Life cycle environment influence evaluation method for electro-catalytic membrane water treatment

Abstract

The invention discloses a life cycle environmental influence evaluation method for electro-catalytic membrane water treatment, and relates to the field of environmental protection of water treatment. According to the method disclosed by the invention, an objective, quantitative and comprehensive environmental influence evaluation method is formed aiming at the environmental influence generated in the water treatment process of the electro-catalytic membrane, so that the electro-catalytic membrane is correctly guided to be continuously improved towards the green and sustainable development direction. According to the method, a life cycle evaluation technical framework provided by ISO14040 is taken as a basis, a material flow and an energy flow in a life cycle of electro-catalytic membrane water treatment are quantified by adopting a list analysis method, and all life cycle stages of micro-pollutant removal of the electro-catalytic membrane are subjected to quantitative analysis. According to the method, comprehensive environmental influence evaluation and quantification are carried out from raw material preparation to final waste disposal, and main stages or links causing environmental influence of the electro-catalytic membrane are identified.

Description

Technical Field

[0001] The present invention relates to the field of environmental protection of water treatment, and in particular to a life cycle environmental impact assessment method for electrocatalytic membrane water treatment. Background Art

[0002] With the development of globalization and the rapid growth of population, 4 billion people are facing serious water shortages. In recent years, the emergence of micropollutants has brought increasingly serious challenges to clean water and human health. Micropollutants including antibiotics, disinfection by-products, perfluorinated compounds, personal care products, etc. have low concentrations in water, are toxic and harmful, and are difficult to biodegrade. Traditional water treatment processes cannot effectively remove them. The widespread presence of micropollutants has greatly increased the potential threat of water to human life and health, so it is urgent to develop water treatment technologies that can effectively deal with micropollutants.

[0003] Electrocatalytic membrane is an emerging and promising water treatment technology. It cleverly couples low-pressure membrane filtration and a variety of electrical phenomena, including electrochemical oxidation, electroadsorption, electrophoresis, etc. It can fully utilize the micro-nano space confinement effect in the membrane pores to enrich pollutants and free radicals, while reducing the reaction path, thereby maximizing the utilization of active species such as free radicals and improving the removal efficiency of micropollutants. It has many advantages such as low consumption and high efficiency, strong robustness, integration and portability.

[0004] Although electrocatalytic membrane technology has made significant progress in catalyst preparation, configuration design, reaction mechanism exploration, etc., there are still some key shortcomings. Although the use of electrocatalytic membrane technology in water treatment has reduced the environmental pollution caused by the presence of micropollutants, a large amount of chemicals and electricity are consumed in the process of removing micropollutants, and corresponding environmental impacts will inevitably occur. The specific type and size of this impact are still unclear. Therefore, only by conducting a comprehensive quantitative analysis of the resource consumption, energy consumption and environmental impact of electrocatalytic membrane technology can we better guide the development of this technology in a low-carbon, green and sustainable direction.

[0005] Life cycle assessment (LCA) is a basic tool for quantifying the comprehensive environmental impact of a product or technology from cradle to grave. However, there is currently no systematic research on life cycle assessment of the process of removing micropollutants by electrocatalytic membranes. Therefore, accurately constructing a life cycle environmental impact load assessment model for the process of removing micropollutants by electrocatalytic membranes is of great significance for efficiently, quantitatively and comprehensively understanding the environmental impact of electrocatalytic membranes. It can point out practical directions for improving the environmental and economic benefits of this technology, thereby promoting its scale-up production and large-scale application. Summary of the invention

[0006] The present invention provides a life cycle environmental impact assessment method for electrocatalytic membrane water treatment to solve the above technical problems.

[0007] Specifically, taking the flow-through electrocatalytic membrane system selected in the present invention as an example, the system boundaries of its life cycle environmental impact assessment include: membrane material preparation stage, membrane component assembly stage, electric filtration operation stage, cleaning and maintenance stage, and waste disposal stage.

[0008] The above five stages selected by the present invention involve the largest material and energy inputs and are most likely to cause greater environmental impacts, while other stages, such as the infrastructure construction stage, have a long lifespan, generally 20 to 50 years, so the converted environmental impact is very small and can be completely ignored.

