WO2023118145A1

WO2023118145A1 - Method for removing nitrate from membrane filtration concentrates

Info

Publication number: WO2023118145A1
Application number: PCT/EP2022/086995
Authority: WO
Inventors: Torsten HENTSCHEL; Ekaterina Vasyukova
Original assignee: Wte Wassertechnik Gmbh
Priority date: 2021-12-21
Filing date: 2022-12-20
Publication date: 2023-06-29

Abstract

The present invention relates to a method for treating reverse osmosis and/or nanofiltration concentrate ("concentrate"), the concentrate originating from the treatment of raw water by means of reverse osmosis and/or nanofiltration for the treatment of drinking and/or process water, the method comprising the step of conducting the concentrate through a filter bed having a granular and/or particulate and biologically activated filter material in order to carry out a microbial denitrification. The invention also relates to a reactor which is designed and configured to carry out the method according to the invention.

Description

Process for removing nitrate from membrane filtration concentrates

The present invention relates to the technical field of water technology, in particular to the treatment of membrane filtration concentrates from drinking and process water treatment.

The present invention relates to a method for treating reverse osmosis and nanofiltration concentrates, in particular reverse osmosis concentrates, and also to a reactor which is set up for carrying out the method according to the invention for treating reverse osmosis and nanofiltration concentrates, in particular reverse osmosis concentrates. In particular, nitrates can be removed from reverse osmosis or nanofiltration concentration with the aid of the method according to the invention or with the reactor according to the invention.

Nitrates are water-soluble salts of nitric acid, which are formed as part of the nitrogen cycle through a metabolic conversion of nitrogen-containing compounds by nitrifying bacteria in the soil. The nitrates, in turn, are taken up by plants and used as a source of nitrogen by plant metabolism or converted into atmospheric nitrogen by so-called denitrifying (soil) bacteria. Under natural conditions, only small amounts of nitrogen are applied overall, so that its availability is the limiting growth factor in almost all terrestrial and some aquatic ecosystems.

Increased nitrate levels in ground, surface and well water as well as other bodies of water are problematic with regard to the health aspects of humans and animals. The "Ordinance on the Quality of Water for Human Use" (Drinking Water Ordinance - TrinkwV) therefore sets a maximum limit of 50 mg/l for the nitrate concentration in drinking water in Germany.

Drinking or process water is usually obtained from so-called raw water, such as spring, surface and ground water or even seawater. Since spring, surface and groundwater that is heavily polluted with nitrate is associated with the health hazards described above, many waterworks have to give up existing groundwater reservoirs and create new, deeper-lying groundwater. develop reserves or alternatively use more complex treatment techniques for water treatment.

One technique for removing low-molecular substances, such as nitrate, from raw water is membrane filtration processes, in particular reverse osmosis or nanofiltration. However, the treatment of industrial or drinking water by means of membrane filtration, in particular reverse osmosis and, in some cases, nanofiltration, leads to a considerable accumulation of nitrate in the waste water stream or in the concentrate or retentate of the filtration process. The nitrate concentration in reverse osmosis concentrates from industrial or drinking water treatment regularly exceeds the statutory limit values for total nitrogen for direct discharge into running water or a public sewage system (for Germany: Ordinance of the Federal Minister for Agriculture and Forestry on the limitation of waste water emissions from water treatment ( AEV water treatment), Federal Law Gazette II No. 128/2019, in short: Direct Discharge Ordinance). For reasons of environmental protection, in particular to prevent further nitrate pollution of ground and surface water, complex treatment of the reverse osmosis concentrate from drinking or process water treatment is usually necessary before disposal or direct discharge. The post-treatment of the concentrates is particularly difficult due to the high content of hardeners in the concentrates, since these tend to precipitate or flocculate. Subsequent precipitation of hardeners in pipes during traditional cleaning stages in sewage treatment plants is particularly problematic. The high content of hardeners also prevents the concentrates from being treated in conventional solid bulk layers or fixed-bed reactors, since the hardeners usually lead to blocking of the fixed bed. Since there are no suitable after-treatment processes for the concentrates to date, the treatment process, i.e. reverse osmosis or nanofiltration, must be adapted in such a way that the nitrate concentration in the waste water is kept low, which, however, reduces the productivity and drinking or process water yield of the treatment.

Against the background of the necessary complex after-treatment processes, the yield of drinking or process water in membrane filtration processes, in particular reverse osmosis and nanofiltration processes, is limited by the high nitrate load in the concentrate or retentate. An increase in yield is usually also associated with an increase in the amount of nitrate remaining in the concentrate. The result is improved productivity of the processing ren, especially membrane filtration processes, desirable for drinking and service water.

Against the background of the disadvantages described above, there is a need in the prior art to improve the treatment of raw water, in particular for the production of industrial or drinking water, with regard to sustainability, environmental compatibility and productivity.

The present invention is therefore based on the object of providing a method or a device which overcomes or at least alleviates the aforementioned disadvantages.

In particular, within the scope of the present invention, a method is to be provided which improves the production of service or drinking water with regard to sustainability, environmental compatibility and productivity.

Within the scope of the present invention, the above-described object is achieved—according to a first aspect of the present invention—by a method for treating reverse osmosis and/or nanofiltration concentrate (“concentrate”).

Another aspect of the present invention is - according to a second aspect of the invention - a reactor with a filter bed for use in the treatment of reverse osmosis and / or nanofiltration concentrate ("concentrate").

It goes without saying that features which are specifically described only in connection with the first aspect apply equally to the second aspect of the invention and vice versa.

The present invention is thus - according to a first aspect - a method for treating reverse osmosis and / or nanofiltration concentrate ("concentrate"), the concentrate from the treatment of raw water by means of reverse osmosis and / or nanofiltration, in particular reverse osmosis, for drinking - and/or process water treatment, comprising:

(a) Introducing the concentrate to be treated into a filter, the filter having a filter bed with a granular and/or particulate filter material and wo- where the filter material has a biofilm with microorganisms for microbial denitrification,

(b) passing the concentrate over the filter bed, the concentrate flowing through the granular and/or particulate filter material to carry out microbial denitrification, and

(c) Discharging the cleaned or denitrified concentrate from the filter bed, the concentrate being conditioned before and/or during the process, preferably in process step (a) or in the feed, for carrying out the microbial denitrification.

In the context of the present invention, it has been possible to provide a post-treatment process for reverse osmosis or nanofiltration concentrates, in particular reverse osmosis concentrates, from drinking or process water treatment, with which the total nitrogen content can be reduced to such an extent that the limit values like. Direct discharger ordinance can be complied with for direct discharge.

The fact that the process according to the invention is suitable for the treatment of reverse osmosis or nanofiltration concentrates, in particular by carrying out a denitrification in the filter bed, is surprising, particularly given the sometimes high content of dissolved salts and hardness components in the concentrates. So far, the high content of salt and hardness components in reverse osmosis or nanofiltration concentrates has been a limiting factor for purification in the filter bed, since salts and hardness components precipitate in the filter bed and can lead to calcification, which ultimately leads to the filter becoming blocked and nitrate degradation stopping would lead. According to the invention, a method using a particulate or granular filter material is therefore provided for the first time, which is also suitable for the treatment of water with a high content of salt, particularly in the form of nitrates, and hardeners and is used to remove nitrate.

With its high nitrate degradation rate, the method according to the invention can be used to achieve a significant increase in the drinking water yield in membrane filtration methods, in particular nanofiltration and reverse osmosis methods, for treating raw water to drinking water or process water quality. As stated at the beginning, the yield of reverse osmosis or sodium nofiltration process is limited by the nitrate or total nitrogen enrichment in the resulting concentrates or waste water, ie the treatment processes are currently not running at full capacity in order to avoid excessive nitrate or nitrogen concentrations in the resulting waste water or concentrate. High nitrate or total nitrogen concentrations, especially above the legally specified limit values, generally prevent the concentrates from being discharged directly into running water or other bodies of water for the purpose of disposal or recycling into the water cycle. The method according to the invention, which follows the reverse osmosis or nanofiltration, in particular reverse osmosis, makes it possible for the treatment to be carried out under increased utilization up to pre-utilization, since efficient nitrate removal from the concentrates produced is possible.

The method according to the invention therefore provides an economical and environmentally friendly and resource-saving separate cleaning stage for waste water from drinking and/or process water treatment, which also enables the removal of large amounts of nitrate from the waste water and thus their direct introduction into the water cycle.

The method according to the invention is associated with further advantages and special features, which are described below and are to be regarded as an indication of the existence of an inventive step:

A nitrate degradation rate or denitrification rate of more than 2.0 kgNO3-N/(m ³ d) can sometimes be achieved with the method according to the invention. With the method according to the invention, the total nitrogen concentration in nitrogen- or nitrate-loaded waste water from the treatment of drinking water or process water can also be brought to values below the legal limit values for direct discharge. As the exemplary embodiments described below demonstrate, the method according to the invention sometimes achieves a degree of degradation of the total nitrogen of more than 90%, even in water or concentrates which are heavily contaminated with nitrate.

