WO2006129132A1

WO2006129132A1 - Biological nitrogen removal from wastewater in a sbr reactor without nitrate production

Info

Publication number: WO2006129132A1
Application number: PCT/GR2005/000019
Authority: WO
Inventors: Gerasimos Lyberatos; Michail Kornaros; Apostolos Katsogiannis
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-05-31
Filing date: 2005-06-06
Publication date: 2006-12-07
Anticipated expiration: 2007-11-30
Also published as: GR20050100268A

Abstract

The present invention concerns a novel Sequencing Batch Reactor (SBR) for biological nitrogen removal from wastewaters. SBR systems are particularly flexible systems that ensure (through a succession of operating phases) nitrification, denitrification and sludge settling in a single tank. A suitably frequent switching between aerobic and anoxic operating conditions suppresses the growth of nitrite oxidizers and leads to an effective bypass of nitrate. The benefits that result from this mode of operation include the reduction in organic carbon requirements for denitrification, in aeration requirements (which implies energy savings) and in the amounts of generated sludge.

Description

BIOLOGICAL NITROGEN REMOVAL FROM WASTEWATER IN A SBR REACTOR WITHOUT NITRATE PRODUCTION

5 The present invention concerns a novel Sequencing Batch

Reactor (SBR) for nitrogen removal from wastewater. SBR systems are very flexible systems, that ensure (through the temporal succession of different operating stages) nitrification, denitrification and sludge settling, all in a single tank. The

10 important discovery that forms the basis of the present patent application is that the frequent enough switching between aerobic and anoxic conditions, suppresses the growth of nitratifying bacteria (the ones converting nitite to nitrate) and leads to nitrogen removal through the effective by-pass of

15 nitrates. This has significant advantages, such as:

• Reduction of the required concentration of organics for denitrification by up to 40%

• Higher denitrification rate up to 63%

» Reduction of the requirements for aeration by up to 25% 20 • Reduction of the generated sludge by up to 75%.

The most important feature is that this efficient nitrogen removal does not require uneconomical modifications and excursions in the physical and chemical wastewater 25 characteristics (such as temperature and pH), but only suitably modified aeration.

The developed technology may also be used for the development of suitably modified continuous-flow activated 30 sludge systems (by appropriate aerobic and anoxic staging).

The proposed process belongs to biological nitrogen removal systems, which is today considered the Best Available Technology. The system of by-passing nitrate generation, 35 followed by subsequent reduction to nitrogen gas, leads to significant savings in raw materials and required reactor volumes, while in parallel it reduces the generated sludge, the management of which is considered as a significant problem in modern wastewater treatment plants The proposed method of nitrate-bypassing is in essence the only acceptable means of bypassing, since the alternative technologies require addition of chemicals, and have as a prerequisite close monitoring and control of the process pH and dissolved oxygen while maintaining the reaction mixture at elevated temperatures is energy-consuming during the treatment of high-volume wastewaters, such as municipal wastewaters Finally it may be used for the retrofit of existing units, improving their performance significantly

The proposed technology may be used for a) the design of small as well as larger units for the treatment of municipal and industrial wastewater It is particularly recommended to apply the proposed technology in combination with the use of Sequencing Batch Reactors, (SBRS) Its advantages include the small capital and operating costs, the high flexibility in its operation and the ease of its handling This type of systems, in its conventional form is already used internationally for the removal of organics and nutrients (nitrogen and phosphorus) from municipal and industrial wastewaters b) the retrofit and the modification of existing biological wastewater treatment processes in order to reduce drastically the operating costs

Relevant technology to the present invention

The removal of nitrogen from wastewaters is a necessary wastewater purification step before disposal to natural water bodies Among the problems associated with the various nitrogen forms found in wastewaters (ammonia, nitrites, nitrates, organic nitrogen) we can mention toxicity to fish, eutrophication and reduction of dissolved oxygen concentration

Nitrogen removal used to be accomplished through physicochemical processes such as ammonia stripping, chlorination and ion-exchange In the recent years, however, biological nitrogen removal has been established as the most economical and environmentally friendly approach to nitrogen removal Nitrification , i e the sequential oxidation of ammonia to nitrites (NO₂ ) (notification) and nitrates (NO₃ ) (n it ratification) is the first stage of biological nutrient removal This conversion is mediated by the action of two bacterial groups, nitritifiers (e g Nitrosomonas) and nitratifiers (e g N.trobacter) N.tπt.fⁱers

