WO2003076340A2

WO2003076340A2 - Method and installation for producing ultrapure water

Info

Publication number: WO2003076340A2
Application number: PCT/EP2003/002475
Authority: WO
Inventors: Herbert KÖRNER
Original assignee: Koerner Herbert
Priority date: 2002-03-11
Filing date: 2003-03-11
Publication date: 2003-09-18
Also published as: AU2003227045A8; WO2003076340A3; AU2003227045A1

Abstract

The invention relates to a method and an installation for producing pure water from untreated water, in particular, surface water. Said method comprises a final treatment stage including a membrane filtration, which is preceded by at least one biological treatment stage (biosorption stage). The aim of the invention is to provide a method and an installation of this type, which permit ultrapure water to be produced from untreated water in the most cost-effective manner possible, whilst at the same time suppressing biofouling to a great extent, without the addition of biocidal active substances or other chemical substances. To achieve this, an inoculum is added to and incubated with the untreated water in the biosorption stage, said inoculum being produced by the external reproduction of at least one part of the biocenosis contained in the untreated water.

Description

Process and plant for ultrapure water production

The invention relates to a method for producing ultrapure water from raw water, in particular surface water, with a final treatment stage including a membrane filtration, which is preceded by at least one biological treatment stage (biosorption stage).

The invention further relates to a plant for producing ultrapure water, which is particularly suitable for carrying out the method according to the invention.

For the production of ultrapure water from raw water, it is known to use processes in which the raw water is first chemically or physically largely freed from undissolved and dissolved organic and inorganic substances by means of conventional sludge contact processes and / or decarbonization processes and by filtration. The raw water pre-cleaned in this way is then purified by membrane filtration in conventional membrane filter systems from the constituents of undissolved, dissolved, dissolved, ionic, organic or inorganic provenance to be separated according to ultrapure water classification to ultrapure water.

Such methods have the disadvantage that the membrane modules of the finishing stage usually block within a few weeks and have to be renewed or chemically cleaned in a complex manner. The cause of this module blocking is a process called bio-fouling, which is caused by the fact that the pre-cleaned raw water still has a large number of dissolved and undissolved biodegradable organic substances which serve as a substrate for microorganisms. The concentration of these substrates, which remain on the process side of the membrane in membrane filtration, naturally increases towards the process-side surface of the membrane modules. As a result, there is an increased multiplication and settlement of microorganisms which feed on the substrate and which settle as biofilm on the process side of the membrane and thus cause module blocking. The disturbance pattern of such module blockages consists in an increase in differential pressure and, as a result, in a sharp decrease in the throughput of the membrane filter systems.

In order to avoid this performance-reducing disturbance during production operation, various methods for preventing bio-fouling are used in the prior art. Conventional processes are based on complete disinfection of the water entering the membrane filter system (feed). The disinfection is carried out using chlorine, chlorine dioxide or similar oxidizing disinfectants within the pre-cleaning stages or the filtrate basin upstream of the membrane filtration.

A significant weakness of this method is that the residual concentration of oxidizing agents such. B. chlorine, hydrogen peroxide or the like must be reduced using sodium bisulfite before membrane filtration to prevent oxidizing damage to the membrane modules. As a result of this reduction in the excess of oxidant, there is a toxicity gap within which there is a large increase in the number of microorganisms which have not been killed. Not only are the organic impurities already dissolved and undissolved in the pre-treated raw water available, but also the microorganisms and their fragments killed by the oxidizing disinfection, as a substrate, which in turn leads to intensive biological growth on the process-side surface of the membrane modules ,

Newer disinfection processes use bromine-formulated organobiocides, which are metered directly into the feed to the membrane filtration system continuously or discontinuously, in order to create a germ-free environment within the system to create. Although these organobiocides reduce bio-fouling to a large extent, due to their redox potential, they have an oxidative effect on the elements of the systems, in particular the membrane modules, and in turn can thus contribute to a reduction in the half-life of the membrane modules. In addition, the addition of organobiocides is associated with considerable costs.

