Method for Purifying Contaminated Water

Abstract

In a purification method for purifying contaminated water, the contaminated water contained in a purification tank is filtered by a membrane module disposed in the purification tank. An adsorption agent with powdered activated carbon is added to the purification tank at a raw side of the membrane module. The membrane module is aerated by inflow of air from below. The steps of filtering, adding, and aerating are carried out in parallel and/or sequentially. The purification method is used as a stage of a purification process of a wastewater treatment plant prior to introducing the water purified by the purification method into a river, lake or the ocean.

Claims

1. A purification method for purifying contaminated water, comprising: filtering contaminated water contained in a purification tank by a membrane module disposed in the purification tank; adding an adsorption agent comprising powdered activated carbon to the purification tank at a raw side of the membrane module; aerating the membrane module by inflow of air from below; carrying out filtering, adding, and aerating in parallel and/or sequentially; using the purification method as a stage of a purification process of a wastewater treatment plant prior to introducing the water into a river, a lake or the ocean.

2. The purification method according to claim 1, further comprising disposing precisely one membrane module in the purification tank to be flowed through in series by the contaminated water and supplying the contaminated water from a sedimentation tank, without flowing through another membrane module, to said precisely one membrane module and introducing the water purified by the purification method into a river, lake or the ocean from the purification tank, without flowing through a further membrane module.

3. The purification method according to claim 1, further comprising producing the powdered activated carbon from wood and/or peat.

4. The purification method according to claim 1, further comprising selecting a nominal grain size of the powdered activated carbon to be between 1 μm and 150 μm.

5. The purification method according to claim 4, wherein the nominal grain size of the powdered activated carbon is selected to be between 1 μm and 50 μm.

6. The purification method according to claim 1, further comprising selecting an iodine number of the powdered activated carbon to be greater than 900 mg/g.

7. The purification method according to claim 6, wherein the iodine number of the powdered activated carbon is selected to be greater than 1,000 mg/g.

8. The purification method according to claim 1, further comprising selecting an inner surface area of the powdered activated carbon to be greater than 800 m.sup.2/g determined according to the BET method.

9. The purification method according to claim 1, further comprising mixing, suspending or dissolving the adsorption agent in water prior to adding the adsorption agent.

10. The purification method according to claim 1, further comprising adding precipitation and/or flocculation agents.

11. The purification method according to claim 10, wherein the precipitation and/or flocculation agents are iron salts or aluminum salts.

12. The purification method according to claim 1, wherein filtering by the membrane module is by microfiltration.

13. The purification method according to claim 1, wherein filtering by the membrane module is by ultrafiltration.

14. The purification method according to claim 1, further comprising selecting the membrane module from the group consisting of a flat membrane module and a hollow fiber membrane module.

15. The purification method according to claim 1, further comprising selecting the purification tank from the group consisting of a concrete tank or a standard container.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG. 1 shows a schematic of a device for the purification method.

[0027] FIG. 2 shows the determination of the optimal suspended solids content.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0028] For illustration of the invention, the method will be explained with the aid of an embodiment.

[0029] The purification method is employed for processing biologically treated water that is still contaminated with various substances. A schematic of a device for performing the method is illustrated in FIG. 1. The embodiment concerns water that has been purified by means of a conventional wastewater treatment plant. In this context, an ultrafiltration membrane technology with powdered activated carbon addition is used as a fourth purification stage after the pre-purification, the biological purification, and the secondary purification. The purification of the contaminated water is carried out with at least one immersed flat membrane module; in another embodiment, it can also be another form of a membrane module, for example, a hollow fiber membrane module. The method can be expanded by adding precipitation and flocculation agents (iron or aluminum salts).

