DEVICE AND METHOD FOR DETERMINING DEGRADATION RATE OF BIODEGRADABLE POLYMERS IN SOIL

Abstract

A device for determining degradation rate of biodegradable polymers in soil, including a micro compressed air pump, a first CO.sub.2 absorption vessel filled with dry soda lime or an aqueous strong alkali solution, a CO.sub.2 indicator vessel filled with a barium hydroxide solution, a hollow leaching device, a second CO.sub.2 absorption vessel and a third CO.sub.2 absorption vessel connected in sequence through connecting pipes. A top of the hollow leaching device is provided with an end cover. An external water distributor filled with a leaching solution and a mechanical stirring device is arranged above the end cover. The external water distributor is in communication with an inner cavity of the hollow leaching device through a pipeline. A stirring shaft of the mechanical stirring device extends into the inner cavity. A stirring shaft is provided with a stirring paddle.

Claims

1. A device for determining a degradation rate of a biodegradable polymer in soil, comprising: a micro compressed air pump; a first CO.sub.2 absorption vessel; a CO.sub.2 indicator vessel; a hollow leaching device; a second CO.sub.2 absorption vessel; and a third CO.sub.2 absorption vessel; wherein the micro compressed air pump, the first CO.sub.2 absorption vessel, the CO.sub.2 indicator vessel, the hollow leaching device, the second CO.sub.2 absorption vessel, and the third CO.sub.2 absorption vessel are connected in sequence through a connecting pipe; a top of the hollow leaching device is provided with an end cover; an external water distributor and a mechanical stirring device are arranged above the end cover; the external water distributor is in communication with an inner cavity of the hollow leaching device through a connecting pipeline; a stirring shaft of the mechanical stirring device extends into the inner cavity of the hollow leaching device; the stirring shaft in the hollow leaching device is provided with a stirring paddle; the first CO.sub.2 absorption vessel is filled with dry soda lime or a first aqueous strong alkali solution; the CO.sub.2 indicator vessel contains a barium hydroxide solution; the external water distributor contains a leaching solution with a preset pH value; an upper part of the inner cavity of the hollow leaching device is filled with a certain mass of soil as a leaching zone; a bottom of the inner cavity of the hollow leaching device has an inverted cone shape and is filled with quartz sand particles as a filter zone; a bottom of the filter zone is provided with a water outlet; a lower part of the water outlet is provided with a leachate collecting container; and each of the second CO.sub.2 absorption vessel and the third CO.sub.2 absorption vessel is filled with a second aqueous strong alkali solution.

2. The device of claim 1, wherein the connecting pipe communicating the external water distributor with the inner cavity of the hollow leaching device is provided with a liquid inlet control valve.

3. The device of claim 1, wherein the hollow leaching device is a hollow cylindrical leaching device; and the water outlet of the hollow leaching device is provided with a leachate control valve.

4. The device of claim 1, wherein a connection between the stirring shaft of the mechanical stirring device and the end cover of the hollow leaching device is provided with a mechanical seal ring.

5. A method for determining the degradation rate of the biodegradable polymer in soil using the device of claim 1, comprising (S1) choosing a soil and a leaching solution according to an actual test objective and experimental conditions; evenly mixing a biodegradable polymer sample to be tested and a certain mass of the soil followed by feeding to the hollow leaching device; (S2) turning on the micro compressed air pump and the mechanical stirring device, and opening a liquid inlet control valve and a leachate control valve; and setting an air inlet flow rate, a liquid inlet flow rate, a stirring speed, and a liquid outlet flow rate according to the actual test objective and experimental conditions to allow the biodegradable polymer sample to be biodegraded in the soil under a set condition; (S3) regularly collecting a leachate in the leachate collecting container and the second aqueous strong alkali solution in the second CO.sub.2 absorption vessel and the third CO.sub.2 absorption vessel; measuring carbon contents in the leachate and the second aqueous strong alkali solution using an organic carbon analyzer or by an acid-base titration; wherein during a biodegradation process, if the barium hydroxide solution in the CO.sub.2 indicator vessel in an air input zone becomes turbid, it is required to replace the first aqueous strong alkali solution in the first CO.sub.2 absorption vessel and the barium hydroxide solution in the CO.sub.2 indicator vessel; (S4) repeating step (S3) until the biodegradable polymer sample is completely degraded or the degradation rate meeting the test objective is reached; and (S5) based on a measured data, determining a biodegradability and the degradation rate of the biodegradable polymer sample in the soil according to equation (1) shown as follows: $\begin{array}{cc}{D}_t=\frac{\left(m_{\mathrm{slt}}+m_{\mathrm{sct}}\right)-\left(m_{\mathrm{blt}}+m_{bct}\right)}{m_s{w}_c}\times 100;& \left(1\right)\end{array}$ wherein D.sub.t is a degradation rate of the biodegradable polymer sample in the soil from a beginning of the test to time t, expressed by %; m.sub.slt is a carbon content of all leachate samples collected from a treatment of the biodegradable polymer sample from the beginning of the test to the time t, with a unit of mg; m.sub.sct is a carbon content of all CO.sub.2 released from the biodegradation process of the biodegradable polymer sample from the beginning of the test to the time t, with a unit of mg; m.sub.blt is a carbon content of all leachate samples collected in a blank treatment from the beginning of the test to the time t, with a unit of mg; m.sub.bct is a carbon content of all CO.sub.2 released in the blank treatment from the beginning of the test to the time t, with a unit of mg; m.sub.s is a total mass of the biodegradable polymer sample added at the beginning of the test to the time t, with a unit of mg; and w.sub.c is a carbon content of the biodegradable polymer sample added at the beginning, expressed by %, wherein the carbon content is calculated from a chemical molecular formula of the biodegradable polymer sample or determined by an organic carbon analyzer or an elemental analyzer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] This FIGURE is a structural diagram of a device for determining a degradation rate of a biodegradable polymer in soil according to an embodiment of this application;