Because of the problems associated with the prior art, the object of the invention is to provide a method and a system combination which enables the most cost-effective generation of ultrapure water from raw water by largely preventing bio-fouling, specifically without the addition of biocidal agents or other chemical substances.

This object is achieved according to the invention by a method of the type mentioned in the introduction, in which the raw water is mixed and incubated with an inoculum in the biosorption stage, which is generated by external multiplication of at least part of the biocenosis contained in the raw water.

The invention is based on the knowledge that a large amount of substrate is a prerequisite for intensive bio-growth. This knowledge is used in such a way that, in departure from the dogma that the feed fed into the membrane filter system must be as germ-free as possible, the available substrate is largely removed to avoid bio-fouling. Instead of ridding the feed of germs as possible by chemical treatment methods (or also radiation, as also used in the prior art) by killing the biocenosis contained in the raw water, according to the invention there is an intensive increase in the raw water germ count contained in order to reduce the substrate content in the raw water to a minimum before membrane filtration.

It has surprisingly been found that the sterility of the environment sought in the prior art within the membrane filtration process is only poorly suited to effectively prevent bio-fouling. Instead, in the method according to the invention, the addition of the inoculum in the Substrate containing pipe water (ie biologically assimilable substances, in particular dissolved carbon, nitrogen and phosphate compound) assimilated and converted into biomass, which leads to a lack of substrate ("substrate-depleted water"). Due to the lack of substrate, the biocenotic microorganisms change into an endogenous respiratory state , in which the respiration of one's own cell substance (catabolism, ie metabolism through the degradation of organism's own biomass for energy generation) is effective as a bacterial survival strategy. As a result, the existing organisms cannot build up any mucus substances necessary for attachment to the module membrane surface and are also not able to rely on themselves to increase the module membrane surface because there is not a sufficient concentration of assimilable substrates The method according to the invention is therefore based on the principle that the bioavailable and assimilable portion before membrane filtration of the DOC, the so-called AOC (assimilated organic carbon), is largely eliminated by an intensive, microbial metabolic process in the upstream biological pre-cleaning stages.

The most complete possible substrate depletion is achieved by adding the inoculum. H. as many of the different microorganisms contained in the biocenosis of the raw water are used. The inoculum is therefore essentially the (as complete as possible) biocenosis contained in the raw water in multiples of the bacterial count, which naturally has the same substrate preferences and nutrient requirements as the biocenosis of the raw water. After adding the enriched biocenosis, the strong increase in the number of bacteria leads to an increased degradation of the substrates in the raw water. Since no organobiocidal substances are still used, there is also no release of new substrates as a result of a massive death of the biocenotic organisms.

It is important to dimension the incubation time of the raw water with the inoculum so that there is sufficient substrate consumption on the one hand, but on the other hand there is no massive death of the biocenotic organisms due to the lack of nutrients. This dimension nation can be easily determined by the competent specialist using conventional measures, for example measuring the bioavailable DOC content and metabolic parameters on the one hand and microscopic examinations of the raw water in the pre-treatment stages on the other.

When the raw water is contaminated with substances that are particularly difficult to degrade and which are not degradable by the biocenosis inherent in the raw water (and thus cannot cause bio-growth of the biocenosis, but represent an environmental problem), special organisms can also be added if necessary, which specialize in breaking down certain toxins. Such special organisms are well known in the prior art.

In order to enable sufficient substrate consumption of the raw water, it is expedient to increase the bacterial count of the biocenosis contained in the raw water by adding the enriched biocenosis to more than 10 times, preferably more than 50 times and particularly preferably more than 100 to enrich.