Furthermore, it is possible to carry out the process according to the invention in continuous operation, as a result of which the process efficiency can be further increased. In the case of continuous operation, in particular only a one-time start-up phase or one-time adaptation of the microorganisms to the process conditions for denitrification is required. In addition, the method according to the invention is environmentally friendly and resource-friendly, since it does not require the addition of chemicals that are harmful to the environment or difficult to dispose of. The method can also be carried out without temperature regulation, ie no energy is required for cooling or heating.

The advantages and special features of the present invention described above are to be regarded as an indication of the existence of an inventive step.

Preferred embodiments of the method according to the invention are described in detail below. In this context, the terms used to describe the present invention are also explained in more detail:

In the context of the present invention, the term “reverse osmosis or nanofiltration concentrates” is understood to mean concentrates or waste water which occurs during the treatment of raw water by means of membrane filtration processes, in particular reverse osmosis or nanofiltration. The term “retentate” can also be used synonymously for the concentrates. In particular, the concentrates that are treated with the method according to the invention come from the treatment of raw water into drinking or process water. The concentrate or waste water contains the low-molecular substances retained during treatment by filtration, such as salts, which also include nitrates. According to a particularly preferred embodiment of the present invention, the concentrate to be treated comes from the treatment of raw water by means of reverse osmosis for drinking water treatment.

In the context of the present invention, the term "raw water" means any untreated water which comes from surface sources such as ponds, dams, lakes or rivers, or from subsurface water sources such as wells or groundwater. In addition, within the scope of the present invention, seawater is also understood to be raw water within the meaning of the invention.

In the context of the present invention, the term "denitrification" refers to the microbial conversion of the nitrogen bound in the form of nitrate to molecular nitrogen or nitrogen gas and nitrogen oxides by denitrifiers or denitr rificante understood. Denitrification includes - without wanting to be limited to this theory - as the first part, the reduction of nitrate to nitrite, which is catalyzed by the enzyme nitrate reductase. Denitrification also includes the reduction of nitrite to nitrogen monoxide, which is catalyzed by the enzyme nitrite reductase. In addition, denitrification includes the reduction of nitrogen monoxide to dinitrogen monoxide as a further sub-step, with the reaction being implemented by the enzyme nitric oxide reductase. As the final step, the reduction of dinitrogen monoxide to molecular nitrogen or nitrogen gas is catalyzed by the enzyme nitrous oxide reductase.

According to the invention, it is provided that the biofilm with microorganisms, which are able to catalyze a microbial denitrification, is settled or grows on the filter material, in particular its particles or grains. The microorganisms that carry out or bring about the denitrification can also be referred to as denitrifiers or denitrifiers. Among other things, denitrifying bacteria or denitrifiers can be facultatively anaerobic bacteria of different genera, which preferably gain energy through denitrification under essentially anaerobic conditions. Bacteria which are capable of denitrification belong, for example, to the genera Agrobacterium, Alcaligenes, Azospirillum, Acidovorax, Arcobacter Bacillus, Flavobacterium, Hydrogenophaga, Hyphomicrobium, Paracoccus, Pseudomonas, Rhodopseudonomas, Thiobacillus, Thiomicrospira, Simplicispira, Streptomyces or Actonomyces, in particular Acidovorax, Arcobacter, Flavobacterium, Hydrogenophaga and/or Simplicispira, although the present list is not to be understood as conclusive. As explained below, the biocenosis of the biofilm on the filter material depends in particular on the concentrates treated with the process, i.e. the microorganisms contained therein. Within the scope of the method according to the invention, a mixed population of a wide variety of microorganisms preferably occurs in the biofilm, which ultimately bring about the elimination of nitrogen, in particular nitrate, in the concentrates to be treated.

The biocenosis in the biofilm required for carrying out the denitrification or nitrate elimination occurs in particular as a result of the conditioning of the reverse osmosis or nanofiltration concentrate used, as described below. The settlement and setting of the biocenosis takes place in As part of the method according to the invention, preferably in a start-up phase of the filter bed over the period of time required in this regard. Before loading the filter bed with the concentrates or before starting up with concentrates, the filter bed can be inoculated with a starter culture, eg based on Paracoccus denitrificans. The biocenosis in the biofilm usually occurs depending on the microorganisms already contained in the reverse osmosis or nanofiltration concentrate used, or varies depending on the reverse osmosis or nanofiltration concentrate used. In this regard, reference is already made at this point to the exemplary embodiments according to the invention, which describe a start-up or the commissioning of a suitable filter by way of example.

With the conditioning of the concentrate according to the invention, environmental conditions are created which enable the colonization and maintenance of the microorganisms or biocenosis required for denitrification on the carrier material and their maintenance:

Reverse osmosis and/or nanofiltration concentrate, in particular from drinking and/or process water treatment, as such is usually at least essentially free of or at least low in carbon compounds or has no appreciable chemical oxygen demand. Against this background, it is preferred within the scope of the present invention to adjust the reverse osmosis or nanofiltration concentrate to a defined chemical oxygen demand before or during the process.

The chemical oxygen demand (COD) is a measure of the sum of all organic compounds in the water. The COD characterizes the amount of oxygen that is used to oxidize all the organic substances contained in the water. The COD can be determined in particular using a photometric measuring method in accordance with DIN 15705 or using a dimensional analytical measuring method in accordance with DIN 38409-H41. The materials and substances forming the COD can serve as a source of energy, especially carbon, for the microorganisms in the biofilm.

According to a particularly preferred embodiment in this regard, it can be provided according to the invention that the concentrate before and/or during the process, preferably in process step (a) or in the feed, to a COD (chemical oxygen demand) in the range from 5 to 200 mg/l, in particular 20 to 160 mg/l, preferably 30 to 150 mg/l, preferably 40 to 130 mg/l.

In this context, it can also be provided to adapt the COD to the nitrogen or nitrate content in the concentrate, in particular with the COD being adjusted in such a way that the nitrate degradation is not limited by a lack of organic energy sources, but the denitrified concentrate is released when it is discharged or .in the effluent only shows a COD below the limit values for the COD specified in the Direct Discharge Ordinance. The Direct Discharge Ordinance currently sets a maximum limit of 90 mg/l for the COD.

The COD is preferably adjusted by adding a carbon source for the microorganisms contained in the biofilm, in particular by adding easily biodegradable organic acids, in particular acetic acid. Acetic acid is an easily degradable, inexpensive and therefore overall process-economical source of carbon. Nevertheless, the method according to the invention can also be carried out with all other carbon sources for microorganisms with a preferably heterotrophic metabolism that are known in principle to the person skilled in the art, such as citric acid, succinate or various saccharides. The selection of a suitable carbon source is known in principle to a person skilled in the art and does not require any further explanation.

In addition, it has proven to be advantageous with regard to the bacterial metabolism if the concentrate before and / or during the process, preferably in process step (a) or in the feed, a phosphorus source for the microorganisms contained in the biofilm is metered, in particular phosphoric acid is used as the source of phosphorus. According to a particularly preferred embodiment, 0.3% phosphoric acid is used as the phosphorus source.

The source of phosphorus is also preferably metered in such a way that nitrate degradation is not limited by a phosphorus deficiency, but the phosphate concentration in the denitrified concentrate does not exceed the statutory limit values for phosphorus - currently 2 mg/l in Germany - for direct discharge. In addition, it has proven advantageous, especially with regard to high nitrate concentrations in the feed, preferably nitrate concentrations of more than 2,000 g/m ³ , if the concentrate is added before and/or during the process, preferably in process step (a) or in the feed , an iron source, preferably an iron(II) source, is metered in. Iron(II) sulfate, in particular in the form of FeSO4·7H2O, is preferably used as the iron(II) source. According to the invention, it can be provided in particular that a concentration of iron in the feed is in the range from 0.0001 mg/l to 10 mg/l, in particular 0.001 to 5 mg/l, preferably 0.01 to 2 mg/l, particularly preferably 0 1 to 1 mg/l, based on the feed, is used. According to a particularly preferred embodiment, a concentration of 0.2 mg/l iron, in particular iron(II) sulfate, based on the feed, is used in the feed.

Furthermore, with regard to the promotion of denitrification by the microorganisms, it has proven advantageous if trace elements for the microorganisms contained in the biofilm are metered into the concentrate before and/or during the process, preferably in process step (a) or in the feed become. In the context of the method according to the invention, the trace elements are preferably selected from the group consisting of zinc, manganese, boron, cobalt, copper, nickel and/or molybdenum and/or their salts.

In connection with the addition of trace elements, it is particularly preferred if the trace elements are added to the concentrate in the form of zinc sulfate (ZnSO4), manganese chloride (MgCh), boric acid (H3B03), cobalt chloride (C0Cl2), copper chloride (CuCh), nickel chloride (NiCh) and /or sodium molybdate (Na2MoO4), preferably in dissolved form, are supplied or metered in.

