WO2013041893A1

WO2013041893A1 - Modified continuous flow sequencing batch reactor and a method for treating waste water

Info

Publication number: WO2013041893A1
Application number: PCT/HU2012/000093
Authority: WO
Inventors: Charandeep Singh BHASIN
Original assignee: Utb Envirotec Zrt.
Priority date: 2011-09-19
Filing date: 2012-09-18
Publication date: 2013-03-28
Also published as: HU230285B1; HUP1100519A2

Abstract

The present invention relates to a method for treating municipal and industrial waste water performed in a sequential batch reactor (SBR) system, where the biological oxidation, nitrification, denitrification, phosphorous removal processes and solid separation takes place in one or multiple treatment basin(s), and more particularly to a process performed in a sequencing batch reactor (SBR) system for efficiently removing phosphorous from waste water treated. The invention also relates to an apparatus to perform the method according to the invention.˙

Description

Modified continuous flow

sequencing batch reactor and a method for treating waste water

Field of the invention

The present invention relates to a method for treating municipal and industrial waste water performed in a sequential batch reactor (SBR) system, where the biological oxidation, nitrification, denitrification, phosphorous removal processes and solid separation takes place in one or multiple treatment basin(s), and more particularly to a process performed in a sequencing batch reactor (SBR) system for efficiently removing phosphorous from waste water treated. The invention also relates to an apparatus to perform the method according to the invention.

Background

Environmental Legislation nowadays has become more restrictive in the nutrient contaminant wastewaters discharge, all over the world.

European Directives are also more restricted on the urban wastewater treatments, and focusing on the nutrient discharging. Considerable emphasis has been placed on reducing the quantities of nutrients (Nitrogen and Phosphorous) discharge, because they promote the growth of algae and other photosynthetic aquatic life, which lead to accelerated eutrophication, excessive loss of oxygen sources, and undesirable changes in aquatic life. Because of these facts the biological nutrient removal is the object of many studies, and researches, experts are working on improving the biological nutrient removal.

Description of biological nutrient removal

Biological nitrogen removal

Biological nitrogen removal can be accomplished in a two steps treatment: aerobic nitrification, and anoxic denitrification. This two-step system is the most common and economical for total nitrogen removing.

Term of nitrification describes a two steps biological process, where under aerobic conditions, using oxygen as the electron acceptor the ammonium (NH₄) is oxidized to nitrite (N0₂), and nitrite is oxidized to nitrate (N0₃). Aerobic autotrophic bacteria are responsible for nitrification in activated sludge processes.

As mentioned above, nitrification is a two steps process, two groups of autotrophic bacteria is involving. When ammonium is oxidized to nitrite Nitroso-bacteria, (or Ammonia Oxidizing Bacteria) is involved. When nitrite is oxidized to nitrate, another group of autotrophic bacteria, Nitro-bacteria, (or Nitrite Oxidizing Bacteria) is involved. The two groups of autotrophic bacteria are different.

These autotrophic bacteria derive energy for growth from the oxidation of inorganic nitrogen compounds, using inorganic carbon as source of their cellular carbon.

Denitrification, is the biological reduction of nitrate to nitric-oxide, nitrous-oxide, and nitrogen gas. Nitrite and nitrate is used as electron acceptor for the oxidation of a variety of organic and inorganic electron donors. Wide range of bacteria are capable of denitrification, they can be heterotrophic and autotrophic. Most these heterotrophic bacteria are aerobic facultative bacteria, and they able to use oxygen as well as nitrite or nitrate. Biological denitrification involves oxidation of many organic substrates in wastewater treatment, using nitrite or nitrate as the electron acceptor instead of oxygen. The electron donor as an organic substrate is obtained through: the easily biodegradable organic material in the influent wastewater, produced during endogenous process or an exogenous source as alcohol or acetate. ;

During biological denitrification in absence of oxygen, nitrate is converted to nitrogen gas, and is released to the environment. Opposite with biological nitrification, biological denitrification occurs in absence of oxygen and uses organic compounds present in wastewater as a source of carbon. Energy is obtained by oxidizing the organic substrate. In this process nitrate acts as electron acceptor, in absence of oxygen.

