JP5569352B2 - Wastewater treatment method - Google Patents

Description

  The present invention relates to a wastewater treatment apparatus and a wastewater treatment method for treating concentrated alkaline defatted wastewater generated from a steel manufacturing process.

  In general, wastewater generated at a steelworks or the like is separated into solid and liquid in order to reduce the volume and reduce the amount of waste generated. However, concentrated alkaline wastewater containing concentrated alkaline components, especially alkaline degreasing wastewater generated from steelworks, contains concentrated oils, so it is difficult to separate solid and liquid, and it is necessary to multistage wastewater treatment equipment. there were. For this reason, there is a problem that the wastewater treatment apparatus becomes complicated. Further, the higher the oil concentration in the waste liquid, the more difficult the solid-liquid separation becomes and the volume of the waste cannot be reduced, resulting in an increase in the amount of waste. Furthermore, there has been a problem that a large amount of pH adjuster needs to be added in the treatment of concentrated alkaline degreasing wastewater.

  In order to solve these difficulties, an evaporation and concentration apparatus has been proposed in which moisture is evaporated in a reduced-pressure atmosphere to extract a solid content as a residue (see, for example, Patent Document 1). In the evaporative concentration apparatus of Patent Document 1, waste water is batch-fed from a raw water tank via a measuring tank to a vacuum distillation kettle, and the inside of the distillation kettle is reduced in pressure (−80 kpa to 90 kpa, 40 to 50 ° C.) using a vacuum pump. ). The evaporated water is condensed in the condenser via the mist filter. The condensed moisture passes through the heat exchanger and is recovered in the recovery liquid tank. The separated waste water becomes a solid content that is a residue and is deposited in the distillation still, and is discharged by a scraper.

Japanese Patent Laid-Open No. 10-202001

  However, the wastewater from each line of the steelworks has a large difference in water quality depending on the source of the wastewater, and the load fluctuations applied to the facilities are large when each wastewater is treated. Therefore, stable operation is possible even if the evaporative concentration apparatus of Patent Document 1 is used. There was a problem that it was difficult. In addition, when the evaporation process is performed using the evaporation and concentration apparatus of Patent Document 1, it is only a mist filter that removes pollutants and the like in the evaporated water. For n-Hex, COD, etc., the water pollution prevention method is used. There was a risk that the wastewater could not be treated to the water quality within the range of the standard value. In particular, COD can be treated by a method such as chemical oxidation or activated carbon adsorption, but it becomes a large water treatment facility, resulting in an enormous capital investment.

Therefore, the present invention has been made in view of the above problems, and the object of the present invention is to separate solid-liquid using a device that can easily and stably operate waste water that is difficult to solid-liquid separate and has a large water quality difference. the waste while volume reduction, without the need for COD treatment such as a chemical oxidation and activated carbon adsorption, to provide a waste water treatment method capable of processing up to the water quality within the range of legal standard value .

In order to solve the above-described problems, according to one aspect of the present invention, a liquid component is evaporated in a reduced pressure atmosphere from an alkaline wastewater that is an alkaline wastewater containing an oil component generated in a steel production process, and a solid content that is a residue. An evaporative concentrator for separating and recovering the evaporated liquid component, and an oil separator that is installed at a subsequent stage of the evaporative concentrator and that separates and removes oil from the liquid component separated and recovered by the evaporative concentrator , a waste water treatment method using the waste water treatment apparatus Ru equipped with, and set a threshold for recovery time required for recovery of the liquid component from said alkali waste liquid in the evaporative concentration apparatus for performing one, the recovery A wastewater treatment method is provided in which when the time exceeds the threshold value, the recovery of the alkaline wastewater is temporarily stopped and sludge is discharged from the evaporative concentration apparatus .

  The wastewater treatment apparatus is installed in a stage preceding the evaporative concentration apparatus, and stores a raw water tank that stores the alkaline wastewater while stirring, and a wastewater supply apparatus that supplies the alkaline wastewater from the raw water tank to the evaporative concentration apparatus. Furthermore, you may provide.

