Search

The pit structure optimized drip irrigation emitter (PODE) is a novel type of irrigation emitter that may provide shunts, quick diversion, and mixed flow to maximize energy loss. To study the influence of the geometric parameters of the flow channel on the hydraulic characteristics and energy loss effect, twenty-five sets of orthogonal test schemes were established. Using numerical simulation and verification tests, the flow index and energy loss coefficient were obtained. The results showed that the flow index of the PODE was 0.4632-0.5265, and its hydraulic performance was good. The energy loss coefficient under the pressure head of 5-15 m was 510-2221, which showed that the energy loss effect was obvious. The influence order of the geometric parameters on the flow index was B>P>C>D>A, the optimal solution was P0.6D1.4A85B0.25C0.12. The determination coefficient of the regression model based on geometric parameters and flow index was 0.85. In addition, the verification test showed that the relative error among the test value, simulated value, and estimated value were less than 5%, and the flow index can be estimated reliably. The research can provide a reference for the pre-research and evaluation of the hydraulic performance and energy loss effect of the PODE.

Agricultural non-point source pollution has become a matter of increasing public concern, and modern agriculture is gradually transforming into agglomeration, so it is important to study the influence of agricultural agglomeration on agricultural non-point source pollution to coordinate the relationship between resources, environment, and agricultural economic growth for guidance. With a focus on 89 prefecture-level cities in the main agricultural production areas of the Yangtze River basin in China, the authors analyzed the spatial and temporal evolution trends of agricultural agglomeration and agricultural non-point source pollution from 2000 to 2020 and then empirically tested the spatial spillover effects of agricultural agglomeration on agricultural non-point source pollution based on the spatial Durbin model (SDM). The results show that: (1) Between 2000 and 2020, agricultural agglomeration, in general, decreased from 0.364 to 0.342, and cities with agglomeration values in the third and fourth ranks are mainly located in the area north of the Yangtze River and have a tendency to extend southward over time. Agricultural non-point source pollution shows a general trend of increasing and then decreasing; its emissions rose from 404.319 × 104 tons in 2000 to 464.341 × 104 tons in 2015, and then fell to 373.338 × 104 tons in 2020, emissions in the third and fourth class of cities are mainly located in the middle and lower basin of the Yangtze River; High-value hots-pot areas of agricultural agglomeration, that is, areas with high spatial correlation, are mainly located in the upper and lower Yangtze River basin, and the areas with the higher spatial correlation of agricultural non-point source pollution are distributed in the upper, middle and lower basin of the Yangtze River. (2) The whole basin and upper basin exhibit positive and negative spatial spillover effects of agricultural non-point source pollution, Spillover effects values are 0.300 and −1.086, respectively; Agricultural agglomeration of the Whole Basin has a positive direct effect and a negative spatial spillover effect on agricultural non-point source pollution, the effect values are 0.846 and −0.520, respectively. (3) In addition to the core explanatory variable, agricultural production conditions and the share of livestock and poultry industry have a positive direct effect (the effect values are 0.109 and 0.048, respectively) and a negative spatial spillover effect (the effect values are −0.520 and −0.910, respectively) on agricultural non-point source pollution, while agricultural population size has a positive direct effect and spatial spillover effect, the effect values 0.099 and 0.452 respectively; The urbanization rate exacerbates the emission of agricultural non-point source pollution, the effect value is 0.110. while the industrial structure reduces the emission of agricultural non-point source pollution, the effect value is −0.438, but neither has a spatial spillover effect. The results imply that some effective policy measures, such as strengthening research on nutrient requirements and fertilization techniques for major crops, improving farmland infrastructure, scientifically planning and monitoring the scale of livestock farms, and strengthening inter-regional coordination and cooperation in the fight against pollution, should be taken to achieve ecological and sustainable objectives.

To explore the performance of the ground source thermal energy management system under the cold and heat sources, based on the cold and heat auxiliary technology, a ground source thermal energy composite management system is constructed and simulated. The constructed ground source heat pump-refrigeration unit-hybrid heating management system of urban heating networks, as well as the simple system, are analyzed and investigated in terms of power consumption and underground temperature control. The research results show that the constructed ground source heat pump-refrigeration unit-hybrid heating management system of the urban heating network has lower power and energy consumption than a simple system during the same period, which meets the economic requirements and guarantees the system with relatively low energy consumption. For underground temperature control, the constructed system is more stable than a simple system without excessive temperature fluctuations. The operation control strategy of the constructed system is mainly for chiller units, heat pump units, cooling towers, source side, and side circulation water pump modules. In summary, the constructed ground source heat pump-refrigeration unit-hybrid heating management system of an urban heating network based on the ground source heat pump meets the requirements for energy consumption and temperature control and can operate the control strategy normally. The results are significant for subsequent researches on the ground source thermal energy management system based on cold and heat auxiliary technology.

In this study, Anaerobic Digestion Model No. 1 (ADM1) were modified to simulate anaerobic digestion (AD) process of microcrystalline cellulose (MCC) and five lignocellulosic substrates, with the goal of predicting the hydrolysis rates of holocellulose fractions in environments with and without lignin inhibition. After model verification, the hydrolysis rate constant of MCC, i.e., the hydrolyzability of cellulose without lignin inhibition, was 3.227 d-1, while those of the holocellulose fractions of five lignocellulosic substrates (I_khyd) were in the range of 1.270 d-1 to 3.364 d-1 (average of 2.242 d-1), which demonstrated remarkable suppression of holocellulose hydrolysis by lignin. Lignin inhibition index (LII) was proposed as an indicator to intuitively quantify and characterize the lignin inhibitory strength in a specific substrate. A series of factors with the potential to affect the LII were analyzed sequentially. This study provides an advanced understanding of the participation and behavior of lignin in the AD process.

Crystalline cellulose is fully resistant during anaerobic digestion (AD), which brings uncertainty to the use of mathematical models to simulate the dynamic AD process of lignocellulosic waste. In present study, a modified mathematical model, with crystalline cellulose as the primary consideration, was established based on Anaerobic Digestion Model No.1 to simulate the anaerobic bioconversion of vegetable crop residues (VCR) under mesophilic condition. In this model, VCR was divided into inert fraction (contained lignin and crystalline cellulose), as well as biodegradation parts of slowly hydrolysis fraction (SHF, contained hemicellulose and amorphous cellulose), and readily hydrolysis fraction (RHF, contained other organic components in the VCR). Data from a series of batch experiments have been used for the calibration and verification of this model. As a result, the calibrated model was found to match reasonably well the methane production data of three different VCRs, which implies that it was feasible to fractioned VCR into three fractions (SHF, RHF and inert part), and the operation that classified crystalline cellulose into the inert part, while regarded amorphous cellulose as SHF was appropriate. In order to be suitable for simulating the AD process of more other types of lignocellulosic waste, the model needs further modification and inspection.