Nitratifiers

Both are autotrophic organisms that use C02 as a carbon source Nitrification, however, is not adequate as a method of nitrogen removal, since the generated nitrates may not be ieleased to the sensitive water bodies Nitrate removal may also be carried out biologically through a process called denitπfication Many of the naturally occurring heterotrophic bacteria in the activated sludge may either use oxygen or NO₃ and/or NO₂ as terminal electron acceptors during their respiration By securing anoxic conditions, these bacteria reduce nitrate and nitrite generating nitrogen gas, which passes io the atmosphere due to its low solubility in water The overall reaction mauy be written as (if methanol is used a carbon source)

NO₃ + 1 08CH₃OH + H⁺ → O 065C₅H₇O₂N + O 47N₂ + O 76CO₂ + 2 44H₂O

This overall reaction is the sum of four sequential reaction steps Nθ₃→Nθ₂→NθT →N₂0t→N₂ t

The nitrogen that is generated by denitrification is released to the atmosphere The existing systems for biological nitrogen removal are all based on some form of switching between aerobic and anoxic conditions that allow nitrification and denitrification to take place sequentially, eventually converting nitrogen in its gaseous form From now on we will be referring to these systems as Conventional Biological Nitrogen Removal Systems (CBNR systems)

Since nitrites are an intermediate chemical form for boxh nitrification and denitrification, in the recent years there have been significant research efforts aiming at bypassing nitrate, i e Direct reduction of the generated nitrites to gaseous nitrogen Such a bypass would lead to β (Reduction of the required concentration of organies for denitrification by up to 40%

• Higher denitrification rate up to 63%

• Reduction of the requirements for aeration by up to 25% • Reduction of the generated sludge by up to 75%

(Turk and Mavinic, 1986, 1987, Abeling and Seyfπed 1992)

With obvious economic benefits, due to the reduction of both the capital (smaller tank size) and the operating costs

(cost for chemicals, electricity for aeration and treatment of the generated sludge) of the wastewater treatment plants

It becomes apparent that nitrate bypass during biological nitrogen removal requires the suppression of nitralifiers, such as Nitrobacter, something particularly difficult because of the close symbiotic relationship of such baceria with ammonia oxidizers To this end, several different alternatives have been considered, such as maintaining high free ammonia concentration (Abeling and Seyfπed, 1992), which has high p H as a prerequisite (Cecen and Gonenc, 1994), maintaining temperature above 25⁰C (Balmelle ef a/ , I992), maintaining low dissolved oxygen (DO) concentration (Cecen and Gonenc, 1994), delaying the transient from aerobic to anoxic conditions (Turk and Mavinic, 1986), maintaining presence of free hydroxylamine (FH) (Yang and Alleman, 1992), as weli as selective addition of chemical inhibitors of nitratifiers, such as NaCIO₃ These methods all generally require significant deviations from the conditions normally prevailing in a wastewater treatment environment, and are therefore very costly It should also be mentioned, that any method requires the eventual removal of nitrites, since their presence in the wastewater treatment effluent is also regulated

The important discovery made, which forms the basis for the current patent application, is that a sufficient frequent switching between aerobicandaoxic opeiating conditions suppresses the growth of nitratifiers and leads to an effective bypass of nitrates, without the limitations of the other methods and with all the previously mentioned advantage si" The proposed method requires no economically infeasiblemodifications in the physical and cherrucal characteristics of the wastewater, but only a modified aeration mode

The developed technology may also be used for the development of suitably modified effective continuous activated sludge systems (through the frequent interchange of aerobic and anoxic regions)

Announcement of the invention:

Laboratory experiments in an SBR

SBR operation (Sequencing Batch Reactor) is periodic The wastewater to be treated is fed in a given feeding time to the reactor, undergoes various treatments in a single tank, in a succession of discrete time periods and is removed periodically It is therefore apparent that the SBR accomplishes in time what a continuous-flow activated sludge process accomplishes in space. Its operation is divided into five discrete temporal stages: the fill phase, the react phase (for organics and nutrient removal), the settle phase (aiming at separation of biosolids from the treated wastewater), the draw phase (aiming at collection of treated wastewater), and the idle phase (preparation of the reactor for the next cycle).