  The wastewater treatment apparatus may further include an antifoaming agent supply device that supplies an antifoaming agent to the evaporation concentrating device.

  According to the present invention, as a wastewater treatment facility for alkaline defatted wastewater, by providing an oil separator that further separates the liquid component separated by solid-liquid separation with an evaporative concentration device, it is easy to separate wastewater that is difficult to solid-liquid separation and has a large water quality difference. In addition to reducing the volume of waste by solid-liquid separation with an apparatus that can be operated stably, water quality within the legal standard range can be processed without the need for COD treatment such as chemical oxidation or activated carbon adsorption. It becomes possible.

It is explanatory drawing which shows the whole structure of the waste water treatment apparatus which concerns on the 1st Embodiment of this invention. It is explanatory drawing which shows the oil-water separation method by the oil separator which concerns on the same embodiment. It is a graph which shows an example of the relationship between the collection | recovery interval in a collection | recovery liquid tank, and the frequency | count of collection | recovery.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

(Configuration of wastewater treatment equipment)
First, the configuration of a wastewater treatment apparatus 100 according to a preferred embodiment of the present invention will be described with reference to FIG. FIG. 1 is an explanatory diagram showing an overall configuration of a wastewater treatment apparatus 100 according to the present embodiment.

  As shown in FIG. 1, the wastewater treatment apparatus 100 according to the present embodiment mainly includes a raw water tank 110, an evaporating and concentrating apparatus 120, an oil separator 130, and an antifoaming agent supply apparatus 140. Hereinafter, each of these components will be described in detail.

<Raw water tank 110>
The raw water tank 110 is a tank that is installed upstream of the evaporative concentration apparatus 120 and stores alkaline waste water that is alkaline waste water containing oil generated in the steel manufacturing process while stirring. Here, the “preceding stage of the evaporative concentrator 120” means the inlet side of the alkaline waste water into the evaporative concentrator 120, that is, between the various lines in the ironworks where the alkaline waste water is generated and the raw water tank 110. . Further, the “alkaline wastewater” in the present embodiment is not particularly limited as long as it is wastewater containing an alkali component and an oil component. To give a specific example, alkaline degreasing performed as a pretreatment for galvanization and other surface treatments. Examples include waste water after treatment (such as waste water from a plating line or waste water from an electrolytic line).

  The raw water tank 110 is supplied with alkaline waste water drained from each line of the steelworks. Here, Table 1 shows an example of waste water generated in the steelworks line. In Table 1, as a water quality index, the standard value of concentration is set by the Water Pollution Control Law, the amount of suspended solids (SS), chemical oxygen demand (COD), amount of normal hexane extract (n-hex) ) Each concentration is shown.

  As shown in Table 1, the wastewater from each line has a large difference in water quality depending on its source. Therefore, if each wastewater is processed by the same apparatus (for example, the evaporative concentration apparatus 120), the fluctuation | variation of the operation load given to an apparatus is large. As described above, when the fluctuation of the operation load due to the water quality difference of the wastewater is large, the replacement frequency of a filter (such as a mist filter) for removing substances such as oil from the liquid component separated by the evaporation concentrator 120 varies, and the maintenance load is also increased. Since it becomes large, stable operation may be difficult.

  Therefore, in the wastewater treatment apparatus 100 according to the present embodiment, a raw water tank 110 is provided, and in this raw water tank 110, alkaline waste water having a large water quality difference from each line is stirred and mixed, and the alkaline waste water supplied to the evaporative concentration apparatus 120 is mixed. By making the water quality uniform, the operation load on the evaporative concentration apparatus 120 is made substantially constant. Thus, in order to stir the alkaline waste water having a large water quality difference from each line, the raw water tank 110 is provided with, for example, an impeller 113 using a motor 111 as a driving means as a stirring means. In this way, by stirring waste water having various water qualities in the raw water tank 110, not only can the water quality be made uniform, but also suspended matter in the alkaline waste water is prevented from precipitating in the raw water tank 110. You can also.

