CN117125850A - Method for realizing zero wastewater discharge in corn starch production by using process water purification sleeve - Google Patents
Method for realizing zero wastewater discharge in corn starch production by using process water purification sleeve Download PDFInfo
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Classifications
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F9/00—Multistage treatment of water, waste water or sewage
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/02—Treatment of water, waste water, or sewage by heating
- C02F1/04—Treatment of water, waste water, or sewage by heating by distillation or evaporation
- C02F1/048—Purification of waste water by evaporation
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
- C02F1/441—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by reverse osmosis
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/66—Treatment of water, waste water, or sewage by neutralisation; pH adjustment
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
- C02F2103/02—Non-contaminated water, e.g. for industrial water supply
- C02F2103/04—Non-contaminated water, e.g. for industrial water supply for obtaining ultra-pure water
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
- C02F2103/32—Nature of the water, waste water, sewage or sludge to be treated from the food or foodstuff industry, e.g. brewery waste waters
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2301/00—General aspects of water treatment
- C02F2301/04—Flow arrangements
- C02F2301/046—Recirculation with an external loop
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- Life Sciences & Earth Sciences (AREA)
- Hydrology & Water Resources (AREA)
- Engineering & Computer Science (AREA)
- Environmental & Geological Engineering (AREA)
- Water Supply & Treatment (AREA)
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Separation Using Semi-Permeable Membranes (AREA)
Abstract
The invention relates to a method for realizing zero wastewater discharge in corn starch production by purifying process water, which comprises the following steps: 1. the method comprises the steps of (1) reserving steam condensate water obtained by evaporating and concentrating corn soaking water in the corn starch production process for later use; 2. carrying out heat exchange cooling on the steam condensate; 3. regulating the pH value of the cooled steam condensate; 4. reverse osmosis filtration is performed and purified water and concentrated water are obtained. The invention takes the steam condensate water obtained by evaporating and concentrating the corn soaking water as a raw material, and adjusts the pH value after heat exchange and cooling. And then performing reverse osmosis filtration and purification to obtain purified water of the steam condensate, wherein the quality of the purified water of the steam condensate is close to the standard of drinking water, and the purified water can replace fresh drinking water required in production to realize the recycling of water resources. The purified water of the steam condensate obtained after the treatment of the invention can completely realize the replacement of fresh water for twelve-stage cyclone washing in the corn starch production, and finally achieves the aim of zero wastewater discharge in the corn starch production.
Description
Technical Field
The invention belongs to the technical field related to corn related product processing, and particularly relates to a method for realizing zero wastewater discharge in corn starch production by using process water purification sleeve.
Background
At present, when a corn starch factory processes one ton of corn to produce starch milk, 0.6-1.0 ton of sewage is discharged, and the sewage (the sewage produced in the production process of producing the starch milk by the corn) can reach the discharge standard after being treated by a precipitation separation method, a chemical flocculation method, a simple aeration method, a biological treatment method (an activated sludge method, an anaerobic biological method, a biological membrane method, a biological pond and the like), a membrane separation technology, a photosynthetic bacteria method and the like.
The sewage discharge generated in the corn starch production process is not caused by the fact that the water quality of the water in the production process can not meet the requirement of process recycling, but is caused by the fact that the last procedure of starch refining in the starch production, namely twelve-stage cyclone washing, needs to be filled with a large amount of fresh water, the filling amount of the fresh water is larger than the increment of the production discharge water, and the process recycling water of the production system of the whole starch production workshop is unbalanced, so that part of the production process water is forced to be discharged to maintain the water balance of the production process. The new solution is to eliminate the generation and discharge of sewage from the source in the production process, rather than returning the discharged sewage to the production line after treatment and purification.