Previous research led us to the assumption that multiple switching between aerobic and anoxic conditions, and reduced duration of the aerobic phase may lead to suppression of nitrate production. We selected, therefore, a six-hour cycle for the SBR, which included three aeobic/anoxic phase pairs. The duration of the aerobic and anoxic phases were 20 and 60 m i n , respectively. The duration of the fill phase, the final aerobic reaction phase, the sludge settling phase and the idle phase were 30, 15, 60 and 15 min, respectively. Synthetic wastewater was used for these experiments (Tables 1 and 2), while no excess sludge was wasted during the idle phase.

Table 1. Synthetic Wastewater Composition.

Compound Concentration

CH₃COONa 3H₂O 0.85 g/l

(NH₄)₂SO₄ 0.235 g/l

MgSO₄ 7H₂O 0.2 g/l

CaCI₂ 2H₂O 0.026 g/l

K₂HPO₄ 5 g/l

KH₂PO₄ 3 g/l

NaHCO₃ 0.7 g/l

Trace elements 0.1 ml/I

Table 2. Trace element solution composition.

Compound Concentration

CuSO₄ 5H₂O 0.786 g/l FeSO₄ 7H₂O 5 g/ι

NaMoO₄ 2H₂O 12.609 g/ι

NiCI₂ 6H₂O 4.05 g/ι

ZnSO₄ 7H₂O 4.398 g/ι

CoCI₂ 6H₂O 2.453 g/l

Kl 0.75 g/ι

H₃BO₃ 3 g/ι

Mn Cl₂ 4H₂O 5 g/ι

EDTA 5 g/ι

The reactor was originally loaded with activated sludge.

During startup, feeding was carried out on a daily basis with sodium acetate and ammonium sulfate, corresponding to final concentration of 150 mg/l organic carbon and 50 mg/l nitrogen in the form of ammonia. Supernatant liquid was removed following sludge settling and the reactor was replenished with feed medium buffered at pH 7.0. The rector was periodically aerated for 15 min and allowed to become anoxic for 45 min, respectively.

Description of Figures

Figure 1 presents graphically the various SBR phases. Figure 2 presents the variation of the concentrations of ammonia-nitrogen in the beginning and the various nitrogen forms (ammonia, nitrite, nitrate) at the end of each aerobic phase.

Figure 3 presents effluent concentrations for ammonia, nitrite and nitrate nitrogen for the three aerobic/anoxic couples operating strategy.

Figure 4 presents ammonia nitrogen, nitrite nitrogen and dissolved oxygen concentration profiles during an operating cycle for the three aerobic/anoxic couples operating strategy.

Figure 5 presents the temporal variation (transient) of the concentrations of ammonia-nitrogen in the beginning and the various nitrogen forms (ammonia, nitrite, nitrate) at the end of each aerobic phase, during the reactor operation, following its inoculation (spiking) with nitratifiers

Figure 6 presents the transient in the overall nitrite, nitrate and oxidized nitrogen amounts in all aerobic phases, following its spiking with nitratifiers

Figure 7 presents the variation in ammonia, nitrite and nitrate nitrogen in the effluent, during reactor operation, following its spiking with nitratifiers

Figure 8 presents ammonia, nitrite and nitrate nitrogen profiles during an operating cycle, in the first and last reactor operating period, following its spiking with nitratifiers

Figure 9 presents concentration profiles tor (a) ammonia nitrogen, and (b) nitrite nitrogen for two SBR experiments with different C N ratios (C N 3 1 and 1 5 1) Figure 10 presents concentration profiles for (a) ammonia nitrogen and dissolved oxygen, and (b) nitrite nitrogen for two SBR experiments with C N 3 1, but with different carbon source (glucose and acetate)

Detailed presentation of the invention

SBR operation (Sequencing Batch Reactor) is periodic The wastewater to be treated is fed in a given feeding time to the reactor, undergoes various treatments in a single tank, in a succession of discrete time periods and is removed periodically It is therefore apparent that the SBR accomplishes in time what a continuous-flow activated sludge process accomplishes in space Its operation is divided into five discrete temporal stages the fill phase, the read phase (for organics and nutrient removal), the settle phase (aiming at separation of biosolids from the treated wastewater), the draw phase (aiming at collection of treated wastewater), and the idle phase (preparation of the reactor for the next cycle)

