CN103969419A - Indoor simulation system applied to pollutant migration process researches under artificial rainfall - Google Patents

Abstract

The invention provides an indoor simulation system applied to pollutant migration process researches under artificial rainfall. The indoor simulation system can satisfy similarity conditions of the rainfall uniformity, the median raindrop diameter, the terminal velocity and the raindrop spectrum, can be directly used in the researches and stimulation of the migration process of soil (deposit)-water interface pollutants under the artificial rainfall conditions, and mainly includes a rainfall control system, a pollutant vertical transport simulation system and a sample collection system; and the above simulation device can be used as an experimental device for carrying out migration conversion and repair mechanism researches of pollutants in soil/sediment. The simulation device has the characteristics of strong practicability, high reliability, low cost, compact structure, convenient installation, demounting and replacement of parts, suitable simulation conditions, maneuverability and good application popularization value.

Description

Indoor Simulation System Applied to the Study of Pollutant Migration Process under Artificial Rainfall Conditions

technical field

The invention relates to laboratory simulation equipment for studying pollutant interface migration and physical process, in particular to an indoor simulation control system applied to the research of pollutant migration and transformation in soil and water interface process, which belongs to the field of geology and environmental science.

Background technique

When carrying out soil pollutant migration process tests, soil infiltration tests, and other scientific experiments that require simulated rainfall, in order to avoid the influence of natural factors, it is necessary to quickly obtain the data required for the test within a predetermined time and successfully complete the planned test. Usually, artificial simulated rainfall devices are used to artificially simulate rainfall. The current artificial simulated rainfall is usually divided into two types: nozzle type and needle tube type. Influenced by the effect, the water flow is broken to form raindrops of different sizes, which fall to the surface to form rainfall. By changing the number of swings of the nozzle, 3-10 fixed rainfall intensities (hereinafter referred to as rain intensities) can be obtained. In the current nozzle-type artificial simulated rainfall device, the raindrops are closer to natural rainfall, but the uniformity of rainfall is not very good, and the cost is also relatively expensive.

At present, it is difficult to fully consider the experimental conditions, such as rainfall, dynamic monitoring and collection of profile samples, and interface environmental gradient control, in the research of pollutant migration process and soil-water interface in the laboratory. The main reason lies in the lack of experimental equipment. Perfect and unintegrated. The artificial rainfall produced by an ideal simulation device should be similar to natural rainfall. The main rainfall indicators include rainfall intensity, rainfall uniformity, raindrop diameter distribution, and raindrop terminal velocity. For the simulation experiment of rainfall runoff, as long as it has the similarity of rainfall uniformity and rainfall intensity, it can meet the experimental requirements; for the simulation experiment of rainfall erosion, as long as it has the requirements of rainfall uniformity, raindrop median diameter, terminal velocity and raindrop spectrum The similarity condition also meets the experimental requirements.

Due to the long period of natural rainfall, strong seasonal distribution, and extremely uneven annual division, the observation period of field and experimental plots based on natural rainfall is long and the speed of data acquisition is slow. The chemical, physical, and biological processes at the soil-rainfall interface and soil (sediment)-water interface are the most active in farmland, and these processes are affected by field experimental conditions, wind waves, ships, and benthic animals in actual processes. , and difficult to capture. Therefore, it is necessary to develop an artificial rainfall simulation device to replace natural rainfall as much as possible, to accelerate the progress of experiments such as soil erosion, rainfall runoff, and infiltration, to avoid the influence of natural factors, and to quickly obtain the data required for the experiment within a given time.

Contents of the invention

1. Purpose of the invention

The purpose of the present invention is to be aimed at the practical problem existing in the prior art, considering that the main factor that influences pollutant migration transformation in the actual process is rainfall, is the pollutant migration of specific soil-rainfall interface and soil (sediment)-water interface The research provides convenience, and provides an indoor simulation system applied to the research of pollutant migration process under artificial rainfall conditions, which can meet the similarity conditions of rainfall uniformity, raindrop median diameter, terminal velocity and raindrop spectrum, and can be directly used in artificial rainfall conditions Research and simulation of the migration process of pollutants at the soil (sediment)-water interface.

2. Technical solutions

The above-mentioned purpose of the present invention is achieved in that a kind of indoor simulation device applied to soil/sediment-water interface process research under artificial rainfall conditions is characterized by a rainfall control system, a pollutant vertical migration simulation system, a sample The collection system consists of three parts; the rainfall control system is mainly composed of water supply, rain, water supply pipes and valves. The characteristic is that the water supply device uses a larger diameter container to ensure that the water level in the water supply device will not change significantly in a short period of time under the condition of a certain water supply intensity, and the water head difference between the water supply device and the rainfall device is adjusted by the water level controller. The rainfall device is made of a 16mm cable outer tube drilled and connected with a No. 8 medical injection needle. By using different numbers of needles and adjusting the water level of the rainfall device, it can meet the needs of simulating different rainfall. One end of the rainfall device is connected to the water supply device through a water supply pipe with a control valve, and the other end is closed with a rubber plug as the discharge switch of the rainfall device; the vertical migration simulation system of pollutants is characterized in that the soil column cabinet is mainly composed of plexiglass columns . The glass column plate on the side of the soil column is marked with scale lines to facilitate the observation and recording of the seepage process in the soil column. Sampling round holes are arranged at different depths on the side wall of the surrounding soil column. The diameter of the hole is 4cm to monitor the change process of pollutant concentration in the soil/sediment at different depths in the simulation system. It can also be sealed with a cover, and there is a sealing rubber ring inside the cover. There are water inlets and outlets outside the cover, and there are threads in the water inlet and outlets, which can be sealed by sealing screws; the sample collection system is characterized in that it can realize the regular collection and replacement of infiltrating soil aqueous solution through the combination of rubber tubes and glass tubes, which can be conveniently To realize the collection of water samples.