[0030] With the ultrafiltration membrane, suspended particles, dirt particles, viruses, bacteria, and inter alia powdered activated carbon are retained. The added powdered activated carbon serves in this context as an adsorption agent for removing contaminants from the contaminated water, for example, micro pollutants, in particular microplastics, dissolved pharmaceutical substances, corrosion protection agents. Due to the addition of precipitation and flocculation agents, dissolved substances such as phosphates are converted into insoluble ones and also separated as solids from the wastewater by the ultrafiltration membrane.

[0031] The combination of the method elements ultrafiltration technology with filtration and sedimentation, addition of powdered activated carbon for adsorption, and optionally addition of precipitation and flocculation agents for chemical precipitation constitute the efficient method in this context.

[0032] The contaminated water that is to be processed enters the purification tank B1 as feed from the secondary clarification 110. It is conveyed by a feed pump P1 into the purification tank B1 in which immersed flat membrane modules 112 with a membrane of polyether sulfone (PES) or polyvinylidene fluoride (PVDF) with a nominal pore size of 0.01 μm to 0.1 μm are installed.

[0033] The purification of the contaminated water is carried out by conveying through the membrane 112 to the so-called permeate side (into permeate tank B4). For this purpose, a vacuum is generated by a pump. The flow performance of the method is net at 4-31 LMH (liter/m.sup.2h).

[0034] Below the membrane module 112, an aeration device 114 is installed through which air generated by a compressor G1 is distributed. For the operation of the method, specific air volume flows, relating to the surface of rise, of 0.15-0.35 m.sup.3/m.sup.2*h are used.

[0035] The membrane modules 112 are operated in the following filtration cycles: filtration, relaxation, backwashing, relaxation. In the relaxation phase, the membrane unit without filtration operation is flushed with air.

[0036] The purification of the membrane unit is realized depending on the degree of soiling, with sodium hypochlorite, hydrogen peroxide, and/or citric acid (schematically shown in store B2 delivered by pump P2). However, other acids, bases or oxidation agents can be used also.

[0037] Adding powdered activated carbon with a nominal grain size of 1-50 μm is carried out from a powdered activated carbon store B5 directly into the filter chamber B1. The target concentration of the powdered activated carbon in the filtration tank is between 5-20 mg/l.

[0038] The employed powdered activated carbon is produced from wood and/or peat.

[0039] The suspended solids contents in the filter container to be adjusted by the addition of powdered activated carbon lies between 2 and 6.5 g/l but it can also be in a range of 1 to 10 g/l. For controlling the total solids in the purification tank, a portion of the activated carbon is discharged discontinuously.

[0040] The diagram of FIG. 2 shows the determination of the optimum suspended solids contents depending on the permeability of the membrane unit detected in operation. According to the prior art, the immersed flat membrane is operated as membrane bioreactor (MBR) application with suspended solids contents of 8 to 12 g/l and maximally 15 g/l.

[0041] Due to the use as a membrane-based method for processing biologically treated contaminated water and the addition of powdered activated carbon, it was possible to lower the suspended solids content in the filter chamber and to obtain at the same time a higher permeability and process stability.

[0042] For mixing in the filter chamber and maintaining a powdered activated carbon suspension, a stirrer can be supplemented in the filter chamber in addition to the aeration.

[0043] Adding iron and aluminum salts that are used as precipitation and flocculation agents is realized from a precipitant store 118 directly into the filter chamber B1 by pumps P6. The added quantity depends on the composition of the medium to be processed and the phosphorus content contained therein. Due to the chemical precipitation of dissolved phosphorus (orthophosphate) in a solid insoluble form, this substance can be removed from the medium. Due to the nominal pore width, the ultrafiltration membrane retains particulate solid-bound phosphorus and the chemically precipitated phosphorus. Due to this method component, total phosphorus concentrations in the permeate, the water purified by the ultrafiltration membrane, of less than 0.2 mg/l, preferably less than 0.1 mg/l, are obtained.

[0044] Bacteria and germs are also separated from the medium with the method combination, in addition to micro pollutants by the powdered activated carbon addition and phosphorus elimination by the precipitation and flocculation agent addition.