Wastewater zero discharge process for ethanol preparation through industrial tail gas fermentation

Abstract

The invention relates to a zero-discharge treatment process for wastewater generated in ethanol production through industrial tail gas fermentation. The process comprises the following steps: homogenizing and adjusting pH, reducing organic matters by an IC system, removing organic matters and nitrogen by a two-stage A / O process, removing suspended matters by coagulating sedimentation, filtering by a medium, removing chromaticity and organic matters by an ozone BAC system, performing ultrafiltration, performing reverse osmosis treatment, performing concentrated water treatment and the like. The process aims to realize resource utilization and zero emission of wastewater, reduce environmental pollution and reduce the operation cost of enterprises, and has important significance in promoting sustainable development of the fuel ethanol industry.

Description

Technical Field

[0001] The invention relates to a zero-discharge process for producing ethanol wastewater by fermentation of industrial tail gas, and belongs to the technical field of water treatment. Background Art

[0002] With the rapid development of social economy and the continuous increase in population, energy issues have become increasingly prominent development issues, and the development of clean and environmentally friendly renewable energy has attracted more and more attention. Fuel ethanol, as a clean renewable energy, is accepted and studied by more and more countries. According to statistics, every ton of ethanol produced will produce 20 tons of wastewater. Fuel ethanol wastewater is an organic wastewater with high concentration, high temperature and high suspended matter, and contains a large amount of volatile acid substances with a pH of 4 to 5. Direct discharge of these wastewaters will cause serious environmental pollution. Therefore, the wastewater problem is a common problem that restricts the sustainable development of the fuel ethanol industry. How to treat fuel ethanol wastewater economically and efficiently has always been one of the important research topics of common concern. Using appropriate methods to treat organic matter in wastewater and reuse water will provide a new opportunity for the treatment of industrial tail gas fermentation to produce ethanol. Turning wastewater into treasure can greatly reduce the operating costs of enterprises, and at the same time reduce or avoid the impact of industrial production on the environment. Exploring suitable wastewater treatment methods is of great significance to the sustainable development of fuel ethanol production and environmental protection. Summary of the invention

[0003] The present invention relates to a "zero discharge" treatment method and device for wastewater, which is mainly used for the treatment of wastewater produced by industrial tail gas fermentation to produce ethanol. After the wastewater is treated by anaerobic treatment, aerobic biochemical treatment, deep treatment, membrane integration technology, and evaporation crystallization, the wastewater is utilized as a resource and the discharge of wastewater is reduced.

[0004] A zero-discharge process for producing ethanol wastewater from industrial tail gas fermentation, characterized in that it comprises the following steps:

[0005] Step 1: homogenize and adjust the pH value of the wastewater to between 6 and 9;

[0006] Step 2: The wastewater treated in step 1 is pumped to the IC system to reduce the organic matter in the wastewater;

[0007] Step 3: using a two-stage A / O process to further remove organic matter, ammonia nitrogen and total nitrogen from the wastewater treated in step 2;

[0008] Step 4, the wastewater treated in step 3 is subjected to secondary sedimentation tank, coagulation reaction and tertiary sedimentation tank to remove suspended solids in the wastewater;

[0009] Step 5, the wastewater treated in step 4 is further filtered through a media filter to remove suspended solids;

[0010] Step 6: The wastewater treated in step 5 is treated with an ozone BAC system to remove color from the wastewater and further remove organic matter;

[0011] Step 7: The wastewater treated in step 6 enters the ultrafiltration system to further remove suspended solids and colloids;

[0012] Step 8, treating the wastewater treated in step 7 with a first reverse osmosis membrane;

[0013] Step 9, removing hardness from the concentrated water of the first reverse osmosis membrane by using a hardness removal system;

[0014] Step 10, further concentrating the low-hardness first reverse osmosis membrane concentrated water obtained in step 9 through a second reverse osmosis membrane;

[0015] Step 11, the reverse osmosis concentrated water obtained in step 10 is used for ash spraying or evaporation crystallization in a power plant;

[0016] Step 12, recycling the produced water of the two reverse osmoses;

[0017] Step 13: The muddy water obtained from the treatment in steps 4 and 9 is collected and enters the sludge system, and the filtrate is returned to step 4 for further treatment. The moisture content of the sludge after dehydration is less than 70%;

[0018] The waste water mentioned refers to the waste water produced by fermenting industrial tail gas to produce ethanol.