Biological phosphorous removal

The advantages of biological phosphorous removal are the reduction of chemical cost, and lower sludge production than in the chemical phosphorous precipitation, and no chemical contamination in the sludge.

The biological phosphorous removal consists of incorporating the phosphorous present in the influent into cell biomass, what subsequently is removed from the process. The phosphorous accumulating organisms (PAOs) are responsible for this process.

The metabolism of PAOs can be characterized as a cyclic storage and consumption process of glycogen and polyphosphate. An anaerobic phase and a rapid uptake of substrate in the anaerobic phase are the key factors in maintaining the PAOs in a biological phosphorous removal process.

Phosphorous exists in the wastewater as orthophosphate, polyphosphate, and organic phosphate. During biological phosphorous removal, a certain kind of facultative heterotrophic bacteria, when subjected to anaerobic (absence of oxygen and nitrate) conditions that favors the growth of phosphorous accumulating bacteria, they assimilate and store the fermentation products (acetate and other volatile fatty acids produced by other facultative bacteria). These microorganisms derive energy for this assimilation from stored polyphosphates, which are hydrolyzed to liberate energy. The free phosphorous that results from the hydrolysis reaction is released to the mixed liquor (MLSS). The same microorganisms, when are exposed to aerobic conditions consumes both phosphorous (which is used for cell synthesis, and stored as polyphosphates), and oxygen to metabolize the previously stored substrate, for energy production and cell synthesis. The organisms take up the phosphorous in excess, to remedy their phosphorous- starved condition. That is, why they take more phosphorous than previously released. The phosphorous is taken out the system with sludge wasting procedure.

Conventional SBR description

Conventional SBR systems are well known in the art, it has been utilized extensively for COD, nitrogen and phosphorous removal.

The Sequencing Batch Reactor (SBR) process is a wastewater treatment system, which works on the basis of activated sludge and operated in fill-and-draw cycle. The most important difference between SBR and conventional activated sludge system is that in SBR system the process reaction and settling take place in the same reactor. Basically all SBR can have five phases, which are carried out in sequence as follows:

FILL: Raw wastewater flows into the reactor, and mixes with the biomass held in the tank.

REACT: The biomass consumes the substrate under controlled conditions i.e. aerobic, anoxic, or anaerobic reaction, depending on the kind of treatment applied. Biological nutrient, (nitrogen and phosphorous) removal is accomplished within the SBR process by incorporating of alternating phases of aeration (with air) and mixing only; known as aerobic and anaerobic/anoxic phases. During the aeration phase the influent wastewater is mixed with the MLSS (Mixed Liquor Suspended Solids) aerated, and biological oxidation of influent organic matter takes place simultaneously. The organic components of wastewater are degraded, nitrification takes place, and ammonia nitrogen is converted to nitrite and then nitrate by bacteria in the presence of oxygen. The conditions applied in the fill and react phases must be adjusted according to the treatment objectives, belonging to the concentration of organic material, nitrogen and phosphorous removal to meet the requirements. The aerobic phase promote BOD (Biochemical Oxygen Demand) removal, nitrification and phosphorous uptake, the anoxic-anaerobic phases promote denitrification and phosphorous release. During the non-aerated or mix only part of the REACT phase, the influent water is mixed with mixed liquor MLSS, but the aeration is stopped. In these phases anoxic and anaerobic processes are going, namely denitrification and P releasing.

SETTLE: Mixing and aeration are stopped, and the biomass is allowed to settle from the liquid, resulting a clarified supernatant.

DECANT: Clear supernatant is removed from the upper part of liquid. The excess sludge wasting from the bottom of basin is incorporated usually in this phase.

IDLE: This is the time between cycles. Idle is not a necessary phase, it is sometimes omitted. Sludge wasting can be done in this phase as well.

While most SBR designs incorporate a single tank where all process reactions take place, several variations of the SBR process incorporate an initial zone for mixing of the wastewater with the liquid (Mixed Liquor Suspended Solids), in the basin to provide process advantages. This initial mixing zone (mentioned as first compartment in this patent application) is separated from the main react zone by means of a baffle wall. Wastewater enters the first compartment, which may or may not incorporate back mixing from the main react zone.

Continuous flow SBR

Conventional state-of-the-art SBR as described above are batch fed i.e. wastewater only enters during the fill/react period and none during the settle/decant phases. Continuous flow SBR are unique because wastewater is allowed to enter the SBR basin even during the settle and decant phases.