In the prior art, taking 1000 tons of broken daily corn for producing starch milk as an example, the method comprises the following steps of: corn (14% moisture) brings 140 tons of water; the DS44% zebra starch milk 700 tons of water output is about 700 x 0.86/0.44-700 x 0.86 = 766 tons; the average water content in the byproducts (pulp fiber, dried embryo and protein powder) is about 10%, and the water carried out by 270 tons of byproducts is about 27 tons; in the process of evaporating and concentrating Cheng Yu m pulp by using waste heat (tail gas dried by a tube bundle) to drive corn steep water, the waste heat cannot be fully utilized, and about 40 tons of water is volatilized and carried away along with noncondensable gas (tail air) in the waste heat; thus, the total amount of the produced water is about 766+27+40=833 tons, so the increment of the produced water=833-140=693 tons, however, the fresh water filling amount of the twelve-stage cyclone washing process of the last process of starch production is about 1300 tons, and the fresh water filling amount is about 607 tons more than the increment of the produced water by 693 tons, that is, about 607 tons of the produced water needs to be discharged every day in the production process to achieve the water balance in the production process.
Therefore, in order to achieve water balance to realize zero emission of the corn starch production wastewater, three methods are not required, and the following steps are discussed one by one:
the first is to treat about 607 tons of redundant production process water discharged in production by biological, physical or chemical methods and then purify the water until the water quality is qualified, and return the water to the twelve-stage cyclone washing process to replace part of fresh water. The existing corn starch industry adopts the method to treat about 607 tons of redundant production process water through a sewage treatment station, but the treated water only reaches the discharge standard and is discharged, and the purpose of returning to the twelve-stage cyclone washing process to replace part of fresh water for utilization is not realized, so that the corn starch production zero discharge is realized, because the requirement of the water quality of the twelve-stage cyclone washing process cannot be met even though the high-cost treatment is carried out, and even if the requirement of the water quality of the water is met, the sewage treatment station can not treat the purified water to return to the food production line, and the food safety and the ethical demonstration of occupational moral can not be realized. This approach is not feasible or practical.
The second method is to reduce the fresh water charge of the twelve-stage cyclone washing process from 1300 tons to 693 tons by 607 tons. In theory, the washing device can be realized by adding a great number of stages or inventing more efficient washing equipment with low water consumption, but the problems of economy (namely, the electricity consumption cannot be greatly increased) and equipment development and manufacturing are solved at the same time. This approach is theoretically viable, but no idea or method is currently available in the industry, and is possible in the future through full industrial effort.
In the third method, namely the method provided by the invention, a part of water is taken out in the production process to be purified to obtain 607 tons of purified water, so that the fresh water filling amount of the twelve-stage cyclone washing process is partially replaced, the fresh water filling amount is reduced from 1300 tons to 693 tons, and the water filling amount is 1300 tons after 693 tons of washing water and 607 tons of purified water are used for the twelve-stage cyclone washing process, so that the quality of the washed starch milk can be ensured, and the water balance of corn starch production under the state of no wastewater discharge is achieved. Namely 607 tons of water is taken out from the process, not taken out to be sent to a decontamination water station for treatment, but the fresh water is taken to the twelve-stage cyclone washing process to partially replace the filled fresh water, which is equivalent to 607 tons of fresh water filled in the twelve-stage cyclone washing, and the water balance of the corn starch production process is realized without taking out the water to be sent to the decontamination water station for treatment. Therefore, the generation and discharge of sewage can be eliminated from the source in the production process, so that the sewage is not required to be discharged, and the zero discharge of the wastewater in the corn starch production is realized. The method of the invention is feasible and can be implemented, and is not only economical and cost-effective, but also the purified water obtained after the purification of the process water can meet the water quality requirement of the twelve-stage cyclone washing procedure for washing the starch milk, because a good purification method is found. The purification method described in the claims of the invention has the advantages of reasonable process water taking point selection, simple and efficient purification flow and low cost, ensures that the quality of the purified water can meet the requirements, and is also quite economical. The inventor has performed pilot-test verification, and the quality of purified water obtained by pilot-test verification is ideal.