Figure 1 presents graphically the various SBR phases according to the multiple aerobic/anoxic reaction phase couples The SBR was operated in a 6-h cycle for approximately three months Figure 2 presents the variation of the concentrations of ammonia-nitrogen in the beginning and the various nitrogen forms (ammonia, nitrite, nitrate) at the end of each aerobic phase, during the last 50 d of reactoi operation It is obvious that nitrate nitrogen never surpassed 0 5 mg/l, throughout this operation On the contrary nitrite nitrogen was the only oxidized nitrogen form at the end of every aerobic reaction phase In addition, in every anoxic phase, nitrite reduction is complete It is also notable, thai no organic carbon accumulation was observed during the fill phase throughout the operating period

The concentrations of the various nitrogen forrrib at the system effluent (their variation is given in Fig 3) are vfiy low Ammonia nitrogen is kept below 1 mg/l on the average and is in essence equal to the total nitrogen, while nitrite and nitrate nitrogen concentrations are almost zero

Figure 4 presents typical ammonia nitrogen nitrite nitrogen and dissolved oxygen concentration profiles during an operating cycle for the three aerobic/anoxic couples operating strategy In all aerobic reaction phases (shaded regions in the figure) nitrate nitrogen concentrations was maintained below 0 2 mg/l, and therefore is not presented in the figure During the fill phase, there is no organic carbon accumulation, while ammonia nitrogen, on the contrary, reaches its maximum at the end of this phase In the first aerobic reaction phase, ammonia nitrogen is significantly reduced, accompanied by nitrite nitrogen generation In the sequel, when the first anoxic phase is imposed, there is a smaller ammonia nitrogen reduction and a sharp decrease in nitrite nitrogen, which is completely consumed at approximately the midpoint of this phase Analogous comments may be made regarding the two subsequent aerobic/anoxic couples During the ultimate aerobic phase, the concentration of ammonia nitrogen has been reduced to very low levels and no further change is observed in this phase There is a sequential increase in the attained dissolved oxygen concentration as one moves from the first to the second, and then to the third aerobic phase. This fact reflects the reduced biological demand for oxygen Thus, in the ultimate aerobic phase, when practically no further biological activity takes place, the dissolved oxygen approaches saturation.

Spiking the reactor with Nitatifiers

The ability of the reactor to accomplish nitrogen removal via nitrites, was wattributed to the selected operating slrategy. It was thought that the small duration (20 moinutes) of the aerobic reaction phase in combination with the multiple switching between aerobic and anoxic conditions led to suppression of nitrate production during the aerobic phase. In order to prove the validity of this hypothesis, the reactor was spiked with nitrite oxidizers (nitratifiers). Thus, an enriched nitratifier culture was added to a percentage of 1% of the volatile solids in the reactor.

Figure 5 presents the temporal variation (transient) of the concentrations of ammonia-nitrogen in the beginning and the various nitrogen forms (ammonia, nitrite, nitrate) at the end of each aerobic phase, during the reactor operation, following its inoculation (spiking) with nitratifiers. It is apparent from this figure that the amount of nitrate produced in each cycle is progressively reduced to zero. This becomes more apparent in Fig.6 which presents the transient in the overall nitrite, nitrate and oxidized nitrogen amounts in all aerobic phases, following its spiking with nitratifiers. The corresponding nitrite nitrogen concentration and the sum of the two oxidized nitrogen forms (nitrite and nitrate) are also presented in the same Figure. It is therefore safely concluded that the overall nitrate nitrogen production progressively decreased, while the corresponding nitrite nitrogen concentration increased. In addition, since the sum of the two oxidized forms produced remained constant, the nitritifying capacity of the sludge was not affected On the contrary, the nitratifying capacity of the sludge was suppressed, and this suppression many be indeed attributed to the operating conditions of the reactor The reduction of nitrite and nitrate was complete during the anoxic reaction phases, throughout the experimentation period For this reason, no nitrites or nitrates are detected in the beginning of every phase in Fig 5

