NO344809B1 - Procedure for purification of heavy metal-containing waste water from the processing and cleaning of nets from fishing and fish farming - Google Patents

Description

The invention relates to a method for cleaning waste water containing heavy metals from the treatment and cleaning of nets from fisheries and fish farming.

Nets and net arrangements used in fish farming and fisheries must be regularly cleaned of organic contaminants, algae and mussel appendages. The yarns are usually impregnated with heavy metal compounds, such as e.g. copper oxide, before use. During the cleaning of the yarns in washing facilities, waste water is produced which, in addition to organic and inorganic dissolved and undissolved residues, also contains dissolved and undissolved heavy metals, especially copper. Up until now, the waste water has been discharged untreated or only provisionally purified via mechanical devices directly into waterways or the sea. The waste water then contains the organic dirt as well as heavy metals.

Prior art

DE 44 13 895 A1 describes a process for the purification and detoxification of waste water, especially from tanneries and which contains large amounts of heavy metal (e.g. chromium). The waste water is stored in a storage basin which feeds a reaction basin where the toxins, heavy metals and impurities are separated by adding acetic acid and flocculant. The effluent is then transferred to a sedimentation basin and drips slowly from there (to avoid turbulence) into a clear phase separation basin, where the clear liquid is separated from the sludge. The liquid is then decalcified in a decalcification unit, monitored by instrumentation and fed into an ultrafiltration unit. Should the water from the ultrafiltration unit be insufficiently purified, it is taken to a clear phase separation base II and not immediately returned at the end of the process. The water from the ultrafiltration unit flows via a measuring station to a recycling basin from where it is used to clean the module units, or is recycled back to the storage basin to dilute the waste water, or used as process water in the work.

DE 103 36 534 A1 describes a process which reduces the concentration of heavy metals in liquid industrial waste water produced in one- or two-stage sulfur dioxide gas scrubbers. In a preliminary process, a precipitant is added to the liquid wastewater, followed by a mixture of a flocculant and the use of a solids separator. The process is intended mainly against the precipitation of mercury compounds. The precipitating agent is e.g. an alkali sulfide, thiol and/or triazine. The flocculent is sodium sulphide and/or 1,3,5-triazine-2,4,6-trithol. The flocculent and/or flocculent additive is mixed in a separator composition for solids and liquids.

The flocculent and/or flocculent additive is a non-ionic, anionic or cationic vinyl polymer. The flocculent and/or flocculent is a cation flocculant and is water-in-water polymer dispersion. The separator is a hydrocyclone.

NO 971 047 A describes: A method and device for treating wastewater from the shrimp industry, where the water is passed over a first sieve belt filter where the sludge forms a valuable protein-rich feed. A flocculant is then added which together with microscopic air bubbles form accumulations of particles which are removed in a flotation process in a second sieve belt filter. The water's pH is adjusted during the process and at the end, and other quality measurements are carried out.

US 3,577,341 A is directed to a method of treating raw water to remove unwanted material therefrom, which comprises (a) passing the raw water from a raw water source through a mixing zone and then (b) mixing it with one or more additives, (c) feeding the resulting mixture to a settling zone where settled material is separated from the water, (d) passing the separated water from the settling zone to a filtering zone and then (e) further removing unwanted material therefrom, and (f) passing the filtered water from the filtration zone, where there is a flow path from the raw water source through said mixing zone and said sedimentation zone to a place of centrifugal force. The improvement comprises (g) feeding an aqueous solution or suspension of material from the settling zone to said location by centrifugal force and there (h) separating it into an inner layer comprising purified water and an outer layer comprising concentrated undesirable material in an aqueous suspension of flowable consistency, (i) separately discharging said purified water and said concentrated material from the respective layers and said location, and (j) recycling the purified water that is separately discharged from said centrifuge location and mixing it with the flow through the flow path.

The task of the present invention consists in providing a method for the purification of heavy metal-containing waste water from the treatment and cleaning of nets from fisheries and fish farming so that the organic dirt as well as the heavy metals, especially copper, are removed in a safe manner.

This task is solved by the features specified in patent claim 1.

With the method according to the invention as stated in patent claim 1, the organic dirt as well as the heavy metals can be removed from waste water that is formed during the purification process, removed in a safe manner. The method according to the invention is a combination of circuit management and final treatment with the aim of using the washing water several times and of directing it in a partial flow - freed from heavy metals - harmlessly into waterways or the sea.

