CA2036245A1 - Process for biologically purifying waste waters - Google Patents
Process for biologically purifying waste watersInfo
- Publication number
- CA2036245A1 CA2036245A1 CA002036245A CA2036245A CA2036245A1 CA 2036245 A1 CA2036245 A1 CA 2036245A1 CA 002036245 A CA002036245 A CA 002036245A CA 2036245 A CA2036245 A CA 2036245A CA 2036245 A1 CA2036245 A1 CA 2036245A1
- Authority
- CA
- Canada
- Prior art keywords
- stage
- waste water
- oxygen
- activated sludge
- cod
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F3/00—Biological treatment of water, waste water, or sewage
- C02F3/006—Regulation methods for biological treatment
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F3/00—Biological treatment of water, waste water, or sewage
- C02F3/30—Aerobic and anaerobic processes
- C02F3/302—Nitrification and denitrification treatment
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2209/00—Controlling or monitoring parameters in water treatment
- C02F2209/04—Oxidation reduction potential [ORP]
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2209/00—Controlling or monitoring parameters in water treatment
- C02F2209/06—Controlling or monitoring parameters in water treatment pH
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2209/00—Controlling or monitoring parameters in water treatment
- C02F2209/22—O2
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W10/00—Technologies for wastewater treatment
- Y02W10/10—Biological treatment of water, waste water, or sewage
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Biodiversity & Conservation Biology (AREA)
- Microbiology (AREA)
- Hydrology & Water Resources (AREA)
- Engineering & Computer Science (AREA)
- Environmental & Geological Engineering (AREA)
- Water Supply & Treatment (AREA)
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Health & Medical Sciences (AREA)
- Molecular Biology (AREA)
- Purification Treatments By Anaerobic Or Anaerobic And Aerobic Bacteria Or Animals (AREA)
- Activated Sludge Processes (AREA)
- Biological Treatment Of Waste Water (AREA)
Abstract
Abstract:
Process for biologically purifying waste waters The invention relates to a continuous process by which waste water containing low to high concentrations of organic constituents and total nitrogen is biologically purified to such an extent that the organic constituents are minimized, the content of total nitrogen is completely nitrified, if it exceeds the assimilation demand, and the nitrate formed is reduced.
In this process, the expenditure on the oxygen introduction and the expenditure on the denitrification are minimized. The amount of excess sludge is extremely small.
Process for biologically purifying waste waters The invention relates to a continuous process by which waste water containing low to high concentrations of organic constituents and total nitrogen is biologically purified to such an extent that the organic constituents are minimized, the content of total nitrogen is completely nitrified, if it exceeds the assimilation demand, and the nitrate formed is reduced.
In this process, the expenditure on the oxygen introduction and the expenditure on the denitrification are minimized. The amount of excess sludge is extremely small.
Description
2~2~
_rocess for bioLocTi~ally purif~in~l waste waters rrhe invention rela~es to a continuous ~rocess by which waste waters cont~ining low to high concen-trations oE organic constituents and total nitro~en (definition as given in the German standard method for the examination of water, was-te water and sludge H 12) are biolo~ically purified -to such an extent that: the said organic constituents are minimized, the saicl content of total nitrogen is completely nitrified if it exceeds the assimilation demand, and the nitrate formed is reduced.
In this process, the expenditure on the oxygen introduction, the expenditure on the denitrification and the quantity of excess sludge are minimiz~d.
It i.s known that, when waste water is treated in an upstream denitrification stage, substantial propor-tions of the oxygen which serves to oxidize the nitrogen compounds can be recovered by feeding back activated sludge from the settling basin of the activated sludge plant and/or by feeding back a wast:e water flow from the nitrification basin ~1] [2] [3] [4l.
It is furthermore known that the load of organic constltuents flowing into the 1st stage is reduced b~
said denitrification and that a low BOD5 sludge loading is necessary for a nitrification ~1].
It is furthermore known that a complete danitri fication of the water fed to the 1st stage is only possible if the COD feed/NO3-nitrogen feedback ratio corresponding to the stoichiometry is 4 kg/kg or higher .
[2J. In ~he ca~e of industrial waste waters, in parti-cular, the ra-tio of organic load an~ total nitrogen is, ho~ever, often subject to large variati.ons. If, during these varia~.ions, the COD fee~/NO3-nitrogen feedback ratio exceeds the abovementi.oned amount of 4 kg/kg, the excess COD has to be degraded in the nitrifica-tion s-tage.
Surprisingl.y, it has now been found that it is possible to achieve both a complete denitrification and also a s~bstantial biological degradation of -the excess organic constituents by a controlled aeration of the first (denitrification) stage.
The invention accordingly relates to a process for biologically purifying waste waters containing low to high concentrations of organic constituents and total nitrogen in which the waste water to be purified i9 aerated or exposed to oxygen in two stages, a partial flow of the waste water/activated sludge mixture draining from the second stage being fed back to the first stage, and the waste water/activated sludge mixture draining from.the second biological reactor being separated in a settling tank, the settled activated sludge being fed to the first stage and the purified waste water being removed, which process- is characterized in that a preselected redox potential is not exceeded while the first stage is aerated or exposed to oxygen.
Preferably, the aeration or oxygen supply in the first stage is regulated by means of the redox potential.
In doing so, a redox potential Eh (pH7) below ~100 mV, ~ 3 ~ 2~
prefer~bly in the r~nge from 0 to 50 Illv~ Ls preferably m~lntainecl.
Prefera!)ly, during -the aeration or exposure of the second s-tage to oxygen, a specified range of values is maintained for ~he oxyge~ content, in particular the range from 0.5 to lO mg/l, preferably 2 to 4 mg/l.