Based on the previously described conditioning of the concentrate to be treated, the environmental conditions for the microbial denitrification or the microorganisms contained in the biofilm can be set in a targeted manner, which ultimately leads to an improved or high nitrate degradation rate, as the microorganisms have optimal denitrification metabolism conditions are created.

In order to keep the nitrate degradation performance of the microorganisms in the biofilm constantly high or maintained, it is also preferred according to the invention if the formation of the biofilm on the granular and/or particulate filter material is regulated and/or controlled. The regulation or control ensures, on the one hand, that excessive growth of the microorganisms or excessive formation of the biofilm, which would lead to blockage of the filter bed, is prevented. At the same time, it is ensured that the biofilm on the particulate or granular filter material is nevertheless sufficiently developed to allow efficient denitrification.

According to a particularly preferred embodiment, the formation of the biofilm on the filter material is regulated or controlled by reducing the biofilm on the granular and/or particulate filter material. Biofilm reduction can be continuous or intermittent.

Particularly preferred embodiments with regard to the regulation of the biofilm and the adjustment of the filter material or filter bed are described below:

According to the invention, with regard to the adjustment or regulation of the biofilm, it has proven to be advantageous if the formation of the biofilm is regulated and/or controlled by introducing at least one fluid into the filter bed. In other words, it is preferred according to the invention if the filter bed and/or the filter material is completely or partially fluidized.

Without wanting to be limited to this theory, turbulent flows are generated by the fluid entry in the filter bed, which on the one hand leads to a boundary layer around the particles and on the other hand to a shearing off of part of the biomass on the particles.

According to the invention, the difficulty of fluidization consists in particular in the fact that on the one hand the flow through the filter bed with its specialized microorganisms should be so slow and uniform that the longest possible contact time with the surrounding medium is ensured. At the same time, however, it must also be ensured that the growing biomass does not block the filter bed and thus prevent the exchange of substances with the surrounding medium. If the fluid input or the currents generated by fluid input are too strong, the biofilm on the carrier is sheared off too much and the biomass is reduced too much and at the same time the time for a mass exchange with the surrounding fluid is reduced. If the fluid entry is too weak or too low, the constant growing biomass block the filter bed, so that a media exchange is disadvantageously prevented. In addition, with particulate or granular filter materials there is a risk of precipitation of hardeners and salts, since the reverse osmosis or nanofiltration concentrates have a high salt and nitrate content.

In other words, it is desirable according to the invention to adjust the biofilm or the amount of microorganisms on the filter material, in particular to regulate it in such a way that blocking of the filter is prevented, but at the same time sufficient biomass is retained on the filter material for denitrification. At the same time, a failure of hardening agents and salts should be prevented.

According to a particularly preferred embodiment, the fluid is selected from air, technical gases and/or water, particularly preferably air and/or technical gases.

In the context of the present invention, it has also been shown that the problems described above with regard to under certain circumstances too much or too little detachment of the biomass from the particles or granules of the filter material can be overcome if the fluid entry is controlled as a function of the filter resistance becomes. According to a particularly preferred embodiment, the introduction of fluid is controlled by means of time-pause control as a function of the filter resistance.

The filter resistance has proven to be a suitable, indirect measure for the formation of the biofilm on the filter material. With regard to the process according to the invention, the filter resistance is understood to mean the pressure drop occurring when the concentrate to be treated flows through the filter bed, measured or stated in cm water column [cm Ws]. One meter of water column (= WO cmWs) corresponds to 9.80665 kPa under normal case acceleration. With increasing biofilm formation and thus denser filter material, the filter resistance or pressure loss also increases, whereas a reduction in the biofilm leads to a reduction in filter resistance or a lower pressure loss. The measurement or monitoring of the filter resistance takes place within the scope of the method according to the invention using means or measuring devices or pressure sensors which are fundamentally known to the person skilled in the art. According to the invention, in particular when regulating the fluid entry by means of time-pause control, provision can be made in particular for the fluid entry to be increased and/or started when the filter resistance increases, in particular when a limit value is exceeded. Equally, it can be provided in this context that the fluid entry is reduced and/or stopped when the filter resistance falls, in particular when the filter falls below a limit value.

Suitable values for the filter resistance or a time-pause control can vary widely and depend in particular on the particulate or granular filter material, but also on the dimensioning of the filter bed and must be selected or determined accordingly by the person skilled in the art. The nitrate degradation rate is preferably used to determine a suitable filter resistance. Both a filter resistance that is too low and one that is too high would negatively affect the nitrate degradation rate.

When using a granular or particulate filter material based on sand with a grain size in the range from 1 mm to 2 mm in a semi-technical system, it has proven to be advantageous in the context of the present invention if the fluid entry is used to achieve a filter resistance in the range of 20 cmWs and 60 cmH2O. If the particles or granules of the filter material have a larger or coarser grain size, higher values are conceivable. If the filter material has a finer grain, lower values should be advantageous.

As a result, it is preferred according to the invention to set the quantity or the volume flow and/or the intensity or the pressure of the fluid introduced in such a way that there is a certain flow through the filter material in order to renew the boundary layer around the particles of the filter material or to maintain the exchange of substances between the filter material or biofilm and the concentrate to be treated, and on the other hand to prevent excessive biofilm formation on the filter material. It is particularly important to ensure that the fluid input is not overdosed, as this would lead to excessive or almost complete detachment of the biofilm from the particles or granules of the filter material. According to the invention, the filter resistance has proven to be a suitable reference value for setting or controlling the fluid input. The entry of the fluid into the filter bed or filter material preferably takes place via fluid inlets, in particular air or gas inlets, which are basically known or customary to those skilled in the art. In this context, it can be provided that the at least one fluid is introduced into the filter bed and/or filter material via at least one, preferably several, fluid inlets. The arrangement or positioning of the fluid input into the filter bed depends primarily on the areas of the filter bed that are to be fluidized, in particular on whether complete or only partial fluidization is provided. In addition, the fluid inlets or their number and arrangement must be adapted to the shape and dimensions of the filter bed.

In order to remove removed and/or dead biomass and other particulate residues of the method according to the invention from the concentrate, it can also be provided according to the invention that the treated or denitrified concentrate, when it is discharged from the filter bed, preferably in the outlet, undergoes further filtration, in particular via a particle and/or sterile filter.

Further special embodiments with regard to the fluid entry are described below:

According to a first possible embodiment, within the scope of the method according to the invention it can be provided that the fluid is introduced via at least one fluid inlet in the area of the longitudinal axis of the filter bed. A fluidization or a fluid entry via at least one fluid inlet in the area of the longitudinal axis of the filter bed has proven to be particularly advantageous with regard to a continuous, but only partial fluidization of the filter bed.

According to a further embodiment, provision can be made for the fluid to be introduced via fluid inlets in the wall and/or in the base of a filter module and/or reactor enclosing the filter bed. Introducing fluid via inlets in the wall or in the base of a filter module or reactor enclosing the filter bed has proven particularly useful for intermittent, preferably essentially complete, fluidization of the filter material or filter bed. The two embodiments described above with regard to the selection of the fluid inlets in the area of the longitudinal axis or in the wall or in the bottom of the filter module or reactor enclosing the filter bed can also be used in combination or the fluid entry can be carried out both by means of fluid inlets in the Area of the longitudinal axis as well as in the wall or in the bottom of the reactor. In this context, it is particularly preferred if continuous fluidization of the filter bed takes place via the fluid inlet in the area of the longitudinal axis, whereas via the inlets in the wall or in the bottom of the filter module or reactor only intermittently, in particular by means of time-pause control, at least one fluid is introduced, for example when the filter resistance increases excessively or a limit value for the filter resistance is exceeded.

In addition, it can be provided according to the invention that the fluid input takes place via lances for fluid input that protrude and/or are immersed into the filter bed. A particularly targeted control of the fluid input into the filter material is possible via lances projecting and/or immersed into the filter bed. The complete fluidization of the filter bed is particularly advantageous in this embodiment. The number and arrangement of the lances depends on the size and shape of the filter and the areas of the filter bed to be fluidized.

Provision can also be made for the fluid to be introduced via a line arranged axially along the longitudinal axis of the filter bed to the inlet of at least one fluid. In particular, fluid can be introduced into the lower, central area of the filter bed via a line arranged axially along the longitudinal axis. In this embodiment, continuous fluidization has proven particularly advantageous.

With regard to the two aforementioned embodiments, too, it is possible for the fluid to be introduced via lances that protrude and/or are immersed into the filter bed and, moreover, a line arranged axially along the longitudinal axis for the introduction of the fluid.

A particularly targeted control or regulation of the formation of the biofilm and removal of other particulate residues of the process is possible in the process of the invention if the filter material is a is subjected to cleaning outside the filter bed, particularly when the biomass reduction is predominantly outside the filter bed:

In this context, it can be provided according to the invention that the particulate and/or granular filter material is conveyed to a rinsing unit arranged outside of the filter bed. According to a preferred embodiment, the filter material is conveyed to the rinsing unit by introducing at least one fluid, preferably air or a technical gas, into the filter bed, in particular as a function of the filter resistance.

