EP1618073A1

EP1618073A1 - Method for purifying coke waste water using a gas-permeable membrane

Info

Publication number: EP1618073A1
Application number: EP04724283A
Authority: EP
Inventors: Holger Thielert
Original assignee: Uhde GmbH
Current assignee: ThyssenKrupp Industrial Solutions AG
Priority date: 2003-04-25
Filing date: 2004-03-30
Publication date: 2006-01-25
Also published as: ZA200508611B; WO2004096719A1; MXPA05011489A; BRPI0409732A; CN1802322A; JP2006524562A; DE10318736A1; US20070012619A1; AR044047A1; TW200505804A; NO20054903D0; PL378165A1; KR20060014037A; RU2005136658A; CA2523360A1; NO20054903L; CN100355673C

Abstract

The invention relates to a method for purifying coke waste water that is charged with nitrogen compounds, cyanides and sulfides. According to the inventive method, the coke waste water passes through a reactor (3) that is integrated into a liquid cycle (2) and that comprises at least one gas-permeable membrane tube (5) whose interior is impinged upon by an oxygenous pressurized gas (4). On the exterior of the membrane tube (5) which is immersed in the liquid, a biofilm (6) is maintained in whose inner region (7) rich in oxygen due to the gas-permeability of the membrane tube (5) nitrogenous compounds are selectively nitrified to nitrates while at the same time nitrates are denitrified to elemental nitrogen in an oxygen-poor outer region (8) of the biofilm (6).

Description

METHOD FOR PURIFYING COOKERY WASTE WATER WITH A GAS-PERMEABLE MEMBRANE

Description:

The invention relates to a process for the purification of coking plant wastewater which is contaminated with nitrogen compounds such as N -, NO ₂ ^" -, NC» 3 ^- ions as well as cyanides and sulfides.

In the prior art, the cleaning of this coking plant wastewater is carried out in multi-stage processes within large-volume containers. In general, denitrification takes place in the absence of oxygen, in which Nθ ₃ ^~ ions are broken down. Then a carbon breakdown or COD breakdown is carried out with the help of aerobic bacterial strains. This is followed by an intermediate clarification in which the biomass that is washed away is separated off. This is followed by nitrification, which is generally designed as carrier biology. Plastic fillers are used as carrier material to immobilize the microorganisms. In this process step, Nh ions are converted into NÜ ₂ - or NÜ ₃ - ions. This is followed by a second denitrification stage, in which the NÜ ₂ - and NÜ ₃ - ions are converted to elemental nitrogen (N ₂ ). This is followed by post-aeration to enrich the activated sludge with oxygen and a final clarification in which the activated sludge is separated from the waste water.

The chemical processes taking place during nitfication and denitrification can be described by the reaction equations given below:

Conversion of nitrogenous compounds by nitrification: NH ₄ ⁺ + - O ₂ D N0 ₂ ~ + H ₂ 0 + 2H ⁺

2

N0 ₂ ^" + - O ₂ D N0 ₃ ^~

2

Degradation of nitrates by denitrification in the absence of oxygen:

10H + 2N0 ₃ ^~ D 20H ^" + N ₂ + 4H ₂ 0

Organic carbon compounds can serve as hydrogen donors in denitrification.

A major disadvantage of conventional biological cleaning processes is that oxygen and substrate are transported in the same direction from the outside into the bacterial flakes. The nitrification is therefore limited to oxygen and a large part of the nitrificants contained in the bacterial flakes do not participate in the turnover. This can be seen as an essential reason for the fact that the conventional biological cleaning processes require a lot of space and, as a result, large investment and operating costs.

The invention has for its object to provide a method for cleaning coke oven wastewater contaminated with nitrogen compounds, cyanides and sulfides, which allows low investment and operating costs.

The object of the invention and the solution to the problem is a process for the purification of coking plant wastewater which is contaminated with nitrogen compounds, cyanides and sulfides, wherein the coking plant wastewater flows through a reactor which is integrated in a liquid circuit and which contains at least one gas-permeable membrane hose to which an oxygen-containing compressed gas acts on the inside, and

whereby a biofilm is maintained on the outside of the membrane tube around which the liquid flows, in which, owing to the gas permeability of the membrane tube, an oxygen-rich inner region is subjected to a selective nitrification of nitrogen-containing compounds contained in the wastewater to nitrates and, at the same time, a denitrification of nitrates to elementary nitrogen occurs in an oxygen-poor outer region of the biofilm he follows.