It is particularly expedient to dimension the incubation time of the raw water with the inoculum and / or the number of added germs depending on the metabolic balance of the raw water. The variable dimensioning of the incubation time can be varied by the residence time of the raw water mixed with the enriched biocenosis in the biological treatment stage or stages preceding the final treatment stage. Another possibility, in addition to the aforementioned purpose of varying the incubation period, is to add the enriched biocenosis at different (temporal and local) intervals before the final treatment stage. In a special case, an exclusive inoculum dosage into the feed stream is also provided immediately before the membrane filtration process. The quantification of the bioavailable DOC's required for the different dimensioning of the incubation time can be determined by the person skilled in the art, well known measuring and analysis methods for the incoming and the raw water being pre-cleaned. It is particularly advantageous if the finishing stage is preceded by several process stages. These can be process steps assigned to the biosorption step (ie process steps in which incubation with the enriched biocoenosis takes place alone or in addition to other process measures) as well as process steps which are not assigned to the biosorption step (in which chemical or physical purification processes only take place) ,

The process stages upstream of the final stage can expediently comprise one or more sludge contact stages, in particular decarbonization processes, processes for flocculation (preferably acid flocculation) and sedimentation and / or clear water basin pre-cleaning processes, as well as multi-layer filtration processes.

In processes with a biosorption stage, which in turn is composed of several process stages, the incubation time of the inoculum can be varied particularly simply by adding the enriched biocoenosis optionally to one or more of the process stages assigned to the bioreaction stage.

The inoculum is produced separately and not in the purification stages themselves, in order to rule out that the nutrients which are necessary for the multiplication of the biocenotic organisms and are added from outside are carried into the cleaning process. An enrichment of the biocenosis contained in the raw water by simply adding nutrients during the cleaning process or in a directly upstream stage would only lead to a new equilibrium between the bacterial count and the substrate, so that there could be no substrate depletion. According to the invention, the production of the inoculum is therefore carried out separately.

Part of the raw water to be fed into the process or of the raw water in the process is preferably transferred to a separate incubator, where the addition of nutrients and possibly other growth-promoting measures leads to the enrichment of the biocenosis by increasing the biocenotic organisms contained in the raw water. The addition of the nutrients is followed by the intensive (logarithmic) multiplication, in which no further nutrients are added, but an intensive supply of oxygen takes place. This stage guarantees the metabolism of the added nutrients and their conversion into species-specific mass and is carried out until the organisms of the inoculum change to the steady state of respiration. The person skilled in the art can do this by conventional measures, for example microscopic analyzes for determining the morphology and proliferation rate of the biocenotic organisms, in particular with a metabolic balance or with the quantitative detection of the analyzable nutrients still in the water.

Another object of the invention is a system for carrying out the method according to the invention described above, which has a membrane filtration system and at least one, preferably several devices upstream of the membrane filtration system for biological AOC degradation by the inoculum (biosorption stage), with an incubator for producing the inoculum , which is connected at least to the first biosorption stage, preferably to several and in particular to all biosorption stages by means of supply lines and discharge lines. In the system according to the invention, part of the raw water to be purified is transferred to the incubator via the feed lines and is used there to produce the inoculum, which is then introduced into one or more biosorption stages via the discharge lines.

The incubator is part of the system for carrying out the method according to the invention. In principle, however, it can also be installed elsewhere, so that the generation of the inoculum not only takes place separately from the water treatment, but also externally of the system for ultrapure water production.

If the incubator is part of the system, it is particularly expedient if it has several discharge lines which can be acted upon independently, so that the incubation time of the raw water with the added enriched biocenosis can be varied depending on the DOC or AOC load. The independent loading enables, on the one hand, a biosorption stage to load or not. On the other hand, several biosorption stages can be applied to the inoculum simultaneously or in succession.

It is expedient if the device for ultrapure water production also has one or more physical or chemical cleaning devices upstream of the biosorption stage, in particular sludge contact plants (e.g. decarbonization plants and / or those for acid flocculation and / or sedimentation).

Expediently large biocoenosis carrier systems are arranged in the biosorption stage or stages, which preferably consist of backwashable internals in the clear water and storage tanks. These biocoenosis carrier systems can also consist of a multi-layer filter system that contains a fixed biocoenosis.

The biocoenosis carrier systems including a filter system used as such are characterized by the homogeneous coating with a large-area biosorptive bacterial film, which is developed and operated by setting special, variable operating parameters. This operating characteristic is far from the usual operating parameters of mechanical or chemical / mechanical (flocculation filtration) filter systems.