[0019] The COD range of wastewater is 15000-25000mg / L, the total hardness range is 50-300mg / L, the total nitrogen range is 500-900mg / L, the total phosphorus range is 80-150mg / L, the suspended solids are 500-1000mg / L, and the TDS is 3000-4000mg / L; during the pH adjustment treatment, the pH value is adjusted to between 6-9.

[0020] In step 2, the IC reactor is equipped with an external three-phase separator, and the design load of the IC reactor is 5-15kg / (m 3 .d), the operating pressure is 0.5-1.5Mpa.

[0021] In the third step, the two-stage A / O process is used to remove nitrogen and reduce organic matter in the wastewater. The sludge load rate is 0.05-0.4KgCOD / KgMLSS·d, and the ammonia nitrogen load is 0.02-0.1gTKN / (gMLSS·d).

[0022] In step 4, the second sedimentation tank is used for the sedimentation of A / O sludge, the coagulation reaction tank and the third sedimentation tank are used for phosphorus removal, and the dosage of coagulant in the coagulation reaction is 10-50 mg / L.

[0023] In step 5, medium filtration refers to the use of one or a combination of manganese sand, magnetite, ceramsite, quartz sand, activated carbon or fly ash as the filtration medium; the particle size of the medium particles gradually increases from top to bottom, the particle size of the top layer is 0.4-0.6mm, the particle size of the middle layer is 0.6-1.6mm, and the particle size of the bottom layer is 2-4mm.

[0024] In step 6, ozone BAC refers to the coupling process of ozone catalytic oxidation and biological activated carbon filter. The ozone dosage is 20-200 mg / L, the ozone catalytic reaction time is 10-100 min, and the activated carbon empty bed residence time is 1-5 h.

[0025] The first reverse osmosis membrane in step 8 has a water recovery rate of 60-75% and an operating pressure range of 1-4 MPa.

[0026] In step 9, chemicals need to be added to the hardness removal system. The chemicals include but are not limited to sodium carbonate, sodium hydroxide, calcium hydroxide, and lime. The amount of chemicals added to the hardness removal system exceeds the theoretical value of 1-200 mg / L, and the pH value of the wastewater is not lower than 11 after the addition of the chemicals. The filtration methods used by the hardness removal filter include cross-flow filtration and dead-end filtration, and the operating pressure is 0.01-1Mpa.

[0027] In step 9, the water produced by the hardness removal filter enters the ion exchange resin. The resin used is a strong acid cation resin. The flow rate of the wastewater in the resin column is 3-5BV / h, and the water produced by the hardness removal filter is less than 5mg / L.

[0028] Beneficial Effects

[0029] 1. Use anaerobic technology to treat high-concentration wastewater, degrade most of the organic matter in the wastewater, and produce biogas. The anaerobic reactor and biogas treatment facilities are closed systems and will not be emitted into the surrounding environment. The biogas has considerable economic value and can be supplied to boilers.

