Method for treating wastewater produced by alkaline pretreatment of cellulose raw material

Abstract

The invention relates to the technical field of environmental engineering, in particular to a method for treating wastewater produced by alkaline pretreatment of a cellulose raw material. The method comprises the following steps: step 1, carrying out solid-liquid centrifugal separation; 2, adjusting the pH value of the wastewater I; step 3, diluting the wastewater II; step 4, performing solid-liquid separation on the kettle residues to obtain wastewater IV; 5, carrying out anaerobic biochemical reaction on the wastewater; step 6, carrying out catalytic ozonation reaction on the wastewater; and 7, carrying out biochemical treatment on the wastewater. Fuel biogas is generated in the anaerobic biochemical treatment process of the cellulosic ethanol wastewater, and the fuel biogas belongs to a biological energy source, so that the energy utilization rate is increased; the biodegradability of the wastewater can be improved through the catalytic ozonation reaction, the biochemical effect can be improved by adopting a biological aerated filter in aerobic biochemical treatment, and the COD value of the cellulosic ethanol wastewater can be greatly reduced, so that the energy consumption is reduced.

Description

Technical Field:

[0001] The present invention relates to the technical field of environmental engineering, and particularly relates to a method for treating wastewater produced by pretreating cellulose raw materials by an alkali method. Background Art:

[0002] The production technology of cellulosic fuel ethanol is developing rapidly, and multiple pilot plants and demonstration factories have been built in China. The chemical structures of cellulosic raw materials such as wheat straw and corn straw are complex. Among them, cellulose has a highly ordered crystal structure, and cellulose and hemicellulose are wrapped by lignin, and hemicellulose is covalently bonded to lignin. Corn fiber, that is, the seed coat of corn kernels, mainly contains hemicellulose, cellulose, lignin, bound starch and proteins, accounting for 6% - 10% of the kernel mass. The corn fiber fuel ethanol technology is to pretreat the seed coat of corn kernels to break the dense structures of components such as cellulose, hemicellulose and lignin, then use cellulase systems for enzymatic hydrolysis, and finally use pentose / hexose yeast fermentation to prepare ethanol.

[0003] The structure of corn fiber is complex, its hemicellulose content is high, there are a large number of branches and linkages, and it needs to be pretreated before conversion.

[0004] Lignocellulosic raw materials must be pretreated to break the crystal structure and reduce the degree of polymerization. Pretreatment usually adopts techniques such as pulverization, steam explosion, acid method, alkali method, etc. The wastewater produced contains some difficult-to-biodegrade substances such as cellulose, lignin and hemicellulose, and may also contain volatile acids, furfural and volatile phenolic substances. Generally, it has the characteristics of high concentration, high salinity, pungent smell, high chroma and high turbidity, and is a typical high-concentration industrial organic wastewater.

[0005] At present, the treatment of wastewater generated in the cellulosic fuel ethanol industry is an important technical problem. For every 1t of cellulosic fuel ethanol produced, about 25t - 35t of industrial wastewater will be generated. The treatment and resource utilization of these high-concentration organic wastewaters have become influencing factors restricting the development of the cellulosic ethanol production industry. How to economically and effectively treat the difficult problem of cellulosic ethanol wastewater urgently needs to be solved.

[0006] Patent CN201611229215.6, titled "Treatment System and Method for Cellulose Ethanol Production Wastewater", the system includes: a biochemical treatment device for biochemical treatment of cellulose ethanol production wastewater; a clear water collection tank with its inlet connected to the outlet of the biochemical treatment device; an acid precipitation unit with its inlet connected to the outlet of the clear water collection tank; a first coagulation unit connected to the outlet of the acid precipitation unit; a first sedimentation unit with its inlet connected to the first coagulation unit, and the first sedimentation unit has an outlet. After the cellulose ethanol workshop wastewater is treated by the biochemical treatment device, it is collected in the clear water tank. This invention mainly uses acid precipitation technology to treat cellulose ethanol wastewater. Under acidic conditions, the lignin in the wastewater is transformed from a dissolved state into suspended matter and precipitated. Then, through coagulation and sedimentation, the suspended matter is effectively removed, which can significantly reduce the COD of the wastewater and has a good treatment effect. This invention mainly aims to remove lignin and does not fundamentally solve the pollution problem.

[0007] Patent CN201510158780.7, titled "Biochemical Treatment Method for Cellulose Ethanol Wastewater, Wastewater Treated by This Method and Its Application", discloses a biochemical treatment method for cellulose ethanol wastewater, the wastewater treated by this method and its application. The biochemical treatment method for cellulose ethanol wastewater of this invention includes: successively performing first solid-liquid separation treatment, pH adjustment treatment, dilution treatment, anoxic treatment, anaerobic treatment, desulfurization treatment, aerobic treatment and second solid-liquid separation treatment on the cellulose ethanol wastewater.