It is particularly advantageous if the incubator has several zones or rooms, in particular an activation zone or an activation room and an aeration zone or an aeration room. Such an incubator enables the exponential multiplication of the supplied biocenotic organisms to be initiated in the aeration room by adding nutrients and oxygen and, if appropriate, with the aid of further measures which are well known to the person skilled in the art.

After passage through the aeration room, the enriched biocenosis generated in this way is transferred to the aeration room, where there is no further addition of nutrients. Instead, oxygen is supplied through aeration, which leads to the metabolism of a substantial proportion of the CNP nutrients supplied. The dwell time in the ventilation divided into several chambers Space is preferably dimensioned so that the organisms change to a steady state of breathing. The connection of the ventilation space ensures that the enriched biocenosis in the raw water does not lead to excessive nutrient input. This is the only way to achieve the desired shift in the biocoenosis-substrate ratio from the state of equilibrium in the raw water to an extreme excess of biocenosis or a lack of substrate.

To determine the DOC concentration, the bacterial population density and / or the monitoring of the process-side metabolic parameters, it is expedient if at least one, preferably several, distributed measuring devices are distributed over the various systems or facilities of the ultrapure water production system (including the incubator).

The invention is explained in more detail below on the basis of an exemplary embodiment illustrated in the process flow diagram.

The raw water 1 to be treated first goes to a decarbonization plant 2, in which the carbon hardness is extracted from it by adding lime milk. The DOC value is also reduced by eliminating organic carboxyl compounds. The water is then transferred to a flocculation and sedimentation system 3, in which the pH of the water is reduced by the addition of iron (III) chloride, which causes the isoelectric point of many organic compounds to fall below, which leads to coagulation. The coagulated substances are separated by flocculation and sedimentation. The clear water flows into a clear water basin 4 of the pre-cleaning stage. The clear water basin 4 can be equipped with large, flushable biocoenosis support internals.

From there, the pre-treated water reaches a multi-layer filter system 5, where extensive mechanical separation of undissolved particles with a grain size of approximately 20 to 100 μm takes place. The multi-layer filtration system can be designed as an open or closed system and contains a fixed biocenosis. After the multi-layer filtration, the pre-cleaned water is transferred to a filtrate basin 6, which is used to buffer the quantity of the flowing wave serves. The pre-cleaned water is passed from the filtrate basin 6 without conventional disinfection into a membrane filtration system 7 which serves as a final stage, which in the present case represents a reverse osmosis and delivers ultrapure water 8 as a filtrate. The ventilated filtrate basin 6 can also be equipped with large, flushable biocoenosis support internals and with an aeration unit.

The adapted inoculum is produced in an incubator 9 which is integrated in the ultrapure water treatment system and has several aeration chambers. To grow the inoculum, pre-cleaned, pH-neutral water is taken from the pre-cleaning, in the present case from the clear water tank 4 of the pre-cleaning and / or from the filtrate tank 6. This medium is continuously passed through the incubator 9, with C / N / P- Nutrients are added to initiate an exponential growth of the biocenosis contained in the water. When it is passed through the incubator 9, the nutrients supplied are metabolized and the biocenotic organisms proliferate. The nutrient supply and residence and enrichment of the biocenosis in the incubator 9 are made dependent on corresponding metabolic parameters and the required bacterial population density of the biosorption process.

By measuring the microbial density and determining the nutrient concentration still present in the water, it is ensured that the multiplication stop is not caused by too high a microbial density, but by a lack of nutrients.

The inoculum thus produced is finally added to the water at one or more points shown in the process flow diagram depending on its DOC content and / or another corresponding metabolic parameter. A partial stream of the inoculum is returned to the activation room of the incubator to accelerate the biosynthesis process.

If the incoming raw water 1 has a particularly high DOC load, it is appropriate to add the biocoenosis contained in the raw water 1 by adding a particularly large amount of inoculum to be enriched to ensure DOC / biomass conversion even under extreme loads. Inoculum is expediently added at a particularly early stage, in particular at the entrance to the raw water pre-treatment.