[0009] The present invention provides a life cycle environmental impact assessment method for electrocatalytic membrane water treatment. The assessment method is implemented based on a total environmental impact load assessment model for the electrocatalytic membrane. According to the results obtained by the total environmental impact load assessment model for the electrocatalytic membrane, the environmental impacts of different life cycle stages of the electrocatalytic membrane are compared to obtain the electrocatalytic membrane life cycle stage with the greatest impact on the environmental impact index, thus completing the life cycle environmental impact assessment method for electrocatalytic membrane removal of micropollutants in water.

[0010] The total environmental impact load evaluation model of the electrocatalytic membrane is:

[0011]

[0012] Where Y j is the jth environmental impact indicator, X i is the amount of the i-th resource or energy invested in the life cycle of the electrocatalytic membrane in the life cycle assessment model of the electrocatalytic membrane, C ij Yes X i Corresponding to Y j Characterization factors of environmental impacts;

[0013] Among them, the environmental impact indicators are global warming potential, terrestrial acidification, freshwater eutrophication, mineral resource depletion, marine eutrophication and stratospheric ozone depletion;

[0014] The life cycle assessment model of the electrocatalytic membrane is to collect the resource and energy inventory during the life cycle of the electrocatalytic membrane, and establish a correspondence model between the life cycle stages of the electrocatalytic membrane and the resource and energy inventory. The life cycle stages of the electrocatalytic membrane include the membrane material preparation stage, the membrane component assembly stage, the electric filtration operation stage, the cleaning and maintenance stage, and the waste disposal stage.

[0015] The membrane material preparation stage refers to the process of reducing the abundant raw material titanium dioxide powder into high-conductivity titanium oxide powder by high-temperature reduction, mechanical extrusion molding, and high-temperature sintering, and then preparing an integrated titanium oxide electrocatalytic membrane; the process involves titanium dioxide, hydrogen, electricity consumption, water resource consumption, etc., wherein the single preparation amount of titanium oxide electrocatalytic membrane is 1-20g, the heating power is 1-4kWh, and the high-temperature treatment time is 3-8 hours. According to the above consumed resources and energy, the material energy list of the membrane material preparation stage is obtained.

[0016] Among them, the membrane assembly stage refers to the process of assembling the membrane with various parts to form a complete membrane assembly. This process involves counter electrodes, reference electrodes, pipes, valves, and connecting and fixing accessories, etc. The amount of stainless steel used is 20-200g, and the amount of plastic used is 50-500g. The membrane assembly also involves assembly processes such as packaging, welding, and heating, and its electricity consumption and water resource consumption are 0.01-1kWh and 0.1-100mL, respectively. Based on the above consumed resources, energy, and pollutant emissions, the material energy list of the membrane assembly stage is obtained.

[0017] The electrofiltration operation stage refers to the process in which water containing micropollutants flows into the membrane assembly, then passes through the electrocatalytic membrane in a penetrating manner, is efficiently removed in the electrocatalytic membrane under constant voltage or current, and the treated water flows out of the membrane assembly to obtain purified water. Specific pollutant removal mechanisms include: direct electron transfer, indirect free radical oxidation, electrosorption, electrophoretic force, etc. The process involves electrolytes, power consumption for degrading pollutants, and power consumption of pumps for transporting liquids, wherein 1-100mM dipotassium hydrogen phosphate is added as a supporting electrolyte to provide sufficient conductivity for the electrochemical system and maintain pH stability. The specific dosage is determined according to the system objectives and the conductivity of the influent water body; the power consumption for degrading pollutants is calculated by W=UIt, which is 0.01-5kWh; the power consumption of the pump for transporting liquids is 0.01-5kWh, which is specifically determined by the pore size and transmembrane pressure difference of the electrocatalytic membrane used. According to the above consumed resources, energy and pollutant emissions, the material energy list of the electrofiltration operation stage is obtained.

[0018] The cleaning and maintenance phase refers to the process of reducing membrane pollution by means of physical flushing and chemical cleaning to restore membrane flux as much as possible. The process includes gas flushing, forward flushing, backwashing, online chemical cleaning, and offline chemical cleaning, involving power consumption, water resource consumption, and consumption of various chemicals used for membrane cleaning, such as sodium hypochlorite, sodium chloride, sodium hydroxide, and oxalic acid. The frequency of gas flushing, forward flushing, and backwashing is 3-40 times per day, the frequency of online chemical cleaning is once every 1-10 days, and the frequency of offline chemical cleaning is once every 3-6 months. The specific frequency is determined and adjusted according to the influent water quality and the decrease in membrane flux or the increase in transmembrane pressure difference. Based on the above consumed resources, energy, and pollutant emissions, a material and energy list for the cleaning and maintenance phase is obtained.