[0040] in the drawing, 1: micro compressed air pump; 2: first CO.sub.2 absorption vessel; 3: CO.sub.2 indicator vessel; 4: external water distributor; 4-1: liquid inlet control valve; 5: hollow leaching device; 5-1: biodegradable polymer sample to be tested; 5-2: soil; 5-3: quartz sand particle; 5-4: leachate control valve; 6: mechanical stirring device; 7: leachate collecting container; 8: second CO.sub.2 absorption vessel; and 9: third CO.sub.2 absorption vessel.

DETAILED DESCRIPTION OF EMBODIMENTS

[0041] This application will be described in detail below with reference to the embodiments and accompanying drawings.

Embodiment 1

[0042] As shown in the FIGURE, a device for determining a degradation rate of a biodegradable polymer in soil provided herein includes an air input zone, a water inlet zone, a leaching zone, a leachate collecting zone and a gas collecting zone. The air input zone includes a micro compressed air pump 1 configured to continuously and stably feed an airflow into the device, a first CO.sub.2 absorption vessel 2 filled with dry soda lime or the aqueous strong alkali solution to absorb CO.sub.2 in the airflow, and a CO.sub.2 indicator vessel 3 containing a barium hydroxide solution to determine whether there is CO.sub.2 mixed in the airflow by its turbidity. The water inlet zone is an external water distributor 4 containing a leaching solution with a preset pH value to realize a continuous and stable liquid feeding or an intermittent liquid feeding through the external liquid inlet control valve 4-1. The leaching zone is formed by a hollow leaching device 5 together with a mechanical stirring device 6. An upper part of an inner cavity of the hollow leaching device 5 is filled with a certain mass of soil 5-2 to biologically degrade a biodegradable polymer sample 5-1 to be tested in soil. A filter zone at a bottom of the inner cavity of the hollow leaching device 5 is designed into an inverted cone shape and is filled with quartz sand particles 5-3 to filter a leachate to prevent the soil and solid undegraded biodegradable polymer from flowing out. An upper part of the hollow cylindrical leaching device is provided with the mechanical stirring device 6. A connection between the stirring shaft of the mechanical stirring device and the end cover of the hollow leaching device is provided with a mechanical seal ring. The mechanical stirring device 6 is configured to evenly mix the biodegradable polymer and degradation products with the soil and promote the gas exchange between the soil and the upper air layer. A lower end of the hollow leaching device 5 is provided with an outlet and a leachate control valve 5-4 to control the discharge of the leachate. The leachate collecting zone is formed by a leachate collecting container 7, which configured to collect the leachate. The gas collecting zone includes a second CO.sub.2 absorption vessel 8 and a third CO.sub.2 absorption vessel 9, both of which contain an aqueous strong alkali solution to collect the CO.sub.2 gas generated from the biodegradation and mineralization of the biodegradable polymer.

Embodiment 2

[0043] A method for determining a degradation rate of a biodegradable polymer in soil using the device in Embodiment 1 is provided, which includes the following steps.

[0044] (S1) A soil and a leaching solution corresponding to an actual test objective and experimental conditions are chosen to obtain desired biodegradation conditions of the biodegradable polymer, and then a biodegradable polymer sample 5-1 to be tested and a certain mass of the soil are mixed evenly, and the device is assembled according to the FIGURE.

[0045] (S2) A micro compressed air pump 1 and a mechanical stirring device 6 are turned on, and a liquid inlet control valve 4-1 and a leachate control valve 5-4 are opened. An air inlet flow rate, a liquid inlet flow rate, a stirring speed, and a liquid outlet flow rate are set according to the actual test objective and experimental conditions to allow the biodegradable polymer sample to be biodegraded in the soil under a set condition.