It is advantageous to regulate the aeration or oxygen supply in the second stage by means of the measured oxygen content.
Denitrification in the presence of atmospheric oxygen is, according to earlier opinion, not possiblè [1]
_rocess for bioLocTi~ally purif~in~l waste waters rrhe invention rela~es to a continuous ~rocess by which waste waters cont~ining low to high concen-trations oE organic constituents and total nitro~en (definition as given in the German standard method for the examination of water, was-te water and sludge H 12) are biolo~ically purified -to such an extent that: the said organic constituents are minimized, the saicl content of total nitrogen is completely nitrified if it exceeds the assimilation demand, and the nitrate formed is reduced.
In this process, the expenditure on the oxygen introduction, the expenditure on the denitrification and the quantity of excess sludge are minimiz~d.
It i.s known that, when waste water is treated in an upstream denitrification stage, substantial propor-tions of the oxygen which serves to oxidize the nitrogen compounds can be recovered by feeding back activated sludge from the settling basin of the activated sludge plant and/or by feeding back a wast:e water flow from the nitrification basin ~1] [2] [3] [4l.
It is furthermore known that the load of organic constltuents flowing into the 1st stage is reduced b~
said denitrification and that a low BOD5 sludge loading is necessary for a nitrification ~1].
It is furthermore known that a complete danitri fication of the water fed to the 1st stage is only possible if the COD feed/NO3-nitrogen feedback ratio corresponding to the stoichiometry is 4 kg/kg or higher .
[2J. In ~he ca~e of industrial waste waters, in parti-cular, the ra-tio of organic load an~ total nitrogen is, ho~ever, often subject to large variati.ons. If, during these varia~.ions, the COD fee~/NO3-nitrogen feedback ratio exceeds the abovementi.oned amount of 4 kg/kg, the excess COD has to be degraded in the nitrifica-tion s-tage.
Surprisingl.y, it has now been found that it is possible to achieve both a complete denitrification and also a s~bstantial biological degradation of -the excess organic constituents by a controlled aeration of the first (denitrification) stage.
The invention accordingly relates to a process for biologically purifying waste waters containing low to high concentrations of organic constituents and total nitrogen in which the waste water to be purified i9 aerated or exposed to oxygen in two stages, a partial flow of the waste water/activated sludge mixture draining from the second stage being fed back to the first stage, and the waste water/activated sludge mixture draining from.the second biological reactor being separated in a settling tank, the settled activated sludge being fed to the first stage and the purified waste water being removed, which process- is characterized in that a preselected redox potential is not exceeded while the first stage is aerated or exposed to oxygen.
Preferably, the aeration or oxygen supply in the first stage is regulated by means of the redox potential.
In doing so, a redox potential Eh (pH7) below ~100 mV, ~ 3 ~ 2~
prefer~bly in the r~nge from 0 to 50 Illv~ Ls preferably m~lntainecl.
Prefera!)ly, during -the aeration or exposure of the second s-tage to oxygen, a specified range of values is maintained for ~he oxyge~ content, in particular the range from 0.5 to lO mg/l, preferably 2 to 4 mg/l.
It is advantageous to regulate the aeration or oxygen supply in the second stage by means of the measured oxygen content.
Denitrification in the presence of atmospheric oxygen is, according to earlier opinion, not possiblè [1]
[3] [4]. In other publications, reference is made to a possible denitrification with air being supplied [5] [6], but no defined conditions are specified for conducting the process. In addition, a warning is given against an accumulation of nitrite [6] ~7] [8].
Surprisingly, it was found that denitrification in an industrially applicable degxadation process with simultaneous gasiication with air or oxygen is possible under certain conditions without a harmful accumulat.ion of nitrite occur~ing.
In summary, the process according to the inven-~ion offers the following advantages:
1. In addition to reducing the organic load by denitrify-ing the nitrogen compounds, such a large proportion of the organic load is oxidized ~y the oxygen introduced that the organic loading of the second stage is minimized.
~ ~ 3 ~
2. With a l?reselt~cted low redox potential, the oxygen transfe~ in the Eirst s~ge is appreciably higher than in the c~lse of a full aero~ic aeration. Depending on the height of the water col~n, the o~ygen u-tili~ation rnav amount to up to 90~. As a result, substantial proportions of the organic constituents are oxidized with lcwer aeration cos-ts than in the ca~e of the standard process. The design of ~he aeration in ths second stage consequently depends mainly on the oxygen demand for the nitrification.
3. The volume of the nitri~ication basin (first stage) can be min~mized; it should be designed above all in accordance with the data of the expected loading of the biomass with the total nitrogen to be oxidized.
Surprisingly, it was found that denitrification in an industrially applicable degxadation process with simultaneous gasiication with air or oxygen is possible under certain conditions without a harmful accumulat.ion of nitrite occur~ing.
In summary, the process according to the inven-~ion offers the following advantages:
1. In addition to reducing the organic load by denitrify-ing the nitrogen compounds, such a large proportion of the organic load is oxidized ~y the oxygen introduced that the organic loading of the second stage is minimized.
~ ~ 3 ~
2. With a l?reselt~cted low redox potential, the oxygen transfe~ in the Eirst s~ge is appreciably higher than in the c~lse of a full aero~ic aeration. Depending on the height of the water col~n, the o~ygen u-tili~ation rnav amount to up to 90~. As a result, substantial proportions of the organic constituents are oxidized with lcwer aeration cos-ts than in the ca~e of the standard process. The design of ~he aeration in ths second stage consequently depends mainly on the oxygen demand for the nitrification.