Therefore, as shown in Figure 7 the concentrations of ammonia, nitrite and nitrate nitrogen in the effluent remained low throughout the experimentation period Total nitrogen concentration (in essence ammonia nitrogen, as the other forms are negligible) in the reactor effluent was 0 88 ± 0 22 mg/l, while Volatile Solids concentration was 93 ± \A mg/l A more detailed presentation of the change in the reactor performance in the transient, is shown in Figure 8 This Figure gives the profiles from two operating cycles during the first and last day of experimentation following spiking with nitratifiers While the reactor performance is excellent in both cases (above 95%), there is a substantial qualitative difference in the two cycles In the first day, nitrate nitrogen was produced in every aerobic reaction phase, while in the last day its concentration did not surpass 0 5 mg/l (and is thereiore not shown in the Figure 8b)

Effect of C N ratio on nitrogen removal

In order to explore the influence of the ratio of carbon to nitrogen (C N), on nitrogen removal, two batch experiments were carried out In the first experiment, ammonia nitrogen concentration was increased from 50 mg/l to 100 mg/l, while the concentration of organic carbon was maintained at 150 mg/l (λόyoς C N = 1 5 1) This experiment tested in addition the ability of the reactor to handle higher ammonia nitrogen in the feed characteristics In the second experiment, in addition to increasing ammonia nitrogen, the concentration of organic carbon was also increased to 300 mg/l (ratio C N = 3 1) In every case, since ammonia nitrogen in the feed was doubled, the concentration of NaHCO₃ in the feed was also changed in proportion, so that nitrification may be not limite by alkalinity The results of these two experiments are given in Figure 9 The average VSS concentration was almost the same in the two experiments (8 70 g VSS/I for C N 1 5 1 and 8 85 g VSS/I for C N 3 1) In both cases, the nitrate nitrogen concentration was maintained at very low values (below 0 5 mg/l) throughout the operating cycle and is therefore not shown in the figure In addition, mo organic carbon accumulation was observed in either experiment during the reactor fill phase, despite the high organic carbon concentration in the feed in [he second case (300 mg/l) Upon comparison of the two experiments, it becomes apparent that higher nitrogen removal is accomplished in the case of C N 3 1, in which lower nitrite nitrogen concentrations in the reactor effluent is observed However, in the case of C N 1 5 1, in which in compaiison with the previous experiments only the concentration of ammonia nitrogen has been increased (from 50 to 100 mg/l), the reactor performance continues to be satisfactory (approximately 90%)

Influence of the organic carbon source on nitrogen removal

In order to explore the dependence of nitrogen removal on the carbon source, an additional experiment was carried out with elevated ammonia nitrogen concentration, but using glucose in place of acetate as a carbon source The C N ratio was again 3 1 Figure 10 presents the results from this experiment in comparison with the corresponding experiment with acetate as the source of carbon In this case, nitrate nitrogen was maintained very low as well (below 0 ^ mg/l) throughout the operating cycle, and for this reason is not shown in the figures Upon comparison of the two experiments, it is seen that nitrogen removal is higher when using acetate as a carbon source The difference is not attributed to the effluent ammonia nitrogen concentration (in both cases the values were comparable) as in the nitrite nitrogen concentration. When using glucose as a carbon source, nitrite nitrogen at the effluent was approximately 6.7 mg/l, while in the case of acetate it was 2.7 mg/l. Based on total nitrogen concentration, the reactor performance in the case of glucose was approximately 82%, while the corresponding performance for the case of acetate was 97%. From Figure 9b, which presents the profiles of nitrite nitrogen in each case, it becomes apparent that the reduced performance is attributed mainly to the lower denitritification rate in the case of glucose Nitrite nitrogen concentrations are not zeroed in any of the three anoxic cycle phase, contrary to the case of acetate, in which complete nitrite removal is effected within this phase.

Conclusions

SBR experiments were carried out with multiple aerobic/anoxic phases in order to study the removal of nitrogen through nitrite nitrogen, The reaction phase in the 6h operating strategy consisted of three aerobic/ anoxic couples (aerobic phase: 20 min Ken anoxic phase: 60 min). The reactor was operated for almost three moths under hese conditions, and the production of nitrate was suppressed. This way, the 50 mg/l of ammonia nitrogen fed to the reactor led only to production of nitrite, which was completely reduced in the subsequent anoxic reaction phases. It should be noted that no organic carbon (feed concentration of 150 mg/l as acetate) accumulaton in the fill phase. In a second experimental period, the reaclor was spiked with nitratifiers, so that the hypothesis of nitrate production suppression could be validated. In addition, experiments were carried out with different C:N ratios, i.e.1.5:1 καi 3:1 (organic carbon 150 και 300 mg/l in the feed and ammonia nitrogen 100 mg/l) and different carbon sources (replacement of acetate with glucose, both at organic carbon concentration of 300 mg/l) The main conclusions drawn from this work are