In this regard, provision can be made for the filter material to be cleaned in the rinsing unit. The introduction of the at least one fluid and/or the cleaning in the rinsing unit reduces the biofilm by at least 10%, in particular at least 20%, preferably by at least 30% and/or by at most 80%, in particular by at most 70%. preferably by at most 60%.

In order to improve the efficiency of the process and to maintain the process continuously, it has also proven to be advantageous if the cleaned filter material with reduced biofilm is returned from the rinsing unit to the filter bed.

According to a particularly preferred embodiment of the present invention, the rinsing unit is arranged above the filter bed in the area of the outlet for the cleaned concentrate. In the rinsing unit, the filter material is cleaned and/or rinsed with filtrate flowing in the opposite direction or in the direction of the outlet and sinks back onto the filter bed with reduced biofilm.

The waste water from the rinsing unit containing the biomass removed from the filter material and other particulate residues is preferably discharged via a rinsing water outlet.

According to a further embodiment, it can also be provided that the waste water occurring during the rinsing and/or cleaning of the filter material is cleaned by means of particle retention and is preferably fed back into the filter bed via the inlet. In a particularly preferred embodiment, it can be provided that the filter material is conveyed from the lower region of the filter bed to a rinsing unit arranged above the filter bed by means of a compressed air lifter (also known as a mammoth pump) that is preferably arranged axially along the longitudinal axis of the filter bed. In this context, the intake of air is preferably adjusted as a function of the dimensioning of the filter bed, the filter material, in particular its grain size, and/or the filter resistance. In the embodiment described here, the rinsing unit is preferably a sand washer, with the particulate or granular filter material being washed in a counterflowing, already denitrified or treated concentrate and sinking back onto the filter bed after cleaning.

Various filter beds with particulate or granular filter material and filter modules or reactors for accommodating the filter bed can be used for the process according to the invention. An example of a reactor for carrying out the process according to the invention is shown in FIG. 2, which is described in detail below.

Preferred embodiments with regard to suitable filter materials and their properties are described below:

As far as the particulate or granular filter material is concerned, it must on the one hand provide a sufficiently large surface area for the biomass to grow and on the other hand ensure that the concentrate to be treated can flow through it and also be able to form a filter bed. In this context, it has proven to be advantageous to use particulate or granular material with defined particle or grain diameters for the method according to the invention. In this context, it has proven to be particularly advantageous if the filter material used is a particulate and/or granular material with particle or grain sizes, in particular average particle or grain diameters, preferably determined according to DIN EN 120904, in the range from 0.1 to 15 mm, in particular 0.2 to 10 mm, preferably 0.5 to 5 mm, preferably 0.7 to 3 mm, particularly preferably 1 to 2 mm.

In connection with the selection of the filter material, it has also proven to be advantageous if a particulate and/or granular material is used as the filter material with a specific density in the range from 0.7 to 6 g/cm ³ , in particular 1 to 5 g/cm ³ , preferably 1.5 to 4 g/cm ³ , preferably 2 to 3.5 g/cm ³ , particularly preferred 2.5 to 3.2 g/cm ³ , based on a single grain or particle, is used. The use of particles or granules with the previously defined specific density has proven to be advantageous with regard to the formation of the filter bed. By using a filter material with the previously defined specific density, an undesired buoyancy of the particles or grains in the concentrate to be treated can be counteracted.

As far as the filter material is concerned, sand, bentonite and/or crushed lava stones are preferably used according to the invention as the particulate and/or granular material. Due to their surface properties, the aforementioned filter materials allow the biofilm to grow, since they have a certain surface roughness.

According to a particularly preferred embodiment, the method according to the invention is operated in a sand filter or sand, in particular quartz sand, is used as the particulate or granular filter material.

In the following, special embodiments are described in relation to the further procedure and process parameters:

With regard to the biofilm on the particulate filter material, the situation in the method according to the invention is preferably such that the microorganisms for the microbial denitrification grow sessile on the grains and/or particles of the filter material.

The process according to the invention can be carried out continuously or intermittently, preferably continuously. A continuous procedure has proven to be particularly advantageous with regard to the process efficiency, especially against the background that a start-up phase or adaptation of the biocenosis to the denitrification conditions is only necessary once.

Furthermore, it is preferred if the concentrate has a bed load (amount of total nitrogen per cubic meter of filter material per day) in the range from 100 to 2500 g/m ³ /d, in particular 300 to 2200 g/m ³ /d, preferably 500 to 2000 g/m ³ /d, preferably 800 to 1800 g/m ³ /d, into the filter bed. It is equally possible according to the invention that the concentrate with a bed loading (amount of total nitrogen per cubic meter of filter material per day) of at least 200 g/m ³ /d, in particular at least 400 g/m ³ /d, preferably at least 600 g/m ³ /d , preferably at least 800 g / m ³ / d, is passed into the filter bed.

In addition, it can be provided according to the invention that the concentrate with a bed load (amount of nitrate nitrogen per cubic meter of filter material per day) in the range of 80 to 2,500 g / m ³ / d, in particular 100 to 2,100 g / m ³ / d, preferably 200 to 1,900 g/m ³ /d, preferably 400 to 1,700 g/m ³ /d, is passed into the filter bed. In addition, it can also be provided in this connection that the concentrate has a bed load (amount of nitrate nitrogen per cubic meter of filter material per day) of at least 80 g/m ³ /d, in particular at least 100 g/m ³ /d, preferably at least 200 g/m m ³ /d, preferably at least 400 g/m ³ /d, particularly preferably at least 600 g/m ³ /d, into the filter bed.

In the context of the present invention, the bed loading is understood to be the total amount of nitrogen (unit: g) with which a defined volume of the filter mass (unit: m ³ ) in the filter, ie the “filter bed” in the filter, per unit of time (unit: d or day) will be charged. Taking into account or consulting the bed load, the method according to the invention can be transferred to all types of filters or filter beds, since the amount of nitrogen introduced into the filter bed or filter per unit of time is independent of the type, size or volume of the reaction space on the volume of the Filter mass relates.

The volume flow of the concentrate to be treated can vary within a wide range and depends primarily on the dimensioning of the plant or the filter bed for carrying out the process according to the invention. For carrying out the method according to the invention in semi-industrial plants, it has proven advantageous if the concentrate with a volume flow Q (volume of concentrate per hour) in the range of 0.3 to 4 m ³ / h, in particular 0.5 to 3.5 m ³ /h, preferably 6.0 to 3.0 m ³ /h, preferably 0.9 to 2.5 m ³ /h, into the filter bed. In addition, it can equally be provided that the concentrate with a volume flow Q (volume of concentrate per hour) of at least 0.7 m ³ / h, in particular at least 1, 0 m ³ / h, preferably at least at least 1.3 m ³ /h, preferably at least 1.8 m ³ /h, is passed into the filter bed. For carrying out the process according to the invention in large-scale plants, it is advantageous if the concentrate is treated with a volume flow Q (volume of concentrate per hour) of at least 4.0 m ³ /h, in particular at least 6.0 m ³ /h, preferably at least 8 0 m ³ / h, preferably at least 10.0 m ³ / h, is passed into the filter bed.

The concentrates from reverse osmosis or nanofiltration processes to be treated with the process according to the invention can be traced back to all types of raw water. In particular, it can be provided according to the invention that the concentrate comes from reverse osmosis and/or nanofiltration processes, in particular reverse osmosis processes, for the treatment of groundwater, spring water, seawater and/or surface water to process and/or drinking water, preferably drinking water.

Furthermore, it can be provided according to the invention that the concentrate in the feed has a total nitrogen concentration TNb of at least 30 mg/l, in particular at least 40 mg/l, preferably at least 50 mg/l, preferably at least 60 mg/l. In particular, it can be provided within the scope of the method according to the invention that the concentrate in the feed has a nitrate nitrogen concentration of at least 20 mg/l, in particular at least 30 mg/l, preferably at least 40 mg/l, preferably at least 50 mg/l.

As already mentioned, the large amounts of hardness components in reverse osmosis concentrates pose a problem in the post-treatment of the concentrates from drinking water treatment . As far as the concentrate to be treated is concerned, this can usually have a water hardness [total hardness] in the inflow in the range from 10 to 150 °dH, in particular 20 to 120 °dH, preferably 30 to 100 “dH, preferably 40 to 80 °dH, preferably determined according to DIN 38409-6. As stated above, it was completely surprising that the method according to the invention is also suitable for water with the previously defined total hardness.

In addition, it can be provided within the scope of the method according to the invention that the concentrate in the feed has a temperature in the range from 2 to 40 °C, in particular 3 to 30 °C, preferably 4 to 25 °C, preferably 5 to 20 °C.

With regard to the concentrate to be treated with the method according to the invention, it can also be provided that the concentrate has a pH value in the range from 6 to 8.5, preferably 7 to 8, in the feed. It is equally preferred according to the invention if the concentrate in the feed has a pH of at least 6, in particular at least 6.5, preferably at least 7.