3. The volume of the nitri~ication basin (first stage) can be min~mized; it should be designed above all in accordance with the data of the expected loading of the biomass with the total nitrogen to be oxidized.
4. The formation of excess sludge is low (it is less than 0.2 kg of dried solid matter/kg of COD degraded) since the sludge loading in the nitrification basin (second stage) is low.
In addition, the process is also applicable and effective in the case of waste waters which contain such low levels of nitrogen compounds that the physiological demand of the bacteria has to be covered by adding nitrogen compounds.
The mode of operation and the advantages, achieved in detail, of the process according to the invention are explained in greater datail below.
The waste water to be purified, the waste wateri activated sludge mixture from the second stage 2~3~
(bioloqical re~ctor 2) and the settle~ activated sludge from the settlir-~ t~nk are fed to the fLrst stage (biolocJical reactor 1, equipped with a ~evice for mixing, an aeration device and a devlce for measuring the redox potential) and all the components are mixad well. In this process, the organic constituents of the waste water are absorbed by the organisms of the activated sludge and reacted with -the o~ygen of the nitrate to form carbon dioxide and hydrogen. The redox potential established depends on the ratio of the nitrate oxygen originating from the waste water/activated sludge mixture fed back from the 2nd stage to the COD content (chemical oxygen demand as an expression of the concentration of the organic constituents) in the feed water. If the COD feed exceeds the supply of nitrate oxygen, the redox potential drops below the specified value. In the preferred embodiment of the process according to the invention with regulation of oxygen introduction by means of the redox potential, feeding of air andtor oxygen then starts. The components of organic load remaining after the oxidation by denitrification are now oxidized by the organisms in the activated sludge with the aid of free oxygen. At the same time, the redox potantial rises until the specified value for the redox potential is reached and consequently results again in a reduction in the air/oxygen feed.
The redox potential value to be maintained should be below Eh (pH) of ~100 mV, preferably in the range from 0 to 50 mV.
- 7 - ~3 concentr~ion is reduced further. In order to achieve complete nitrLfication, it is necessar~ for a minimum conten~ o~ oxygen, ~Jhich in the experiments wa5 3 mg 02/l, to be dissolved in the waste water. Below this concentration, the nitrification was not always complete.
The volumetric flows should be regulated as a function of the concen-tration of the waste water con-stituents so tha-t, in biological reactor 1, a volume loading of organic constituents expressed as COD does not substant.ially e~ceed a value of 15 kg COD/m3 d, but should preferably be in a range of 10 kg COD/m3.d in order to cope with variations in -the waste water concentration reliably. (If no complete nitrification or at least substantial nitxification is desired, it is possible, lS depending on the characteristics of the waste water, to set the COD volume loading o~ biological reactor 1 higher). No upper lLmit for the nitrogen volume loading in biological reactor 2 has so far been determined.
Volume loadings of up to 0.4 kg of total nitrogen/m3.d were completely nitrified.
The feedback o~ the activated sludge/water mlxture from biological reactor 2 to biological reactor 1 may vary within a wide range. It is expediently calcu-lated and so chosen that an operating cost optimum, which is dependent on the pumping ener~y to be delivered, on the one hand, and on the costs of the neutralizing agent and the costs of the reducing agent in biological reactor 3, on the othex hand, is achieved.
. . ~
I~ necess~ry, the proportion of nitrate which excee-.ls the possibility of denitrification in biological reactor l c~n additi.onally ~e reduced in a third stage (biological reactor 3) by adding biologically oxidizable S substance (for example methanol) as a function of the specified redox potential so that, in the event of the specified value of the redox potential being exceeded or fallen short of, the amount of the said substance supplied is reduced or increased respectively.
For this purpose, the biological reactor 3 is equipped with a device for mixing, a device for measuring the redox potential and a device for the metered addition of biologically oxidizable material for the purpose of denitrif.ication. This reactor should be safegu~rded against access of air.
This achieves the result that a) the purified waste water is free of nitrate and/or nitrite, b) problems in the settling basin due to denitrification processes which may result in partial flotation of the settled sludge due to the nitrogen bubbles formed are avoided.
In the subsequent settling basin, the activated sludge/waste water mixture is separated in the known way.
The puriied waste water drains of f, and the settled activated sludge is fed back to biological reactor 1.
The proportion of sludge fed back is calcula$ed in a known way as a function of the amount of wa~te water - 9 _ 6~3~2 (feedbdck/sludg~ ratio) fe~ in and of the settling behavior.
Particularly good results can be achLeved if the wast~ water is p~rtially pretreated aerohically as in EP
0,038,017. In that case, the waste water constituents are oxidatively reduced by approximatel~ 60% with the aid of dispe~se, nonflocculated bacteria using a minimum aera-tion reglllated by means of the redox potential. Some of the waste water constituents are converted into disperse bacteria. This portion leaves the system together with the treated waste water.
If this waste water pretreated in this way is then subjected to the process accordiny to the in~ention, both the disperse bacteria and also the dissol~red organic residues are minimized to such an extent that effic-iencies are achieved for the COD degradation of >80~ and for the BOD5 degradation of >90%, based on the process according to the invention.
Based on the entire process (partial aerobic pretreatment plus the process according to the inven-tion)~ the efficiencies of the COD degradation can be increased to >90~ and that of the BOD5 dPgradation to >95%.