3. Technical effects

Advantage and effect of the present invention:

(1) The rainfall uniformity coefficient of the device is greater than 85%, which has high rainfall stability and good repeatability. The characteristics of the generated raindrops have a high similarity to those of natural rainfall.

(2) The device is composed of independent nozzles with different aperture sizes, and each simulated rainfall unit device is composed of 16 nozzles, which can be expanded arbitrarily as required. After the lightweight improvement of the device, it can be moved from one location to another;

(3) It can simulate the migration and transformation characteristics of pollutants in the process of soil and water interface under the control of different rainfall intensities, and the simulated soil and soil characteristics can be carried out according to actual conditions;

(4) 4. During the operation of the device, as long as the power supply is normal and the water quality is clean, it can ensure the continuous progress of the experimental research and has high reliability. Routine maintenance is mainly to clean the pool and prevent nozzle clogging;

(5) The cost of the device is low, which is convenient for coordination and collaborative testing with the scale model rainfall device under construction, so that the test data can be compared.

Brief Description of Drawings and Drawings

Fig.1 Side view of rainfall simulation device

Figure 2 Top view of rainfall simulation device

Figure 3 Side view of soil column

Figure 4 Stereoscopic view of the simulation device

In the figure: 1, pulley; 2, water level lifting controller; 3, hanging rope; 4, water supply device; 5, water level; 6, water level control faucet; 7, rainfall simulator; 8, pinhole rainfall device; 9, sensor; 10, homogeneous soil; 11, plexiglass column; 12, permeable membrane; 13, soft conduit; 14, surface runoff hole; 15, runoff collection bottle; 16, sampling/buffer bottle; 17, quartz sand layer.

Detailed ways

(1) According to Fig. 2, carry out the installation of rainfall device;

(2) According to Fig. 1, carry out the pre-experiment of rainfall intensity under different liquid level (5) conditions, obtain the rainfall intensity values of different depths, and mark on the cylinder surface of the rainfall control system in Fig. 1;

(3) Collect the soil medium that needs to be tested, fill it according to the soil quality of the layer, mix the soil quality of the same layer evenly before filling, and fill it layer by layer into the pollutant vertical migration simulation system in Figure 3 according to the experimental requirements and purposes ;

(4) Install sensors and sampling holes at different depths in the pollutant vertical migration simulation system, and seal the sampling holes with rubber stoppers;

(5) Fix the rainfall control system Figure 1 and the pollutant vertical migration simulation system Figure 3 according to the schematic diagram 4 to ensure the stability and reinforcement of the device during the experiment;

(6) according to Fig. 3, carry out the installation and fixing of surface runoff device (15) and underground seepage device (16) sample collection system;

(7) Check each sampling device and water inlet device until all pipes and devices are connected;

(8) Start the rainfall device, adjust the frequency motor, and adjust to the preset rainfall intensity;

(9) (according to the purpose of the experiment) calculate the time and carry out routine sampling; until all samples are collected; analyze the physical, chemical and biological properties of the water samples according to the experimental requirements;

(10) Observe the reading change process of the sensor, set the monitoring time frequency (according to the experimental purpose), and simultaneously collect and analyze the solutions at different depths of the soil;

(11) (according to the purpose of the experiment) after taking out the sampling tube containing the sediment, carry out layered sampling of the sediment or only take the surface sample, and then analyze the physical, chemical and biological properties of the sediment sample;

(12) Check the accessories of the instrument, and the experiment is over.

