HK1190696B - Device and method for reducing the hydrogen peroxide and peracetic acid content in a water flow - Google Patents

Description

Apparatus and method for reducing hydrogen peroxide and peracetic acid content in an aqueous stream

Technical Field

The present invention relates to an apparatus and a method for reducing the content of hydrogen peroxide and peracetic acid in a water stream, in particular a water stream discharged from ballast tanks of a ship.

Background

Peracetic acid is a bactericide which has many advantages over other bactericides. Peracetic acid exhibits broad bactericidal activity against bacteria, phytoplankton and zooplankton even at low concentrations of less than 5ppm without resistance. In contrast to most other fungicides, peracetic acid in dilute aqueous solutions rapidly degrades by hydrolysis and decomposition into substances that are no longer biologically active. Compared to ozone or chlorine dioxide, peracetic acid can be safely transported and stored in the form of balanced peracetic acid. In contrast to chlorine or hypochlorite, treatment of the water stream with peracetic acid does not or only slightly lead to the formation of halogenated organic compounds and thus does not lead to an increase in the AOX content. Peroxyacetic acid is therefore suitable for use in aqueous streams after treatment for large amounts of release to the surrounding environmentSuch as the sterilization of cooling water streams or discharge from sewage treatment plants, in particular ship ballast water. In thatThe treatment of ballast water with peracetic acid in the process is approved by the International Maritime Organization (IMO) for the removal of phytoplankton and zooplankton.

Although peracetic acid and hydrogen peroxide present in equilibrium peracetic acid due to the production process degrade rapidly in treated water, it is necessary in some applications, particularly in the treatment of ballast water, to remove any residual amounts of peracetic acid and hydrogen peroxide still present after the treatment before the treated water is released into the surrounding environment.

To remove chloramine or bromamine from treated ballast water, WO02/072478 proposes adding a reducing agent such as sodium thiosulfate or sodium sulfite in molar excess to the treated ballast water. However, in the present method, after reduction of chloramine or bromamine, the treated water must be aerated with oxygen before it can be released into the surrounding environment.

WO2004/054932 proposes adding a sodium thiosulfate solution to the ballast water and controlling the amount of addition by the redox potential of the chlorine-containing ballast water for removing chlorine generated from electrolysis in the treated ballast water.

WO2006/058261 and WO2008/153808 propose adding a sodium sulfite solution to the ballast water and passing through a sulfurous acid analyzer (which releases SO by acidic addition)₂And measuring SO with a sensor₂) The amount added is controlled so that the treated ballast water contains an excess of sodium hypochlorite sulfite for removal of electrolytically generated hypochlorite from the treated ballast water.

US2010/072144 proposes to add a sodium sulfite solution to ballast water, the amount of addition being controlled by measuring the redox potential in the ballast water after the addition of the sodium sulfite solution, in such a way that the redox potential is in the range of 200-500 mV to remove hypochlorite from the treated ballast water.

US7,776,224 proposes measuring the concentration of hydrogen peroxide in ballast water and adding a reducing agent to remove the hydrogen peroxide in the treated ballast water in dependence on the measured value. It also proposes that after the addition of the reducing agent, the redox potential be detected or measured with a hydrogen peroxide densitometer to verify the presence of unreacted hydrogen peroxide.

EP1671932 proposes the addition of an oxidizing agent and one of ferric (II) sulphate, iodide or catalase to treat ballast water with hydrogen peroxide or to equilibrate peroxyacetic acid in order to effect decomposition of hydrogen peroxide during treatment of the ballast water.

However, there is still a need for an apparatus and method that can reduce the hydrogen peroxide and peracetic acid content of an aqueous stream when needed, and with which the water after removal of the hydrogen peroxide and peracetic acid does not contain substances that are harmful to water.

The inventors of the present invention have established that the method for removing hypochlorite known from US2010/072144 is not suitable for removing hydrogen peroxide in a water stream, because by measuring the redox potential in water after addition of the reducing agent, it cannot be reliably determined that the water does not contain unreacted hydrogen peroxide or excess reducing agent. Likewise, the method for removing chlorine known from WO2004/054932 is not suitable for removing peracetic acid and hydrogen peroxide in an aqueous stream, since the required amount of reducing agent for removing peracetic acid and hydrogen peroxide cannot be calculated in advance from the redox potential of the aqueous stream comprising peracetic acid and hydrogen peroxide.

Accordingly, the present inventors have developed an apparatus and process by which the levels of hydrogen peroxide and peracetic acid in an aqueous stream can be reliably reduced.