The continuous flow SBR described herein has two compartments: • a first compartment for mixing influent wastewater, which is separated from main reaction zone with a baffle wall with orifices on the bottom part, to let the wastewater mixed with biomass (named as: Mixed Liquor Suspended Solids, or MLSS) flow into the main reactor zone,

• main reaction zone for biological oxidation, nitrification, denitrification, phosphorous removal, solid/liquid separation and for decanting.

Wastewater enters continuously into the first compartment, that can occupy 5-25% of the total basin volume, with the rest being devoted to the main reaction zone. In the main reaction zone, the time-based phases follow each other in cycles. The continuous SBR process consists of: aeration, mixing, settling and decant phases. Sludge wasting is accomplished in the decant phase normally, but can be accomplished during other phases as well.

Background Art

Discontinuous sequential batch reactor system is known from the US patent No. 5,395,527. The document discloses a process for treating wastewater in a dynamic bio-sequenced manner in a single sequencing batch (SBR) reactor already filled with an actuated sludge-mixed liquor up to a relatively constant level and provided with decantation means which are fixedly mounted inside the SBR reactor at a given height, and in and through which supernatant water on top of said mixed liquor within the SBR reactor may freely enter and be discharged out of the SBR reactor when the level of said mixed liquor within the SBR reactor reaches said decantation means, said SBR reactor being also provided with scum and excess sludge removal means which are fixedly mounted within the SBR reactor at a short elevation under said clear water level and in and through which floating scum and excess sludge in suspension may be collected whenever desired and discharged out of the SBR reactor, said process comprising the steps of: a) rapidly introducing a given amount of wastewater to be treated into the SBR reactor below the clear water level, such a rapid introduction causing the level of the mixed liquor within the SBR reactor to raise selectively Uniformly and vertically and the supernatant clarified water to enter the decantation means and be discharged out of the SBR reactor; b) actuating the scum and excess sludge removal means to collect and discharge the scum floating on top of the wastewater filling the SBR reactor, such an actuation also causing the level of the wastewater within the SBR reactor to move down below the clear water level of the decantation means; c) mixing and aerating the mixed liquor within the reactor SBR to achieve the required wastewater treatment; d) stirring the mixed liquor within the SBR reactor in a controlled manner and adding a supplemental amount of wastewater into the SBR reactor so as to cause a given amount of sludge to overflow into the scum and excess sludge removal means and thus to be removed from the SBR reactor; and e) allowing the sludge in suspension in the liquor to settle for a period of time sufficient to avoid solids to be carried out with the supernatant water when another given amount of wastewater is introduced into the reactor.

Another sequential batch reactor system is known from the patent No.US 5,525,231 where a method of operating a sequencing batch reactor having a cycle consisting of FILL, REACT, SETTLE, and DRAW periods and optionally an IDLE period, wherein supply of feed to the sequencing batch reactor comprises distributing the feed into settled sludge in the bottom part of reactor; and wherein the FILL period includes at least one non-mixed period; wherein the non-mixed period comprises up to all of the FILL period; wherein the FILL period comprises up to about half of the sequence batch reactor cycle; a method wherein the FILL period includes one non-mixed period and a single mixed period, wherein the non-mixed period and mixed period comprise about the same portions of the FILL period, and the FILL period comprise up to about half of sequence batch reactor cycle; wherein the FILL and REACT periods each include at least one non-mixed period, and the REACT period includes one non- mixed period, wherein the non-mixed REACT period comprises up to about half of the sequence batch reactor cycle; a method wherein the sequencing batch reactor cycle consists of the following reaction sequence: a non-mixed FILL period; a mixed FILL period; an aerated mixed REACT first period; a non-mixed REACT period; an aerated mixed REACT second period; a SETTLE period; and a DRAW period, and the sequencing batch reactor cycle further includes an IDLE period.

The Problem we are solving with the invention

It has been found that for biological nutrient removal, continuous carbon source is beneficial in maintaining consistent performance. Organic compounds of raw influent are used as the source of carbon, which is essential of nitrogen and phosphorous removal efficiency. The other important factors for nutrient removal: the BOD/TN/TP ratios, aerobic/anaerobic conditions, contacting time and intensity between the MLSS (Mixed Liquor Suspended Solids) and raw hydrolyzing wastewater, which contains the easily degradable soluble organic carbon.