Some corn starch production lines are used for producing the dried commercial starch partially or completely, the starch milk is not completely directly sent to a starch sugar workshop for producing starch sugar, but partially or completely is centrifugally separated by a horizontal scraper siphon centrifugal machine to obtain wet starch, and the wet starch is dried by air flow to obtain the commercial dry starch. Under the condition, the water quantity taken away by the wet starch is smaller than the water quantity taken away by the starch milk, so that the method only can realize great emission reduction but can not completely realize zero emission, however, the method does not influence the zero emission of sewage for corn starch production enterprises which all produce the starch milk after being popularized, and the method also has no influence on the important significance of greatly reducing the sewage emission in the whole industry.
Disclosure of Invention
First technical problem
In summary, if zero wastewater discharge of the corn starch production process is to be achieved, a part of process water must be taken out from the process water to perform purification treatment, so as to obtain purified water (about 607 tons for 1000 tons of corn for daily grinding) meeting the water quality requirement of twelve-stage cyclone washing, which is used for partially replacing fresh water, thereby achieving water balance of the production process, achieving zero wastewater discharge of the corn starch production process, and solving the problem of high water resource consumption of corn starch production in the prior art. In the process water source problem for purifying treatment, the water quality of the steam condensate distilled in the process of evaporating and concentrating the corn soaking water is closest to the water quality requirement of twelve-stage cyclone washing compared with the water quality of the process water of other production parts, so that the purifying method is used as the process water source for purifying treatment.
(II) technical scheme
The invention provides a method for realizing zero wastewater discharge in corn starch production by purifying process water, which comprises the following steps:
step one, taking steam condensate water of a corn soaking water evaporation concentration process for standby in the corn starch production process;
step two, carrying out heat exchange and cooling on the steam condensate water to 35-45 ℃;
step three, regulating the pH value of the cooled steam condensate water and enabling the pH value of the steam condensate water to be 7.0-8.0;
and fourthly, performing reverse osmosis filtration on the steam condensate water with the pH value regulated to obtain purified water (permeate water) with the pH value of 7.0-8.0, the conductivity of 30 mu S/cm-70 mu S/cm and the COD of 800mg/L-1200mg/L, wherein the purified water is used for partially replacing twelve-stage cyclone washing fresh water in corn starch production.
Preferably, in the method for realizing zero wastewater discharge in corn starch production by using the process water purification sleeve provided by the invention, the pH value of the steam condensate water reserved in the first step is 2.8-3.5, the conductivity is 150 mu S/cm-500 mu S/cm, and the COD is 2800mg/L-3200mg/L.
Preferably, in the method for realizing zero wastewater discharge in corn starch production by using the process water purification sleeve provided by the invention, in the third step, the pH value is 7.0-8.0 by adding sodium hydroxide aqueous solution or sodium carbonate aqueous solution into steam condensate.
Preferably, in the method for realizing zero wastewater discharge in corn starch production by using the process water purification sleeve provided by the invention, in the fourth step, the steam condensate water with the pH value regulated is subjected to the purification water obtained by reverse osmosis filtration, wherein the pH value is 7.0-8.0, the conductivity is 30 mu S/cm-70 mu S/cm, and the COD is 800mg/L-1200mg/L.
Preferably, in the method for realizing zero wastewater discharge in corn starch production by using the process water purification sleeve provided by the invention, in the fourth step, the pH value of the membrane interception concentrated water remained after the purified water is obtained by reverse osmosis purification is 7.0-8.0, the conductivity is 9500 mu S/cm-10500 mu S/cm, and the COD is 38000mg/L-42000mg/L.
Preferably, in the method for realizing zero wastewater discharge in corn starch production by using the process water purification sleeve provided by the invention, the purified water obtained by reverse osmosis filtration is used for partially replacing fresh water used in the twelve-stage cyclone washing process in corn starch production.
Preferably, in the method for realizing zero wastewater discharge in corn starch production by using the process water purification sleeve provided by the invention, the membrane interception concentrated water remained after the reverse osmosis purification is obtained and combined with the steam condensate water of the residual corn soaking water evaporation concentration process which is not used as a purified water source, and the steam condensate water is still used for preparing the sulfuric acid liquid for soaking corn.
Preferably, in the method for realizing zero wastewater discharge in corn starch production by using the process water purification sleeve provided by the invention, a heat exchanger is adopted to cool the steam condensate in the third step.