With a synthetic waste water it was found tha~
the nitrification in biological reactor 2 was always complete up to a COD volume loading in biological reactor 1 of 17.5 g COD/l-d. The pH was between 7.5 and 8.3 and the temperature was 25C. At the same time, it was , - ] o ~ 2 '~ ~
possible to reduc~ the hydr~ullc retention time in biological reactor 1 -to one hour~ It was possible to increase the total nitrogen loading of hiological reactor 2 to 310 mg N/l d without the n;trificatlon being re-stricted. If -the said limit of the COD volume loading of biological reactor 1 of 17.5 g COD/l-d was exceeded, there was no lonc~er complete nitrification. Obviously it was adversely affected by a hi~her feed of organic constituents to biolo~ical reactor 2.
With othex waste waters, lower limits for the COD
vol~ne loading in the first stage were found as the li.mitation on complete nitrification.
It can therefo.re be assumed that the conditions for complete nitrification have to be redetermined for every application case of the process according to the invention.
On the okher hand, if complete nitri~ication is dispensed with and the COD reduction i5 limited to COD
volume loadings of up to 30 g COD/l-d in biological reactor 1, a substantially higher loading of the system was possible; in this case, the COD reduction of the entire system was >90~.
At the same time it was found that certain organic compounds cannot be biologically attacked at the low redox potentials in biological reactor 1 a~ned at in the process. These compounds include aromatic compounds (for exa~nple toluene, tetrahydrofuran) and chlorinated hydrocarbons (for example ethylene chloride, d ichloromethane) .
It was f~-und furtilermore that certaill metabolites wllich do not occur in a full aerobic process are produced at tlle low redo~ potentials aimed at in biolosical reactor ]. These compounds include ethene (C2H4) and c~rbon morloxide (CO). It is furthermore known from the literature that the nitrate reaction chain passes through -the stages NO3 ---> NO2 --' N2O --> N2.
It may be expected of these compounds (aromatics, chlorinated hydrocarbons, ethene, CO, N~O) that they are present in measurable concentrations in the exhaust gas of bioloyical reactor 1.
I'he exhaust gas of biological reactor 1 will therefore be advantageously fed to biological reactor 2 so that these constituents are dissolved in the aqueous phase of biological reactor 2, adsorbed by the biomass and oxidized biologically, in order to minim.ize the emissions of the process. That îs achieved by either adding the exhaust gas of biologic:al reactor 1 to the gasification air of biological reactor 2 or by introduc ing it in a separate gasifica~ion device into the aqueous phase of biological r~actor ~.
~xample (cf. Figure l) A waste water from the chemical-pharmaceutical industry, partially pretreated in accordance with EP
0,038,017 (cf. page 9), is fed to an apparatus comprising biological reactor 1 (1) having a capacity of 10 1 an~
equipped with a stirrer (5), a redox electrode (6) and an ~, 12 - 2~3~
~e~ation device (7).
A flow of ~aste water (8) having a COD concentra-t.ion of 1,000 mg/l to 2,500 mg/l, a BOD5 concentration of ~00 to 700 mg/l and a total nitrogen content of 120 mg/l to 200 mg~l is fed to said biological ~eactor 1 (1) in amo-lnts of 48 l/d.
A feedback flow (11) of waste water/activated sludge mixture of 30 l/d and also a mixture of settled activated sludge and waste water (9) from the settling tank (4) in an amount of 10 l/d is furth~rmore fed to the biological reactor 1 (l).
Air is fed to said biological reactor 1 (1) as a function of the redox potential in a manner such that a potential of Eh ~pH 7) = t20 mV ~ 10 mV is maintained (measurement with an electrode (supplied by Ingold, Pt 4805-60).
The waste water/activated sludge mixture (1) then flows into biological reactor 2 (2) which has a capacity of 36.8 l. The latter is equipped with a pH electrode (12), a metering addition device for neutralization agent (13), an o~ygen electrode (15) ancl an aeration device (16).
A.ir is fed to biological reactor 2 as a function of the measured oxygen content in a manner such that the concentration does not fall below 3 mg O2/l.
Neutralization agent is fed to biological reactor 2 as a function of the measured pH in a manner such that a pH of approximately 8.0 is not ~subs~.antially fallen .-- , . . .
short of ~r exceeded.
'i'he waste water/~ctivat:ed slu~ge mixture from biologicaL re~ctor 2 (17) is fed to the biological reactor 3 ~3) whlch has a cap~city of 5 l. The latter is equiyped with a stirrer (18), a redox electrode (19) and a metharlol adding device (20).
Methanol is added ~s a function of the redox potential so that a potential of Eh (pH 7) - -~60 mV is not exceeded and a potential of Eh (pH 7) = +40 mV is not fallen short of.
The waste water/activated sludge mixture from reactor 3 (21) then 10ws into a settling basin (4) which has a capacity of 33 1. Here the activated sludge separ-ates from the waste water and is fed as flow (9) to biological reactor l (1), as described above.
The purified water separated from the activated sludge in the settling tank (4) drains off (22).
The waste water flows are examined as follows:
The feed water (8) for COD, BOD5, total nitrogen and phosphate content.
The waste water/activated slud~e mixture (lO) from reactor 1 (1) to reactor 2 (2) for the COD of the settled sample and for the content of nitrite NO2-.
The waste water of the feed flow (17) to bio-logical reactor 3 for nitrite NO2 and nitrate NO3-.
The drainage water from the enti.re system (22) for COD, BQD5, ammonium ion NH4+, nitrate NO3 and nitrite NO-, ~
3 ~
The activated sludge content of the mixture inreactor 2 (2), in g DSM (ciry so:Lid matter)/l and the sediment volume in ml/l are dete~mined and the microscope pic-ture of the activated sludge are examined. The conten-t of dry solid mat-ter found is between 9 and 15 g/l, with a calcination residue of between 40 and 45%.