With regard to the method, it can also be provided that the filter is operated as a downstream or upstream filter, preferably as an upstream filter. With regard to operation of the filter as an upflow filter, it is particularly preferred if the concentrate is fed into the lower area of the filter bed or the concentrate is distributed in the filter bed, preferably in the lower area of the filter bed, and the filter bed, in particular the filter material, is flows from bottom to top. "Lower part" in this case means the lower half, preferably the lower third, of the filter bed. An embodiment according to the invention, which provides for operation as an upflow filter, is described in FIG. Nevertheless, other embodiments are equally possible and are within the ordinary skill of the person skilled in the art.

With regard to the economics of the process, in particular with regard to the energy consumption, it is advantageous if the process is not temperature-controlled and/or carried out at ambient temperature.

In addition, it has proven to be advantageous to determine the measured values listed below during the process in order to be able to adjust the process parameters if necessary or to check the quality of the concentrate to be treated or treated or denitrified:

In particular, it can be provided according to the invention that during the process the pH value, the temperature, the electrical conductivity, the nitrite concentration, the turbidity and/or the concentration of substances that can be filtered off in the concentrate to be treated and/or in the denitrified concentrate are measured, in particular in the Feed and/or in process step (a) and/or in the course and/or in process step (c). The measurements are carried out using measuring devices which are fundamentally known to those skilled in the art.

As a result, the method according to the invention provides a high-performance, separate cleaning stage for concentrates or waste water from the treatment of industrial or drinking water from raw water, which is suitable for removing large amounts of nitrate from the concentrate or waste water. With the method according to the invention, the statutory limit value for nitrogen or nitrate for direct discharge is generally achieved or can be complied with. Against this background, the yield of drinking water treatment can be significantly increased, since large amounts of nitrate in the resulting waste water or concentrate are no longer a limiting factor.

The present invention is also - according to the second aspect of the present invention - a reactor 1 for use in the treatment of reverse osmosis and / or nanofiltration concentrate ("concentrate"), the concentrate from the treatment of raw water by means of reverse osmosis and / or Nanofiltration for drinking and/or process water treatment originates, in particular the reactor being set up and designed to carry out a method according to one of the preceding claims, comprising an inlet 2 for the concentrate to be treated, an outlet 3 for the denitrified concentrate, a fluidized filter bed 4, wherein the filter bed 2 has a granular and/or particulate and biologically activated filter material 32 with a biofilm for microbial denitrification, and at least one device for fluidizing the filter bed 5, in particular wherein the device for fluidizing controls the fluid input depending on the filter resistance, in particular such that the formation of the biofilm on the particulate and/or granular filter material is regulated and/or controlled.

The reactor according to the invention is preferably set up and designed for carrying out the method described above. The reactor is equipped with a device for fluidization, which allows targeted regulation or control of the formation of the biofilm on the granular or particulate filter material, in particular as a function of the filter resistance measured in the operating state. For further details on the regulation and/or control of the formation of the biofilm, reference can be made to the relevant statements in connection with the method according to the invention.

A plant and a reactor which are set up for carrying out the method according to the invention are described below by way of example with reference to FIGS. 1 and 2 .

It shows

1: a flow chart of a plant for carrying out the method according to the invention; and

2A: a schematic representation of a reactor suitable for the method according to the invention, which has a filter bed based on a particulate or granular filter material with a biofilm growing thereon for microbial denitrification;

2B: a schematic representation of a further reactor suitable for the process according to the invention, the embodiment shown in FIG. 2B having additional lances arranged in the region of the reactor wall for introducing fluid in comparison to the reactor shown in FIG. 2A.

1 shows a flow chart of a plant for the treatment of reverse osmosis and/or nanofiltration concentrate, which originates from the treatment of raw water by means of reverse osmosis and/or nanofiltration for drinking and/or process water treatment:

In the plant, the concentrate to be treated in the feed 6 is first fed into a feed receiver 8 and fed into the reactor 1 via a feed line 18 and an inlet 2 . The inflow is adjusted via valves 16 and pumping devices 14 . Provision can preferably also be made to monitor and further regulate the inflow of the concentrate to be treated by means of a flow meter 22 . The concentrations of relevant water constituents, such as total nitrogen TNb, nitrate concentration, COD, water hardness, pH value, phosphorus content, etc., can be measured via measuring devices 17 . In order to condition the concentrate to be treated for denitrification, chemicals such as a carbon source, preferably in the form of acetic acid, and/or a phosphorus source, preferably in the form of 0.3% phosphoric acid, can be added to the concentrate via dosing devices 10, 11. Iron(II) sulfate, preferably at a rate of 0.2 mg/l based on iron(II) sulfate in the feed, and various trace elements are metered in. The metering can be adjusted or controlled via pump devices 14 . The substances for conditioning are fed to the concentrate to be treated, preferably in dissolved form, via a mixer 21 in the inlet 6 or in the inlet line 18 .

In reactor 1, the concentrate is treated by filtration through the filter material with microbial denitrification to remove the nitrate. The filter bed is preferably fluidized via a fluidization system 13 . The fluid input is preferably controlled via a control cabinet 23 . According to a preferred embodiment, the fluid is air, in particular compressed air, and/or at least one industrial gas, it being possible for the fluid to be introduced from the fluidization system 13 via a fluid line 24 into the reactor 1 or the filter bed. The reactor 1 is also equipped with sensor devices for measuring or monitoring the filter resistance.

Gases arising in the process according to the invention, in particular the molecular nitrogen arising during the denitrification, can escape from the reactor 1 via an exhaust air system 12 which preferably has a fan 15 .

In the process, in particular, the rinsing water produced by the cleaning of the filter material can be discharged from the reactor 1 via a rinsing water line 20 . The waste water discharged via the flushing water line 20 is preferably recycled via the inflow receiver 8 in order to further reduce the amounts of waste water occurring in the context of the method according to the invention.

The denitrified or treated concentrate is routed via the outlet 3 and a discharge line 19 into a discharge receiver 9 for the denitrified concentrate or treated concentrate. According to the invention, it can be provided in the outlet 7 by means of measuring devices 17 the concentration of relevant water constituents to determine fe or properties in the treated concentrate, in particular the total nitrogen content, the pH value, the nitrate concentration and/or the total hardness.

In addition, FIG. 2A shows a reactor 1 which is set up and designed for carrying out the method according to the invention.

The reactor 1 has an inlet 2 for the concentrate to be treated, an outlet 3 for the denitrified or treated concentrate and a filter bed 4 based on a granular or particulate filter material 32, in particular based on sand, with a biofilm for microbial denitrification on. The reactor 1 shown in FIG. 2 is set up for operation as an upflow filter. For this purpose, the reactor 1 has an internal feed line 31 for the concentrate to be treated, which opens into a preferably star-shaped distribution device 26 reaching into the filter bed for the even distribution of the concentrate to be treated in the filter bed 4 .

The concentrate to be treated flows through the filter bed 4 from bottom to top, as indicated schematically by the flow direction 27 for the concentrate to be treated.

In order to prevent the filter from becoming blocked, the method according to the invention provides for the formation of the biofilm on the granular or particulate filter material 32 to be regulated or controlled, preferably by continuously or intermittently reducing the biofilm on the granular or particulate filter material 32. This is preferably done by fluidizing the filter bed 4 or filter material 32. In this context, it is particularly preferred to measure or monitor the filter resistance of the filter bed and to control the fluid entry as a function of the filter resistance.

In the reactor shown in FIG. 2, the fluidization of the filter bed 4 takes place via a mammoth pump 25 arranged axially along the longitudinal axis of the filter bed 4 or of the reactor, with the introduction of compressed air as the fluid. In this embodiment of the method according to the invention, the fluid, preferably in the form of compressed air, is introduced into the mammoth pump (compressed air lifter) 25 via a fluidization system 13 (not shown in FIG. 2) and a fluid line 24 . The compressed air introduced into the mammoth pump 25 causes particulate or granular total filter material 32 sucked from the lower area of the filter bed 4 by the mammoth pump and promoted in the fluid flow from bottom to top. The entry of the fluid is preferably controlled via a control cabinet 23 depending on the filter resistance.

In the embodiment of the method according to the invention shown here, the filter material 32 is conveyed with the aid of the mammoth pump 25 to a rinsing unit 28 arranged above the filter bed, here in the form of a sand washer, and washed in the rinsing unit 28 with counterflowing, denitrified concentrate 30. The cleaned filter material 32 sinks back onto the filter bed 4, while the waste water flow arising in the rinsing unit 28, which in particular contains removed biomass and possibly other particulate residues, such as fine abrasion of the filter material or precipitated hardeners, is removed from the reactor 1 via a rinsing water outlet 29 becomes.

The denitrified concentrate 30 is routed out of the plant via an outlet 3 and the outlet 7 .