[0030] 2. The ozone BAC process can effectively remove the chromaticity of wastewater, and the produced water can be directly partially reused;

[0031] 3. The wastewater produced by the reverse osmosis membrane has the advantages of good water quality and stable process. It can be reused as production water, cooling circulating water and low-pressure boiler feed water as needed, greatly reducing the water consumption of the production process;

[0032] 4. The use of membrane concentration greatly reduces the amount of wastewater discharged, making the "zero" emission process of industrial tail gas fermentation to produce ethanol wastewater economically feasible. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is the process diagram of this patent. DETAILED DESCRIPTION

[0034] The wastewater to be treated by the present invention comes from the industrial tail gas fermentation to produce ethanol production industry. The industrial tail gas fermentation to produce ethanol production wastewater mainly contains organic matter, total nitrogen, total phosphorus, etc. The COD range of the wastewater is 15000-25000 mg / L, the total hardness range is 50-300 mg / L, the total nitrogen range is 500-900 mg / L, the total phosphorus range is 80-150 mg / L, the suspended matter is 500-1000 mg / L, and the TDS is 3000-4000 mg / L. The treatment steps are as follows:

[0035] A zero-discharge process for producing ethanol wastewater from industrial tail gas fermentation comprises the following steps:

[0036] Step 1: homogenize and adjust the pH value of the wastewater;

[0037] Step 2: The wastewater treated in step 1 is pumped to the IC system to reduce the organic matter in the wastewater;

[0038] Step 3: using a two-stage A / O process to further remove organic matter, ammonia nitrogen and total nitrogen from the wastewater treated in step 2;

[0039] Step 4: The wastewater treated in step 3 is subjected to a secondary sedimentation tank, a coagulation reaction and a tertiary sedimentation tank to remove suspended solids in the wastewater;

[0040] Step 5, the wastewater treated in step 4 is further filtered to remove suspended solids;

[0041] Step 6: The wastewater treated in step 5 is treated with an ozone BAC system to remove color from the wastewater and further remove organic matter;

[0042] Step 7: The wastewater treated in step 6 enters the ultrafiltration 1 system to further remove suspended solids and colloids;

[0043] Step 8, the wastewater treated in step 7 is treated by reverse osmosis 1 to achieve wastewater desalination;

[0044] Step 9, using a hardness removal system to remove hardness from the concentrated water of the reverse osmosis 1;

[0045] Step 10, further concentrating the low-hardness reverse osmosis 1 concentrated water obtained in step 9 through reverse osmosis 2;

[0046] Step 11, the reverse osmosis concentrated water obtained in step 10 is used for ash spraying or evaporation crystallization in a power plant;

[0047] Step 12, recycling the produced water of the two reverse osmoses;

[0048] In step 13, the muddy water obtained from step 4 and step 9 is collected and sent to the sludge system. The muddy water is dehydrated and then outsourced for treatment. The filtrate is returned to step 4 for further treatment.

[0049] Example 1

[0050] Wastewater quality after homogenization: water volume 100m 3 / h, COD is 22000mg / L, total nitrogen is 800mg / L, total hardness is 500mg / L, suspended solids is 600mg / L, influent TDS is 3500mg / L, pH is 4.2. After the wastewater pH is adjusted to enter the anaerobic IC system, the COD in the wastewater after the anaerobic system is 1500mg / L, and the anaerobic system produces 20,000m 3 / d, this part of biogas is recycled to the boiler system of the production system. After the anaerobic effluent is treated by two-stage A / O, COD <150mg / L, total nitrogen <30mg / L. After the two-stage A / O effluent is precipitated and deeply treated, COD <50mg / L, total nitrogen <30mg / L, SS <5mg / L. The filter effluent is filtered through a tubular ceramic membrane, the operating pressure is 0.18MPa, the recovery rate is 95%, the effluent turbidity is 0.1NTU, and the effluent SDI is 3. The ultrafiltration effluent is concentrated by reverse osmosis 1, the operating pressure is 2.5MPa, and the recovery rate is 75%. The TDS of the clear liquid of reverse osmosis 1 is 120mg / L, the COD is 5mg / L, and the TDS of the concentrated liquid is 13040mg / L. The concentrated liquid of reverse osmosis 1 is filtered by a hardness removal filter, and the hardness of the water produced by the hardness removal filter is 1mg / L. After the hardness is removed, the RO 1 concentrate is further concentrated by RO 2, with an operating pressure of 4.0MPa, a recovery rate of 70%, a concentrate TDS of 40000mg / L, a RO 2 clear liquid TDS of 650mg / L, and a COD of 20mg / L. The RO 2 concentrate enters the power plant for ash spraying. After the two-stage RO water is mixed, it is guaranteed that the COD of the recycled water system is less than 15mg / L, the salt content does not exceed 280mg / L, and the water volume is 90m 3 / h.