Preferably, in the method for realizing zero wastewater discharge in corn starch production by using the process water purification sleeve provided by the invention, in the fourth step, the steam condensate is filtered and purified by a reverse osmosis device.
Preferably, in the method for realizing zero wastewater discharge in corn starch production by using the process water purification sleeve provided by the invention, the pressure difference of the reverse osmosis device in the fourth step when the reverse osmosis device filters the steam condensate is 4Bar-10Bar.
Preferably, in the method for realizing zero wastewater discharge in corn starch production by using the process water purification sleeve provided by the invention, in the first step, the steam condensate obtained by evaporating and concentrating the corn soaking water is the heating steam condensate and the secondary steam condensate obtained when the evaporator is used for concentrating the corn soaking water in corn starch production.
(III) beneficial effects
The corn starch factory can discharge 0.6-1.0 ton of sewage when producing starch milk by processing 1 ton of corn, the prior art must discharge a part of sewage to reach water balance, and after the process treatment of the method, the purified water obtained by purifying a part of process water can partially replace fresh drinking water, so that the filling amount of the fresh drinking water is reduced, the water balance of the production process can be achieved without discharging sewage, and the double purposes of saving water resources and reducing pollution discharge are achieved. After the invention is put into practical production, the zero emission of starch production can be realized through the process water purification and application, so that not only is pollution discharge eliminated, but also the problem of high water resource consumption in corn starch production in the prior art is solved.
The invention takes the steam condensate water obtained by evaporating and concentrating the corn soaking water in the production process of a corn starch factory as a raw material, the steam condensate water is subjected to heat exchange and cooling to below 40 ℃, then the pH value of the steam condensate water is regulated, and reverse osmosis purification is carried out to obtain pure steam condensate water, the quality of the steam condensate water is close to the standard of drinking water, and the steam condensate water can replace fresh drinking water required in the production to realize the recycling of water resources. The recovered purified water treated by the method can completely replace fresh water for twelve-stage cyclone washing, and finally achieves the aim of zero wastewater discharge in corn starch production.
The method of the invention is feasible and can be implemented, and is not only economical and cost-effective, but also the purified water obtained after the purification of the process water can meet the water quality requirement of the twelve-stage cyclone washing procedure for washing the starch milk, because a good purification method is found. The purification method disclosed by the invention has the advantages that the water taking point of the process water is quite reasonable to select, the purification process is concise, efficient and low in cost, and the water quality of the purified water can meet the requirements and is quite economical. The inventor has performed pilot-test verification, and the quality of purified water obtained by pilot-test verification is ideal.
Some corn starch production lines are used for producing the dried commercial starch partially or completely, the starch milk is not completely directly sent to a starch sugar workshop for producing starch sugar, but partially or completely is centrifugally separated by a horizontal scraper siphon centrifugal machine to obtain wet starch, and the wet starch is dried by air flow to obtain the commercial dry starch. Under the condition, the water quantity taken away by the wet starch is smaller than the water quantity taken away by the starch milk, so that the method only can realize great emission reduction but can not completely realize zero emission, however, the method does not influence the zero emission of sewage for corn starch production enterprises which all produce the starch milk after being popularized, and the method also has no influence on the important significance of greatly reducing the sewage emission in the whole industry.
Drawings
FIG. 1 shows a flow chart of a method for realizing zero wastewater discharge in corn starch production by using process water purification sleeve in an embodiment of the invention;
FIG. 2 is a schematic diagram of a system for implementing a zero wastewater discharge method for corn starch production using process water purification cartridges in accordance with an embodiment of the present invention.
Detailed Description
As shown in fig. 1 and 2, the invention provides a method for realizing zero wastewater discharge in corn starch production by using process water purification sleeve, which specifically comprises the following four steps:
step one, reserving steam condensate water obtained by evaporating and concentrating corn soaking water in the corn starch production process for later use;
step two, carrying out heat exchange and cooling on the steam condensate water to 35-45 ℃;
step three, regulating the pH value of the cooled steam condensate water and enabling the pH value of the steam condensate water to be 7.0-8.0;
and fourthly, performing reverse osmosis filtration on the steam condensate water with the pH value regulated to obtain purified water with the pH value of 7.0-8.0, the conductivity of 30 mu S/cm-70 mu S/cm and the COD of 800mg/L-1200mg/L, wherein the purified water is used for partially replacing fresh water used in a twelve-stage cyclone washing process in corn starch production.
