FR2712581A1 - Fixed bed process for wastewater treatment. - Google Patents

Abstract

Fixed-bed process for the purification of wastewater, to effect the simultaneous reduction of the biological oxygen demand and of the chemical oxygen demand and to perform the nitrification and denitrification of wastewater by intermittent aeration of at least one reactor at fixed bed (F1-F6), so that the wastewater is aerated in the reactor for a first time interval, to effect the reduction of BOD5 and COD until nitrification, is covered with new wastewater during a second reactor time interval and that the aeration is turned off at least at times while the reactor is being charged with new wastewater.

Description

The invention relates to a fixed bed method for simultaneously performing the

  reduction in the demand for biological and chemical oxygen (BOD5 / COD) for nitrification and denitrification of wastewater.5 The components of wastewater from municipal and industrial sources can be subdivided, among others, into the following two main groups: - an organic filler, essentially comprising organic carbon compounds, - an inorganic filler essentially containing

nitrogen compounds (ammonium).

  Other harmful substances, which characterize the quality of wastewater and must be destroyed, are

  consisting of phosphorus, or as the case may be phosphorus-containing compounds.

  The biological destruction of these components presupposes having different microorganisms which, each in turn, only act when they are in completely different environmental conditions.20 The reduction of organic carbon is preferably carried out under aerobic conditions. By the supply of air / oxygen, heterotrophic (aerobic) microorganisms are formed, which consume the source of organic carbon giving C02 and H20. Products corresponding to BOD5 and COD see in a way

  corresponding their quantity decrease.

  To carry out the oxidation of ammonium (NH4-N) to nitrate (N03-N), therefore to carry out what is called nitrification, it is also necessary to have aerobic conditions. The nitrifying bacteria then use ammonium as a hydrogen donor to

  instead of using organic products.

  Two groups of bacteria always participate in the oxidation of ammonium to nitrate, in particular those which are called nitrosomonas (I) and those which are called nitrobacters (II), which lead to the following development5 of reactions : I NH4 + +1.5 02 II N02- + 0.5 02 I + II NH4 + + 202 In addition, nitrifying bacteria use C02 as an inorganic oxygen source, which is why they are associated with autotrophic bacteria.10 It results from the above that the nitrification is preferably planned downstream of a reduction or according to the case of elimination of the BOD5 / COD, in order to provide the source of inorganic oxygen and thus the conditions of medium necessary for the nitrifying bacteria. 15 Denitrification, therefore the reduction of nitrate (NO3-N) to elemental nitrogen (N2) is a reducing process which presupposes anoxic conditions in the wastewater. There must therefore be no trace of dissolved oxygen in the wastewater. At the same time, there must be organic substrates, biologically decomposable and serving as hydrogen donors. The elimination of these previously during the elimination of BOD-COD, creates problems because we are no longer in the presence of organic carbon source or we are in

  presence of insufficient source of organic carbon.

  The bacteria intended for the process mentioned above can be introduced both in the form of a suspension biology (activated sludge process) and also in the form of a fixed bed biology. So far, activation processes have been at the forefront. The biomass is then kept in suspension. The process requires a sedimentation tank, in which the biomass is decanted and it is again reintroduced into the activated sludge reactor with high recirculation rates (several hundred percent). Only a small part is extracted as so-called excess sludge.5 Such activated sludge processes are of considerable cost linked to the measures and regulations necessary for recycling sludge. On the other hand, the fixed bed processes (submerged body and drip body process) have notable advantages. In the fixed bed process, microorganisms are provided with growth surfaces. A tray of

  sedimentation is not necessarily necessary in principle, since microorganisms cannot be eliminated.

  Research on nitrification and denitrification in one- and two-stage activation systems is described by Decker in "Korrespondenz

  Abwasser ", 39th year, notebook 2/92, 197.

  To prepare the organic carbon source necessary for denitrification, it would in principle be possible, in the case of a multi-stage reactor, to pass a partial stream from the first reactor used for the reduction of BOD5 / into the denitrification tank. COD. However, there is a risk that too many organic products have passed through the denitrification tank and that, in this way, it will no longer be possible to achieve purity of the wastewater. This process technique also requires

  sludge recirculation for each partial reactor.

  The connection upstream of the denitrification stage (upstream of the stage used for the reduction of BOD5-COD) does not bring here any facility concerning the technique of

measurement and regulation.

  Insofar as the biological purification of wastewater takes place in a single reactor, it would be conceivable to have the reduction of BOD5-COD and the nitrification with the addition of oxygen take place, then, after deactivation of the air intake, to run the denitrification. However, this also requires

  again, a significant cost in measurement and regulation, to ensure that a sufficient quantity of biologically decomposable organic substrate is available as a hydrogen donor in the denitrification stage.