In the following, the present invention will be described in more detail with the help of an embodiment shown in the drawing.

There shows

fig. 1 a schematic presentation of a waste water treatment plant for cleaning waste water containing heavy metals from the treatment and cleaning of nets from fisheries and fish farming.

As can be seen from fig. 1, the contaminated nets from fish farming or fisheries are cleaned in a net washing plant 1. The cleaning process in the net washing plant 1 takes place with tap or sea water. A seawater supply line 2 is used for this. The polluted waste water that comes from the yarn washing plant 1 is led after the cleaning process via a drain line 3 into a mechanical screening device 4 where coarse solids are filtered out. This aiming device 4 can be designed e.g. such as a screening drum, arc strainer or suction strainer.

The waste water that has been freed from the coarse solids is then transported into an inline flocculation device 5. As shown in the schematic representation in fig. 1, flocculants are added via a supply line 7 in front of the corresponding pipe section of the inline flocculation device 5 in portions from a corresponding storage container 6. Hereby, one to three specific flocculants can be added. Polyaluminium chloride is preferably added to the inline flocculation device 5 as a flocculant. In order to improve the flocculation-separation properties, additional flocculation aids are added in a subsequent pipe section. The flocculation aids are stored in a corresponding storage container 8 and can be added in portions via a supply line 9. By adding these flocculation aids, the microparticles can be aggregated into macroparticles. These macroparticles then meet the requirements for the subsequent solid/liquid separation in a solids separator 10 which is downstream of the inline flocculation device 5 in the direction of flow.

In the solids separator 10, the ingredients bound by the flocculation are separated from the clear water which still contains the dissolved heavy metals. The solids separator 10 is designed e.g. as a slant filtering device. Here, a sedimentation process takes place whereby the sludge substances that collect in the lower area of the solids separator 10 are led via a line 11 to a further solids separator 12 by means of a pump.

The clear water which still contains dissolved heavy metals is led via a line 13 which is arranged in the upper area of the solids separator 10 into a buffer tank 14. The water which still contains the dissolved heavy metals is stored in the buffer tank 14. The buffer tank 14 is designed with two outlet lines. Via the first discharge line 15, the water stored in the buffer tank 15 is fed back to the yarn washing plant 1. Via the second discharge line 16, a partial quantity of approx. 10 to 50% of the stored water batchwise, i.e. discontinuously, to a reactor 17.

The reactor 17 is designed as a pressureless thoroughly mixed mixing container and has a funnel or sloping bottom 18 with a slope of between 0 and 30%. In addition, a rotary mixer 19 is arranged in the middle of the reactor container, which disposes of a stirring effect of between 0.1 and 1.5 kW/m<3 >reactor content. The speed of the agitator is between 50 and 1,500 rpm. After program-controlled filling of the reactor 17 with water from the buffer tank 14 via the supply line 16, the pH value inside the reactor 17 is determined by a sensor 20, and transferred via a signal line to a dosing pump which adds lye from a storage container 21 via a supply line 22 into the reactor 17 to adjust the pH value in it. Hereby, the supply of lye in the reactor 17 is regulated so that an environment with a pH value of 6.5 to 7.5 is formed within the reactor 17. In addition, program-controlled primary flocculating agents in the form of aluminum or iron compounds, organosulphide and flocculation aids in the form of organic polymers are added from corresponding storage containers 22, 23, 24 via corresponding supply lines 25, 26, 27 to the reactor 17. This takes place under constant stirring and control of the pH value via the sensor 20. The dosing process with the above-mentioned chemicals lasts between 5 and 30 minutes, depending on the load of the waste water. After the end of dosing, a precipitation and flocculation process that lasts between 0 and 15 minutes takes place during the pipe organ 19's further operation, and where the partially complex bound heavy metals precipitate out. After completion of the precipitation process, the pipe member 19 is disconnected, and the precipitation product located in the funnel 18 in the lower area of the reactor is led with the water to the solids separator 12.