  In addition, the wastewater treatment apparatus 100 is provided with a raw water pump 115 that supplies alkaline wastewater, which is stirred and mixed in the raw water tank 110 and made uniform in water quality, from the raw water tank 110 to the evaporation concentrator 120. The raw water pump 115 is an example of a waste water supply device according to the present embodiment, and is provided between the raw water tank 110 and the evaporative concentration device 120. There is no particular limitation on the method of supplying (feeding) the waste water to the evaporation concentrating device 120 by the raw water pump 115.

  In the wastewater treatment apparatus according to the present invention, the raw water tank 110 and the raw water pump 115 may be provided as necessary. For example, when treating wastewater from a single line, or in a plurality of lines Even in the case where wastewater having a small water quality difference is treated, the raw water tank 110 and the raw water pump 115 are not necessarily provided.

<Evaporation concentration apparatus 120>
The evaporative concentrator 120 is an apparatus that evaporates liquid components in a reduced pressure atmosphere from alkaline waste water supplied from the raw water tank 110 by the raw water pump 115 to take out solid components as residues, and separates and recovers the evaporated liquid components. is there. Specifically, the evaporative concentration apparatus 120 mainly includes a vacuum distillation apparatus 121 and a condenser 123.

  The inside of the vacuum distillation apparatus 121 is set to a reduced pressure atmosphere (−80 kpa to 90 kpa) using a vacuum pump (not shown) or the like, and is heated to a predetermined temperature (40 ° C. to 50 ° C.). Therefore, when alkaline waste water is supplied from the raw water tank 110 to the vacuum distillation apparatus 121, the alkaline waste water is distilled, and volatile components in the alkaline waste water are vaporized to separate the volatile components. Volatile components (mainly water) vaporized in the vacuum distillation apparatus 121 are removed from a predetermined oil component by a mist filter (not shown) arranged on the outlet side of the vacuum distillation apparatus 121. On the other hand, the alkaline waste water after separation of the liquid component becomes a solid content that is a residue, and this solid content is deposited in the vacuum distillation apparatus 121. The accumulated solid content is discharged as a dehydrated cake from the vacuum distillation apparatus 121 by a scraper (not shown) or the like. The discharged dehydrated cake is used as a combustion aid in, for example, an incinerator. Thus, by separating the alkaline waste water into solid and liquid and discharging the solid content as a dehydrated cake, the volume of waste can be reduced by significantly reducing the volume of alkaline waste water generated in each line of the steelworks.

  The condenser 123 is connected to the upper part of the vacuum distillation apparatus 121. The inside of the condenser 123 is set to a reduced pressure atmosphere (−80 kpa to 90 kpa) using a vacuum pump (not shown) or the like, and a predetermined temperature (40 ° C.). ˜50 ° C.). Therefore, when the volatile component that has passed through the mist filter is supplied into the condenser 123, the volatile component is condensed and liquefied in the cooled condenser 123. The liquefied volatile component (liquid component) is recovered in the recovery liquid tank 150 as necessary via a heat exchanger (not shown).

  Here, according to the present inventors, although the liquid component recovered in the recovery liquid tank 150 is relatively clear, a small amount of low-boiling oil leaked from the mist filter is suspended in this liquid component. I found out. The low boiling point oil component floats in the liquid component in the recovered liquid tank 150, so that the value of COD and n-hex increases, and the quality of the liquid component of the alkaline waste water after wastewater treatment (solid-liquid separation) It turned out to be worse. Therefore, the wastewater treatment apparatus 100 according to the present embodiment is provided with an oil separator 130 described below.