[0008] In summary, most of the existing treatment processes for cellulose ethanol wastewater currently adopt biological anaerobic treatment and aerobic treatment for cellulose ethanol wastewater, but there is still a key problem, that is, the refractory organic pollutants still exist in the secondary biochemical effluent and are not effectively removed. Summary of the Invention:

[0009] The technical problem to be solved by this invention is to provide a treatment method for the wastewater produced by alkali pretreatment of cellulose raw materials. This method realizes the generation of fuel biogas during the anaerobic biochemical treatment of cellulose ethanol wastewater. Fuel biogas belongs to bioenergy and improves the energy utilization rate; the ozone catalytic oxidation reaction can improve the biodegradability of the wastewater, and the aerobic biochemistry uses a biological aerated filter, which can improve the biochemical effect and can greatly reduce the COD value of cellulose ethanol wastewater, thereby reducing energy consumption.

[0010] The technical solution adopted by this invention is: a treatment method for the wastewater produced by alkali pretreatment of cellulose raw materials, the method includes the following steps:

[0011] Step 1: Pretreat the cellulose raw material by the alkali method to obtain a black liquid. The black liquid is centrifuged to obtain solids and Wastewater I. The solids are washed with fresh water and then centrifuged again. The obtained solids are enzymatically hydrolyzed, saccharified, and fermented to produce ethanol, and the obtained washing liquid is reserved for use.

[0012] Step 2: Add an acidic solution to Wastewater I for neutralization until the pH of Wastewater I is adjusted to 6.5 - 7.5. Wastewater I is allowed to stand for a period of time and then filtered to obtain Wastewater II and solids, and the solids are reserved for use.

[0013] Step 3: Add the washing liquid obtained in Step 1 to Wastewater II for dilution to obtain Wastewater III.

[0014] Step 4: The fermentation broth produced by enzymatic hydrolysis, saccharification, and ethanol fermentation enters the rectification system. Ethanol is obtained by rectification, and the stillage is subjected to solid-liquid separation to obtain Wastewater IV.

[0015] Step 5: Mix Wastewater III and Wastewater IV and enter an anaerobic biological reactor for anaerobic reaction. The biogas generated is metered, and the effluent of the anaerobic biological reactor is Wastewater V.

[0016] Step 6: Add Wastewater V to an ozone catalytic oxidation reactor, and the effluent is Wastewater VI.

[0017] Step 7: Add Wastewater VI to an aerated biological filter for biochemical treatment.

[0018] Further, the acidic solution in Step 2 is hydrochloric acid, sulfuric acid, or phosphoric acid solution.

[0019] Further, the COD of Wastewater III obtained by dilution in Step 3 is 7000 mg / L - 10000 mg / L.

[0020] Further, the anaerobic biological reactor in Step 5 uses anaerobic granular sludge, and the inoculation amount of anaerobic granular sludge is 5% - 15%.

[0021] Further, the temperature of the anaerobic biological reactor in Step 5 is set at 30°C - 40°C, mechanical stirring is started, the anaerobic biochemical test begins, and the gas meter measures the volume of biogas generated by the anaerobic test.

[0022] Further, a non-noble metal catalyst is added to the ozone catalytic oxidation reactor in Step 6, and the ozone generator generates ozone.

[0023] Further, the aerated biological filter in Step 7 uses activated carbon as a filler.

[0024] The beneficial effects of the present invention are:

[0025] (1) The cellulose ethanol wastewater treated by the present invention generates fuel biogas during the anaerobic biochemical treatment process. The fuel biogas belongs to bioenergy, which improves the energy utilization rate. The ozone catalytic oxidation reaction can improve the biodegradability of the wastewater. The aerobic biochemical treatment uses a biological aerated filter, which can improve the biochemical effect and greatly reduce the COD value of the cellulose ethanol wastewater, thereby reducing energy consumption.

[0026] (2) Compared with the traditional method, the present invention has the characteristics of simple operation, low cost and high efficiency. It is economical and practical and is of great significance for accelerating the industrialization pace of cellulose ethanol fuel. Specific implementation method:

[0027] Example 1:

[0028] 100 kg of corn straw was pretreated by the alkali method to obtain 1000 L of black liquid. The black liquid was centrifuged by a centrifuge, and the solid and wastewater I were respectively retained. The obtained solid was washed once with 300 kg of fresh water and then centrifuged again. The solid was enzymatically hydrolyzed, saccharified and fermented to produce ethanol, and the washing liquid obtained from the washing was reserved.

[0029] Wastewater I was measured: COD was 45242 mg / L, pH was 12, total salt content was 12500 mg / L, suspended solids were 1048 mg / L, and total carbon was 15870 mg / L. 70 L of wastewater I was taken, stirred, and sulfuric acid solution (5 mol / L) was added dropwise thereto to adjust the pH of wastewater I to 7.0. Wastewater I was allowed to stand for 30 minutes and then filtered to obtain wastewater II and solids.