♦ Bypassing nitratification, and consequently denitralification as well, is feasible through the use of multiple aerobic/ anoxic reaction couples in an SBR

♦ Suppression of nitratification may be attributed to the operating conditions (multiple switching between aerobic and anoxic conditions) as well as the small duration of the aerobic phase (20 mm) An important issue in this direction is the effective mass transfer of oxygen to the reactor o The use of a 6h-cycle with three aerobic/anoxic reaction phase couples and a duration ratio of 1 3 leads to high nitrogen removal (98% ± 1 6%) through nitrites, for a synthetic wastewater with 150 rng/l organic carbon concentration (in the form of acetate) and 50 mg/l ammonia nitrogen

♦ Nitrogen removal is accomplished without the need for an external carbon source during the anoxic reaction phases, in order to accomplish denitrif ication

♦ The reactor, operated so, leads to high nitrogen removal (91 %) even for an ammonia nitrogen of 100 mg/l in the feed, without an increase in organic carbon (150 rng G/l, ratio C N 1 5 1) However, a higher removal percentage (97 %) may be accomplished when increasing the feed organic carbon concentration accordingly (300 mg C/l, ratio C N 3 1)

♦ Higher organic carbon concentrations in the feed (300 mg/l) seems to be associated with maintaining high denitritification rates in two of the three denilritification phases, compared with only one in the case of lower concentration (150 mg/l)

♦ The use of acetate as a carbon source leads to higher nitrogen removal in comparison with glucose (82%), for both the same ratio C N 3 1 (97%) as well as The smaller ratio

C N 1 5 1 (91%) REFERENCES

Abel ing U. and Seyfried CF. (1992). Anaerobic -aerobic treatment of high-strength ammonia wastewater - nitrogen removal via nitrite. Wat. Sci. Tech. 26 (5-6), 1007-1015. Balmelle B., Nguyen M., Capdeville B., Cornier J. C. and Deguin A. (1992). Study of factors controlling nitrite build-up in biological processes for water nitrification. Wat. Sci. Tech. 26 (5-6), 1017-1025.

Cecen F. and Gonenc I.E. (1994) Nitrogen removal characteristics of nitrification and denitrification filters. Wat. Sci. Tech. 29 (10-11), 409-416.

Turk O. and Mavinic D. S. (1986) Preliminary assessment of a shortcut in nitrogen removal from wastewater. Can. J. Civ.

Eng. 13, 600-605.

Turk O. and Mavinic D. S. (1987) Selective inhibition: a novel concept for removing nitrogen from highly nitrogenous wastes. Environ. Technol. Lett. 8, 419-426. Yang L. and Alleman J. E. (1992) Investigation of batch-wise nitrite build-up by an enriched nitrification culture. Wat. Sci. Tech. 26 (5-6), 997-1005.

Claims

1. A reactor for biological nitrogen removal from wastewaters which is based on bypassing the production of nitrates and is characterized by sufficiently frequent switching between of aerobic and anoxic operating conditions, so that the action of nitrite oxidizers is suppressed, through the controlled aeration of the treated wastewaters.

2. A reactor which, according to Claim 1, is characterized by cyclic operation, to which the wastewater to be treated is fed periodically, undergoes various treatments in a single tank through a sequence of discrete temporal phases and is collected treated periodically, whereas its operation is divided into five discrete temporal stages: the fill phase, the react phase (for organics and nutrient removal), the settle phase (aiming at separation of biosolids from the treated wastewater), the draw phase (aiming at collection of treated wastewater), and the idle phase (preparation of the reactor for the next cycle).

3. A reactor, which according to claim 1, is characterized by continuous operation, and to which the wastewater to be treated is continuously fed, undergoes various treatments in a single tank through appropriate aeration zoning (possibly separated by baffles and is continuously removed to be fed to the secondary sedimentation tank .

4. A reactor , which according to Claim 1 can treat both municipal and industrial wastewaters.

5. A reactor, which according to Claim 1, is either designed from scratch or already exists and has its operation properly modified according to the proposed operation mode.