The nitrogen removal by known SBR systems above is generally very good, but the phosphorous removal is usually poor. The reason of this disadvantage is that when influent is fed in SBR cycle, the left-over nitrate consumes the soluble carbon, before it becomes available to the so-called Phosphorous Accumulating Organisms (PAO's). Depending on the level of nitrification/denitrification incorporated in the plant design, the amount of easily biodegradable substrate is reduced after the initial anoxic phase at start of a reaction period. As PAO's totally depend on the easily degradable soluble substrate to perform their function effectively (phosphorous release before luxury uptake), biological phosphorous removal has always remained the "Achilles Heel" of SBR processes. Designers have sought to circumvent this problem by adding additional equalization volume or hydrolyzing reactors, thereby increasing the cost and complexity of the process. Another area of untracked efficiency is that in a general SBR reactor, the active (reaction) period is somewhere between 30-50% of the total cycle time. The non-reaction phase time is primarily devoted to settling and decanting functions.

Accordingly, it is an object of the present invention to provide a solution that overcomes disadvantages of the prior art methods and apparatuses providing an apparatus and a method significantly contributing to the advancement of the art.

Another object of this invention is to provide a system for treatment waste water by continuous flow process performed in a sequential batch reactor (SBR) system.

A further object of the present invention is to provide a system for treatment waste water by continuous flow process performed in a sequential batch reactor (SBR) system suitable for efficiently removing not only nitrogen but also phosphorous from waste water.

Another object of the invention is to provide a system for treatment waste water by continuous flow process performed in a sequential batch reactor (SBR) system having reduced treatment time and, therefore, greater treating capacity.

Summary of the invention

Continuous flow sequential batch reactor for treating waste water comprising:

a basin divided into first and second treatment compartments by a baffle wall, said baffle wall having orifices near the bottom of said basin fluidly connecting said first and second treatment compartments, an inlet for the waste water influent into said first compartment, aeration system in both said compartments, a decanter unit arranged along the side of the basin opposite said inlet for waste water, sludge wasting means to drain a part of said sludge placed in the bottom of said basin, and a distribution manifold system adapted to pipe the influent waste water and MLSS from said first compartment directly to the bottom of said second compartment is provided, a manifold system having a piping duct and distributing ducts branching out said piping duct and having distributed holes in said second compartment, and a pump adapted for feeding waste water and MLSS from said first compartment to said manifold system.

Preferably a mixing system is arranged to mix the contents of second compartment.

The first compartment functions as a selector zone and to aid in the mixing and biological preselection of screened influent waste water with MLSS, serving as an intermittently aerated and hydraulically mixed zone as well.

A method for treating waste water in a continuous flow sequential batch reactor according to any preceding claims, consisting of REACT, SETTLE and DECANT phases, and the method comprising the steps of: feeding waste water in to a first compartment of the reactor basin, periodically aerating said waste water in said first compartment, allowing the waste water mixed with biomass to flow into a second compartment throughout orifices formed under a baffle wall separating said first and second compartments, allowing said waste water and biomass from the first compartment entering the second compartment to form a mixture with a biological sludge settled therein, during SETTLE and partially the DECANT phases, by pumping and distributing raw waste water with MLSS into said sludge settled in the second compartment by means of a distribution manifold system to form a mixture with said biological sludge and allowing solid particles of said mixture to settle, and its liquid part to rise, decanting and removing said liquid part from the reactor basin, and wasting sludge from the second compartment or basin during any of said phases.

Each cycle of the method according to the invention consisting of the steps of aerating, mixing, settling and decanting take 1-24 hours, and repeated at least 1 times a day.

Advantageously, continuously distributing influent flow during the SETTLE and partially of DECANT phase by a submersible MLSS pump which is placed in the first compartment. Preferably distributing the raw wastewater and MLSS mixture under the surface of the sludge in second compartment arriving from the first compartment by means of said distribution manifold system, with pipes having holes, that assures that the easily degradable carbon content of the mixture can meet with the phosphorous accumulating and denitrifying bacteria in settled sludge. Given pieces and diameter of distribution holes (H) in predetermined distances between each other on the bottom or angular side of the pipes are arranged, and the diameter and the number of holes assures, preventing the undesirable turbulence which would disturbing the biomass settling and clear water decanting.