[0051] Example 2

[0052] Water quality after homogenization: water volume is 120m 3 / h, COD is 21800mg / L, total nitrogen is 800mg / L, total hardness is 450mg / L, suspended solids is 600mg / L, influent TDS is 3500mg / L, pH is 4.2. After the wastewater is adjusted to pH, it enters the anaerobic IC system. After the anaerobic system, the COD in the wastewater is 1500mg / L, and the anaerobic system produces 22,000m 3 / d, this part of biogas is recycled to the boiler system of the production system. After the anaerobic effluent is treated by two-stage A / O, COD <150mg / L, total nitrogen <30mg / L. After the two-stage A / O effluent is precipitated and deeply treated, COD <50mg / L, total nitrogen <30mg / L, SS <5mg / L. The filter effluent is filtered through a tubular ceramic membrane, the operating pressure is 0.18MPa, the recovery rate is 95%, the effluent turbidity is 0.1NTU, and the effluent SDI is 3. The ultrafiltration effluent is concentrated by reverse osmosis 1, the operating pressure is 2.5MPa, and the recovery rate is 75%. The TDS of the clear liquid of reverse osmosis 1 is 120mg / L, the COD is 5mg / L, and the TDS of the concentrated liquid is 13040mg / L. The concentrated liquid of reverse osmosis 1 is filtered by a hardness removal filter, and the hardness of the water produced by the hardness removal filter is 1mg / L. After the hardness is removed, the RO 1 concentrate is further concentrated by RO 2, with an operating pressure of 4.0MPa, a recovery rate of 70%, a concentrate TDS of 40000mg / L, a RO 2 clear liquid TDS of 650mg / L, and a COD of 20mg / L. The RO 2 concentrate enters the triple-effect evaporation system, which produces 0.48t / d of salt, and the evaporated condensate is reused. After the second-stage RO water is mixed with the evaporated condensate, it is ensured that the COD of the reused water system is less than 15mg / L, the salt content does not exceed 280mg / L, and the water volume is 115m 3 / h.

Claims

1. A zero-discharge process for producing ethanol wastewater from industrial tail gas fermentation, characterized in that: The following steps are involved: Step 1: homogenize and adjust the pH value of the wastewater to between 6 and 9; Step 2: The wastewater treated in step 1 is pumped to the IC system to reduce the organic matter in the wastewater; Step 3: The wastewater treated in step 2 is further treated with a two-stage A / O process to remove organic matter, ammonia nitrogen and total nitrogen in the wastewater; Step 4: The wastewater treated in step 3 is treated with a secondary sedimentation tank, a coagulation reaction and a tertiary sedimentation tank to remove suspended solids in the wastewater; Step 5, the wastewater treated in step 4 is further filtered through a media filter to remove suspended solids; Step 6: The wastewater treated in step 5 is treated with an ozone BAC system to remove color from the wastewater and further remove organic matter; Step 7: The wastewater treated in step 6 enters the ultrafiltration system to further remove suspended solids and colloids; Step 8, treating the wastewater treated in step 7 with a first reverse osmosis membrane; Step 9, removing hardness from the concentrated water of the first reverse osmosis membrane by using a hardness removal system; Step 10, further concentrating the low-hardness first reverse osmosis membrane concentrated water obtained in step 9 through a second reverse osmosis membrane; Step 11, the reverse osmosis concentrated water obtained in step 10 is used for ash spraying or evaporation crystallization in a power plant; Step 12, recycling the produced water of the two reverse osmoses; Step 13: The muddy water obtained from steps 4 and 9 is collected and enters the sludge system, and the filtrate is returned to step 4 for further treatment; The waste water mentioned refers to the waste water produced by fermenting industrial tail gas to produce ethanol.