Disclosure of Invention

The invention relates to a device for reducing the hydrogen peroxide and peracetic acid content (1) in a water stream, comprising a first measuring device (2) for determining the flow rate of the water stream, a second measuring device (3) for determining the hydrogen peroxide concentration in the water stream, a third measuring device (4) for determining the peracetic acid concentration in the water stream, a metering device (5) for metering a reducing agent into the water stream downstream of the second and third measuring devices, and a control device (6) which calculates the amount of reducing agent for reducing the hydrogen peroxide and peracetic acid content to a desired value from the flow rate of the water stream, the hydrogen peroxide concentration in the water stream and the peracetic acid concentration in the water stream and activates the metering device for metering the reducing agent.

The invention also relates to a process for reducing the hydrogen peroxide and peracetic acid content of an aqueous stream, comprising metering a liquid reducing agent into the aqueous stream using the apparatus according to the invention. The water stream is preferably discharged from a ballast water tank (10) of the vessel.

Fig. 1 shows an apparatus according to the invention in one embodiment with an additional measuring device (7) for determining salinity and an arrangement of a second and a third measuring device in a side stream (9).

The device according to the invention comprises a first measuring means (2) for determining the flow rate of the water flow (1). For this purpose, both measuring devices for determining mass flow rates and measuring devices for determining volume flow rates are suitable. For the device according to the invention, all measuring devices known from the prior art for determining the flow rate of a water flow can be used, such as mass flow meters, orifice plate differential pressure measurements and inductive flow meters. Preferably, a mass flow meter is used to measure the flow rate of the water stream to reliably determine the flow rate of the water stream, even water streams having different salt contents.

The apparatus according to the invention further comprises a second measuring device (3) for determining the concentration of hydrogen peroxide in the water stream (1). Suitable measuring devices are all those known from the prior art by means of which the concentration of hydrogen peroxide in water can be determined and which do not show or show only to a slight extent a cross-sensitivity to peracetic acid. Suitable measuring devicesDevices are for example those which: the concentration of hydrogen peroxide is determined colorimetrically and a device is used which has a specific color reaction with hydrogen peroxide, for example the reaction of hydrogen peroxide with titanyl sulfate, to form a soluble peroxo complex of titanium (IV). Preferably, the concentration of hydrogen peroxide is determined with an amperometric sensor, particularly preferably in an amperometric sensor according to the reaction equation: h₂O₂→O₂+2H⁺+2e^-The oxidation reaction of hydrogen peroxide is carried out.

Sensors for suitable amperometric analysis of hydrogen peroxide which do not show a lateral sensitivity to peroxyacetic acid are available on the market, for example fromIs named asPEROX. The response time of these sensors can be adjusted by the manufacturer to accommodate the rate of change of hydrogen peroxide concentration in the treated water stream by exchanging the membrane covering the sensor.

The apparatus according to the invention also comprises a third measuring device (4) for determining the concentration of peracetic acid in the water stream (1). Suitable measuring devices are all those known from the prior art by which the concentration of peracetic acid in water can be determined and which do not show or show only to a small extent a cross-sensitivity to hydrogen peroxide, for example by colorimetrically determining the concentration of peracetic acid and using a device having a specific color reaction with peracetic acid, for example the reaction of peracetic acid with 2, 2' -dinitrobis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), to form a soluble dye. Preferably, the concentration of peroxyacetic acid is determined using a current sensor, and particularly preferably the reduction of peroxyacetic acid in the amperometric sensor is according to the reaction equation: CH (CH)₃COOOH+2H⁺+2e^-→CH₃COOH+H₂And O, performing.

Show a sufficiently low hydrogen peroxideCross-sensitive sensors for suitable amperometric analysis of peroxyacetic acid are commercially available, for example fromIs named asPAA. The response time of these sensors can be adjusted by the manufacturer to accommodate the rate of change of peracetic acid concentration in the treated water stream by exchanging the membrane covering the sensor. Also suitable are commercially available amperometric sensors for determining the total chlorine content, for example commercially available amperometric sensorsIs/are as followsCET-1 sensor. Due to the rapid reaction of chlorine and hypochlorite with hydrogen peroxide, the hydrogen peroxide-containing aqueous stream can only contain small amounts of chlorine and hypochlorite, and an amperometric sensor for determining the total chlorine content can also determine peracetic acid with low cross-sensitivity to hydrogen peroxide, and the content of peracetic acid in the aqueous stream can also be reliably determined by using such a sensor.

The use of amperometric sensors for measuring the concentrations of hydrogen peroxide and peracetic acid allows the apparatus of the present invention to be automated substantially by personnel, such as a crew member without the training of the apparatus for operational analysis.