The first compartment functions as a selector and mixing zone for screened influent waste water and biomass held in the first compartment, forming the MLSS. This intermittently aerated zone allows natural selection of floc-forming bacteria over filamentous bacteria and therefore performs as a selector zone.

Distributing the raw wastewater and MLSS mixture using the aforementioned piping system with a calculated number and diameter of holes on the bottom or angular side of the piping system to prevent any turbulence in the liquid body to which it is discharged.

Although the FILL is continuous, the first and second compartments go through different intervals of aerate and non-aerate phases during the REACT period. After the REACT period, a SETTLE and DECANT period are followed. After the DECANT period, an optional IDLE period is provided, or the REACT period resumes. During the SETTLE period, said MLSS transfer pump from first compartment to second compartment is operated. During the DECANT period, said MLSS transfer pump from first compartment to second compartment is operated discontinuously.

This process of distributing MLSS mixed with hydrolysing influent wastewater into said sludge settled in the second compartment (during SETTLE and partially of the DECANT periods) by means of a distribution manifold system to form a mixture with said biological sludge and allowing solid particles of said mixture to settle, and its liquid part to rise, decanting and removing said liquid part from the reactor basin, is the focus of this invention.

The invention centers on the distribution of the raw wastewater mixed with MLSS from the first compartment to the biomass settled in the bottom of the second compartment (in the SETTLE and DECANT phase), arriving from the-first compartment by help of distribution manifold system, with a given diameter of pipes with holes that assures that the hydrolyzing carbon content of influent wastewater can meet with the phosphorous accumulating and denitrifying bacteria which are settled in the biomass.

The distribution manifold system consists of a piping system which includes header pipes and multiple number of pipe branches, drilled with series of distribution holes in pre-determined distances between each other on the bottom and/or angular side of the pipes. The diameter of the pipes and the number of holes is calculated to ensure that the undesirable turbulence effect is fully prevented that would disturb the clear water settling and decanting in their respective phases.

Detailed description of the drawings

Fig. 1. is a schematic representation of an existing SBR reactor,

Fig. 2. is a schematic representation of this invention, and

Fig. 3 a perspective view of the inside of a batch reactor according to the invention. Detailed description of a preferred embodiment

In Figure 1. a sequencing batch reactor according to the prior art is shown. The raw wastewater W after usual screening enters into an intermittently aerated first compartment 2, and from there under a baffle wall 3 via orifices O continuously into a second compartment 4, which is the main reaction zone. The first compartment 2 and second compartment 4 together represent the whole volume of a basin B. Aeration system A and mixing device M, Decanter 8 and sludge wasting means 7 e.g. a discharge pump, form an integral part of basin B in addition. When raw wastewater W enters into the first compartment 2, its velocity in the prior art is too slow during the SETTLE and DECANT phases, and in this case the fresh easily degradable carbon source can't meet with the biological sludge which is settled on the bottom of the second compartment 4, to provide the favorable conditions for denitrifying and phosphorous accumulating bacteria. In this case the phosphorous accumulation and denitrification do not takes place efficiently during these phases.

We performed fluorescent hydrological dye tracing during the SETTLE and DECANT phases. Under this test the influent wastewater W flow rate was at its highest designed value, yet the raw wastewater W moved so slowly, that it did not reach more than 10 % of total length of the second compartment 4.

This dye tracing verified for us clearly, that by hydraulic force we never can reach an intensive mixing of the raw wastewater W with the biomass if we want to have biological reactions take place in the SETTLE and DECANT phases.

As shown in Figure 2 and 3, the continuous flow SBR system described herein is provided by a raw wastewater W distribution system, which comprising: a submersible feeding pump 1 located in the first compartment 2, a distribution pipe 5 and distributing ducts 6. In the continuous flow SBR according to the invention (Fig. 2.) the influent hydrolyzing raw wastewater W mixed with MLSS held in the first compartment 2 is distributed by an MLSS feeding pump 1 along on the bottom of second compartment 4 through distribution manifold 5 into the sludge which is in the bottom of second compartment 4 during the non- mixed, non- aerated settling and partially in decanting phase.