Measuring devices before, after and in the different plants and facilities of the ultrapure water production plant guarantee the online determination of the DOC content and corresponding metabolic parameters. The bacterial count - curve - is also recorded analytically over the individual preparation stages up to membrane filtration. In addition, a test device specially developed for monitoring and balancing the membrane germination process is installed in front of the membrane filtration system 7.

Since the DOC biomass conversion cannot be completely completed up to the filter system 5 (primary vaccination), the filtrate basin 6 is also supplied with an inoculum (secondary vaccination).

Due to the extreme biomass excess to the existing residual substrate generated in this way, the organisms contained in the water cannot handle the synthesis of mucilages (extracellular polysaccharides) for adhesion to the process-side membrane surface of the membrane filtration system. At the same time, due to the deficiency of carbon sources in the feed, the proliferation of germs on the surface of the process is prevented.

By using crossflow filtration modules in the membrane filtration system 7, the formation of deposits on the process-side surface of the module membranes is further prevented, which could support the formation of a biofilm. By shifting the equilibrium between substrate concentration and population density of the biocenotic organisms in favor of the number of bacteria, bio-fouling on the process-side surface of the membrane filtration modules is prevented without the addition of chemical additives.

Claims

claims

1. A process for the production of ultrapure water from raw water, in particular surface water, with a final filtration stage including a membrane filtration, which is preceded by at least one biological treatment stage (biosorption stage), characterized in that the raw water is mixed and incubated in the biosorption stage with an inoculum, which is caused by external Propagation of at least part of the biocenosis contained in the raw water is generated.

2. The method according to claim 1, characterized in that the bacterial count of the biocenosis contained in the raw water by the addition of the inoculum to more than 10 times, preferably to more than 50 times and particularly preferably to more than 100 times becomes.

3. The method according to any one of the preceding claims, characterized in that the incubation time of the raw water with the inoculum and / or the number of added germs is dimensioned depending on the metabolic balance of the raw water.

4. The method according to claim 3, characterized in that the finishing stage is preceded by several biological and / or physical or chemical process stages.

5. The method according to claim 4, characterized in that the addition of the inoculum is optionally carried out to one or more biological treatment stages.

6. The method according to claim 1, characterized in that the addition of the inoculum is carried out exclusively in the feed stream to the membrane filtration process.

7. The method according to any one of claims 4 or 5, characterized in that the upstream process stages one or more

Include mud contact stages and / or a multilayer filtration stage.

8. The method according to any one of the preceding claims, characterized in that for the production of the inoculum, part of the process water to be supplied or the raw water in the process is transferred to a separate incubator, where the addition of nutrients and possibly other growth-promoting measures, the enrichment of the Biocenosis is carried out by multiplying the biocenotic organisms contained in the raw water.

9. Plant for carrying out the method according to one of the preceding claims, with a membrane filtration plant (7), at least one, preferably several upstream biosorption stages for biological DOC degradation by the inoculum (biosorption stage), and an incubator (9) for producing the Inoculum, which is connected to at least one, preferably to all, biosorption stages by means of inlets and outlets.

10. Plant according to claim 9, characterized in that large-area, ventilatable and flushable biocoenosis carrier units are arranged in the or the biosorption stages.

11. Plant according to claim 10, characterized in that the biocoenosis carrier unit is designed as a filtration system (5).

12. Plant according to claim 9, characterized in that the derivatives of the incubator (9) can be acted upon independently of one another.

13. Plant according to claim 9, characterized by one or more chemical and / or physical cleaning devices (2, 3) upstream of the bio-sorption stage.

14. Plant according to claim 9, characterized in that the incubator (9) has an activation zone and an aeration zone.

15. Plant according to claim 14, characterized in that the activation zone and / or ventilation zone of the incubator has a plurality of compartments divided by baffles.

16. Plant according to one of claims 9 to 15, characterized by at least one, preferably a plurality of online measuring devices for determining and accounting for the DOC degradation and corresponding metabolic parameters.

17. Plant according to claim 8, characterized by a test device for checking the membrane contamination of the membrane filter system (7).