In the four steps above: firstly, preparing a clean container (such as a stainless steel tank and the like) with larger capacity, and filling steam condensate for evaporating and concentrating corn soaking water for later use; secondly, obtaining steam condensate with the temperature lower than 40 ℃ through a heat exchange cooling mode; step three, the pH value of the steam condensate is adjusted, and the neutralization of the steam condensate can be realized by using a small amount of alkaline materials; in step four, the substitute product of fresh water (i.e. recovery of reverse osmosis permeate purified water) can be obtained by reverse osmosis filtration of the steam condensate. According to the invention, through the four steps, the replacement of fresh water can be realized after the steps of cooling, pH value adjustment, reverse osmosis filtration and the like are carried out on the steam condensate, and the reverse osmosis concentrated water is combined with the steam condensate of the residual corn soaking water evaporation concentration process which is not used as a purified water source, and is still used for preparing the sulfuric acid liquid for soaking the corn.
Obtaining purified water through reverse osmosis and concentrated water trapped by reverse osmosis in the step four, wherein the pH value of raw material steam condensate before filtration is 2.8-3.5, the conductivity is 150 mu S/cm-500 mu S/cm, and COD (chemical oxygen demand) is 2800mg/L-3200mg/L; 7.0-8.0 of purified water which is permeated by reverse osmosis, the conductivity is 30 mu S/cm-70 mu S/cm, and the COD is 800mg/L-1200mg/L; the pH value of the concentrated water trapped by reverse osmosis is 7.0-8.0, the conductivity is 9500 mu S/cm-10500 mu S/cm, and the COD is 38000mg/L-42000mg/L.
In order to meet the filtering requirement of the reverse osmosis device on the steam condensate, the temperature and the pH value of the steam condensate are firstly regulated, specifically, in the second step, the steam condensate is firstly cooled by a heat exchanger until the temperature is between 35 ℃ and 45 ℃, specifically, 35 ℃, 36 ℃, 37 ℃, 38 ℃, 39 ℃,40 ℃, 41 ℃, 42 ℃, 43 ℃, 44 ℃, 45 ℃ and preferably 40 ℃.
Specifically, in the third step, the pH value is neutralized to 7.0-8.0 by adding sodium hydroxide aqueous solution or sodium carbonate aqueous solution into the steam condensate.
Because the temperature and the pH value of the steam condensate are adjusted in advance (the temperature is 40 ℃ and the pH value is 7.0-8.0), the method is the optimal technological parameter for obtaining high-purity permeate water by filtering raw material water through a reverse osmosis device, and in the fourth step, the pressure difference of the reverse osmosis device when filtering the steam condensate is only 4Bar-10Bar, so that the excellent water quality and the permeate water yield can be obtained.
Specifically, in the first step of the invention, the steam condensate obtained by evaporating and concentrating the corn steep water is the heated steam condensate and the secondary steam condensate obtained when the corn steep water is concentrated by an evaporator in the production of corn starch.
The invention takes the steam condensate water obtained by evaporating and concentrating the corn soaking water in the production process of a corn starch factory as a raw material, the steam condensate water is firstly cooled to below 40 ℃ through a heat exchanger, then the pH value of the steam condensate water is regulated, and then reverse osmosis purification is carried out to obtain purified water of the steam condensate water, the quality of the purified water is close to the standard of drinking water, and the purified water can partially replace fresh drinking water required in the production to realize the recycling of water resources and the water balance of a production line.