2. The zero-discharge process for producing ethanol wastewater from industrial tail gas fermentation according to claim 1, characterized in that: The COD range of wastewater is 15000-25000mg / L, the total hardness range is 50-300mg / L, the total nitrogen range is 500-900mg / L, the total phosphorus range is 80-150mg / L, the suspended solids are 500-1000mg / L, and the TDS is 3000-4000mg / L; during the pH adjustment treatment, the pH value is adjusted to between 6-9.

3. The zero-discharge process for producing ethanol wastewater from industrial tail gas fermentation according to any one of claims 1 to 2, characterized in that: In step 2, the IC reactor is equipped with an external three-phase separator, and the design load of the IC reactor is 5-15kg / (m 3 .d), the operating pressure is 0.5-1.5Mpa.

4. The zero-discharge process for producing ethanol wastewater from industrial tail gas fermentation according to any one of claims 1 to 2, characterized in that: In the third step, the two-stage A / O process is used to remove nitrogen and reduce organic matter in the wastewater. The sludge load rate is 0.05-0.4KgCOD / KgMLSS·d, and the ammonia nitrogen load is 0.02-0.1gTKN / (gMLSS·d).

5. The zero-discharge process for producing ethanol wastewater from industrial tail gas fermentation according to any one of claims 1 to 2, characterized in that: In step 4, the second sedimentation tank is used for the sedimentation of A / O sludge, the coagulation reaction tank and the third sedimentation tank are used for phosphorus removal, and the dosage of coagulant in the coagulation reaction is 10-50 mg / L.

6. The zero-discharge process for producing ethanol wastewater from industrial tail gas fermentation according to any one of claim 1, characterized in that: In step 5, medium filtration refers to the use of one or a combination of manganese sand, magnetite, ceramsite, quartz sand, activated carbon or fly ash as the filtration medium; the particle size of the medium particles gradually increases from top to bottom, the particle size of the top layer is 0.4-0.6mm, the particle size of the middle layer is 0.6-1.6mm, and the particle size of the bottom layer is 2-4mm.

7. The zero-discharge process for producing ethanol wastewater from industrial tail gas fermentation according to any one of claim 1, characterized in that: In step 6, ozone BAC refers to the coupling process of ozone catalytic oxidation and biological activated carbon filter. The ozone dosage is 20-200 mg / L, the ozone catalytic reaction time is 10-100 min, and the activated carbon empty bed residence time is 1-5 h.

8. The zero-discharge process for producing ethanol wastewater from industrial tail gas fermentation according to any one of claim 1, characterized in that: The first reverse osmosis membrane in step 8 has a water recovery rate of 60-75% and an operating pressure range of 1-4 MPa.

9. The zero-discharge process for producing ethanol wastewater from industrial tail gas fermentation according to any one of claim 1, characterized in that: In step 9, chemicals need to be added to the hardness removal system. The chemicals include but are not limited to sodium carbonate, sodium hydroxide, calcium hydroxide, and lime. The amount of chemicals added to the hardness removal system exceeds the theoretical value of 1-200 mg / L, and the pH value of the wastewater is not lower than 11 after the addition of the chemicals. The filtration methods used by the hardness removal filter include cross-flow filtration and dead-end filtration, and the operating pressure is 0.01-1Mpa.

10. The zero-discharge process for producing ethanol wastewater from industrial tail gas fermentation according to claim 9, characterized in that: In step 9, the water produced by the hardness removal filter enters the ion exchange resin. The resin used is a strong acid cation resin. The flow rate of the wastewater in the resin column is 3-5BV / h, and the water produced by the hardness removal filter is less than 5mg / L.

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