In the apparatus according to the invention, two separate devices for determining the hydrogen peroxide concentration and the peracetic acid concentration can be replaced by one measuring device for simultaneously determining the hydrogen peroxide concentration and the peracetic acid concentration. An example of such a measuring device is an automatic titration for determining the concentration of hydrogen peroxide using a continuous cerium titration and for determining the concentration of peroxyacetic acid using a continuous iodometry.

The measuring device for determining the concentration of hydrogen peroxide and peracetic acid is preferably arranged in a side stream (9) of the water stream in order to avoid damage to the measuring device by solids carried by the water stream. For the same purpose, it is preferred that the filter is placed upstream of the branch flow of the measuring device.

The device according to the invention also comprises a metering device (5) for metering the reducing agent into the water flow (1) downstream of the second and third measuring devices. Suitable metering devices are those for the continuous or intermittent metering of the reducing agent, which is preferably gaseous or liquid, particularly preferably liquid. Preferably, the metering device comprises a storage container (8) for the liquid reducing agent and a controllable metering pump (5), so that a continuous metering of the liquid reducing agent is possible at variable volumetric flow rates. Particularly preferably, the metering device comprises a volumetric metering pump, for example a diaphragm pump, a gear pump or a piston pump, which enables a calculated volumetric flow rate to be set for metering the liquid reducing agent.

The apparatus according to the invention further comprises a control device (6), which control device (6) is capable of calculating the amount of reducing agent that reduces the content of hydrogen peroxide and peracetic acid to the desired value from the flow rate of the water stream (1), the concentration of hydrogen peroxide in the water stream and the concentration of peracetic acid in the water stream, and activating the metering device (5) for metering the reducing agent. The control device can be designed as a hard-wired controller or as a computer and control program on a process control computer. The calculation of the amount of reducing agent from the flow rate of the water stream, the concentration of hydrogen peroxide in the water stream and the concentration of peracetic acid in the water stream can be performed by using a test conversion factor determined experimentally or, preferably, using a conversion factor calculated from the stoichiometry of the reduction reaction. For the reduction reaction of the brine-free aqueous stream and using an aqueous solution of sodium sulfite, the conversion factor can be calculated according to reaction equations (I) and (II).

(I)H₂O₂+Na₂SO₃→H₂O+Na₂SO₄

(II)CH₃COOOH+Na₂SO₃→CH₃COOH+Na₂SO₄

For metering the liquid reducing agent with a volumetric metering pump, the volumetric flow rate set at the metering pump can be calculated directly from the calculated amount of reducing agent and the metering pump can be actuated accordingly.

In a preferred embodiment, the device according to the invention comprises an additional measuring device (7) for determining the salinity in the water stream (1). The term "salinity" as used herein refers to a dimensionless salinity S of a practical salinity (practical salinity Scale 1978). The salinity can be determined from density measurements and preferably from conductivity with a conductivity sensor. In this embodiment, the amount of reducing agent is calculated by the control means using salinity. Preferably, the amount of reducing agent calculated here for the brine-free water stream is corrected by an experimentally determined correction factor for salinity. For the reduction reaction with the brine-containing stream and with the aqueous sodium sulfite solution, it is preferred that the calculated amount of reductant for the brine-free stream increases in proportion to the salinity fraction. The salinity is taken into account when metering the reducing agent, so that the content of hydrogen peroxide and peracetic acid can be reliably reduced below predetermined limits even for cases in which the salt content in the water stream is variable, without an excess of reducing agent occurring.

In the process according to the invention for reducing the hydrogen peroxide and peracetic acid content of an aqueous stream, a liquid reducing agent is metered into the aqueous stream (1) by the apparatus according to the invention. The water stream is preferably a water stream treated by adding balanced peracetic acid as a bactericide, in particular a cooling water stream, or a sewage treatment plant effluent, most preferably a water stream discharged from a ballast water tank (10) of a ship.

In the process according to the invention, preferably an aqueous solution of sodium sulfite is used as liquid reducing agent.

The process according to the invention makes it possible to reliably reduce the hydrogen peroxide and peracetic acid content of an aqueous stream below predetermined limits, wherein the aqueous stream after treatment no longer has properties that impair the water quality by using sodium sulfite as reducing agent. This makes it possible to discharge ballast water treated with balanced peracetic acid for destroying phytoplankton and zooplankton into a water body, for example, ballast water is only insufficiently diluted in narrow harbor ponds without impairing the water quality in the water body.

Detailed Description

Example (b):

for the working embodiment herein, water extracted from a drinking water supply network was treated with 80ppm of equilibrium peroxyacetic acid comprising 14.4 wt% peroxyacetic acid and 13.5 wt% hydrogen peroxide. After treatment with the equilibrium peroxyacetic acid, the water contained 11.9ppm peroxyacetic acid and 13.3ppm hydrogen peroxide by weight.