  The object of the invention is to indicate a possibility of carrying out, with a process technique as simple as possible, a biological purification of waste water, to effect a simultaneous reduction in the demand for biological and chemical oxygen, to effect nitrification and denitrification, preferably simultaneously targeting

  remove phosphorus and phosphorus compounds.

  The invention is based on the surprising discovery that this object can be achieved, in the context of a fixed bed process, in a surprisingly simple manner by intermittent aeration of at least one fixed bed reactor insofar as it is respected the following criteria: - the aeration or reactors with a fixed bed are aerated, for a first time interval, to effect the reduction of BOD5 and COD until nitrification, - the and / or the bed reactors are covered fixes new waste water for a second subsequent time interval, - the aeration is deactivated at least at times during the filling of the reactor (s) with

new wastewater.

  The process according to the invention can be carried out in a particularly advantageous manner, according to a form of

  embodiment, when the wastewater is treated in a reactor composed of several partial reactors (chambers) 5 connected one behind the other, within the meaning of the fluid technique.

  We then use, for example, a first partial reactor for the destruction of organic products, a second partial reactor for the continuation of the reduction in the demand for biological and chemical oxygen, as well as, at the same time, for nitrification, a third partial reactor for nitrification, a fourth partial reactor for the continuation of nitrification and parallel denitrification as well as a fifth reactor and, if necessary, a sixth reactor, for denitrification. Dirty wastewater is

  then brought to the first partial reactor and this purified waste water is withdrawn from the last partial reactor.

  The process takes place in such a way that the partial reactors, each equipped with fixed beds, are first ventilated during a first treatment phase (first time interval). The reduction / elimination of organic products as well as the nitrification are then carried out in the corresponding partial reactors. Denitrification is initially impossible under the given environmental conditions (oxidizing). During a second subsequent time interval, the reactor (the first partial reactor) is filled with a renewal of new waste water, the stream of waste water going from a partial reactor to another partial reactor, in the direction of the discharge end, therefore also in the denitrification stages provided for denitrification. During this loading phase with new (non-purified) waste water, the aeration is put out of service, at least temporarily. 5 The deactivation can then be carried out simultaneously for all the reactors, at least however

  in the partial chambers used for denitrification.

  Due to the parallel loading of the reactor with new waste water, it is simultaneously ensured that, in the denitrification stages, a given quantity of organic products, therefore a quantity of organic substrates which can be biologically decomposed which is in the form of hydrogen donors and which allows the reduction of oxidized nitrogen compounds (nitrate, nitrite) into nitrogen

  elementary (N2), can be introduced.

  The process then continues, from the beginning, so with an aeration phase, during which the loading

  of the reactor with new waste water is interrupted.

  It has surprisingly been found that the organic products brought in this way into the denitrification stages are sufficient, also in the case of a fixed bed process (without recirculation of the sludge), to create

  the environmental conditions necessary for micro-

  organisms, in the denitrification stage. The effect can be observed optically by the rise of CO2 and N2 gas. Denitrifying bacteria are indistinguishable,

  other heterotrophic bacteria in an aerobic environment.

  The breathability of nitrates exists however in the case of many bacteria used in the present case, to effect denitrification in a unitary "simultaneous process". The corresponding heterotrophic microorganisms are formed in the upstream nitrification stage and are guided into the denitrification cells when the reactor is loaded (

reactor chambers).

  The ventilation can then be deactivated for the entire second time interval (loading the reactor with new waste water). In general, however, it is sufficient that ventilation is not

  only partially interrupted during charging.

  The loading of the multilayer reactor with new wastewater during a second time interval can be carried out, according to the invention, according to three process variants: According to a first variant, the loading is carried out in partial currents in the partial reactors used to reduce BOD5 / COD and denitrification, to

  start and end of the flow path.

  According to a second embodiment, the loading of the reactor with new waste water takes place during the second time interval in partial currents in

all partial reactors.

  It is however sufficient in principle as indicated below.

  above load the reactor only through the first partial chamber with new waste water and simultaneously open the flow paths between the different partial reactors, so that the waste water flows

  to the partial reactors used for denitrification.

  In this way the necessary quantity of

  organic products in denitrification reactors.

  The denitrification then takes place under anoxic conditions (when the aeration is put out of service). If necessary, you can connect to the

  last partial reactor post-clarification.

