WO2024043798A1

WO2024043798A1 - A system for water treatment with a flow electrode and a method for treating water and wastewater using this system

Info

Publication number: WO2024043798A1
Application number: PCT/PL2023/000041
Authority: WO
Inventors: Aleksander Widuch; Marcin Malicki; Wojciech ŁOBODY
Original assignee: Net Spółka Z Ograniczoną Odpowiedzialnością Water Technologies Spółka Komandytowa
Priority date: 2022-08-23
Filing date: 2023-08-18
Publication date: 2024-02-29
Also published as: PL442075A1

Abstract

The invention relates to a wastewater treatment system 'with a flow electrode and to a method of wastewater treatment using this system. Wastewater to be treated chamber (1) and treated wastewater chamber (2) separated by a partition (3) supplied with water to be treated using the wastewater inlet pipeline ( 4) and from which treated water is discharged using the outlet pipeline (5) of treated water. In the wastewater to be treated chamber (1) on the surface of the wastewater there is a sludge scraper (6) and electrodes (7) recessed in it, connected to the direct current source (8) alternately to the positive and negative poles. From the outlet pipeline (5) of treated water there is a pipeline (9) with installed pump (10) led out, which is led to the generator (11) of micro-nano bubbles connected to the gas source (12) and from generator (11) of micro-nano bubbles there is a pipeline (13) of water with micro bubbles led out which is led to the wastewater to be treated chamber (1) in the part between the bottom and electrodes (7), where the part of the pipeline (13) located inside the chamber (1) contains perforations and the pipeline (13) ending in the chamber (1) is capped at the end and from the generator (11) there is a pipeline (14) of water with nano bubbles led out, connected to each of the electrodes (7), which are flow electrodes.

Description

A system for water treatment with a flow electrode and a method for treating water and wastewater using this system

The subj ect of the invention is a system f or water and wastewater treatment using a flotation and electrocoagu lation systems supported by micro-nano bubbles .

The invention belongs to the field of the water and wast ewater treatment systems and installations .

The invention solves the technical problem of wastewater treatment and the related problem of the neces sity of frequent cleaning of the electrodes used in the electrocoagulation proces s and reducing their wear and tear .

Popularly used methods of primary wastewater treatment are sedimentation and flotation. Sedimentation, as a proces s based on the use of gravity, is a slow process and its ef fectiveness depends on the correct selection of chemicals for the type of wastewater . Sedimentation requires large tanks called settlers . Flotation is a faster proces s than sedimentation and requires smaller tanks , but its implementation requires dosing of coagulant , polyelectrolyte and continuous supply of gas bubbles to the tank, which attach to solid particles precipitated chemically and carry them to the surface of the liquid, creating a scum that is easy to remove mechanically . The effectiveness of removing suspensions by flotation depends on the amount and type of chemicals used in the process and the size of gas bubbles inserted into the flotation chamber . The bubbles generated for flotation are usually in the range of 50-150 micrometers and have a negative Zeta potential. The zeta potential, otherwise known as electrokinetic potential, is the potential that exists at the phase interface of a molecule and is responsible for the attraction of molecules with different charges. The amount of chemicals that is required to carry out the flotation process correctly depends mainly on the type of wastewater and its chemical composition. In the case when fats and oils in th.e form of emulsions are present in the sewage, significant amounts of coagulant are required for the so-called "emulsion breaking" leading to high operating costs and low efficiency.

Chemical coagulation is carried out by dosing a coagulant, for example FeaCl, whose chemical reaction in contact with water occurs as follows:

FeC13+3H₂O<—> Fe (OH) ₃+3HCL

Fe(OH)3 hydroxide is a positively charged colloid so that it attaches contaminant molecules from the wastewater with a negative potential on its surface, and this process is called coagulation. After the coagulation process, pH correction usually needs to be carried out. Adjusting the wastewater to the correct pH is required for proper operation of the polyelectrolyte, most often it is 5.5-7.5. After correcting the pH, polyelectrolyte is dosed, whose task is to agglomerate the colloidal molecules into larger polymer chains. In the last stage, air bubbles are added whose Zeta potential is negative. Thanks to the negative potential, the bubbles attach to the polymer chains and then bring them to the surface using the flotation effect.