At present, the sewage is discharged by 0.6 to 1.0 ton when 1 ton of corn is processed in a corn starch factory to produce starch milk, a part of sewage is discharged to achieve water balance in the prior art, and after the process treatment of the invention, part of process water can be purified to enable the obtained purified water to partially replace fresh drinking water, so that the filling amount of the fresh drinking water is reduced, the water balance of the production process can be achieved without discharging the sewage, and the double purposes of saving water resources and reducing pollution discharge are achieved. After the invention is put into practical production, the zero emission of starch production can be realized through the process water purification and application, so that not only is pollution discharge eliminated, but also the problem of high water resource consumption in corn starch production in the prior art is solved.
The invention provides a method for realizing zero wastewater discharge in corn starch production by purifying process water, wherein in the method, starch production process water with the water quality closest to fresh water (namely corn soaking water evaporating and condensing water) is selected, and the purification treatment flow of the starch production process water is as follows:
and (3) placing the steam condensate obtained by evaporating and concentrating the corn soaking water in a container for standby, then cooling the steam condensate to below 40 ℃ through a heat exchanger for measuring the pH value, neutralizing the steam condensate according to the pH value measurement result, and finally performing reverse osmosis filtration on the neutralized steam condensate to obtain the permeated purified water.
In the purification treatment process, the pH (pH value) of the steam condensate water obtained by evaporating and concentrating the corn steep water is about 2.8-3.5, the conductivity is about 150 mu S/cm-500 mu S/cm, and the COD is about 3000mg/L.
The steam condensate water obtained by evaporating and concentrating the corn soaking water is heated steam condensate water and secondary steam condensate water which are obtained when an evaporator is generally adopted to concentrate the corn soaking water in corn starch production, the temperature of the steam condensate water is higher, the condensate water can be cooled to 40 ℃ by adopting a natural cooling mode at the moment (the method does not need to consume cooling water, but the cooling time is longer), and the quick cooling of the steam condensate water can be realized by adopting cooling equipment, or the heat energy recycling can be realized while the cooling of the condensate water is realized by adopting heat exchange equipment. Specifically, the steam condensate concentrated by evaporation of the corn steep water is rapidly cooled to 40 ℃ by cooling of circulating cooling water by using a heat exchanger. And (3) performing reverse osmosis filtration after the vapor condensate is cooled to 40 ℃, wherein the water temperature of 40 ℃ meets the temperature requirement of a subsequent reverse osmosis device.
The concentrated steam condensate of the corn steep water after cooling to 40 ℃ has a pH of about 2.8-3.5 and is neutralized to pH7.0-8.0 by adding aqueous sodium hydroxide or aqueous sodium carbonate.
It should be noted that: the steam condensate from the evaporation concentration of the corn steep water is neutralized to pH7.0-8.0 from about pH 2.8-3.5 with a much lower alkali consumption than the corn steep water is neutralized to pH7.0-8.0 from about pH 2.8-3.5. The reason for this is that: the corn steep water contains a large amount of organic acid and sulfurous acid mainly containing lactic acid, and the alkali consumption for neutralization is about 3.0-6.0Kg (NaOH dry basis) per ton of corn steep water. The steam condensate water of the corn soaking water evaporation concentration contains only a small amount of organic acid and sulfurous acid mainly comprising formic acid and acetic acid, and the alkali consumption is about 0.5-1.0Kg (NaOH dry basis) for each ton of condensate water. The corn steep water is evaporated and concentrated to pH7.0-8.0, and compared with the corn steep water which is not neutralized, the corn steep water enters a subsequent reverse osmosis device for purification, the acid removal rate is at least 5 times higher, and the acid removal rate is 80-90%.
The reverse osmosis device filters and purifies and is the last process of purifying the steam condensate water of the corn soaking water evaporation concentration, because the pretreatment process of cooling and neutralizing of the preamble is adopted, the reverse osmosis purification process becomes very simple and efficient, the water yield of 90-95% of purified water can be obtained only by applying the pressure difference of 4-10Bar, and the obtained purified water is very high-quality, and the specific expression is that: the pH of the purified water is about 7.0-8.0, the conductivity is about 30-70 mu S/cm, and the COD is about 1000mg/L. The quality of the purified water can completely meet the water quality requirement for twelve-stage cyclone washing. The concentrated water obtained by evaporating and concentrating the corn steep water has pH of 7.0-8.0, the conductivity is about 10000 mu S/cm, the COD is about 40000mg/L, and the reverse osmosis concentrated water is combined with the steam condensate of the residual corn steep water evaporating and concentrating procedure which is not used as a purified water source, and is still used for preparing the sulfuric acid solution for soaking the corn.