[0019] The waste disposal stage refers to the treatment and disposal of any part of the electrocatalytic membrane system after it reaches the end of its life. The objects of this process include: waste electrocatalytic membranes, waste counter electrodes, waste reference electrodes, waste membrane components and wastewater generated during material preparation and cleaning and maintenance. The service life of the electrocatalytic membrane is 3-15 years, the service life of the counter electrode and reference electrode is 5-15 years, and the service life of various membrane components (including pipes, valves, etc.) is 10-20 years. Metal waste is disposed of by recycling or landfilling, and other solid waste is disposed of by landfilling. For the wastewater generated during material preparation and cleaning and maintenance, it can be treated and disposed of as industrial wastewater or urban domestic wastewater according to its specific water quality. Based on the above consumed resources, energy and pollutant emissions, a material and energy list for the waste disposal stage is obtained.

[0020] Calculate the service life t of the electrocatalytic membrane as anode w , which is calculated by the following formula:

[0021]

[0022] Where t0 is the test current density j0 = 1000mA cm -2 Accelerated life (150 hours) under w It is a common working current density (10-30 mA cm) in laboratory-scale electrocatalytic membrane filtration process. -2 ), n is a dimensionless number, usually ranging from 1.4 to 2.0.

[0023] The material and energy lists of each stage obtained above were summarized to obtain the total material and energy list, as shown in Table 1, and then input into SimaPro's offline LCA evaluation system to quantify the environmental impact factors of the life cycle of micropollutants removed by electrocatalytic membranes. The six types of environmental impacts, namely global warming potential, marine ecotoxicity, freshwater eutrophication, human toxicity, mineral resource depletion, and stratospheric ozone depletion, were analyzed to obtain the environmental impact results of the life cycle of micropollutants removed by electrocatalytic membranes.

[0024] Furthermore, the resource and energy list of the electrocatalytic membrane is as follows:

[0025] Resource list: raw materials, chemical reagents, stainless steel, plastics, electrolytes, cleaning water, influent, treated effluent, solid waste and wastewater;

[0026] Energy list: electricity for material preparation and assembly, electricity for pollutant degradation, electricity for cleaning and maintenance, and electricity for water pump operation.

[0027] Furthermore, the corresponding relationship model between the electrocatalytic membrane life cycle stages and the resource and energy inventory is as follows:

[0028]

[0029] Furthermore, the electric energy consumption of the water pump to transport liquid is calculated by the following formula:

[0030] E pump =Q×TMP×t÷3600÷η pump

[0031] Where Q is the flow rate of the electrocatalytic membrane, unit: m 3 / h, TMP is the transmembrane pressure difference, t is the running time, η pump is the energy efficiency of the pump.

[0032] Furthermore, the power consumption for degrading pollutants is calculated by the following formula:

[0033] E degradation =10 -3 ×U×I÷Q÷(C f -C P )

[0034] Where U and I are the voltage and current applied to the electrocatalytic membrane, respectively, and Q is the flow rate of the electrocatalytic membrane, in units of m 3 / h,C f and C p They are the pollutant concentrations in the inlet and outlet water, respectively, in mg / L.

[0035] Furthermore, the unit of the global warming potential is kg CO2-eq to air, and the main listed substances include CO2, N2O and CH4; the unit of the terrestrial acidification is kg 1,4-DCB-eq to marine water, and the main listed substances include heavy metals and pesticides; the unit of freshwater eutrophication is kg P-eq to freshwater, and the main listed substances include total phosphorus and total nitrogen; the unit of mineral resource consumption is kg Cu-eq, and the main listed substances include copper and iron; the unit of marine eutrophication is kg N-eq to marine water, and the main listed substances include total nitrogen and total phosphorus; the unit of stratospheric ozone depletion is kg CFC-11-eq to air, and the main listed substances include perchlorofluorocarbons and chloroform.

