Improving physicochemical characteristics and anaerobic digestion performance of rice straw via ammonia pretreatment at varying concentrations and moisture levels

Rice straw physicochemical characteristics and anaerobic digestion(AD) performance via ammonia pretreatment at varying ammonia concentrations(2%, 4%, and 6%) and moisture contents(30%, 50%, 70%, and 90%)under a mild condition were investigated. The results showed that the ammonia pretreatment effectively damaged the rice straw structure, increased the soluble organic concentration, and improved rice straw hydrolysis and AD performance. After pretreatment, the ester bond and ether bond were ruptured in lignocellulose and the volatile fatty acids(VFAs) were within the range of 1457.81–1823.67 mg·L~(-1). In addition, ammonia pretreatment had high selectivity on lignin removal, resulting in a maximum lignin removal rate of 50.80%. The highest methane yield of rice straw was 250.34 ml·(g VS)~(-1) at a 4% ammonia concentration coupled with a 70% moisture content, which was 28.55% higher than that of the control. The result showed that ammonia pretreatment of rice straw is technically suitable to enhance AD performance for further application.     

A radar coal thickness sensor

A radar coal thickness sensor is being developed by the Bureau of Mines to measure both the dielectric constant and thickness of a coal seam as part of a sensor array supporting a computer-assisted coal mining machine. The noncontacting stepped-CW radar sensor measures the complex reflection of coefficient of the coal-shale interface to resolve the coal thickness to sub-wavelength accuracies. The technique uses a monostatic antenna configuration. Transfer function errors are identified by using spatial modulation created by antenna motion. Synthetic range gating is used for clutter rejection. Finally, polarimetric scattering matrix techniques are used to calculate the dielectric constant and thickness of the multilayered coal/shale media. Data taken both in the laboratory and in an underground mine, in the 0.6-1.4 GHz range, with a network analyzer and dipole antenna, have validated the technique. Accurate in situ measurements were made of a coal seam 6 in (15.2 cm) thick with a dielectric constant of 4. The coal thickness was confirmed by physical measurement. An independent measurement of the coal dielectric constant confirmed the accuracy of the noncontacting dielectric measurement technique     

Comparative analysis of residence and diffusion times in rotating bed used for biogas upgrading

Rotating bed can be used in desorption operation of biogas upgrading as a new technology. For enough time to desorb, it is important to study the relationship between the residence time of liquid in rotating bed and the material diffusion time of liquid droplet in desorption process. By theoretical deduction, the exponential relation between residence time and liquid flow rate and rotational speed and kinematic viscosity is obtained. By analyzing the solution of nonlinear partial differential equation, the time law of material diffusion in the droplet is obtained. Moreover, by comparing the residence and diffusion times, the diffusion time can be within or out of residence time range, which has a direct relationship to rotational speed and liquid flow. By experiment, the comparison between residence and diffusion times is more realistic when the rotational speed is higher.     

Effect on anaerobic digestion performance of corn stover by freezing–thawing with ammonia pretreatment

In order to enhance the biomethane production from corn stover, choosing effective pretreatment is one of the necessary steps before starting anaerobic digestion(AD).This study was aimed to analyze the effectiveness of freezing–thawing with ammonia pretreatment on substance degradation and AD performance of corn stover.Three ammonia concentrations(2%, 4%, and 6%) with two different moisture contents(50% and 70%) were used to pretreat the corn stover at two temperatures(-20 ℃ and 20 ℃).The result showed that an optimum pretreatment condition for corn stover was at the temperature of -20 ℃, moisture content of 70% and ammonia concentration of 2%.Under the optimum pretreatment condition, the maximum biomethane yield reached 261 ml·(g VS)~(-1), which was 41.08% higher than that of the untreated.Under different pretreatment conditions,the highest loss of lignin at -20 ℃ with 2% ammonia concentration was 63.36% compared with the untreated.The buffer capacity of AD system was also improved after the freezing–thawing with ammonia pretreatment.Therefore, the freezing–thawing with ammonia pretreatment can be used to improve AD performance for corn stover.This study provides further insight for exploring an efficient freezing–thawing with ammonia pretreatment strategy to enhance AD performance for the practical application.     

The relationships among sCOD,VFAs, microbial community,and biogas production during anaerobic digestion of rice straw pretreated with ammonia

This study investigated the effects of soluble chemical oxygen demand (sCOD), volatile fatty acids (VFAs), and microbial community on biogas production in the process of rice straw (RS) anaerobic digestion (AD). The results showed that the sCOD concentrations and VFA production appeared the same trend, which was inversely related with that of daily biogas production. The cumulative methane yield of RS was 194.9 ml·(g VS)^-1·^-1. The modified Gompertz model is the best fit for measured methane yields of RS in the three kinetic models of first-order kinetic, Cone and modified Gompertz. Firmicutes, Bacteroidetes, and Euryarchaeota were the dominant microbial phyla throughout AD process. At the genus level, the microorganisms mainly composed of Clostridium, Vadin, Terrisporobacter, Methanosaeta, Methanobacterium, and Methanosarcina. Proteiniphilum showed strong relationship with sCOD and VFA production. Clostridium and Terrisporobacter displayed relationship with biogas production. Therefore, in order to improve the stability of the AD system, the parameter changes of VFAs, sCOD, and biogas yield were monitored in the RS AD process. The study can provide theoretical basis for improving the efficiency of RS AD.