In the prior art, many technicians in the industry try to purify the steam condensate concentrated by evaporating the corn steep water by using a reverse osmosis device, and the pretreatment means of the invention is not adopted, so that the pH of the purified water cannot be raised to be neutral and the smell and the acidic taste of the concentrated corn cooking water cannot be eliminated due to the high transmittance of organic acid, so that the purified water cannot be used for realizing the partial replacement of the twelve-stage cyclone washing fresh water.
Regarding the method for realizing zero wastewater discharge in corn starch production by using the process water purification sleeve, the invention performs practical pilot-scale test verification of the purification process in month 6 of 2023.
In 2023, 27 days of 06 months, evaporating condensed water (evaporating the corn soaking water to obtain evaporating steam condensed water), 10L of water thrown out by a horizontal scraper centrifuge and 10L of corn soaking water are taken from a corn starch production workshop, and several relevant parameters are detected firstly to compare which process water in a production link is selected to be most suitable for being used as raw material water for preparing purified water, wherein the detection results are shown in the following table 1:
TABLE 1
| Item of material name | Conductivity mu s/cm | Bx | pH |
| Evaporating condensed water | 404 | 0 | 3.17 |
| The scraper throws out water | 540 | 0 | 4.31 |
| Corn soaking water | 15330 | 15.1 | 3.84 |
Obviously, corn steep water has high conductivity and dry matter content, and is not suitable for being used as a purified water source. And then respectively carrying out alkali neutralization experiments on the evaporated condensate water and the water thrown out by the scraper:
1g of analytically pure sodium hydroxide is weighed, dissolved in water and 100g of water are added, and the mixture is shaken for later use.
The evaporation condensate and the scraper water for each 100mL were measured separately with a measuring cylinder, the pH was adjusted with the prepared sodium hydroxide solution, the amount of sodium hydroxide solution consumed was recorded, and each sample was tested twice, and the results are shown in tables 2 and 3 below:
TABLE 2
TABLE 3 Table 3
The neutralization alkali consumption and the conductivity of the evaporation condensate water are lower than those of the water thrown by the scraper, and the water thrown by the scraper contains a small amount of suspended starch, and although the water cannot be completely clarified through precipitation, the best water source used for purifying the water is the evaporation condensate water. Then, a purification pilot test of the evaporated condensate water is carried out:
the corn starch production workshop takes about 500L of evaporation condensate water obtained by evaporating and concentrating corn soaking water, and is naturally cooled to 40 ℃ for operation, and conductivity and PH detection are carried out first. The evaporated condensate stock was taken in duplicate and tested as shown in table 4 below.
TABLE 4 Table 4
| Item of material name | pH | Conductivity mu s/cm |
| Evaporating condensed water stock solution | 3.03/3.06 | 335/340 |
Then, the pH value was adjusted, 140g of analytically pure sodium hydroxide was weighed, and 7000mL of water was added for dissolution and shaking for use. 100kg of evaporation condensate was weighed by a scale, the pH was adjusted with a prepared sodium hydroxide solution, and the amount of sodium hydroxide solution consumed was recorded, and the results were as shown in Table 5 below (pH 6.98 jumped to 7.52 and only one drop of alkali was consumed):
TABLE 5
And then respectively regulating pH to about 5.5, 6.0, 6.5 and 7.5 according to the instruction of neutralization alkali consumption data in the table, and performing reverse osmosis purification pilot-scale verification by respectively feeding 100L of evaporated condensate, wherein the verification result is shown in the table 6 below:
TABLE 6
Neutralizing the evaporated condensate water to 7.0 or 7.5 by alkali, and performing reverse osmosis purification to obtain water with a water yield of more than 90% and neutral pH; the conductivity is less than 20 mu S/cm; the COD is less than 1000 in the detection, and the content of formic acid and acetic acid is less than 10ppm; the taste of the corn milk is free from peculiar smell, and is far lower than the slightly boiled corn water taste of the starch milk. Can completely meet the water quality requirement of twelve-stage cyclone washing.