[0036] Furthermore, the stage of the electrocatalytic membrane that has the greatest impact on the life cycle environment of micropollutants in water is the electrofiltration operation stage.

[0037] Furthermore, the electrocatalytic membrane system is a flow-through electrocatalytic membrane system.

[0038] The present invention has the following beneficial effects:

[0039] The method of the present invention aims at the environmental impact generated in the process of removing micro-pollutants by electrocatalytic membranes, and forms an objective, quantitative and comprehensive environmental impact assessment method, so as to correctly guide the continuous improvement of electrocatalytic membranes in the direction of green and sustainable development. The present invention is based on the life cycle assessment technical framework provided by ISO14040, and adopts an inventory analysis method to quantify the material flow and energy flow in the life cycle of electrocatalytic membranes for removing micro-pollutants, and conducts an environmental impact assessment of the entire process of electrocatalytic membranes for removing micro-pollutants, including all life cycle stages from raw material preparation to final waste disposal. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a system boundary diagram of the life cycle environmental impact assessment of the electrocatalytic membrane for removing micro-pollutants in Example 1 of the present invention;

[0041] Figure 2 This is a graph showing the contribution ratio of the process related to the removal of micro-pollutants by the electrocatalytic membrane in Example 1 of the present invention;

[0042] Figure 3 This is a greenhouse gas emission diagram of the electrocatalytic membrane removing micropollutants after replacing the electrolyte type in Example 1 of the present invention;

[0043] Figure 4 This is a graph of greenhouse gas emissions after replacing the electrolyte concentration by removing micropollutants through the electrocatalytic membrane in Example 1 of the present invention. DETAILED DESCRIPTION

[0044] In order to make the objectives, technical solutions and advantages of the embodiments of the present invention more clearly understood, the spirit of the contents disclosed by the present invention will be described in detail below. After understanding the embodiments of the contents of the present invention, any technician in the relevant technical field can change and modify them according to the techniques taught by the contents of the present invention without departing from the spirit and scope of the contents of the present invention.

[0045] The exemplary embodiments of the present invention and the description thereof are used to explain the present invention but are not intended to limit the present invention.

[0046] A life cycle inventory of electrocatalytic membrane for micropollutant removal was compiled based on the system boundaries, literature and experimental data were investigated, and the main input and output data of each process of electrocatalytic membrane for micropollutant removal were collected. The input data included titanium dioxide powder, hydrogen, electrolyte, stainless steel, deionized water, electricity, etc., and the output included the products of each process of electrocatalytic membrane for micropollutant removal as well as pollutants such as wastewater and solid waste.

[0047] Taking "removing 1 gram of perfluorooctanoic acid (PFOA)" as the functional unit, the system boundary is determined to include five stages, namely, membrane material preparation stage, membrane module assembly stage, electrofiltration operation stage, cleaning and maintenance stage, and waste disposal stage. The energy and material lists of each stage are collected to evaluate the life cycle environmental impact of electrocatalytic membrane removal of micropollutants.

[0048] The method for evaluating the environmental impact of the life cycle of micro-pollutants removed by electrocatalytic membranes comprises the following specific steps:

[0049] Step 1: List the energy and material list of the life cycle of the titanium dioxide electrocatalytic membrane to remove the micropollutant PFOA. The life list includes five stages (membrane material preparation stage, membrane component assembly stage, electric filtration operation stage, cleaning and maintenance stage, and waste disposal stage). The core data list after the corresponding relationship between the two is quantified and sorted is shown in Table 1 below:

[0050] Table 1 Total energy material list for removal of micropollutant PFOA by titanium dioxide electrocatalytic membrane

[0051]

[0052]

[0053] Among them, the power consumption of the water pump operation is calculated by the following formula:

[0054] E pump =Q×TMP×t÷3600÷η pump

[0055] Where Q is the flow rate of the electrocatalytic membrane (m 3 / h), TMP is the transmembrane pressure difference, t is the running time, η pump is the energy efficiency of the pump, usually taken as 70%.

[0056] The energy consumption for pollutant degradation is calculated by the following formula:

[0057] E degradation =10 -3 ×U×I÷Q÷(C f -C P )

[0058] Where U and I are the voltage (V) and current (A) applied to the electrocatalytic membrane, respectively, and Q is the flow rate (m 3 / h), C f and C p are the pollutant concentrations in the inlet and outlet water (mg / L), respectively.