In addition, FIG. 2B shows a reactor 1 which is also suitable for carrying out the process according to the invention. In terms of design and equipment, the reactor 1 corresponds to the reactor shown in FIG. 2A, the reactor 1 according to FIG. 2B additionally having at least two lances 33 for introducing at least one fluid into the filter bed 4. As shown in FIG. 2B, the lances may have fluid outlets 34 along their longitudinal axis. Equally, it can also be provided that the lances 33 only have a fluid outlet 34 at the lower end that dips into the filter bed.

With regard to the fluid inflow via the additional lances 33, it is preferred according to the invention that this is controlled independently of the fluid input via the mammoth pump 25. For this purpose, the fluid line 24 can have valves that allow the fluid to be fed in independently via the lances 33 .

The additional lances 33 in the area of the reactor wall can further improve the fluidization of the filter bed 4 with regard to the regulation or control of the formation of the biofilm. By using lances in the area of the reactor wall, an even more uniform fluidization of the filter terbetts 4, which in turn improves the regulation of the biofilm and thus also the nitrate degradation rate.

Preferred embodiments of the present invention are also described below using the exemplary embodiments, which, however, are in no way to be understood as limiting.

EXEMPLARY EMBODIMENTS:

The efficiency of the method according to the invention, in particular with regard to the removal of nitrate from reverse osmosis concentrate, was examined on the basis of the exemplary embodiments described below.

1. Technical background to the objective of the method according to the invention

The starting point for the exemplary embodiments described below is a natural filter system in which raw water, such as well water, is treated to drinking water quality by means of reverse osmosis (synonymous with reverse osmosis, abbreviated to RO). The concentrate obtained during treatment using reverse osmosis is discharged into a watercourse for disposal or recycling in the water cycle. In order not to exceed the legal limit for total nitrogen of 20 mg/l when introducing the concentrate into the body of water, the large-scale natural filter system has so far been operated in such a way that the nitrogen or nitrate concentration in the reverse osmosis concentrate maintains this value.

The previous process has resulted in a reduced drinking water yield from the natural filter system. In other words, the nitrogen load in the reverse osmosis concentrate has so far stood in the way of an improvement in the productivity of the treatment process.

The method according to the invention, described below with reference to a preferred embodiment, makes it possible to reduce the total nitrogen load in reverse osmosis concentrates from drinking water treatment and thus allows an increase in the yield in drinking water treatment.

2. Treatment of reverse osmosis concentrate with the method according to the invention

In order to investigate the efficiency of the method according to the invention, in particular with regard to the reduction of the total nitrogen concentration in reverse osmosis concentrates from the treatment of raw water to drinking water quality, the filtration method described below was used in a plant. Fig. 1, which has a reactor as shown in Fig. 2, carried out. Commissioning of the reactor

The commissioning of the reactor or filter was as follows:

The reactor was first filled with quartz sand according to DIN EN 120904 as filter material, the grains of sand having a particle diameter or a particle size in the range from 1 to 2 mm. The plant and the reactor were then put into operation.

To inoculate the filter bed in the reactor, the inflow reservoir of the plant was fed with a selected bacterial or microorganism culture. In the present case it was a pure culture of Paracoccus dentrificans. In order to avoid stress on the microorganisms when the reactor or filter is started up, the adaptation was initially carried out using only service water with the addition of acetic and phosphoric acid. Further microorganisms were introduced into the filter bed with the service water. After a stable biofilm had formed on the filter material, the process water was replaced by reverse osmosis concentrate, with acetic and phosphoric acid being added to the concentrate for conditioning. After adaptation of the microorganisms or the biofilm to the conditioned concentrate, a significant degradation of nitrate was recorded in the effluent of the plant. The reactor or the filter for the process according to the invention was then ready for operation. RNA analyzes showed that bacteria of the genera Arcobacter, Hydrogenophaga, Bdellovibrio, Flavobacterium, Simplicispira, Acidovorax and Chitinophagaceae had settled in the biofilm.

Carrying out the method according to the invention

Within the scope of the process according to the invention, the reactor was charged with a pump device from the feed reservoir, which was supplied with reverse osmosis concentrate from an upstream reverse osmosis system. In order to avoid emptying the template in different operating states of the reverse osmosis, the inflow volume flow of the concentrate to the inflow template was greater than that to the reactor.

The concentrate to be treated was fed by means of a feed line via the inlet into the reactor to the star-shaped distributor and distributed evenly over the filter bed. The loading of the filter bed with reverse osmosis concentrate was slowly increased. In a 30-day start-up phase, the reverse osmosis concentrate was first fed into the filter bed with a bed loading (amount of total nitrogen per cubic meter of filter material per day) of up to 500 g/m ³ /d. In the subsequent operating phase, the bed load was increased to up to 2,100 g/m ³ /d. Taking into account the nitrate degradation rate, a filter resistance in the range of 20 cmWS to 60 cmWS has proven to be suitable.

The filter was operated as an upflow filter, ie the concentrate flowed through the filter bed from bottom to top for denitrification purposes. In the process, nitrite (NO ₂ ) as an intermediate product and nitrate (NO ₃ ) were reduced to molecular nitrogen (N ₂ ) by the sessile microorganisms growing on the particulate filter material. The molecular nitrogen formed during the denitrification was removed from the reactor via an exhaust air system. The treated or denitrified concentrate was discharged from the reactor via the outlet and a drain line or via the drain.

In order to prevent blockage of the filter and to ensure continuous material exchange and maintenance of the biocenosis, the filter material was continuously fluidized and cleaned in the rinsing unit located above the filter bed. The filter resistance was monitored and adjusted to suitable values with the help of the fluid input. The fluidization of the filter bed and the conveyance of the filter material to the rinsing unit took place by means of a mammoth pump arranged axially along the longitudinal axis of the reactor or filter. By introducing compressed air into the mammoth pump, the filter material was transported or conveyed from the cone at the bottom of the reactor into the rinsing unit in the form of a sand washer in the upper area of the reactor and cleaned using a small part of the outflow or the counterflowing, already treated concentrate . As part of the conveying process and/or cleaning, part of the biofilm was removed from the filter material in order to prevent the filter bed from becoming overgrown with biomass. The rate at which the biofilm was removed was controlled by the compressed air input into the mammoth pump. The rinsing water occurring in the rinsing unit and containing biomass and possibly other particulate residues of the process was conducted out of the reactor via a rinsing water outlet and recycled via the feed receiver. The cleaned filter material in the form of sand was also recycled by sinking back from the rinsing unit onto the filter bed. In order to set the environmental conditions for the denitrifying microorganisms or to condition the concentrate for the microbial denitrification, a carbon source and, if required, a phosphorus source and possibly trace elements, each in dissolved form, were metered into the concentrate in the feed using metering devices within the scope of the process according to the invention. 60% acetic acid was used as the carbon source, 0.3% phosphoric acid as the phosphorus source and ferrous sulfate as the iron source. The trace element solution contained zinc sulfate (ZnSC), manganese chloride (MgCh), boric acid (H3B03), cobalt chloride (C0Cl2), copper chloride (CuCk), nickel chloride (NiCh) and/or sodium molybdate (NazMoO^), each in dissolved form.

The filter resistance and the inflow volume flow were also monitored with the aid of means that are fundamentally known to those skilled in the art, e.g. pressure measuring probes and/or flow meters.

The process was operated continuously and without interruption. The control of the process, in particular the entry of compressed air to fluidize the filter bed, was carried out via a control cabinet.

The concentrations of water constituents that are particularly relevant with regard to the direct discharger ordinance, such as total nitrogen TNb, chemical oxygen demand (COD), hardness components, total phosphorus, total organically bound carbon (TOC), filterable substances and pH value, were measured both in the inflow and in the outflow measured using suitable measuring equipment. - Investigation of the nitrate degradation performance

The efficiency of the method according to the invention was further investigated:

First, the nitrate and nitrogen degradation performance of the process according to the invention was examined with different loading and dwell times of the reverse osmosis concentrate to be cleaned in the filter bed in the start-up and operating phase. The following table shows the volume flow and the total nitrogen concentration in the inlet for the start-up and first operating phases:

The reactor or filter bed was fed continuously with reverse osmosis concentrate, as described above. In order to create optimal environmental conditions for the denitrifiers, acetic acid as a carbon source and phosphoric acid as a phosphorus source were added to the concentrate in the feed.

In later operating phases, the inflow volume flow and the total nitrogen concentration in the inflow were further varied. During test days 193 to 204, for example, the total nitrogen concentration in the inflow was increased from 1.2 m ³ /h or 1.5 m ³ /h to around 49 mg/l to 59 mg/l at a reduced volume flow.

The total nitrogen concentrations TNb in the inflow and outflow were determined in each case. The relevant results for the start-up phase and the operating phases are shown graphically in FIGS. 3A, 3B and 3C.