[0046] (S3) A leachate in a leachate collecting container 7 and a strong alkali solution in a second CO.sub.2 absorption vessel 8 and a third CO.sub.2 absorption vessel 9 are collected regularly. Carbon contents in the leachate and the strong alkali solution are measured using an organic carbon analyzer or by an acid-base titration. During a biodegradation process, if a barium hydroxide solution in a CO.sub.2 indicator vessel 3 in an air input zone becomes turbid, it is required to replace the strong alkali solution in a first CO.sub.2 absorption vessel 2 and the barium hydroxide solution in a CO.sub.2 indicator vessel 3.

[0047] (S4) Step (S3) is repeated until the biodegradable polymer sample is completely degraded or the degradation rate meeting the test objective is reached.

[0048] (S5) Based on a measured data, a biodegradability and the degradation rate of the biodegradable polymer sample in soil are determined according to equation (1) shown as follows;

[00002]$\begin{array}{cc}{D}_t=\frac{\left(m_{\mathrm{slt}}+m_{\mathrm{sct}}\right)-\left(m_{\mathrm{blt}}+m_{bct}\right)}{m_s{w}_c}\times 100;& \left(1\right)\end{array}$

[0049] where D.sub.t is a degradation rate of the biodegradable polymer sample in the soil from a beginning of the test to time t, expressed by %;

[0050] m.sub.slt is a carbon content of all leachate samples collected from a treatment of the biodegradable polymer sample from the beginning of the test to the time t, with a unit of mg;

[0051] m.sub.sct is a carbon content of all CO.sub.2 released from the biodegradation process of the biodegradable polymer sample from the beginning of the test to the time t, with a unit of mg;

[0052] m.sub.blt is a carbon content of all leachate samples collected in a blank treatment, i.e. treatment without adding the biodegradable polymer sample from the beginning of the test to the time t, with a unit of mg;

[0053] m.sub.bct is a carbon content of all CO.sub.2 released in the blank treatment from the beginning of the test to the time t, with a unit of mg;

[0054] m.sub.s is a total mass of the biodegradable polymer sample added at the beginning of the test, with a unit of mg; and

[0055] w.sub.c is a carbon content of the biodegradable polymer sample added at the beginning, expressed by %, wherein the carbon content is calculated from its chemical molecular formula or determined by an organic carbon analyzer or an elemental analyzer.

[0056] Based on the steps in the method provided above, in the biodegradability and biodegradation rate test of the biodegradable polymer in soil, all the samples have the same shape and size, and the air inlet flow rate, the liquid inlet flow rate, the stirring speed and the liquid outlet flow rate are the same too, which not only ensure the comparability of the degradation data, but also enable to choose different soils and leaching solutions to realize the biodegradability tests under different conditions.

Embodiment 3

[0057] A method for determining a degradation rate of a biodegradable polymer in soil using the device in Embodiment 1 is provided, which includes the following steps.

[0058] (S1) A biodegradability of a biodegradable cellulose in Taiyuan city (Shanxi, China) area is investigated. The cellulose powders containing 100 g of carbon is mixed evenly with 6 Kg of a soil sample collected from a suburban farmland in Taiyuan and air-dried and sieved to obtain a mixture. Then the mixture of the cellulose and soil is added into a leaching column with a diameter of 8 cm and a height of 1.2 m. A first CO.sub.2 absorption vessel 2 is filled with a 20 wt % sodium hydroxide solution. A CO.sub.2 indicator vessel 3 is filled with a 1 wt % barium hydroxide solution. A second CO.sub.2 absorption vessel 8 a third CO.sub.2 absorption vessel 9 are both filled with a 10 wt % sodium hydroxide solution. An external water distributor 4 is filled with deionized water with pH=7. The device is assembled according to the FIGURE.

[0059] (S2) A micro compressed air pump 1 and a mechanical stirring device 6 are turned on, and a liquid inlet control valve 4-1 and a leachate control valve 5-4 are opened. An air inlet flow rate is set at 0.1 L/h; a liquid inlet flow rate is set at 0.05 L/h; a stirring speed is set at 10 r/min; and a liquid outlet flow rate is set at 0.05 L/h.

[0060] (S3) A leachate in a leachate collecting container 7 and a strong alkali solution in the second CO.sub.2 absorption vessel 8 and the third CO.sub.2 absorption vessel 9 are collected on the 30.sup.th, 60.sup.th, 90.sup.th, 120.sup.th, 150.sup.th, 180.sup.th and 210.sup.th day of the test, respectively, and analyzed for a carbon content by means of an organic carbon analyzer. During a biodegradation process, if a barium hydroxide solution in the CO.sub.2 indicator vessel 3 in the air input zone becomes turbid, it is required to replace the strong alkali solution in the first CO.sub.2 absorption vessel 2 and the CO.sub.2 indicator vessel 3.

[0061] (S4) According to the equation 1, the degradation rates of cellulose on the 30.sup.th, 60.sup.th, 90.sup.th, 120.sup.th, 150.sup.th, 180.sup.th and 210.sup.th days are determined to be 10%, 26%, 39%, 51%, 62%, 73% and 82%, respectively.