<Oil separator 130>
The oil separator 130 is installed at the subsequent stage of the evaporative concentrator 120, and separates and removes oil from the liquid component separated and recovered by the evaporative concentrator 120 (hereinafter sometimes referred to as “recovered liquid”) (oil-water separation). It is a device to do. Here, “the latter stage of the evaporative concentrator 120” means the discharge side of the alkaline waste water from the evaporative concentrator 120, that is, the wastewater treatment in which the alkaline waste water after the treatment by the evaporative concentrator 120 and the waste water treatment apparatus 100 is discharged It means between the facilities.

  Here, the configuration and function of the oil separator 130 according to the present embodiment will be described with reference to FIG. FIG. 2 is an explanatory view showing an oil-water separation method by the oil separator according to the present embodiment.

  As shown in FIG. 2, the oil separator 130 is provided at the rear stage of the evaporative concentration device 120 (recovered liquid tank 150), and has two partition walls 131 and 133 therein. The partition wall 131 is provided so as to close the top surface side inside the oil separator 130 and open the bottom surface side. The partition wall 133 is provided on the outlet side of the recovered liquid from the partition wall 131 so as to open the top surface side in the oil separator 130 and close the bottom surface side.

  When the recovered liquid is supplied to the oil separator 130 having the above-described configuration, the oil component floating on the surface of the recovered liquid 150 is trapped by the partition wall 131 provided on the top surface inside the oil separator 130. . The trapped oil cannot flow further to the outlet side of the recovered liquid in the oil separator 130 due to the partition wall 131. Therefore, the recovered liquid discharged from the oil separator 130 may have a low boiling point oil leaked from the mist filter, etc. It becomes a very clear liquid from which the mist is removed. In this manner, oil components are separated from the oil separator 130 by the partition wall 131 and the like, and a recovered liquid that is clearer than the recovered liquid that is simply separated into solid and liquid by the evaporation concentrator 120 is discharged. The deterioration of the water quality of the liquid component of waste water can be eliminated.

  In addition, if the number of stages of the partition walls 131 and 133 is appropriately increased in accordance with the floating oil removal status, the floating oil removal effect can be further obtained.

<Defoamer supply device 140>
The antifoaming agent supply device 140 is a device that supplies the antifoaming agent to the vacuum distillation apparatus 121 of the evaporation concentrating device 120. In the wastewater treatment apparatus 100 according to the present embodiment, a mechanism for boiling alkaline wastewater in the vacuum distiller 121 to evaporate volatile components and adsorbing the vaporized volatile components in a mist form to a filter such as a mist filter. Therefore, foaming occurs in the alkaline waste water in the vacuum distillation apparatus 121 by boiling. When foaming is performed by boiling in this way, the oil and suspended matter in the foamed alkaline wastewater may be scattered and accompanied by the vaporized volatile components on the filter side. Thus, when oil content, suspended matter, etc. are accompanied by the filter side, the clarity of the collect | recovered liquid isolate | separated from the alkaline waste water will deteriorate.

  Therefore, in the wastewater treatment apparatus 100 according to this embodiment, in order to suppress the foaming of the alkaline wastewater, the defoaming agent is supplied into the vacuum distiller 121 of the evaporation concentrator 120, so that the oil and suspended matter are scattered. This suppresses the effect on the deterioration of the clarity of the recovered liquid. Specifically, the antifoaming agent supply device 140 includes a storage tank 140 that stores the antifoaming agent, and a supply pump 143 that supplies the antifoaming agent in the storage tank 140 to the evaporation concentrating device 120.

  As the antifoaming agent, known silicone antifoaming agents and organic antifoaming agents can be used. The type of the silicone-based antifoaming agent is not particularly limited, such as an oil type, a solution type, an oil compound type, an emulsion type, and a self-emulsifying type, and any type can be used.

<Multistage filter>
In the present embodiment, scattered mist-like oil or suspended solids are removed by adsorbing to the filter, but maintaining the cleanliness of the filter ensures the quality of the wastewater after treatment. Leads to. Therefore, it is preferable to maintain the function of the entire filter by making the filter a multistage filter in which a plurality of filters are laminated and further replacing only some of the filters sequentially from the upstream side.