[0059] The description of some key parts replacement is as follows:

[0060] During the membrane material preparation stage, the electrocatalytic membrane can also be prepared by other methods, such as physical vapor deposition, chemical deposition, etc.

[0061] During the membrane assembly stage, other inert materials may also be used for the counter electrode, such as titanium mesh, carbon electrode, metal oxide electrode, etc.

[0062] During the electrofiltration operation stage, other chemicals may also be selected as supporting electrolytes, such as disodium hydrogen phosphate, sodium bicarbonate, sodium sulfate, potassium sulfate, sodium chloride, potassium chloride, etc.

[0063] During the waste disposal stage, solid waste can also be disposed of by other methods, such as recycling, reuse, incineration, etc.

[0064] Step 2: Quantitatively evaluate the life cycle environmental impact of titanium dioxide electrocatalytic membrane in removing micropollutants PFOA;

[0065] According to the characteristics of the process of removing micropollutants by electrocatalytic membrane, the types of environmental impacts involved are selected and the influencing factors are classified, as shown in Table 2.

[0066] Table 2 Environmental impact types

[0067]

[0068]

[0069] According to the selected environmental impact type, in order to measure the size of the environmental impact caused by each stage of removal, the collected list is input into the SimaPro offline LCA evaluation system to obtain the life cycle environmental impact results of the electrocatalytic membrane removal of micropollutants process, as shown in Table 3.

[0070] Table 3 Life cycle environmental impact results of titanium dioxide electrocatalytic membrane for removal of micropollutant PFOA

[0071] stage GWP MET FE MRS SOD ME Membrane material preparation 2.51E+00 7.82E-02 1.23E-03 1.68E-03 9.87E-07 8.10E-05 Membrane module assembly 2.01E-01 1.16E-01 1.77E-04 4.68E-02 1.45E-07 1.85E-05 Electric filtration operation 1.70E+01 2.36E+00 1.18E-02 2.36E-01 6.67E-06 4.89E-04 Cleaning and maintenance 6.31E-03 4.37E-04 3.81E-06 4.22E-05 5.00E-09 3.14E-07 Waste Disposal 3.19E-03 7.91E-04 1.32E-05 3.11E-05 7.09E-09 3.11E-05 total 1.97E+01 2.56E+00 1.32E-02 2.85E-01 7.81E-06 6.20E-04

[0072] Step 3: Analyze and interpret the results of life cycle environmental impacts

[0073] According to the life cycle environmental impact results, the contribution analysis diagram of the LCA results of the electrocatalytic membrane removal of micropollutants was obtained (such as Figure 2 shown), from Figure 1 As can be seen from Table 3, the electrofiltration operation stage involves the most indicators, and the environmental impact generated in the electrofiltration operation stage is the greatest, with a contribution of more than 75% to various environmental impacts. The reason for this result is that the electrocatalytic membrane system requires the addition of a large amount of dipotassium hydrogen phosphate as a supporting electrolyte, and the environmental impact of a unit mass of dipotassium hydrogen phosphate is also much higher than that of other electrolytes (such as sodium chloride and sodium sulfate, etc.). At the same time, the degradation of pollutants also requires a large amount of electrical energy. Therefore, in order to reduce the environmental impact of the electrocatalytic membrane process, greener electrolyte types or lower concentrations of electrolytes can be used as much as possible on the basis of ensuring the target. This optimization can greatly reduce the carbon emissions of the electrocatalytic membrane process (such as Figure 3 and Figure 4 As shown in the figure, the energy consumed by degrading pollutants should also be reduced as much as possible, which can be achieved by improving current efficiency and reducing competition for side reactions. The second largest contributor to environmental impact is the membrane material preparation stage or the membrane component assembly stage. For the membrane material preparation stage, the current technical level is still at the laboratory preparation stage, so the energy consumption is relatively large, but in the future, the energy consumption can be reduced by increasing the single preparation volume and improving the energy conversion rate. In the process of membrane component assembly, a large amount of stainless steel is used, which will consume steel metal, so this stage has a greater impact on the consumption of mineral resources.