The was~e water leaves the biological reactor 1 (l) with COD values of between 230 and 470 mg/l. The nitrite NO2- value is always below 0~05 mg/l tlimit of detection).
The waste water drainlng from biological reactor 2 has a nitrate content of between 30 mg/l and 215 mg/l.
The waste water draining from the entire system has a COD value of between 170 and 330 mg/l and a BOD5 value of between <5 and 100 mg/l, the nitrite and nitrate content and also the ammonium content being below the limit of detection (<2 mg NH4 N/l~.
Consequently, a COD degradation of more than 80%, a BOD5 degradation of more than 90~, a nitrification of more ~han 99~ and a denitrification of >99% are demon-strated.
The production of excess sludge is degraded to below 0.1 g/g COD.
r~efererlc-e-s [1] ATV "Lehr- und Elalldbuch der Abwassertechnik" ("Text-book and Manual of W~te ~ater Engineering"), 3rd edition, Vol. IV (1985), Verlag Ernst & Sohn (pages 307 - 317) [2] A. E~ener et al. ~Pre-treatment scheme eases waste water biotreatment~-, Oil and Gas Journal (1987), (pages 40 - 43) [3] H.G. Schlegel "Allgemeine M.ikrobiologie" ("General Microbiology"~, 6th edition, G. Thieme Verlag, Stuttgart, New York (1985), (pages 302 - 306) [~] Yasushi K. et al. "Inhibition of Denitrification by Oxygen in Paracoccus denitrificans", J. Ferment.
Technol. Vol. 63 No. 5 (1985) (pages 437 - 442) [S] S. Christensen, J. Tiedge "Oxygen control prevents denitrif.iers and barley plant roots from directly competing for nitrate", FEMS microbiol. Ecoloyy 53 (1988) (pages 217 221) [6] J. Meiberg et al. "Effect of Dissolved Oxygen Tension on the Metabolism of Methylated Amines in Hypomicrobium X in the Absence and Presence o~
- 16 - ~3~2~
Nitrate: Evidence for Aerobic Denitrification~, J. General Microbiol. Vol. 120 (1980) (pages 453 - 463) [7] M. Samuelsson et al. "Hea-t Production by the De-nitrifying Bacterium Psendomonas fluorescens and the Dissimilatory Ammonium-Producing Bacterium Pseudo-monas putrefaciens during Anaerobic Growth with Nitrate as Electron Acceptor", Appl. Environm.
Microbiol. Vol. 54 (1988), tpages 2220 - 2225) [8~ D. Hernandes, J. Rowe "Oxygen Regulation of Nitrate Uptake in Denitrifying Pseudomonas aeruginosa".
Appl. Environm. Microbiol. Vol. 53 (1987) ~pages 745 - 750) ,.,., . ., -. .-ç-;~ . $
In addition, the process is also applicable and effective in the case of waste waters which contain such low levels of nitrogen compounds that the physiological demand of the bacteria has to be covered by adding nitrogen compounds.
The mode of operation and the advantages, achieved in detail, of the process according to the invention are explained in greater datail below.
The waste water to be purified, the waste wateri activated sludge mixture from the second stage 2~3~
(bioloqical re~ctor 2) and the settle~ activated sludge from the settlir-~ t~nk are fed to the fLrst stage (biolocJical reactor 1, equipped with a ~evice for mixing, an aeration device and a devlce for measuring the redox potential) and all the components are mixad well. In this process, the organic constituents of the waste water are absorbed by the organisms of the activated sludge and reacted with -the o~ygen of the nitrate to form carbon dioxide and hydrogen. The redox potential established depends on the ratio of the nitrate oxygen originating from the waste water/activated sludge mixture fed back from the 2nd stage to the COD content (chemical oxygen demand as an expression of the concentration of the organic constituents) in the feed water. If the COD feed exceeds the supply of nitrate oxygen, the redox potential drops below the specified value. In the preferred embodiment of the process according to the invention with regulation of oxygen introduction by means of the redox potential, feeding of air andtor oxygen then starts. The components of organic load remaining after the oxidation by denitrification are now oxidized by the organisms in the activated sludge with the aid of free oxygen. At the same time, the redox potantial rises until the specified value for the redox potential is reached and consequently results again in a reduction in the air/oxygen feed.
The redox potential value to be maintained should be below Eh (pH) of ~100 mV, preferably in the range from 0 to 50 mV.
- 7 - ~3 concentr~ion is reduced further. In order to achieve complete nitrLfication, it is necessar~ for a minimum conten~ o~ oxygen, ~Jhich in the experiments wa5 3 mg 02/l, to be dissolved in the waste water. Below this concentration, the nitrification was not always complete.
The volumetric flows should be regulated as a function of the concen-tration of the waste water con-stituents so tha-t, in biological reactor 1, a volume loading of organic constituents expressed as COD does not substant.ially e~ceed a value of 15 kg COD/m3 d, but should preferably be in a range of 10 kg COD/m3.d in order to cope with variations in -the waste water concentration reliably. (If no complete nitrification or at least substantial nitxification is desired, it is possible, lS depending on the characteristics of the waste water, to set the COD volume loading o~ biological reactor 1 higher). No upper lLmit for the nitrogen volume loading in biological reactor 2 has so far been determined.
Volume loadings of up to 0.4 kg of total nitrogen/m3.d were completely nitrified.