(Waste water treatment method)
The wastewater treatment apparatus according to the preferred embodiment of the present invention has been described in detail above. Subsequently, the wastewater treatment method according to the preferred embodiment of the present invention will be described. The wastewater treatment method according to this embodiment is a wastewater treatment method for treating alkaline wastewater using the wastewater treatment apparatus 100 according to this embodiment described above. More specifically, in the wastewater treatment method according to the present embodiment, a predetermined threshold value t _T is set for the recovery time required to perform one recovery of the liquid component from the alkaline wastewater in the evaporation concentrator 120, and the recovery time There when greater than or equal to the threshold value t _T set, temporarily stopping the recovery of the alkali waste.

  Here, the reason why the above operation is performed in the wastewater treatment method according to the present embodiment will be described.

  Sufficient solid-liquid separation of alkaline wastewater by the evaporative concentrator 120 will lead to suppression of the amount of generated sludge (the amount of solid content that becomes a residue after solid-liquid separation), but the generated sludge (solid content) is distilled under reduced pressure. This causes a problem of drying and sticking in the vessel 121, adversely affecting the discharge of solids, and leading to troubles.

  Therefore, the present inventors have examined the optimization of the operation method of the evaporative concentration apparatus 120 that balances the improvement of the recovery rate of the recovered liquid and the discharge of the solid content in a well-balanced manner. Usually, for example, 165 L of alkaline waste water is batch-fed to the vacuum distiller 121, and the recovered liquid recovered by evaporation is recovered 4.5 L at a time in the recovered liquid tank 150. In general, the wastewater treatment of alkaline wastewater is a batch operation, and therefore, the specified number of times (for example, 25% when the recovery rate of the recovered liquid is set to 70%, based on the recovery rate of the recovered liquid after the treatment) The operation (operation of the evaporative concentrator 120) is once stopped at about .5 times).

  In the above examination, even after the specified number of collections was exceeded, the operation of the evaporative concentrator 120 was continued, six tests were conducted (No. 1 to No. 4), and the collection interval and number of collections were measured. The result is shown in FIG. FIG. 3 is a graph showing an example of the relationship between the collection interval and the number of collections in the collected liquid tank. The vertical axis in FIG. 3 represents the collection interval (seconds), and the horizontal axis represents the number of collections (times).

  As shown in FIG. 3, since the amount of heat input is constant, the amount of evaporation of the volatile components is considered to be almost constant, so the recovery interval has been around 100 seconds up to the 25th time, but there is no moisture. It can be seen that the collection interval suddenly increases (the time required for collection increases) at the 27th time. That is, it is considered that when the collection interval is increased, moisture is lost, and solid matter is stuck in the vacuum distillation apparatus 121. From the above results, it is conceivable that the sludge (solid content) sticks to the inside of the vacuum distillation apparatus 121 where the collection interval by the collection liquid tank 150 is approximately 200 seconds or more. As described above, by clarifying the relationship between the collection interval and the number of collections in the collection liquid tank 150, it was clarified that the starting point of the sludge sticking in the vacuum distillation apparatus 121 is at the predetermined collection interval.

Therefore, based on the above knowledge, in the wastewater treatment method according to the present embodiment, flexible operation focusing on the collection time interval is performed. That is, when a predetermined threshold value t _T is set for the recovery time required to perform a single recovery of the liquid component from the alkaline waste water in the evaporative concentration apparatus 120, and the recovery time is equal to or greater than the set threshold value t _T , The recovery of alkaline wastewater was temporarily stopped.