The solids separator 12 is designed as a sedimentation device and comprises a rectangular or round clarification device. The container's content volume corresponds to one to four times the volume of the filling quantity per hour. The solids separator 12 likewise comprises an inclined bottom 28 which has an inclination between 0° and 60°. In one embodiment, the solids separator 12 can also be equipped with a motor-driven sludge decanter 29. During the sedimentation process that takes place in the solids separator 12, a phase separation of flocculation sludge and purified water is formed. The clear phase that forms in the upper area of the container is led via an outlet line 30 to a control filter 31 and is then led back into the sea. The sludge phase that is formed on the sedimentation slope 28 with a solids content of between 0.5 and 10% is transported via an outlet line 32 to a subsequently arranged sludge drainage facility 33, and is drained in the sludge drainage facility 33 until a solids content of between 20 and 80% is achieved. The sludge drainage system 33 is preferably designed as a gravity belt filter or a chamber filter press. The water present at the sludge drainage system 33 is likewise led to the discharge line 30 and is led further to the control filter 31.

The drained sludge, which contains the organic dirt as well as the heavy metals, is removed separately.

Claims (11)

Patent claims 1. Procedure for the purification of heavy metal-containing waste water from treatment and the cleaning of nets from fisheries and fish farming, which in addition to organic and inorganic dissolved and undissolved residues also contain dissolved and undissolved heavy metals, comprising the steps to 1.) from the waste water to be treated, precipitate suspended and/or emulsified substances while adding primary flocculants and flocculation aids, 2.) then carry out a solid/liquid separation, 3.) from the clear water that was separated in the second step and which contains the dissolved heavy metals, precipitate the heavy metals by adding primary flocculants, organosulphide, lye and flocculation aids, 4.) then separate the precipitation product and the water from the third step by means of a sedimentation process in flocculation sludge and clear water, 5.) carry out a sludge drainage where the sludge containing at least the heavy metals has a solids content of between 20% and 80%, characterized by the fact that the first and second stages take place in a continuous circuit, and the further stages 3.), 4.) and 5.) take place in a discontinuous operation. 2. Procedure for the purification of heavy metal-containing waste water from the treatment and cleaning of nets from fisheries and fish farming according to claim 1, whereby coarse matter is screened before the first step. 3. Method for cleaning heavy metal-containing waste water from the treatment and cleaning of nets from fisheries and fish farming according to claim 1 or 2, whereby the clear water from the second step is stored in a buffer tank (14) and only a part of the water that is stored in the buffer tank is carried discontinuously to the third stage. 4. Method for purifying waste water containing heavy metals from treatment and cleaning nets from fisheries and fish farming according to one of the preceding claims, whereby the first step comprises an inline flocculation device (5), and whereby in the inline flocculation device (5) area, polyaluminium chloride and organic flocculation aids are added in portions to the waste water to be treated. 5. Method for the purification of heavy metal-containing waste water from the treatment and cleaning of nets from fisheries and fish farming according to one of claims 2 to 4, whereby the screening of coarse material takes place in a mechanical screening device (4) which is designed as a drum sieve with 0.1 mm to 2 mm gap width. 6. Method for the purification of heavy metal-containing waste water from the treatment and cleaning of nets from fisheries and fish farming according to one of the preceding claims, whereby the third step takes place in a reactor (17) and in the reactor (17) a stirring and mixing process is carried out between 1 and 30 minutes. 7. Method for the purification of heavy metal-containing waste water from the treatment and cleaning of nets from fisheries and fish farming according to one of the preceding claims, whereby iron chloride, polyaluminium chloride, organosulphide and an anionic polymeric flocculation aid are added in portions to the reactor (17) during the third step. 8. Method for purifying heavy metal-containing waste water from the treatment and cleaning of nets from fisheries and fish farming according to one of the preceding claims, whereby during the third stage in the reactor (17) there is a used flocculant in powdered form and contains, in addition to anionic polymers, also bentonite. 9. Method for the purification of heavy metal-containing waste water from the treatment and cleaning of nets from fisheries and fish farming according to one of the preceding claims, whereby the flocculation process in the reactor (17) is pH-controlled and process-regulated automatically in the third step, whereby it additionally includes a turbidity measurement in the course of the reactor (17). 10. Method for purifying waste water containing heavy metals from the treatment and cleaning of nets from fisheries and fish farming according to one of the preceding claims, whereby sludge drainage is carried out in a fifth step in a gravity belt filter or a chamber filter press (33). 11. Method for the purification of heavy metal-containing waste water from the treatment and cleaning of nets from fisheries and fish farming according to one of the preceding claims, whereby the clear water extracted in the fourth and fifth steps is supplied to a control filter (31) and the control filter (31) is designed as a paper belt filter or sand layer filter.