The feedback o~ the activated sludge/water mlxture from biological reactor 2 to biological reactor 1 may vary within a wide range. It is expediently calcu-lated and so chosen that an operating cost optimum, which is dependent on the pumping ener~y to be delivered, on the one hand, and on the costs of the neutralizing agent and the costs of the reducing agent in biological reactor 3, on the othex hand, is achieved.
. . ~
I~ necess~ry, the proportion of nitrate which excee-.ls the possibility of denitrification in biological reactor l c~n additi.onally ~e reduced in a third stage (biological reactor 3) by adding biologically oxidizable S substance (for example methanol) as a function of the specified redox potential so that, in the event of the specified value of the redox potential being exceeded or fallen short of, the amount of the said substance supplied is reduced or increased respectively.
For this purpose, the biological reactor 3 is equipped with a device for mixing, a device for measuring the redox potential and a device for the metered addition of biologically oxidizable material for the purpose of denitrif.ication. This reactor should be safegu~rded against access of air.
This achieves the result that a) the purified waste water is free of nitrate and/or nitrite, b) problems in the settling basin due to denitrification processes which may result in partial flotation of the settled sludge due to the nitrogen bubbles formed are avoided.
In the subsequent settling basin, the activated sludge/waste water mixture is separated in the known way.
The puriied waste water drains of f, and the settled activated sludge is fed back to biological reactor 1.
The proportion of sludge fed back is calcula$ed in a known way as a function of the amount of wa~te water - 9 _ 6~3~2 (feedbdck/sludg~ ratio) fe~ in and of the settling behavior.
Particularly good results can be achLeved if the wast~ water is p~rtially pretreated aerohically as in EP
0,038,017. In that case, the waste water constituents are oxidatively reduced by approximatel~ 60% with the aid of dispe~se, nonflocculated bacteria using a minimum aera-tion reglllated by means of the redox potential. Some of the waste water constituents are converted into disperse bacteria. This portion leaves the system together with the treated waste water.
If this waste water pretreated in this way is then subjected to the process accordiny to the in~ention, both the disperse bacteria and also the dissol~red organic residues are minimized to such an extent that effic-iencies are achieved for the COD degradation of >80~ and for the BOD5 degradation of >90%, based on the process according to the invention.
Based on the entire process (partial aerobic pretreatment plus the process according to the inven-tion)~ the efficiencies of the COD degradation can be increased to >90~ and that of the BOD5 dPgradation to >95%.
With a synthetic waste water it was found tha~
the nitrification in biological reactor 2 was always complete up to a COD volume loading in biological reactor 1 of 17.5 g COD/l-d. The pH was between 7.5 and 8.3 and the temperature was 25C. At the same time, it was , - ] o ~ 2 '~ ~
possible to reduc~ the hydr~ullc retention time in biological reactor 1 -to one hour~ It was possible to increase the total nitrogen loading of hiological reactor 2 to 310 mg N/l d without the n;trificatlon being re-stricted. If -the said limit of the COD volume loading of biological reactor 1 of 17.5 g COD/l-d was exceeded, there was no lonc~er complete nitrification. Obviously it was adversely affected by a hi~her feed of organic constituents to biolo~ical reactor 2.
With othex waste waters, lower limits for the COD
vol~ne loading in the first stage were found as the li.mitation on complete nitrification.
It can therefo.re be assumed that the conditions for complete nitrification have to be redetermined for every application case of the process according to the invention.
On the okher hand, if complete nitri~ication is dispensed with and the COD reduction i5 limited to COD
volume loadings of up to 30 g COD/l-d in biological reactor 1, a substantially higher loading of the system was possible; in this case, the COD reduction of the entire system was >90~.
At the same time it was found that certain organic compounds cannot be biologically attacked at the low redox potentials in biological reactor 1 a~ned at in the process. These compounds include aromatic compounds (for exa~nple toluene, tetrahydrofuran) and chlorinated hydrocarbons (for example ethylene chloride, d ichloromethane) .
It was f~-und furtilermore that certaill metabolites wllich do not occur in a full aerobic process are produced at tlle low redo~ potentials aimed at in biolosical reactor ]. These compounds include ethene (C2H4) and c~rbon morloxide (CO). It is furthermore known from the literature that the nitrate reaction chain passes through -the stages NO3 ---> NO2 --' N2O --> N2.
It may be expected of these compounds (aromatics, chlorinated hydrocarbons, ethene, CO, N~O) that they are present in measurable concentrations in the exhaust gas of bioloyical reactor 1.
I'he exhaust gas of biological reactor 1 will therefore be advantageously fed to biological reactor 2 so that these constituents are dissolved in the aqueous phase of biological reactor 2, adsorbed by the biomass and oxidized biologically, in order to minim.ize the emissions of the process. That îs achieved by either adding the exhaust gas of biologic:al reactor 1 to the gasification air of biological reactor 2 or by introduc ing it in a separate gasifica~ion device into the aqueous phase of biological r~actor ~.
~xample (cf. Figure l) A waste water from the chemical-pharmaceutical industry, partially pretreated in accordance with EP
0,038,017 (cf. page 9), is fed to an apparatus comprising biological reactor 1 (1) having a capacity of 10 1 an~
equipped with a stirrer (5), a redox electrode (6) and an ~, 12 - 2~3~
~e~ation device (7).
A flow of ~aste water (8) having a COD concentra-t.ion of 1,000 mg/l to 2,500 mg/l, a BOD5 concentration of ~00 to 700 mg/l and a total nitrogen content of 120 mg/l to 200 mg~l is fed to said biological ~eactor 1 (1) in amo-lnts of 48 l/d.