In the invention, the problem of high transmittance of the reverse osmosis organic acid can be perfectly solved by the design of the process flow. The PH of the purified water obtained by the treatment of the process flow is raised to 7.0-8.0, and the smell of the boiled corn water is far weaker than that of the finished starch milk produced normally, so that the fresh water for twelve-stage cyclone washing can be completely replaced, and finally, the aim of zero wastewater discharge in corn starch production is fulfilled. The method is simple and efficient, the cost of obtaining high-quality purified water from the purified process water is low, the cost of obtaining ton of purified water is lower than 3 yuan (amortization of alkali-containing consumption, electricity cost and film replacement consumption) under the conditions that the current market price of sodium hydroxide is 1.2 yuan/Kg (dry basis) and the electricity price is about 0.7 yuan/degree, and the cost of raw water cost, treatment cost and pollution discharge cost of most of factory ton waste water emission in the current industry are far lower than the cost of approaching or exceeding 10 yuan.
It will be appreciated by those skilled in the art that the present invention can be carried out in other embodiments without departing from the spirit or essential characteristics thereof. Accordingly, the above disclosed embodiments are illustrative in all respects, and not exclusive. All changes that come within the scope of the invention or equivalents thereto are intended to be embraced therein.
Claims (10)
1. A method for realizing zero wastewater discharge in corn starch production by using process water purification sleeve comprises the following steps:
step one, reserving steam condensate water in a corn soaking water evaporation concentration process in the corn starch production process for later use;
step two, carrying out heat exchange and cooling on the steam condensate water to 35-45 ℃;
step three, regulating the pH value of the cooled steam condensate water and enabling the pH value of the steam condensate water to be 7.0-8.0;
and fourthly, performing reverse osmosis filtration on the steam condensate water with the pH value regulated to obtain purified water with the pH value of 7.0-8.0, the conductivity of 30 mu S/cm-70 mu S/cm and the COD of 800mg/L-1200mg/L, wherein the purified water is used for partially replacing fresh water for twelve-stage cyclone washing in corn starch production.
2. The method according to claim 1, wherein the steam condensate water obtained in the first step has a pH of 2.8-3.5, a conductivity of 150-500. Mu.S/cm, and a COD of 2800-3200 mg/L.
3. The method of claim 1, wherein in the second step, the steam condensate is cooled using a heat exchanger.
4. The method according to claim 1, wherein in the third step, neutralization is performed by adding an aqueous sodium hydroxide solution or an aqueous sodium carbonate solution to the steam condensate.
5. The method according to claim 1, wherein in the fourth step, the steam condensate is purified by filtration through a reverse osmosis device.
6. The method according to claim 1, wherein in the fourth step, the membrane-trapped concentrated water remaining after the purification by reverse osmosis has a pH of 7.0 to 8.0, a conductivity of 9500 μS/cm to 10500 μS/cm, and a COD of 38000mg/L to 42000mg/L.
7. The method of claim 1, wherein in the fourth step, the pressure difference of the reverse osmosis unit when filtering the condensed water of the steam is 4Bar to 10Bar.
8. The method of claim 6 wherein the membrane reject concentrate remaining after the reverse osmosis purification to produce purified water is combined with the steam condensate of the residual corn steep water evaporation concentration process not used as a source of purified water and is still used to produce the sulfuric acid solution for steeping corn as it is.
9. The method according to claim 1, wherein in the second step, the steam condensate is cooled to 35 ℃, 36 ℃, 37 ℃, 38 ℃, 39 ℃,40 ℃, 41 ℃, 42 ℃, 43 ℃, 44 ℃, 45 ℃.
10. The method according to claim 1, wherein in the second step, the steam condensate is cooled to 40 ℃.
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