  Thanks to the use of fixed bed reactors, we can - as indicated - forgo any kind of sludge recycling. This significantly reduces the cost of measurement and regulation. The anaerobic (anoxic), aerobic alternating states in the partial reactors simultaneously allow the biological elimination of phosphorus. The invention is explained in more detail below, at

  using an exemplary embodiment.

  Figure 1 shows - schematically - a fixed bed reactor composed of a total of six partial reactors. In FIG. 2, the values of the organic load, in ammonium, nitrate, total nitrogen balance and elemental nitrogen for the various partial reactors are shown in solid line, this when there is a

constant ventilation.

  FIG. 2 also shows in diagram form the evolution in principle of the values for the aforementioned components with use of the method

the invention, this in dotted lines.

  In FIG. 1 is shown a clarification installation, articulated in six partial reactors, the different partial reactors F1 to F6 being arranged the

  one behind the other, from the hydraulic point of view.

  While the wastewater (not purified) enters the first partial reactor F1, in A, the purified wastewater is withdrawn at the end of the last partial reactor F6, in B, a stage of clarification station (usual) which can

  here be connected if necessary.

  In the clarification installation shown diagrammatically - in FIG. 1, it is for example a compact clarification installation according to document DE-39-29 510 C2. This is why it is not necessary for the various partial reactors F1 to F6 to be completely separated from each other; rather, it suffices to separate from one another, by walls, the various partial reactors (chambers), flow openings being provided for the waste water in these walls, or else the waste water flowing each time in the subsequent room passing over the edges

  upper walls.

  All the partial reactors F1 to F6 are each

  made with fixed beds and a ventilation device.

  Also insofar as the document DE 39 29 510 C2 indicates suitable embodiments, no additional representation is given here concerning the

  fixed bed reactors known per se.

  The clarification installation is configured so that the various partial reactors F1 to F6 can perform the following functions: F1: reduction / elimination of organic load (BOD5 - COD) F2: continuation of elimination of organic load and / or nitrification chamber F3: nitrification chamber F4: nitrification and / or denitrification chamber F5: denitrification chamber

F6: denitrification chamber.

  To be able to allow the different reactors

  partial F1 and F2 to fulfill the functions mentioned above

  above, establishing the environmental conditions

  corresponding wastewater, as mentioned above

  above in the different reactors, is necessary.

  To obtain a better understanding of the mechanism of action using the method according to the invention, a more detailed description of a plurality of cases is given below below, for which the various reactors F1 to F6 are permanently aerated (as in the case of a reactor

pure nitrification).

  In FIG. 2 are also represented, in the form of diagrams, the contents of organic carbon, ammonium, nitrate and elemental nitrogen, this for

  the various partial reactors, in solid line.

  It can be seen that the values of the organic charge (organic carbon) fall from a maximum, in the zone of the partial reactor 1, passing through the partial reactor 2, to

a value of about 0.

  The values of the ammonium concentrations in the wastewater have a shape roughly parallel to this one (slightly shifted to the right so towards the

  partial reactors 2,3 and if necessary 4).

  Correspondingly to the nitrification carried out in the partial reactors 2, 3 and 4, the values of nitrates in the wastewater increase between the first partial reactor F1 and the fourth partial reactor F4,

  to go from 0 to a maximum value.

  Because, in the continuous aeration state of the partial reactors F1 to F6, there are no anoxic conditions and,

  only after a largely complete reduction in (BOD5 -

  COD) and after nitrification, there is no organic substrate which can be broken down biologically, serving as a hydrogen donor, denitrification is not possible, which is why heterotrophic microorganisms do not find the conditions necessary for respiration. nitrate and corresponding conversion to elemental nitrogen cannot take place, therefore the values indicated in FIG. 2 in solid lines are equal to 0, for elemental nitrogen, and, in dotted lines, are maximum, for the overall nitrogen content

  (Ng) of wastewater (because there is no escape of N2).

  The values shown in FIG. 2, in solid lines, do not vary fundamentally either when the clarification installation is loaded intermittently with new waste water. In any case, the reduction in the decomposition of the organic charge and of ammonium, as well as the increase in the content of

  nitrate, are shifted in the direction of flow, to the partial reactors further downstream.

  On the other hand, a completely different appearance is indicated by the curves, when the installation of

  clarification operates, according to the invention, by charges.

  If, now, after a first time interval during which the various reactors F1 to F6 are aerated, the reactor A is filled with new waste water and that, during this loading, the aeration is deactivated (it is assumed here completely), there is then a shift to the right of the organic load decomposition curve (in the direction of a partial reactor F3 to F6), a certain partial amount of organic load being simultaneously passed into the partial reactor F4 and , if necessary, in the partial reactors F5 and F6. Because at this time the aeration is put out of service, conditions of anoxic medium have been created simultaneously in the reactors F4 to F6, which is why the reactors F4 to F6 constitute denitrification chambers. In this way, a fixed bed process which is simple to master from the point of view of the process technique is obtained, simultaneously elimination of the BOD5-COD, nitrification and subsequent denitrification. The shape of the evolution, observed using the method according to the invention, of the values of the charge

  organic for ammonium and nitrate are shown in dotted lines in Figure 2.