A feedback flow (11) of waste water/activated sludge mixture of 30 l/d and also a mixture of settled activated sludge and waste water (9) from the settling tank (4) in an amount of 10 l/d is furth~rmore fed to the biological reactor 1 (l).
Air is fed to said biological reactor 1 (1) as a function of the redox potential in a manner such that a potential of Eh ~pH 7) = t20 mV ~ 10 mV is maintained (measurement with an electrode (supplied by Ingold, Pt 4805-60).
The waste water/activated sludge mixture (1) then flows into biological reactor 2 (2) which has a capacity of 36.8 l. The latter is equipped with a pH electrode (12), a metering addition device for neutralization agent (13), an o~ygen electrode (15) ancl an aeration device (16).
A.ir is fed to biological reactor 2 as a function of the measured oxygen content in a manner such that the concentration does not fall below 3 mg O2/l.
Neutralization agent is fed to biological reactor 2 as a function of the measured pH in a manner such that a pH of approximately 8.0 is not ~subs~.antially fallen .-- , . . .
short of ~r exceeded.
'i'he waste water/~ctivat:ed slu~ge mixture from biologicaL re~ctor 2 (17) is fed to the biological reactor 3 ~3) whlch has a cap~city of 5 l. The latter is equiyped with a stirrer (18), a redox electrode (19) and a metharlol adding device (20).
Methanol is added ~s a function of the redox potential so that a potential of Eh (pH 7) - -~60 mV is not exceeded and a potential of Eh (pH 7) = +40 mV is not fallen short of.
The waste water/activated sludge mixture from reactor 3 (21) then 10ws into a settling basin (4) which has a capacity of 33 1. Here the activated sludge separ-ates from the waste water and is fed as flow (9) to biological reactor l (1), as described above.
The purified water separated from the activated sludge in the settling tank (4) drains off (22).
The waste water flows are examined as follows:
The feed water (8) for COD, BOD5, total nitrogen and phosphate content.
The waste water/activated slud~e mixture (lO) from reactor 1 (1) to reactor 2 (2) for the COD of the settled sample and for the content of nitrite NO2-.
The waste water of the feed flow (17) to bio-logical reactor 3 for nitrite NO2 and nitrate NO3-.
The drainage water from the enti.re system (22) for COD, BQD5, ammonium ion NH4+, nitrate NO3 and nitrite NO-, ~
3 ~
The activated sludge content of the mixture inreactor 2 (2), in g DSM (ciry so:Lid matter)/l and the sediment volume in ml/l are dete~mined and the microscope pic-ture of the activated sludge are examined. The conten-t of dry solid mat-ter found is between 9 and 15 g/l, with a calcination residue of between 40 and 45%.
The was~e water leaves the biological reactor 1 (l) with COD values of between 230 and 470 mg/l. The nitrite NO2- value is always below 0~05 mg/l tlimit of detection).
The waste water drainlng from biological reactor 2 has a nitrate content of between 30 mg/l and 215 mg/l.
The waste water draining from the entire system has a COD value of between 170 and 330 mg/l and a BOD5 value of between <5 and 100 mg/l, the nitrite and nitrate content and also the ammonium content being below the limit of detection (<2 mg NH4 N/l~.
Consequently, a COD degradation of more than 80%, a BOD5 degradation of more than 90~, a nitrification of more ~han 99~ and a denitrification of >99% are demon-strated.
The production of excess sludge is degraded to below 0.1 g/g COD.
r~efererlc-e-s [1] ATV "Lehr- und Elalldbuch der Abwassertechnik" ("Text-book and Manual of W~te ~ater Engineering"), 3rd edition, Vol. IV (1985), Verlag Ernst & Sohn (pages 307 - 317) [2] A. E~ener et al. ~Pre-treatment scheme eases waste water biotreatment~-, Oil and Gas Journal (1987), (pages 40 - 43) [3] H.G. Schlegel "Allgemeine M.ikrobiologie" ("General Microbiology"~, 6th edition, G. Thieme Verlag, Stuttgart, New York (1985), (pages 302 - 306) [~] Yasushi K. et al. "Inhibition of Denitrification by Oxygen in Paracoccus denitrificans", J. Ferment.
Technol. Vol. 63 No. 5 (1985) (pages 437 - 442) [S] S. Christensen, J. Tiedge "Oxygen control prevents denitrif.iers and barley plant roots from directly competing for nitrate", FEMS microbiol. Ecoloyy 53 (1988) (pages 217 221) [6] J. Meiberg et al. "Effect of Dissolved Oxygen Tension on the Metabolism of Methylated Amines in Hypomicrobium X in the Absence and Presence o~
- 16 - ~3~2~
Nitrate: Evidence for Aerobic Denitrification~, J. General Microbiol. Vol. 120 (1980) (pages 453 - 463) [7] M. Samuelsson et al. "Hea-t Production by the De-nitrifying Bacterium Psendomonas fluorescens and the Dissimilatory Ammonium-Producing Bacterium Pseudo-monas putrefaciens during Anaerobic Growth with Nitrate as Electron Acceptor", Appl. Environm.
Microbiol. Vol. 54 (1988), tpages 2220 - 2225) [8~ D. Hernandes, J. Rowe "Oxygen Regulation of Nitrate Uptake in Denitrifying Pseudomonas aeruginosa".
