. big pore size, high porosity and short diffusion distance as compared to medium and small granules, thus large granules could improve the performance of reactor.

Lattice Boltzmann investigation of droplet inertial spreading on various porous surfaces.

The spreading of liquid drops on solid surfaces is a wide-spread phenomenon of both fundamental and industrial interest. In many applications, surfaces are porous and spreading patterns are very complex with respect to the case on smooth surfaces. Focusing on the inertial spreading just before the Tanner-like viscous regime, this work investigates the spreading of a low-viscosity droplet on a porous surface using lattice Boltzmann numerical simulations. The case of a flat surface is first considered, and it reveals a dependence on the solid equilibrium contact angle θ(s)(eq), which is in good agreement with published experimental data. We conducted numerical experiments with various surfaces perforated by a regular pattern of holes of infinite length. The results show that the global spreading dynamics is independent of the porosity morphology. Through the assumption that, for wetting, the pores can be regarded as surface patches with a contact angle of θ(pore)(eq)=180°, we deduce an effective equilibrium contact angle θ(eff)(eq) on the porous surface from the Cassie-Baxter law. A spreading model is then proposed to describe both a prefactor and an exponent that are similar to a flat surface whose equilibrium contact angle is θ(eff)(eq). This model compares satisfactorily with a large number of numerical experiments under varying conditions.

[A novel quantitative approach to study dynamic anaerobic process at micro scale].

Anaerobic digestion is attracting more and more interests because of its advantages such as low cost and recovery of clean energy etc. In order to overcome the drawbacks of the existed methods to study the dynamic anaerobic process, a novel microscopical quantitative approach at the granule level was developed combining both the microdevice and the quantitative image analysis techniques. This experiment displayed the process and characteristics of the gas production at static state for the first time and the results indicated that the method was of satisfactory repeatability. The gas production process at static state could be divided into three stages including rapid linear increasing stage, decelerated increasing stage and slow linear increasing stage. The rapid linear increasing stage was long and the biogas rate was high under high initial organic loading rate. The results showed that it was feasible to make the anaerobic process to be carried out in the microdevice; furthermore this novel method was reliable and could clearly display the dynamic process of the anaerobic reaction at the micro scale. The results are helpful to understand the anaerobic process.

Impacts of hydrodynamic shear force on nucleation of flocculent sludge in anaerobic reactor.

The Sludge granulation in an anaerobic reactor consists of two steps: nucleation and maturation of nuclei. Nucleation as the starting point is of particular importance. In this paper, the nucleation of flocculent sludge as seed under weak, strong and violent hydrodynamic shear conditions is studied with an original quantitative method, and then the satisfactory linear correlations between the average sludge diameters and the operation time during the nucleation are demonstrated. Nucleation under strong shear conditions with a shear rate of about 8.28 s(-1), corresponding to superficial liquid and gas velocities of 2.66 and 0.24 m h(-1), develops fastest compared to weak shear conditions with a shear rate of about 0.04 s(-1) and violent shear conditions with a shear rate of about 12.42 s(-1) with the average augmentation rate of average sludge diameter of 0.57, 0.40 and 0.41 microm day(-1) respectively. One of the major mechanisms of the shear force on nucleation is that a high shear force accelerates the extracellular protein secretion of sludge. Although high extracellular protein content benefits nucleation, it is also shown that the extracellular proteins over-produced above around 80.5mg gVSS(-1) leads nuclei to weaken and inhibit nucleation. So the violent shear force would result in disruption and wash-out of nuclei. However, the high extracellular polymers could intensify the shear force by raising the viscosity in the reactor, thus, in practice, it is important to monitor the shear conditions and extracellular protein content of sludge simultaneously in high rate reactors for stable operation.