[0030] The washing liquid was added to wastewater II for dilution to obtain wastewater III with a COD of 8559 mg / L.

[0031] The fermentation broth produced by enzymatic hydrolysis, saccharification and ethanol fermentation entered the rectification system, ethanol was obtained by rectification, and the residue in the kettle was separated by solid-liquid separation to obtain wastewater IV.

[0032] The obtained wastewater III and wastewater IV were mixed and added to an anaerobic biochemical reactor for anaerobic reaction. Anaerobic granular sludge was taken, centrifuged, and the supernatant was poured out. The anaerobic granular sludge at the bottom was used as the test inoculation sludge, and the inoculation amount of anaerobic granular sludge was 10% (mass fraction). The temperature of the anaerobic reactor was set at 35 °C, mechanical stirring was started, and the anaerobic biochemical reaction began. The gas meter measured the volume of biogas produced by the anaerobic reaction.

[0033] The effluent of the anaerobic biochemical reactor was wastewater V. Wastewater V was added to an ozone catalytic oxidation reactor, and the effluent obtained was wastewater VI. Wastewater VI was added to a biological aerated filter for biochemical treatment. The biological aerated filter was filled with ceramsite as a filler, and the final effluent COD was 58 mg / L.

[0034] Example 2:

[0035] 100 kg of corn fiber was pretreated by the alkali method to obtain 1000 L of black liquid. The black liquid was centrifuged by a centrifuge, and the solid and wastewater I were separately retained. 300 kg of fresh water was added to the obtained solid for one-time washing, followed by centrifugation. The solid was enzymatically hydrolyzed, saccharified, and fermented to produce ethanol, and the washing liquid obtained from the washing was retained for use.

[0036] Wastewater I was measured: COD was 34650 mg / L, pH was 12, total salt content was 8750 mg / L, suspended solids were 786 mg / L, and total carbon was 11580 mg / L. 90 L of wastewater I was taken, stirred, and hydrochloric acid solution (8 mol / L) was added dropwise thereto to adjust the pH of wastewater I to 7.0. Wastewater I was allowed to stand for 30 minutes, and then filtered to obtain wastewater II and solids.

[0037] The washing liquid was added to wastewater II for dilution to obtain wastewater III, with a COD of 7996 mg / L.

[0038] The fermentation broth produced by enzymatic hydrolysis, saccharification, and ethanol fermentation entered the rectification system. Ethanol was obtained by rectification, and the still residue was subjected to solid-liquid separation to obtain wastewater IV.

[0039] The obtained wastewater III and wastewater IV were mixed and added to an anaerobic biochemical reactor for anaerobic reaction. Anaerobic granular sludge was taken, centrifuged, and the supernatant was poured off. The anaerobic granular sludge at the bottom was used as the test inoculation sludge, and the inoculation amount of anaerobic granular sludge was 10% (mass fraction). The temperature of the anaerobic reactor was set at 35 °C, mechanical stirring was started, and the anaerobic biochemical reaction began. The gas meter measured the volume of biogas produced by the anaerobic reaction.

[0040] The effluent of the anaerobic biochemical reactor was wastewater V. Wastewater V was added to an ozone catalytic oxidation reactor, and the effluent obtained was wastewater VI. Wastewater VI was added to a biological aerated filter for biochemical treatment. Ceramsite was installed in the biological aerated filter as a filler, and the final effluent COD was 58 mg / L.

[0041] Example 3:

[0042] 100 kg of corn straw was pretreated by the alkali method to obtain 1000 L of black liquid. The black liquid was centrifuged by a centrifuge, and the solid and wastewater I were separately retained. 300 kg of fresh water was added to the obtained solid for one-time washing, followed by centrifugation. The solid was enzymatically hydrolyzed, saccharified, and fermented to produce ethanol, and the washing liquid obtained from the washing was retained for use.

[0043] Determination of Wastewater Ⅰ: COD is 45242 mg / L, pH is 12, total salt content is 12500 mg / L, suspended solids is 1048 mg / L, and total carbon is 15870 mg / L. Take 78 mL of Wastewater Ⅰ, stir it, and dropwise add phosphoric acid solution (10 mol / L) to adjust the pH of Wastewater Ⅰ to 7.0. Let Wastewater Ⅰ stand for 30 minutes, and then filter to obtain Wastewater Ⅱ and solids.

[0044] Add washing liquid to Wastewater Ⅱ for dilution to obtain Wastewater Ⅲ, with COD being 9335 mg / L.

[0045] The fermentation broth produced by enzymatic hydrolysis and saccharification for ethanol fermentation enters the rectification system. Ethanol is obtained by rectification, and the stillage undergoes solid-liquid separation to obtain Wastewater Ⅳ.