The method according to the invention allows an effective breakdown of nitrogen-containing impurities. The use of the described reactor ensures very high nitrification rates with very high denitrification rates. Due to the gas-permeable membrane hose, an independent supply of substrate and oxygen to the microorganisms of the biofilm is possible. While there is a low-oxygen environment on the outside of the biofilm, which allows very high denitrification rates in this area, very good nitrification rates can be achieved in the areas of the biofilm directly adjacent to the surface of the membrane tube due to the abundant supply of oxygen. The separate nitrification and denitrification stages required in conventional biological purification processes can be combined into a single process step in the process according to the invention. As a result, the outlay on equipment, the space requirement and the investment and operating costs can be significantly reduced compared to the conventional method. The compact design allows production-integrated use at significantly higher concentrations than in the final wastewater, which makes cleaning the wastewater considerably easier. The reactor with gas-permeable membrane hose used in the process according to the invention is known per se. So far, however, such a reactor has only been used for experimental purposes with synthetic wastewater and organically contaminated wastewater from slaughterhouses. Surprisingly, however, the reactor is also suitable for cleaning coke oven wastewater, which is contaminated with cyanides and sulfides compared to previously known applications. The biofilm adhering to the surface of the membrane tube arises when microorganisms accumulate at interfaces and grow there. The biofilm can arise either from substances contained in the wastewater and / or from bio-sludge added to the wastewater. Pore-free hoses, for example silicone membrane hoses, are preferably used as membrane hoses. In this context, a polyester yarn coated with silicon has proven particularly useful. Elementary oxygen (0 ₂ ), but also carbon dioxide (CO ₂ ) can be used as the oxygen-containing compressed gas.

Preferably, several reactors are connected in series within the liquid circuit, through which the liquid stream flows in succession. Correspondingly, in the flow space of a reactor, a plurality of membrane hoses acted upon by an oxygen-containing compressed gas can also be arranged one behind the other in the flow direction. The thickness of the biofilm is regulated by the flow rate of the liquid in the reactor. This prevents the denitrification layer from growing too rapidly, which can be associated with blockage of the reactor. From a thickness of 100 to 200 μm, biofilms no longer participate in the material turnover. The formation of too thick biofilms must therefore be prevented. By setting a suitable flow velocity, biofilm areas with a large thickness are sheared off and the formation of excessively large film thicknesses is prevented. On the basis of continuous monitoring of analysis measurement data within the liquid circuit, it can be determined whether there is an optimal flow rate for biological cleaning. The compressed gas flow fed to the membrane hose is preferably regulated with the aid of analysis values of the waste water measured in the liquid circuit. This allows very high denitrification rates on the outside of the biofilm and at the same time very high nitrification rates in the inner area of the biofilm adjacent to the membrane tube. Suitable measurement data are, for example, the O ₂ -, NH ₄ ⁺ -, NO ₃ ^~ -, N0 ₂ ^" -, Cθ ₂ - and N ₂ content in the liquid circuit. The targeted regulation of the compressed gas flow supplied enables precise control and / or regulation the ongoing denitrification and nitrification processes.

Before a cleaned partial flow is removed from the liquid circuit, this partial flow is preferably freed of biofilm particles with the aid of a clarifying device integrated in the liquid circuit. This prevents the cleaned waste water leaving the cleaning system from being contaminated with sludge. A clarifier can be used as a clarifier, within which sedimentation of the biofilm particles takes place, or a centrifuge. A supply of unpurified coke plant wastewater into the liquid circuit is preferably regulated or controlled with the aid of analysis values of the cleaned wastewater. This allows safe compliance with limit values with stable behavior in the reactor. The analysis values in turn include, for example, the content of 0 ₂ , NH, Nθ ₃ ^~~ , Nθ ₂ ^~ , CO ₂ and N ₂ in the liquid circuit. This enables a targeted setting of the dwell time of the wastewater in the liquid circuit.

The unpurified coke plant wastewater can be passed through a chemical precipitation stage before it is introduced into the liquid circuit. This upstream first cleaning stage relieves the biological cleaning process. By adding FeC ^, for example, some of the nitrogen compounds are already removed from the waste water in the chemical precipitation stage. The temperature of the waste water in the reactor is preferably set using a heat exchanger. This ensures a uniformly optimal temperature for the microorganisms. The heat exchanger is integrated in the liquid circuit of the wastewater to be cleaned.

In the following, the invention is explained in detail on the basis of a drawing representing only one exemplary embodiment. They show schematically:

1 is a process flow diagram of the biological purification process according to the invention, and

Fig. 2 shows a cross section through a pressurized gas-permeable, gas-permeable membrane hose in a reactor used according to the invention.