Claims

1. A method for life cycle environmental impact assessment of electrocatalytic membrane water treatment, characterized in that The evaluation method is implemented based on the total environmental impact load evaluation model of the electrocatalytic membrane. According to the results obtained by the total environmental impact load evaluation model of the electrocatalytic membrane, the environmental impact of different life cycle stages of the electrocatalytic membrane is compared to obtain the electrocatalytic membrane life cycle stage with the greatest impact on the environmental impact index, thus completing the life cycle environmental impact evaluation method of the electrocatalytic membrane for removing micropollutants in water; the total environmental impact load evaluation model of the electrocatalytic membrane is: Where Y j is the jth environmental impact indicator, X i is the amount of the i-th resource or energy invested in the life cycle of the electrocatalytic membrane in the life cycle assessment model of the electrocatalytic membrane, C ij Yes X i Corresponding to Y j Characterization factors of environmental impacts; Among them, the environmental impact indicators are global warming potential, terrestrial acidification, freshwater eutrophication, mineral resource consumption, marine eutrophication and stratospheric ozone depletion; the life cycle assessment model of the electrocatalytic membrane is to collect the resource and energy inventory during the life cycle of the electrocatalytic membrane, and establish a correspondence model between the life cycle stages of the electrocatalytic membrane and the resource and energy inventory. The life cycle stages of the electrocatalytic membrane include the membrane material preparation stage, the membrane component assembly stage, the electric filtration operation stage, the cleaning and maintenance stage, and the waste disposal stage.

2. A method for life cycle environmental impact assessment of electrocatalytic membrane water treatment according to claim 1, characterized in that The resource and energy list of the electrocatalytic membrane is as follows: Resource list: raw materials, chemical reagents, stainless steel, plastics, electrolytes, cleaning water, influent, treated effluent, solid waste and wastewater; Energy list: electricity for material preparation and assembly, electricity for pollutant degradation, electricity for cleaning and maintenance, and electricity for water pump operation.

3. A method for life cycle environmental impact assessment of electrocatalytic membrane water treatment according to claim 1, characterized in that The corresponding relationship model between the electrocatalytic membrane life cycle stages and the resource and energy inventory is as follows:

4. A method for life cycle environmental impact assessment of electrocatalytic membrane water treatment according to claim 2 or 3, characterized in that The electrical energy consumption of the water pump to transport liquid is calculated by the following formula: AND pump =Q×TMP×t÷3600÷η pump Where Q is the flow rate of the electrocatalytic membrane, unit: m 3 / h, TMP is the transmembrane pressure difference, t is the running time, η pump is the energy efficiency of the pump.

5. A method for life cycle environmental impact assessment of electrocatalytic membrane water treatment according to claim 2 or 3, characterized in that The energy consumption for pollutant degradation is calculated by the following formula: E degradation =10 -3 ×U×I÷Q÷(C f -C P ) Where U and I are the voltage and current applied to the electrocatalytic membrane, respectively, and Q is the flow rate of the electrocatalytic membrane, in units of m 3 / h,C f and C p They are the pollutant concentrations in the inlet and outlet water, respectively, in mg / L.

6. The method for life cycle environmental impact assessment of electrocatalytic membrane water treatment according to claim 1, characterized in that The unit of global warming potential is kg CO2-eq to air, and the main listed substances include CO2, N2O and CH4; the unit of terrestrial acidification is kg 1,4-DCB-eq to marine water, and the main listed substances include heavy metals and pesticides; the unit of freshwater eutrophication is kg P-eq to freshwater, and the main listed substances include total phosphorus and total nitrogen; the unit of mineral resource consumption is kg Cu-eq, and the main listed substances include copper and iron; the unit of marine eutrophication is kg N-eqto marine water, and the main listed substances include total nitrogen and total phosphorus; the unit of stratospheric ozone depletion is kg CFC-11-eqto air, and the main listed substances include perchlorofluorocarbons and chloroform.

7. The method for life cycle environmental impact assessment of electrocatalytic membrane water treatment according to claim 1, characterized in that The stage of the electrocatalytic membrane that has the greatest impact on the life cycle environment of micropollutants in water is the electrofiltration operation stage.

8. The method for life cycle environmental impact assessment of electrocatalytic membrane water treatment according to claim 1, characterized in that The electrocatalytic membrane system is a flow-through electrocatalytic membrane system.

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