(Summary)
As described above, the wastewater treatment apparatus 100 and the wastewater treatment method according to the present embodiment are configured to remove the alkaline degreasing wastewater containing a thick alkaline component and oil generated from the steel manufacturing process, a conventional pH adjuster, a sedimentation basin, and the like. The solid-liquid separation is performed by using the evaporative concentration apparatus 120 without using the solid-liquid separation apparatus, and the volume of waste is greatly reduced. In addition, the clear recovered liquid that has been separated into solid and liquid is sent to existing wastewater treatment facilities, and the solid content that is the residue is treated as an auxiliary combustor in an incinerator, achieving zero emissions and a unified high concentration. A treatment method for oil-impregnated alkaline wastewater has been established.

Example 1
In this example, alkaline degreased wastewater having a pH of 13.6, an SS value of 1100 mg / L, a COD value of 16000 mg / L, and an n-hex value of 5100 mg / L was used as the raw water for wastewater treatment. This was subjected to wastewater treatment using a wastewater treatment apparatus 100 as shown in FIG. The evaporating and concentrating apparatus 120 used was a processing capacity of 330 L / 75 minutes, operated under conditions of a vacuum degree of −81 to 87 kPa and a vapor pressure of 0.03 to 0.05 MPa. In addition, a silicone-based antifoaming agent was added to the evaporation concentrator 120 so as to have a concentration of 200 mg / L.

  The results of the wastewater treatment as described above are shown in Table 2. As shown in Table 2, the water quality of the recovered liquid separated and recovered from the raw water has a pH of 10.6, an SS value of 1.6 mg / L, and a COD value of 10 mg / L at the maximum after passing through the oil separator 130. A clear recovered liquid was continuously obtained with a maximum n-hex value of 26 mg / L (11 to 26 mg / L). Moreover, the volume reduction rate of the raw water was 70%, and the volume of alkaline waste water could be greatly reduced to 30% of the amount of raw water. Moreover, about pH and n-hex, the process which is within the range of a statutory value was performed by performing neutralization and floating separation by the existing waste water treatment equipment after this.

(Example 2)
Using the same alkaline waste water as in Example 1, 165 L of this alkaline waste water was batch-fed to the vacuum distillation apparatus 121, and the recovered liquid recovered by evaporation was recovered to 4.5 L at a time in the recovered liquid tank 150. Wastewater treatment was performed. At this time, the operation of the evaporation concentrator 120 was once stopped at a collection interval of 200 seconds based on the above examination results. As a result, it was possible to discharge the sludge without causing the trouble of the sludge sticking in the vacuum distillation apparatus 121 of the concentration drying apparatus 120.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 100 Waste water treatment apparatus 110 Raw water tank 111 Motor 113 Impeller 115 Raw water pump 120 Evaporation concentration apparatus 121 Vacuum distillation apparatus 123 Condenser 130 Oil separator 131,133 Partition 140 Defoamer supply apparatus 141 Storage tank 143 Supply pump 150 Recovery liquid tank

Claims (3)

Evaporation concentration device that evaporates liquid components in a reduced-pressure atmosphere from alkaline waste water that is an alkaline waste water containing oil generated in the steel manufacturing process, takes out solid components that are residues, and separates and recovers the evaporated liquid components A wastewater treatment method using a wastewater treatment apparatus, comprising: an oil separator that is installed at a subsequent stage of the evaporative concentration apparatus and separates and removes oil from the liquid component separated and recovered by the evaporative concentration apparatus ,
A threshold is set for the recovery time required for one recovery of the liquid component from the alkaline wastewater in the evaporative concentrator, and when the recovery time exceeds the threshold, the alkaline wastewater is recovered. A wastewater treatment method for temporarily stopping and discharging sludge from the evaporative concentration apparatus . The wastewater treatment device is installed in the front stage of the evaporative concentration device, a raw water tank for storing the alkaline wastewater while stirring,
  A waste water supply device for supplying the alkaline waste water from the raw water tank to the evaporative concentration device;
The wastewater treatment method according to claim 1, further comprising: The wastewater treatment apparatus according to claim 1 or 2, wherein the wastewater treatment apparatus further includes an antifoaming agent supply device that supplies an antifoaming agent to the evaporation concentrating device.

Images