[0046] Mix the obtained Wastewater Ⅲ and Wastewater Ⅳ, and add them to an anaerobic biochemical reactor for anaerobic reaction. Take anaerobic granular sludge, perform centrifugal separation, pour out the supernatant, and use the anaerobic granular sludge at the bottom as the test inoculation sludge. The inoculation amount of anaerobic granular sludge is 10% (mass fraction). Set the temperature of the anaerobic reactor at 35 °C, turn on mechanical stirring, and start the anaerobic biochemical test. The gas meter measures the volume of biogas produced in the anaerobic test.

[0047] The effluent from the anaerobic biochemical reactor is Wastewater Ⅴ. Add Wastewater Ⅴ to an ozone catalytic oxidation reactor, and the effluent is Wastewater Ⅵ. Add Wastewater Ⅵ to a biological aerated filter for biochemical treatment. The biological aerated filter is filled with activated carbon as a filler, and the final effluent has a COD of 48 mg / L.

[0048] As shown in Examples 1 - 3, the cellulose ethanol wastewater treated by the present invention produces fuel biogas during the anaerobic biochemical treatment process. The fuel biogas belongs to bioenergy, which improves the energy utilization rate; the ozone catalytic oxidation reaction can improve the biodegradability of the wastewater, and the aerobic biochemical treatment uses a biological aerated filter, which can improve the biochemical effect and can greatly reduce the COD value of the cellulose ethanol wastewater, thereby reducing energy consumption.

[0049] It can be understood that the above specific description of the present invention is only for explaining the present invention and is not limited to the technical solutions described in the embodiments of the present invention. Those of ordinary skill in the art should understand that the present invention can still be modified or equivalently replaced to achieve the same technical effects; as long as it meets the usage requirements, it is within the protection scope of the present invention.

Claims

1. A method for treating wastewater produced from cellulose raw materials pretreated by an alkaline method, characterized in that: The method comprises the following steps: Step 1: Pretreat the cellulose raw material by the alkali method to obtain a black liquid. The black liquid is centrifuged to obtain a solid and Wastewater I. The solid is washed with fresh water and then centrifuged again. The obtained solid is enzymatically hydrolyzed, saccharified and fermented to produce ethanol, and the obtained washing liquid is reserved for use. Step 2: Add an acidic solution to Wastewater I for neutralization until the pH of Wastewater I is adjusted to 6.5 - 7.

5. Wastewater I is allowed to stand for a period of time and then filtered to obtain Wastewater II and a solid, and the solid is reserved for use. Step 3: Add the washing liquid obtained in Step 1 to Wastewater II for dilution to obtain Wastewater III. Step 4: The fermentation broth produced by enzymatic hydrolysis, saccharification and ethanol fermentation enters the rectification system. Ethanol is obtained by rectification, and the still residue is subjected to solid-liquid separation to obtain Wastewater IV. Step 5: Mix Wastewater III and Wastewater IV and enter an anaerobic bioreactor for anaerobic reaction. The biogas produced is metered, and the effluent of the anaerobic bioreactor is Wastewater V. Step 6: Add Wastewater V to an ozone catalytic oxidation reactor, and the effluent is Wastewater VI. Step 7: Add Wastewater VI to a biological aerated filter for biochemical treatment.

2. The treatment method of the wastewater produced by pretreating cellulose raw materials by the alkaline method according to claim 1, characterized in that: The acidic solution in Step 2 is hydrochloric acid, sulfuric acid or phosphoric acid solution.

3. The treatment method of the wastewater produced by pretreating cellulose raw materials by the alkali method according to claim 1, characterized in that: The COD of Wastewater III obtained by dilution in Step 3 is 7000mg / L - 10000mg / L.

4. The treatment method of the wastewater produced by the alkaline pretreatment of cellulose raw materials according to claim 1, characterized in that: The anaerobic bioreactor in Step 5 uses anaerobic granular sludge, and the inoculation amount of anaerobic granular sludge is 5% - 15%.

5. The treatment method of wastewater produced by pretreating cellulose raw materials by the alkaline method according to claim 1, characterized in that: The temperature of the anaerobic bioreactor in Step 5 is set at 30°C - 40°C, mechanical stirring is started, and the anaerobic biochemical test begins. The gas meter measures the volume of biogas produced in the anaerobic test.

6. The treatment method of the wastewater produced by the alkaline pretreatment of cellulose raw materials according to claim 1, characterized in that: A non-noble metal catalyst is added to the ozone catalytic oxidation reactor in Step 6, and the ozone generator generates ozone.

7. The treatment method of the wastewater produced by the alkaline pretreatment of cellulose raw materials according to claim 1, characterized in that: The biological aerated filter in Step 7 uses activated carbon as a filler.