In phase I of the start-up phase, an average degree of degradation of 88% of the total nitrogen was achieved. The minimum and maximum degrees of degradation were 84% and 93%, respectively. With the increase in the inflow volume flow in phase II of the start-up phase to 1.5 m ³ /h, an average degree of degradation of 86% of the total nitrogen was achieved. With a maximum reduction of 97%, an almost complete reduction of nitrogen in the reverse osmosis concentrate has already been achieved. The minimum degree of degradation in phase II was 77%. During the entire start-up phase, the average total nitrogen concentration in the outflow was around 3.25 mg/l and thus well below the legal limit of 20 mg/l for discharge into running water.

In the subsequent phase III and operating phase, the inflow volume flow was increased further to 1.8 m ³ /h, with the total nitrogen being almost completely reduced (on average by 95%). The values were subject to a small range of fluctuation with a minimum of 90% and a maximum of 100% degree of degradation. In phase IV with an inflow volume flow of 2.0 m ³ /h, a very significant reduction in total nitrogen with an average degree of degradation of 94% was recorded. the. The values for the degree of degradation were in a very small range of variation between a minimum of 90% and a maximum of 97%. The total nitrogen concentration in the effluent was on average 1.38 mg/l in this operating phase and thus also well below the legal limit of 20 mg/l.

As already explained above, the total nitrogen concentration in the inflow was increased later on. The data from test days 193 to 204 are used here as an example, when the total nitrogen concentration in the inflow was increased to approx. 49 mg/l to 58 mg/l. As can be seen from FIG. 3C, a minimum degree of degradation of about 80% and a maximum degree of degradation of more than 99% were achieved even with a significantly increased total nitrogen concentration or nitrogen load. Even with an increased total nitrogen concentration, the legal limit of 20 mg/l for direct discharge was easily complied with.

In FIG. 4A the specific degradation rate versus bed load, based on the total nitrogen concentration, is shown for phases I to IV. Appendix of Fig. 4A it can be seen that with the method according to the invention, after an adjustment phase, the entire nitrogen load that is fed to the plant is degraded in the reactor, so a degree of degradation of almost 100% can be achieved. Against the background of the results, it can even be assumed that the limit for a complete reduction of the nitrogen load has not yet been reached and that the potential for the largest possible loading of the filter bed and the increase in the nitrate concentration has not yet been exhausted.

FIG. 4B shows the specific decomposition rate in relation to the bed load, based on the specific decomposition rate for nitrate nitrogen, as an example for the later test days 193 to 204. It can be seen from FIG. 4B that even after increasing the total or nitrate nitrogen load that is fed to the plant, a degree of nitrate degradation of 85 to almost 100% can still be achieved. The method according to the invention is therefore distinguished by an excellent nitrate degradation rate.

In addition, FIG. 5 graphically shows the nitrate nitrogen concentration in the inflow and outflow for test days 193 to 204. The nitrate nitrogen concentration in the inlet was in the range from 41 to 51 mg/l. In the effluent, on the other hand, only nitrate nitrogen concentrations in the range of approximately 0 mg/l to max. measured at a maximum of 12 mg/l. As a result, large amounts or concentrations of nitrate can be almost completely removed from reverse osmosis filtrates with the method according to the invention and the denitrification carried out therein. On the test days shown here, nitrate degradation levels of around 85% to 99% were achieved. - Control of the fluid entry depending on the filter resistance

As already explained above, it has proved to be advantageous according to the invention to control the fluid input as a function of the filter resistance in order to prevent excessive shearing of the biomass, but at the same time to prevent the filter from becoming blocked. The filter resistance serves in particular as an indirect measure of the formation of the biofilm on the filter resistance. In the system used in the context of the exemplary embodiments with a reactor which had a filter bed based on quartz sand with a particle size in the range from 1 to 2 mm, a filter resistance in the range from 20 to a maximum of 60 cm water column based on the nitrate degradation rate, especially in the Range of 25 to 40 cmWS proven to be suitable. FIG. 7 shows the filter resistance, given in cm of water column [cmWS], and the fluid input, given in volume of standard air per minute [Nl/min], as an example for test days 193 to 204. If the filter resistance increased excessively, as on test days 201 and 202 to 46 to 47 cm water column, the fluid input was increased in order to reduce the biomass on the filter material and thus reduce the filter resistance again. When a filter resistance in the particularly preferred range was reached, in this case in the range from approx. 30 to 35, the fluid input was reduced again in order to avoid further shearing off of the biomass. . Measurement of the COD

For the chemical oxygen demand, the Direct Discharge Ordinance currently sets a limit value of 90 mg/l, which must not be exceeded in water when it is discharged directly into running water and municipal waste water.

However, with regard to microbial denitrification to comply with the limit values for nitrate and in particular the total nitrogen concentration certain COD in reverse osmosis concentrate required for microbial metabolism.

By checking or measuring the COD in the inflow and outflow, it can be ensured that there is sufficient nutrient substrate for the material conversion, but at the same time there is no unnecessary overdose, i.e. the legal limit of 90 mg/l for direct discharge in the outflow is not exceeded. The results of the COD measurement of the method according to the invention are shown graphically in FIGS. 6A and 6B.

In phase I of the start-up phase, the average COD concentration in the outflow was around 7.4 mg/l, so that with a degree of degradation of around 93%, the carbon supplied was optimally used to reduce the total nitrogen. After increasing the feed volume flow in phase II, the dosage of acetic acid was increased twice by 4.5% and 13.6%. The carbon supplied was used up by approximately 91% in each case and was at an average value of 7.8 mg/l in the outflow (cf. FIG. 6A). As a result, the breakdown of the total nitrogen could be increased to up to 97% (cf. FIG. 3A).

Despite an increase in the feed volume flow to 1.8 m ³ /h in phase III, only 83% of the carbon fed in was consumed, with the degree of degradation of the total nitrogen continuing to rise. This indicates an increase in efficiency in the metabolism of the microorganisms (in the biofilm). The average COD concentration in the outflow during this period was 17.9 mg/l. The dosage of acetic acid could therefore be reduced.

With an inflow volume flow of 2.0 m ³ /h in phase IV of the operating phase, consumption of the metered carbon was 80% on average. The COD concentration in the outflow was at an average value of 18.9 mg/l (cf. FIG. 6B). Measurement of turbidity

Like the total nitrogen concentration and the COD, the concentration of cloudy matter and hardeners is regulated by law for direct discharge into running water. A limit value of 30 mg/l is currently being set in Germany for substances that can be filtered off.

In the start-up and operating phase, the concentrations of the filterable substances in the effluent with an average of 12.3 mg/l were below the legal limit of 30 mg/l. In FIG. 8, the outflow, rinsing water and inflow (from left to right) from the previously described process are shown set up next to one another. It is readily apparent that both the influent and the effluent are clear with no turbidity. In contrast, the rinsing water shows a clear turbidity. The mean of the substances in the effluent that could be filtered off was 10.1 mg/l. The filterable substances in the rinsing water were 202 mg/l.

The method according to the invention, in particular the filtration through a particulate filter material with a biofilm, does not result in any accumulation of turbid matter in the effluent. Abrasion of the particulate filter material, which can occur in particular when using sand as the filter material, potentially precipitated hardeners and detached biomass are retained by the filter bed and discharged with the rinsing water. Conclusion and outlook

In summary, it can be stated that with the method according to the invention for the treatment of concentrates with a high nitrate nitrogen load from the treatment of raw water using reverse osmosis, the requirements for the degradation of nitrogen compounds with regard to the legal limit values for direct discharge are reliably met.

After adaptation of the microorganisms and conversion of the inflow from process water to concentrate, an almost complete reduction in the total nitrogen concentration in the inflow (mainly present as nitrate here) was achieved with the selected biological process. The concentrations of other nitrogen compounds, such as nitrite, were in the immeasurable range. Furthermore, the quantity of process-relevant chemicals added, such as easily degradable carbon (acetic acid) and phosphorus, could be adjusted in such a way that no overdosing took place and the respective concentration in the outlet was below the legal limit values to be observed.

Substances that can be filtered off (AFS) are also reliably retained with the method according to the invention at a value in the effluent that is below the legal limit value. A failure of hardness components in the process is also not observed.

The method according to the invention is therefore a promising starting point for increasing the yield of drinking water in the treatment of raw water to increase this by means of reverse osmosis or nanofiltration. Otherwise, the method according to the invention is environmentally friendly and resource-friendly.

Reference list:

1 reactor 19 drain line

2 inlet 20 flush water line

3 outlet 21 mixer

4 filter bed 22 flow meter

5 Device for fluidization 25 23 Control cabinet

6 inlet 24 fluid line

7 drain 25 mammoth pump / compressed air lifter

8 inlet receiver 26 distributor

9 Inlet reservoir 27 Direction of flow of concentrate

10 dosing device 30 28 flushing unit

11 dosing device 29 flushing water outlet

12 exhaust system 30 denitrified concentrate

13 Fluidization system 31 Internal inlet line

14 pumping device 32 filter material

15 Fan 35 33 Lance

16 valve 34 fluid outlet

17 measuring device

18 inlet line

Claims

39 patent claims:

1. A method for treating reverse osmosis and/or nanofiltration concentrate ("concentrate"), the concentrate originating from the treatment of raw water by means of reverse osmosis and/or nanofiltration for drinking and/or industrial water treatment, comprising:

(a) Introducing the concentrate to be treated into a filter, the filter having a filter bed with a granular and/or particulate filter material and the filter material having a biofilm with microorganisms for microbial denitrification,

(c) Discharging the denitrified concentrate from the filter bed, the concentrate being conditioned for microbial denitrification before and/or during the process, preferably in process step (a) or in the feed.