The designing of distribution manifolds 5 shown in Fig. 3. ensures that the sludge in the bottom part of the second compartment 4 is mixed only in a moderate way when the feeding pump 1 is operated, and the feeding of raw wastewater W and MLSS mixture remains in the sludge blanket and does not disturb the clear water in the upper region of basin B. A sludge wasting mechanism by pump 7 may be provided to drain a part of said sludge placed in the bottom of said second compartment 4.

With continuous feeding SBR reactor according to the invention we can achieve more intensive contacting between the MLSS (Mixed Liquor Suspended Solids) and raw wastewater W as easily degradable carbon source, and this results a better phosphorous removal.

Claims

1. Continuous flow sequential batch reactor for treating waste water comprising:

a basin (B) divided into first and second treatment compartments (2, 4) by a baffle wall (3), said baffle wall (3) having orifices (O) near the bottom of said basin (B) fluidly connecting said first and second treatment compartments (2,4),

an inlet for the waste water (W) influent into said first compartment (2), aeration system (A) in both said compartments (2, 4),

a decanter unit (8) arranged along the side of the basin (B) opposite said inlet for waste water (W),

sludge wasting means (7) to drain a part of said sludge placed in the bottom of said basin (B),

wherein a distribution manifold system adapted to pipe the influent waste water (W) and MLSS from said first compartment (2) directly to the bottom of said second compartment (4) is provided, a manifold system having a piping duct (5) and distributing ducts (6) branching out said piping duct (5) and having distributed holes (H) in said second compartment (4), and a pump (1) adapted for feeding waste water (W) and MLSS from said first compartment (2) to said manifold system (5).

2. Continuous flow sequential batch reactor according to claim 1 wherein a mixing system (M) is arranged to mix the contents of second compartment (4).

3. Continuous flow sequential batch reactor according to claim 1 or 2 wherein the first compartment (2) functions as a selector zone and to aid in the mixing and biological preselection of screened influent waste water (W) with MLSS, serving as an intermittently aerated and hydraulically mixed zone as well.

4. Method for treating waste water (W) in a continuous flow sequential batch reactor according to any preceding claims, consisting of REACT, SETTLE and DECANT phases, and the method comprising the steps of:

feeding waste water (W) in to a first compartment (2) of the reactor basin (B), periodically aerating said waste water (W) in said first compartment (2), allowing the waste water (W) mixed with biomass to flow into a second compartment (4) throughout orifices (O) formed under a baffle wall (3) separating said first and second compartments (2, 4),

allowing said waste water (W) and biomass from the first compartment (2) entering the second compartment (4) to form a mixture with a biological sludge settled therein, during SETTLE and partly the DECANT phases, by pumping and distributing raw waste water (W) with MLSS into said sludge settled in the second compartment (4) by means of a distribution manifold system to form a mixture with said biological sludge and allowing solid particles of said mixture to settle, and its liquid part to rise, decanting and removing said liquid part from the reactor basin (B), and wasting sludge from the second compartment (4) or Basin (B) during any of said phases.

5. Method for treating waste water (W) in a continuous flow sequential batch reactor according to claim 4., wherein each cycle of said method consisting of the steps of aerating, mixing, settling and decanting take 1-24 hours, and repeated at least 1 times a day.

6. Method for treating waste water in a continuous flow sequential batch reactor according to claim 4. comprising continuously distributing influent flow during the SETTLE and partially of DECANT phase by a submersible MLSS pump (1) which is placed in the first compartment (2).

7. Method for treating waste water in a continuous flow sequential batch reactor according to claim 4. comprising distributing the raw wastewater and MLSS mixture under the surface of the sludge in second compartment (4) arriving from the first compartment (2) by means of said distribution manifold system, with pipes having holes (H), that assures that the easily degradable carbon content of the mixture can meet with the phosphorous accumulating and denitrifying bacteria in settled sludge.

8. Method for treating waste water in a sequential batch reactor according to claim 4. consisting given pieces and diameter of distribution holes (H) in predetermined distances between each other on the bottom or angular side of the pipes, and the diameter and the number of holes (H) assures, preventing the undesirable turbulence which would disturbing the biomass settling and clear water decanting.