1 shows a schematic structure of the biological process according to the invention for the purification of coking plant waste water contaminated with nitrogen compounds, cyanides and sulfides. The coking plant waste water to be cleaned is fed from a template 1 into a liquid circuit 2, in which a reactor 3 through which the coking plant waste water flows is integrated. The reactor 3 contains a plurality of gas-permeable membrane tubes 5 acted upon on the inside by an oxygen-containing pressure gas 4. In the exemplary embodiment, elemental oxygen is used as the oxygen-containing pressure gas 4. A biofilm 6 is maintained on the outside of the membrane tubes 5 overflowing with liquid. Due to the gas permeability of the membrane tube 5, a selective nitrification of the nitrogen-containing compounds contained in the waste water to nitrates takes place in the oxygen-rich inner region 7 of the biofilm 6. At the same time, denitrification of nitrates to elemental nitrogen takes place in an oxygen-poor outer region 8 of the biofilm 6. This is particularly clear in FIG. 2, which shows a cross section through the biofilm 6 jacketed gas permeable membrane tube 5. While there is an abundant supply of oxygen in the area 7 of the biofilm 6 immediately adjacent to the surface of the membrane tube 5, which ensures very high nitrification rates there, there is a very low oxygen concentration on the outside 8 of the biofilm 6, which in turn is very high in this area 8 enables high denitrification rates. Due to the decoupling of the substrate and oxygen supply to the microorganisms of the biofilm 6, both nitrification and denitrification processes can take place at very high rates in a very small space. Compared to conventional biological cleaning processes, in which the nitrification and denitrification have to be carried out in two separate containers one after the other, the process according to the invention is characterized by a very low outlay in terms of apparatus, a small space requirement and at the same time low investment and operating costs.

The membrane tube 5 used in the exemplary embodiment consists of a polyester yarn coated with silicon. The outer diameter of the membrane hose is 3 mm with a wall thickness of 0.5 mm. The specific surface area of the hose is between 20 and 200 m ² / m ³ . The biofilm 6 adhering to the membrane tube 5 arises from substances contained in the waste water and / or from bio-sludge added to the waste water. Here, microorganisms accumulate on the surface of the membrane tube and grow there.

The thickness of the biofilm 6 is regulated by means of a pump 9 via the flow rate of the liquid in the reactor 3. This prevents excessive growth of the denitrification layer 8, which can lead to blocking of the reactor 3. From a thickness of 100 to 200 μm, biofilms no longer participate in the material turnover. The flow set with the aid of the pump 9 shears off areas of great thickness and thus prevents excessively large biofilm thicknesses. The compressed gas flow 4 fed to the membrane hose 5 is regulated with the aid of analysis values of the waste water measured in the liquid circuit 2. As a result, very high denitrification rates on the outside 9 of the biofilm 6 and very high nitrification rates on the inside 7 of the biofilm 6 can be set at the same time. The analysis values are continuously monitored via measuring instruments 10. Before a cleaned partial stream 11 is removed from the liquid circuit 2, this partial stream 11 is freed from biofilm particles with the aid of a secondary settling tank 12 integrated into the liquid circuit 2. This prevents organic sludge from being entrained in the treated wastewater. A supply of unpurified coke oven wastewater from the template 1 into the liquid circuit 2 is regulated or controlled with the aid of analysis values of the cleaned wastewater. This allows reliable compliance with limit values with stable operation within the reactor 3. The resulting dilution means that problematic constituents, for example cyanides and sulfides, can also be controlled. A heat exchanger 13 is also integrated in the liquid circuit 2 in order to be able to adjust the temperature of the waste water in the reactor 3. In this way, an optimal temperature for the microorganisms of the biofilm 6 can always be guaranteed. The temperature is monitored using an appropriate measuring device 14. Furthermore, a pH value control 15 is provided in order to be able to adjust the concentration of H ⁺ or OH- ions in the liquid circuit 2.

Claims

Patenta.nsprüche:

1. Process for the cleaning of coking plant wastewater contaminated with nitrogen compounds, cyanides and sulfides,

wherein the coking plant waste water flows through a reactor (3) which is integrated in a liquid circuit (2) and which contains at least one gas-permeable membrane hose (5) which is pressurized on the inside by an oxygen-containing compressed gas (4), and

A biofilm (6) is maintained on the outside of the membrane hose (5) around which the liquid flows, in which, due to the gas permeability of the membrane hose (5), the oxygen-rich inner region (7) is subjected to a selective nitrification of nitrogen-containing compounds contained in the waste water to nitrates and at the same time in a low-oxygen state Outside (8) of the biofilm (6) a nitration of nitrates to elemental nitrogen takes place.

2. The method according to claim 1, wherein a plurality of reactors (3) are connected in series within the liquid circuit (2) and the liquid stream flows through them in succession.

3. The method according to claim 1 or 2, wherein the thickness of the biofilm (6) is regulated via the flow rate of the liquid in the reactor (3).

4. The method according to claim 1 to 3, characterized in that the compressed gas flow (4) fed to the membrane hose (5) is regulated with the aid of analytical values of the waste water measured in the liquid circuit (2).

5. The method according to claim 1 to 4, characterized in that before removal of a cleaned partial stream (11) from the liquid circuit (2) this partial stream (11) is freed from biofilm particles by means of a clarifying device (12) integrated in the liquid circuit (2) ,

6. The method according to claim 1 to 5, characterized in that a supply of unpurified coke oven wastewater in the liquid circuit (2) is regulated or controlled with the aid of analysis values of the cleaned wastewater.

7. The method according to claim 1 to 6, characterized in that the unpurified coking plant waste water is passed through a chemical precipitation stage before being introduced into the liquid circuit (2).

8. The method according to claim 1 to 7, characterized in that the temperature of the waste water in the reactor (3) is set via a heat exchanger (13).