Appl. Environm. Microbiol. Vol. 53 (1987) ~pages 745 - 750) ,.,., . ., -. .-ç-;~ . $
Claims (6)
1. Process for biologically purifying waste waters containing low to high concentrations of organic constituents and total nitrogen, in which the waste water to be purified is aerated or exposed to oxygen in two stages, a partial flow of the waste water activated sludge mixture draining from the second stage being fed back to the first stage, and the waste water/activated sludge mixture draining from the second stage being separated in a settling tank, the settled activated sludge being fed to the first stage and the purified waste water being removed, characterized in that a preselected redox potential is not exceeded while the first stage is aerated or exposed to oxygen.
2. Process according to claim 1, characterized in that the aeration or oxygen supply in the first stage is regulated by means of the redox potential.
3. Process according to claim 1 or 2, characterized in that a redox potential Eh (pH 7) of below +100 mV, preferably in the range from 0 to 50 mV, is maintained.
4. Process according to one or more of claims 1 - 3, characterized in that during the aeration or exposure of the second stage to oxygen, a specified range of values is maintained for the oxygen content.
5. Process according to claim 4, characterized in that an oxygen content in the range from 0.5 to 10 mg/l, preferably 2 to 4 mg/1, is maintained.
6. Process according to claim 4 or 5, characterized in that the aeration or oxygen supply in the second stage is regulated by means of the measured oxygen content.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP4004476.9 | 1990-02-14 | ||
| DE4004476A DE4004476C2 (en) | 1990-02-14 | 1990-02-14 | Process for the biological treatment of waste water |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2036245A1 true CA2036245A1 (en) | 1991-08-15 |
Family
ID=6400084
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002036245A Abandoned CA2036245A1 (en) | 1990-02-14 | 1991-02-13 | Process for biologically purifying waste waters |
Country Status (7)
| Country | Link |
|---|---|
| EP (1) | EP0442337B1 (en) |
| JP (1) | JPH04219199A (en) |
| AT (1) | ATE87888T1 (en) |
| CA (1) | CA2036245A1 (en) |
| DE (2) | DE4004476C2 (en) |
| DK (1) | DK0442337T3 (en) |
| ES (1) | ES2041188T3 (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4237387C2 (en) * | 1992-11-05 | 1997-04-30 | Braeutigam Hans Juergen Dr Ing | Method and device for separate biological nitrogen elimination from cloudy water |
| DE4430077C2 (en) * | 1994-08-25 | 1997-04-10 | Aqua Medic Anlagenbau Gmbh | Method and device for regulating and improving water quality |
| FR2753191B1 (en) * | 1996-09-10 | 1998-11-06 | Degremont | PROCESS FOR PURIFYING CARBON POLLUTION AND DENITRIFICATION IN AN OXYGEN MEDIUM OF WASTEWATER |
| DE19716939C2 (en) * | 1997-04-23 | 2002-06-27 | Bernd Diering | Process and wastewater treatment plant for the biological treatment of dye-containing wastewater from the textile and leather industry |
| ES2142738B1 (en) * | 1997-12-05 | 2000-12-01 | Depuracion Biolog Y Bacteriolo | INSTALLATION FOR THE PURIFICATION DEPURATION. |
| AT410439B (en) * | 2001-03-02 | 2003-04-25 | Matsche Norbert Dipl Ing Dr | Method for clarifying waste water containing easily degradable components comprises mixing it with slurry produced by treating municipal waste water in aeration basins and secondary settling basins |
| JP5233498B2 (en) * | 2008-08-19 | 2013-07-10 | 栗田工業株式会社 | Biological treatment method and apparatus for water containing organic matter |
| AU2011292811B2 (en) * | 2010-08-18 | 2014-07-03 | Veolia Water Solutions & Technologies Support | Method of treating municipal wastewater and producing biomass with biopolymer production potential |
| DE102020106761A1 (en) | 2020-03-12 | 2021-09-16 | Hochschule Für Technik Und Wirtschaft Des Saarlandes | Process for the treatment of water and water treatment plant |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3013881C2 (en) * | 1980-04-10 | 1982-08-12 | Schering Ag, 1000 Berlin Und 4619 Bergkamen | Process for controlling the treatment of industrial wastewater in equalization or storage basins |
| DE3543408A1 (en) * | 1985-12-07 | 1987-06-11 | Schreiber Berthold | Process for sewage purification using activated sludge |
| US4810386A (en) * | 1988-01-04 | 1989-03-07 | Zimpro/Passavant Inc. | Two-stage wastewater treatment |
-
1990
- 1990-02-14 DE DE4004476A patent/DE4004476C2/en not_active Expired - Fee Related
-
1991
- 1991-02-02 DE DE9191101416T patent/DE59100072D1/en not_active Expired - Fee Related
- 1991-02-02 DK DK91101416.5T patent/DK0442337T3/en active
- 1991-02-02 EP EP91101416A patent/EP0442337B1/en not_active Expired - Lifetime
- 1991-02-02 AT AT91101416T patent/ATE87888T1/en not_active IP Right Cessation
- 1991-02-02 ES ES199191101416T patent/ES2041188T3/en not_active Expired - Lifetime
- 1991-02-07 JP JP3016414A patent/JPH04219199A/en active Pending
- 1991-02-13 CA CA002036245A patent/CA2036245A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| ATE87888T1 (en) | 1993-04-15 |
| DE59100072D1 (en) | 1993-05-13 |
| EP0442337A1 (en) | 1991-08-21 |
| JPH04219199A (en) | 1992-08-10 |
| DE4004476C2 (en) | 1995-12-07 |
| ES2041188T3 (en) | 1993-11-01 |
| DK0442337T3 (en) | 1993-05-10 |
| DE4004476A1 (en) | 1991-08-22 |
| EP0442337B1 (en) | 1993-04-07 |
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