Implementation case 1: Research on the migration law and leaching flux of nitrogen in the soil of a typical agricultural area of Fuxian Lake in Yunnan under different rainfall intensities. A large amount of farmland is concentrated in the catchment area on the north bank of Fuxian Lake in Yunnan. The nitrogen and phosphorus pollution caused by the application of chemical fertilizers in farmland has attracted more and more attention. Agricultural non-point source pollution has now become an important factor in the water pollution of Fuxian Lake. . The groundwater level in the north bank of Fuxian Lake is relatively shallow, about 60cm. Due to the impact of rainfall infiltration, the groundwater in this area may have been polluted by farmland soil, pesticides and fertilizers, and the north bank plain area has an average slope of 6.4‰ from the north (plain area) Tilting to the south (the lake), the general flow direction of groundwater is from north to south, infiltrating into the lake. Therefore, shallow groundwater has become one of the main carriers for transporting nutrients to the lake. Due to the backwardness of the current monitoring methods and the randomness of the rainfall process, the observation of the vertical migration process and law of nutrients in the soil under natural rainfall conditions has a long cycle, a large workload, and inaccurate data to a large extent. Difficulties and shortcomings. In order to have an accurate, rapid and comprehensive understanding of the rainfall-infiltration-runoff-seepage law and the nitrogen dynamic migration process, it is an effective method to use the method of artificially simulating rainfall and conduct indoor soil column simulation experiments. During the experiment, a representative vegetable field in the Liangwang River Basin in the catchment area of Fuxian Lake was first selected to collect soil samples. The soil column for testing was obtained by layered sampling and filling method according to bulk density. The experiment is based on the probability frequency distribution analysis of the short-term rainfall intensity in the Fuxian Lake area over the years. Based on this, four different rainfall intensities are determined. These four intensities represent the intensity of the common short-term rainfall process in the local area. , the rainfall intensities of Experiment 1 to Experiment 4 were 0.59, 0.47, 0.38, 0.24mm min ^-1 . Four groups of experiments were carried out, and two different initial nutrient salt contents were designed for each group. Among them, the initial nutrient salt contents of the soil in experimental group 1 and experimental group 2 were the same, and they were taken from the test soil at the same time and at the same place; the experimental group 3. The initial nutrient content of the soil in the experimental group 4 is the same, which is the same batch of soil. Indoor simulation experiments were carried out using the indoor simulation system device for the study of pollutant migration process under artificial rainfall. The rainfall intensity of each group of experiments was different. During the experiment, the basic physical properties of the soil, the initial nutrient content and the nutrient salt of the seepage concentration was analyzed. During the experiment, the rainfall intensity is controlled by a PVC cylinder pipe with scale and overflow port. After the water is injected into the PVC cylinder through the rubber pipe, part of it seeps out through 32 evenly distributed pinholes installed at the bottom of the PVC pipe body. It acts on the soil surface, and the excess water is discharged through the lateral overflow port, so that the water pressure of the cylinder is always in a constant state, and the rainfall intensity is also in a constant state. By adjusting different water pressures, different water pressures can be obtained. The constant rainfall of rainfall intensity, the rainfall intensity can be obtained by calculating the water infiltration per unit time. Spread a layer of soft emery cloth and filter paper on the soil surface to allow water to slowly infiltrate into the soil layer to prevent strand flow and preferential flow. The seepage liquid is manually collected with a measuring cup after passing through the quartz sand filter layer for analysis and determination. The simulated experiment soil column is designed by a plexiglass column, with a height of 50cm and a diameter of 18cm. A layer of quartz sand filter layer is added at the bottom of the soil column to prevent the clogging of the infiltration port, and the seepage is collected regularly through the seepage bottle. There is a lateral hole with a diameter of 4cm on the side of the soil column. When the runoff flow is greater than the soil infiltration capacity, it can satisfy the surface runoff to flow out of the lateral hole. As a result of the measurement, the calculation results of the percentage of seepage in the total infiltration of four groups of experiments varied from 0.40 to 0.47, and the average value was 0.44. From the soil column experiment with the same initial nutrient content, the total nitrogen in the seepage liquid shows an increasing trend with the increase of the rainfall intensity, but the influence of the change of rainfall intensity on the total phosphorus in the seepage liquid does not show an obvious rule With the increase of rainfall intensity, the outflow concentration of ammonium nitrogen in the seepage fluid showed a decreasing trend, while the outflow concentration of nitrate nitrogen in the seepage fluid was the opposite. The infiltration capacity and migration speed of nitrate nitrogen are obviously stronger than that of ammonium nitrogen, and the impact of rainfall intensity on nitrate nitrogen is greater than that of ammonium nitrogen. The device can be used to study the migration and transformation of soil/sediment pollutants under artificial rainfall conditions, and the height of the device setting can also meet the needs of the experiment. The numerical simulation of the indoor rainfall test was carried out by HydrusID software. The numerical simulation and the measured results are basically consistent, which further verifies the feasibility and accuracy of the test. This test provides a new way for the study of pollutant migration process under artificial rainfall conditions.

Claims (3)

1. An indoor simulation system applied to the study of pollutant migration process under artificial rainfall conditions, which is characterized by a high water level tank and a rainfall control system, a pollutant vertical migration simulation system and a sample collection system. 2. The rainfall control system according to claim 1, characterized in that the rainfall in the range of 5-25mm/h can be provided by controlling air pressure and water depth. If intermittent rainfall is used, a larger area, especially less intense rainfall, can be obtained. 3. According to the pollutant vertical migration system described in claim 1, it is characterized in that there are sampling circular holes at different depths on the side of the sampling pipe wall, and the diameter of the hole is 4cm, so as to monitor the soil/sediment differences in the simulation system. The change process of pollutant concentration in depth can also be sealed with a cover, and there is a sealing rubber ring inside the cover; there is a water inlet and outlet outside the cover, and there are threads in the water inlet and outlet, which can be sealed by sealing screws.