  The elemental nitrogen values indicate that at the start of the partial reactor 4, it is denitrification which is in action, the elemental nitrogen resulting from the respiration of the nitrates by the denitrifying bacteria15 according to the reaction below, which may be optically observed by the rise of C02 and N2 in gaseous form. 5CH3OH + 6 N03- - 5 CO2 + 7 H20 + 3 N2 + 6 OH Correspondingly there is a decrease in

  total nitrogen content in wastewater.

  Depending on the pollution of the waste water, as well as the design of the clarification installation and its partial reactors, it may be sufficient to deactivate the aeration only during part of the second time interval (loading the installation with

new wastewater).

  After interrupting the loading with new waste water, the system is restarted with the addition of oxygen (via the aerators), to create the oxidizing environment conditions necessary for

  reduction of organic load and nitrification.

  Then the subsequent process step is carried out again which is carried out at least partially without aeration. To this extent the process can be carried out "almost continuously". Due to the alternation of anoxic and aerobic boundary conditions in the different partial reactors, we can operate simultaneously

  biological elimination of phosphorus.

  In the context of the invention - although this has several drawbacks from the point of view of the process technique - the first partial reactor F2 can be produced in the manner of an activation tank, that is to say without fixed bed

  but with a recirculation of the sludge.

  In principle it is also possible to conduct the process according to the invention in a single reactor, but, coinciding with the basic idea of the invention, ensuring in any case that, after a first time interval, during which the reactor equipped with fixed beds is aerated, there is, during a second time interval, loading the reactor with waste water and, simultaneously, putting out of operation, at least at times, of the aeration, during loading. The reaction mechanism then takes place in a manner analogous to what has been described above: thanks to the realization of the reactor in an individual partial chamber, the action mechanism of the process according to the invention is

  however, particularly advantageously optimized.

Claims (10)

  1. Fixed bed process for the simultaneous reduction of the demand for biological oxygen and the demand for chemical oxygen (BOD5-COD), for carrying out the nitrification and denitrification of wastewater by intermittent aeration of at least one reactor with fixed bed, so that the waste water: 1.1 is aerated in the reactor, during a first time interval, to effect the reduction of BOD5 and COD until nitrification, 1.2 is covered with new waste water during a second time interval time of the reactor, and 1.3 the aeration is deactivated at least at times during the loading of the reactor with new waste.   2. Method according to claim 1, according to which the waste water is treated in a reactor composed of several partial reactors (chambers) connected one behind the other, within the meaning of the technique of fluids.   3. Method according to claim 2, according to which, during the loading of the reactor with new waste water, the aeration is put out of service at least partially in the partial reactors used for the   denitrification, at the end of the flow path.   4. Method according to claim 2 or 3, according to which, during the loading of the reactor with new waste water, the aeration is deactivated at least   temporarily in all partial reactors.   5. Method according to any one of claims 1 to   4, according to which the ventilation is deactivated during the entire second time interval (loading of the   reactor by new wastewater).   6. Method according to any one of claims 2 to   , according to which the loading of the reactor with new wastewater takes place during the second time interval in partial currents in the partial reactors used for the reduction of BOD5 / COD and for denitrification, at the beginning and at the end of the flow path.   7. Method according to any one of claims 2 to   , according to which the loading of the reactor with new waste water takes place during the second time interval in partial currents, in all the partial reactors.   8. Method according to any one of claims 2 to   , according to which the loading of the reactor with new waste water takes place during the second time interval, via the first partial reactor, when observed in the direction of the flow of the waste water, and, there, through the reactors   parts located downstream in the circuit.   9. Method according to any one of claims 2 to   8, according to which the waste water is treated in a reactor composed of at least 5, preferably 6, partial reactors o, the reduction of BOD5 / COD, observing in the direction of the flow of the waste water, is carried out in the first or two first partial reactors, nitrification is carried out in the second and third, or else in the second to fourth partial reactors, and denitrification is carried out in the fourth and fifth, or in the fourth to sixth   partial reactors, the wastewater being extracted by the last partial reactor. 10. Method according to any one of claims 2 to   9, according to which the wastewater, extracted from the last partial reactor, observing in the direction   of wastewater flow, are subject to post-clarification.