Applied Mechanics and Materials Vols. 587-589

Abstract: Sand-stabilization may exert enormous effects on plant abundance in interdune lowlands in the active sand dune fields. We investigated the plant abundance of 11 interdune lowlands in stabilized and active dunes, respectively, and analyzed the relationship of plant abundance and lowland area. 1) With the enlargement of lowland area, plant abundance of interdune lowlands in stabilized and active dune increased following logarithmic and power functions, respectively. When the area was the same, abundance of stabilized dunes was more than that of active dunes. 2) With the increasing of lowland area in stabilized and active dunes, psammophytes plant abundance relative to the overall plant abundance decreased exponentially. When the area was the same, the percentage in lowlands of active dunes was more than that of stabilized dunes. We concluded that the practice of sand-stabilization could improve plant abundance in interdune lowlands, however, which is at the cost of loss of psammophytes.

Abstract: Tropical forest plants contain a variety of secondary metabolites, and plant aqueous extracts can be used as urease and nitrification inhibitors to improve nitrogen use efficiency and reduce the negative environmental effects. An incubation experiment was carried out to investigate the effects of aqueous extracts of 60 tropical forest plant species from 16 families on urea hydrolysis and nitrification. The results indicated that the aqueous extracts from 3 of the tropical forest plants (Aphanamixis polystachya, Toona sinensis, Vatica mangachapoi) belonging to meliaceae and dipterocarpaceae showed good inhibitory effects on urease, and the aqueous extracts from 5 of the tropical forest plants (Cryptocarya chinensis, Cryptocarya hainanensis, Toona sinensis, Khaya senegalensis, Hopea hainanensis) belonging to lauraceae, meliaceae and ipterocarpaceae showed good inhibitory effects on nitrification. The inhibitory effects of active substances in plants were affected by extract temperature, and the plants can be divided into three types by solubility and thermal stability. Toona sinensis had the most potential for development in this study as urea additive. The inhibitory effects of aqueous extracts of Toona sinensis leaves on urea hydrolysis and nitrification increased with increasing concentration of aqueous extracts, the strongest inhibitory effect on urease occurred after 2-3 d of incubation, and the strongest inhibitory effect on nitrification occurred after 2-3 weeks of incubation.

Abstract: Sea water utilization projects are catching attention as the seawater utilization industry continues to grow. This paper analyzes the marine environment impact from different kind of sea water utilization projects such as seawater desalination, direct seawater utilization and seawater chemical resource extraction, and brieflypresents relevant countermeasures.

Abstract: Landfill cover systems have to serve as a hydraulic barrier as well as a gas barrier. The ability of multilayered cover systems to mitigate landfill gas migration was assessed. A finite element model, SEEP/W^®, was used to simulate the landfill cover system. It was found that gas advective flux through the single GCL barrier was highly dependent on the differential gas pressure across the cover system and the conditions of soils above the barrier layer. The change from wet to dry condition resulted in the increase of gas flux up to 3000 times. Gas flux variations were much lower for the case of a single CCL. The use of a geomembrane on top of a CCL or a GCL significantly increased the effectiveness of the barrier layer in mitigating gas migration, particularly in a dry climatic condition. Furthermore, the change of the cover conditions had less effect on gas flux through a composite cover system than gas flux through a single barrier cover system. For the effective control of landfill gas migration, the cover system must be maintained at the high moisture content conditions.

Abstract: The application of molecular biology technique to expand the breadth and depth of the study of environmental microbiology, the researchers from the microscopic point of view more detailed deep understanding of the physiological and biochemical mechanisms of microorganisms on the degradation of pollutants, and at the same time, the advanced molecular biology technology for environmental monitoring, environmental pollution treatment, bioremediation of the contaminated environment provides the basis and method for faster, more sensitive, more scientific, which greatly promoted the progress of pollution control practice. The basic theory of molecular biology technology and its application in wastewater through the detection of microorganisms are shown.

Abstract: To discuss the internal effect of urea (CO(NH₂)₂) pretreatment on anaerobic digestion biogas production of rice straw waste, a self-designed laboratory-scale continuous anaerobic biogas digester was used in this study. Anaerobic biogas slurry, urea pretreatment and anaerobic digestion were evaluated for biogas production from rice straw. The results showed that the peak value of biogas production was attained on the 17^th day by using 6% urea pretreatment on rice straw. However, the highest CH₄ content was 49.8% on the 15^th day for the 8% urea-treated rice straw. The cumulative biogas production of 6% urea pretreatment was the highest, about 16 540 mL, which was followed by 2% urea (12 283 mL), 8% urea (9 883 mL), and 4% urea (5 668 mL).

Abstract: Every year our country will produce large amounts of waste concrete, bring negative effect to the ecological environment. How to realize the recycling of waste concrete utilization has great significance for the sustainable development of ecology, environmental protection and social. This paper introduces the characteristics of recycled concrete and domestic experts and scholars research on it, and put forward prospect of the future of recycled concrete.

Abstract: The absorption characteristics of copper and the effect of spermidine on the absorption of copper ions were investigated in Salix Matsudana in a short-term hydroponic experiment. There different concentrations of copper ions with or without the addition of spermidine in nutrition solution were conducted in this experiment. The effect of spermidine on the adsorption by S. Matsudana was also studied. 5, 10, 20 mg/L were chosen as the copper stress concentration. Absorption time and the initial copper concentration influence the absorption process in S. Matsudana. The absorption rates increased very fast at the first hours then increased slightly and attained an asymptotic value. After 72 h, the removal rates of Cu were 75.00%, 61.47% and 43.60% with the initial copper concentrations of 5, 10, 20 mg/L, respectively. The addition of spermidine influenced the absorption process of Cu by S. Matsudana. In 72 h, the treatment with spermidine increased the copper removal by S. Matsudana than the only copper treatment. Results indicated that exogenous spermidine could improve the absorption of copper in S. Matsudana and was beneficial to phytoremediation in heavy metal contaminated environment.

Abstract: The oxygen supply, propelling and mixing performance optimization conditions of a reactor are studied by adopting a pilot-scale system and a production test system for an improved Carrousel oxidation ditch, including the influence of flow velocity on the mass transfer of DO, the influence of the flow state on the denitrification and energy conservation of the oxidation ditch, and the influence of the particle sizes of floc inactivated sludge on simultaneous nitrification and denitrification (SND). The results indicate that as the flow velocity increases, the mass transfer of DO is better. The appropriate operating condition is regulated and controlled so that the denitrification efficiency of the system can be improved. The starting number of aeration wheels is reduced from 5 to 2, the particle sizes of large-ratio floc in the activated sludge are increased from 20 to 130 μm, and the removal rate of total nitrogen is improved from 44%-49% to 69%-75%.

Abstract: Stability of coal-water suspension (WCS) is one of the main criteria for obtaining fuel efficient. In the present work we investigated the sedimentation stability of coal-water suspension of 35% (in the presence and absence of hexane) stabilized by sodium dodecyl sulfate. Found that pretreatment of coal hexane (before being crushed) and further stabilization of coal-water suspension of 35% sodium dodecyl sulfate at concentrations of 0.8-.1.0% helps to ensure a stable dispersion system.