2. The method according to claim 1, wherein the concentrate before and/or during the method, preferably in method step (a) or in the feed, to a COD (chemical oxygen demand) in the range from 10 to 200 mg/l, in particular 20 to 160 mg/l, preferably 30 to 150 mg/l, preferably 40 to 130 mg/l, in particular the COD being adjusted by adding a carbon source for the microorganisms contained in the biofilm, preferably by adding organic acids, in particular Acetic acid.

3. The method according to claim 1 or 2, wherein a phosphorus source for the microorganisms contained in the biofilm is metered into the concentrate before and/or during the process, preferably in process step (a) or in the feed, in particular phosphoric acid being used as the phosphorus source.

4. The method according to any one of the preceding claims, wherein trace elements for the microorganisms contained in the biofilm are metered into the concentrate before and/or during the method, preferably in method step (a) or in the feed, in particular wherein the trace elements are selected from 40

Group of zinc, manganese, boron, cobalt, copper, nickel and / or molybdenum and / or their salts, and / or the concentrate before and / or during the process, preferably in process step (a) or in the feed, an iron source , preferably at least one iron(II) source, particularly preferably iron(II) sulfate, is metered in; in particular where the trace elements are added to the concentrate in the form of zinc sulfate (ZnSC), manganese chloride (MgCh), boric acid (H3B03), cobalt chloride (C0CI2), copper chloride (CUCI2), nickel chloride (N1CI2) and/or sodium molybdate (Na2 oC). in dissolved form.

5. The method according to any one of the preceding claims, wherein the formation of the biofilm on the granular and/or particulate filter material is regulated and/or controlled, preferably by reducing the biofilm on the granular and/or particulate filter material.

6. The method according to any one of the preceding claims, wherein the formation of the biofilm is regulated and/or controlled by introducing at least one fluid into the filter bed, in particular wherein the at least one fluid is selected from technical gases, air and/or water, preferably technical gases and/or air; in particular wherein the fluid entry and/or the regulation of the biofilm is controlled as a function of the filter resistance, and/or in particular wherein the fluid entry is controlled by means of time-pause control as a function of the filter resistance.

7. The method according to claim 6, wherein the at least one fluid is introduced into the filter bed and/or filter material via at least one, preferably several, fluid inlets, in particular wherein the fluid is introduced via at least one inlet in the area of the longitudinal axis of the filter bed and/or the fluid is introduced takes place via inlets in the wall and/or in the bottom of a filter module and/or reactor enclosing the filter bed; and/or wherein the fluid is introduced via lances projecting into and/or immersed in the filter bed and/or wherein the fluid is introduced via a line arranged axially along the longitudinal axis of the filter bed to the inlet of at least one fluid. 41

8. The method according to any one of the preceding claims, wherein the particulate and/or granular filter material is conveyed to a rinsing unit arranged outside the filter bed, in particular by introducing at least one fluid, preferably air and/or a technical gas, and wherein the filter material the rinsing unit is cleaned; in particular wherein the filter material is conveyed from the lower region of the filter bed to a flushing unit arranged above the filter bed by means of a compressed air lifter preferably arranged axially along the longitudinal axis of the filter bed, in particular wherein the entry of the compressed air is controlled as a function of the filter resistance.

9. The method according to any one of the preceding claims, wherein the filter material used is a particulate and/or granular material with particle or grain sizes, in particular mean particle or grain diameters, preferably determined according to DIN EN 120904, in the range from 0.1 to 15 mm , in particular 0.2 to 10 mm, preferably 0.5 to 5 mm, preferably 0.7 to 3 mm, particularly preferably 1 to 2 mm, is used; and/or wherein the filter material used is a particulate and/or granular material with a specific density in the range from 0.7 to 6 g/cm ³ , in particular 1 to 5 g/cm ³ , preferably 1.5 to 4 g/cm ³ , preferably 2 to 3.5 g/cm ³ , particularly preferably 2.5 to 3.2 g/cm ³ .

10. The method according to any one of the preceding claims, wherein the microorganisms for the microbial denitrification grow sessile on the grains and / or particles of the filter material.

11 . Method according to one of the preceding claims, wherein sand, bentonite and/or crushed lava stones is or are used as the particulate and/or granular material; and/or wherein the method is operated in a sand filter and/or wherein sand, in particular quartz sand, is used as the particulate and/or granular filter material.

12. The method according to any one of the preceding claims, wherein the method is carried out continuously or intermittently, preferably continuously.

13. The method according to any one of the preceding claims, wherein the concentrate with a bed load (amount of total nitrogen per cubic meter of filter material per day) in the range from 100 to 1,500 g/m ³ /d, in particular 200 to 1,300 g/m ³ /d, preferably 300 to 1,200 g/m ³ /d, preferably 400 to 1,000 g/m ³ /d, is passed into the filter bed, and/or the concentrate having a bed load (amount of total nitrogen per cubic meter of filter material per day) of at least 200 g/m ³ /d, in particular at least 400 g/m ³ /d, preferably at least 600 g/m ³ /d, preferably at least 800 g/m ³ /d, is passed into the filter bed; and/or wherein the concentrate has a volume flow Q (volume of concentrate per hour) in the range from 0.5 to 4 m ³ /h, in particular 0.7 to 3.5 m ³ /h, 1.0 to 3.0 m ³ / h, preferably 1.3 to 2.5 m ³ / h, is passed into the filter bed and/or the concentrate having a volume flow Q (volume of concentrate per hour) of at least 0.7 m ³ / h, in particular at least 1.0 m ³ /h, preferably at least 1.3 m ³ /h, preferably at least 1.8 m ³ /h, is passed into the filter bed.

14. The method according to any one of the preceding claims, wherein the concentrate from reverse osmosis and / or nanofiltration process, in particular reverse osmosis, for the treatment of ground, spring, sea and / or surface water to process and / or drinking water, preferably drinking water, comes .

15. The method according to any one of the preceding claims, wherein the concentrate in the feed has a total nitrogen concentration TNb of at least 30 mg/l, in particular at least 40 mg/l, preferably at least 50 mg/l, preferably at least 60 mg/l and/or wherein the concentrate in the feed has a nitrate concentration of at least 20 mg/l, in particular at least 30 mg/l, preferably at least 40 mg/l, preferably at least 50 mg/l.

16. The method according to any one of the preceding claims, wherein the concentrate in the feed has a water hardness [total hardness] in the range from 10 to 150 °dH, in particular 20 to 120 “dH, preferably 30 to 100 °dH, preferably 40 to 80 °dH, preferably determined according to DIN 38409-6; and or wherein the concentrate in the feed has a temperature in the range from 2 to 30° C., in particular 3 to 25° C., preferably 4 to 20° C., preferably 5 to 15° C.; and/or wherein the concentrate has a pH in the range from 6 to 8.5, preferably 7 to 8, in the feed.

17. The method according to any one of the preceding claims, wherein the filter is operated as a downstream or upstream filter, preferably as an upstream filter.

18. The method according to any one of the preceding claims, wherein the concentrate is fed into the lower area of the filter bed and/or wherein the concentrate is distributed in the filter bed, preferably in the lower area of the filter bed, and the filter bed, in particular the filter material, from bottom to top flows through.

19. The method according to any one of the preceding claims, wherein the method is not temperature-controlled and/or carried out at ambient temperature.

20. The method according to any one of the preceding claims, wherein during the process the pH value, the temperature, the electrical conductivity, the nitrite concentration, the nitrate concentration, the total nitrogen TNb, the COD, the phosphorus content, the turbidity and/or the concentration of substances that can be filtered off in the Concentrate and/or be measured in the denitrified concentrate, in particular in the inflow and/or in the outflow.

21. Reactor (1) for use in the treatment of reverse osmosis and/or nanofiltration concentrate ("concentrate"), the concentrate originating from the treatment of raw water by means of reverse osmosis and/or nanofiltration for drinking and/or industrial water treatment, in particular wherein the reactor is set up and designed for carrying out a method according to one of the preceding claims, comprising an inlet (2) for the concentrate to be treated, an outlet (3) for the denitrified concentrate, a fluidized filter bed (4), the filter bed ( 2) has a granular and/or particulate and biologically activated filter material (32) with a biofilm for microbial denitrification, and at least one device for fluidizing the filter bed (5), in particular wherein the device for fluidizing controls the fluid input depending on the filter resistance, in particular in such a way that the training 44 formation of the biofilm on the particulate and/or granular filter material is regulated and/or controlled.