In the apparatus according to the invention shown in FIG. 1, an aqueous sodium sulfite solution is metered continuously into an aqueous stream which has been treated with the equilibrium peracetic acid. Concentrations of Hydrogen peroxide and Peroxyacetic acid produced by use of a catalyst hereinIs determined by the amperometric sensor. In example 1, the stoichiometric amount of sodium sulfite was measured 1.03 times as calculated from the concentration of hydrogen peroxide and the concentration of peracetic acid and the water flow rate according to the reaction equations (I) and (II). In example 2, 1.21 times the calculated stoichiometric amount of sodium sulfite was metered.

In example 1, the water contained 0.1ppm by weight of peracetic acid and 1.0ppm by weight of hydrogen peroxide after the metering of sodium sulfite. In example 2, the water contained 0.2ppm by weight of peracetic acid and 0.1ppm by weight of hydrogen peroxide after the metering of sodium sulfite.

For the water treated with balanced peracetic acid and the streams obtained in examples 1 and 2, the inhibition of algae growth and the acute motility inhibition (inhibition) of daphnia species was determined according to OECD guidelines 201 and 202 for testing chemicals.

The water treated with the equilibrium peracetic acid resulted in complete inhibition of the growth of algae (complete inhibition), EC, of desmodian algae (Desmodesmus subspecies) in an undiluted manner₅₀The values are 46% for the growth inhibition rate and 25% for the inhibition yield. In contrast, the aqueous stream obtained in example 1 resulted in a growth rate of inhibition of only 5% which was statistically insignificant in an undiluted manner. The aqueous stream obtained in example 2 resulted in a growth inhibition rate of 13% in an undiluted manner.

The water treated with the equilibrated peracetic acid results in complete motility inhibition (EC) of daphnia magna (Daphniamagna) in an undiluted manner₅₀The value was 12%. In contrast, the streams obtained in examples 1 and 2 had no movement inhibition for daphnia even in undiluted form and showed no discernible effect.

The examples show that with the apparatus and method of the present invention, the hydrogen peroxide and peracetic acid content of an aqueous stream containing hydrogen peroxide and peracetic acid can be reliably reduced so that once introduced into a body of water, the aqueous stream has no deleterious effect on aquatic life.

List of reference numerals:

(1) water flow

(2) Measuring device for determining a flow rate

(3) Measuring device for determining hydrogen peroxide concentration

(4) Measuring device for determining concentration of peroxyacetic acid

(5) Metering device for metering a reducing agent

(6) Control device

(7) Measuring device for determining salinity

(8) Storage container for liquid reducing agent

(9) Branch flow

(10) Ballast water tank

Claims (10)

1. An apparatus for reducing the hydrogen peroxide and peracetic acid content in a water stream (1), the apparatus comprising:

a first measuring device (2) for determining the flow rate of the water flow,

a second measuring device (3) for determining the concentration of hydrogen peroxide in the water stream,

a third measuring device (4) for determining the concentration of peracetic acid in the water stream,

an additional measuring device (7) for determining salinity in the water flow,

a metering device (5) for metering the reducing agent into the water flow downstream of the second and third measuring devices, and

a control device (6) which calculates the amount of reducing agent used to reduce the content of hydrogen peroxide and peracetic acid to the required value from the flow rate of the water stream, the concentration of hydrogen peroxide in the water stream and the concentration of peracetic acid in the water stream, and activates the metering device for metering the reducing agent.

2. The apparatus of claim 1, wherein: the second measuring means for determining the concentration of hydrogen peroxide in the water stream comprises an amperometric sensor.

3. The apparatus of claim 1, wherein: a third measuring device for determining the concentration of peracetic acid in the water stream includes an amperometric sensor.

4. The apparatus of claim 2, wherein: a third measuring device for determining the concentration of peracetic acid in the water stream includes an amperometric sensor.

5. The apparatus of any of claims 1 to 4, wherein: the additional measuring means for determining salinity comprise a conductivity sensor.

6. The apparatus of any of claims 1 to 4, wherein: the metering device for metering the reducing agent comprises a storage container (8) for the liquid reducing agent and a controllable metering pump (5).

7. The apparatus of any of claims 1 to 4, wherein: the second and third measuring devices are arranged in a partial flow (9) of the water flow.

8. A process for reducing the hydrogen peroxide and peracetic acid content of an aqueous stream, the process comprising metering a liquid reducing agent into the aqueous stream using the apparatus of any one of claims 1 to 7.

9. The method of claim 8, wherein: the water stream is discharged from a ballast water tank (10) of the vessel.

10. The method of claim 8 or 9, wherein: the liquid reducing agent is an aqueous sodium sulfite solution.