A process similar to coagulation with iron or aluminium salts is electrocoagulation. Electrocoagulation is an electrochemical process of water purification, through the flow of charge through the anode and cathode there is a process of destabilization and aggregation of contaminated particles. In the electrocoagulation process, iron or aluminium anodes are most often used, which are electrolytically dissolved using flowing electricity. In this way, electrode metal ions are supplied to the wastewater further fulfilling the function of electrolytic coagulant. As a result of electrochemical insertion of coagulating Fe²⁺ ions into the wastewater, which are oxidized to Fe³⁺ using oxygen dissoLved in the water. In electrocoagulated wastewater, Fe³⁺ cations react with hydroxide ions to form iron hydroxides Fe(OH)3, and from this point the negatively charged colloids are destabilised and agglomerated, the same as with chemical coagulation.

During electrocoagulation operation with micro-nano bubbles, the anode's operating model remains without significant changes: during operation, iron or aluminium, depending on the material of manufacture, from the anode dissolves in water to form free ions.

For iron: Fe -> Fe²⁺ + 2e~

For aluminium: Al -> Al³⁺ + 3e~

During the operation of the cathode, electrolysis takes place, during which the water molecule is split according to the following reaction:

2H₂O + 2e" -> H₂ + 20H-

In electrocoagulated wastewater, Fe³⁺ cations form positive hydroxides {Fe (OH)3}, which further function as colloidal sorbents of such wastewater pollutants as suspended solids, phosphorus compounds or substances responsible for COD.

The formation of micelles is in accordance with the following reaction :

Fe³⁺ + 30H- = Fe (OH) ₃ The generated micro-nano bubbles have a very high gas pressure inside, resulting from balancing the hydrostatic pressure of the liquid. A characteristic feature of micro-nano bubbles is that when they collapse, they generate a significant amount of energy dissipated using an ultrasonic wave, leading to the formation of free hydroxyl radicals OH°, which are very strong oxidants that additionally support wastewater treatment.

Since the generated bubbles have a negative Zeta potential and during chemical coagulation there is iron in various degrees of oxidation with a positive potential, the bubbles stabilize on their surface and the nano bubbles do not collapse. If the bubble does not collapse, no free hydroxyl radical is formed and therefore no advanced oxidation occurs.

From the state of the art there are known methods of electrocoagulation consisting of a tank, electrodes, a current source, where the flow of wastewater through the electrodes can be horizontal or vertical depending on the orientation of the electrodes. Due to the structure of the electrodes, we can distinguish single or multi-channel flow. In most solutions, the tanks are filled with electrodes, which can be connected to each other unipolar in parallel, bipolar in parallel or unipolar in series. Tank aeration is used to ensure mixing. After the electrocoagulation process, the sludge is most often separated using a press. However, the above design solutions have limitations mainly related to the growing micelles on the electrodes, which reduces the efficiency of the system and increases its energy consumption. Mixing is necessary to ensure movement of the wastewater between the electrodes. The solution according to the invention is able to remove not only colloids but also contaminants that are dissolved, while maintaining the cleanliness of the electrodes. Replacing standard bubbles with nano bubbles inserted directly through the electrode significantly increases coagulation efficiency by directly removing the coagulated sludge from the space between the electrodes , while preventing electrode clobbering . Feeding micro bubbles from the bottom into the space between the electrodes leads to additional floating , increasing the speed and effi ciency of the process . Dosing micro-nano bubbles reduces operating costs and reduces the neces sary working volume of the electrode chamber . Additionally , cracking nano bubbles generate ultrasonic waves that mechanically clean all solid surfaces . As a result of the cracking of the nanobubbles , hydroxyl radicals OH ° are formed, which are very strong oxidants , stronger than ozone and atomic oxygen . Hydroxyl radicals decompose both colloidal and dis solved organic substances , thus improving the efficiency of the system and wastewater treatment , where currently the main method of removing such di ssolved pollutants is biological treatment .

In the application no . CN106495372A entitled „Equipment and method for enhanced coagulation and clarification treatment in emergent water supply treatment" Zhou Wenqi , Ye Hui , Liu Shuang, Han Yaqiong , Ji Qinghua , Zhang Pingyun , Jin Lei present a system using electrocoagulation supported by a coagulant and micro-nano bubbles dosed into the entire wastewater for treatment , having the fundamental difference from the invention according to the application in the form of the lack of feeding nano bubble s into the electrode . Thanks to this , the solution according to the invention leads to the additional effect of cleaning the electrodes and eliminating the need to use a large amount of coagulant .

In the application WO2018164480A1 entitled „Electrocoagulation Device" Lee Jin and Han Kyung present a method and device f or the e lectrocoagulation proces s , using stratification of the purified medium and gravity separation . The invention according to the application di ffers from the solution of the above authors in that it does not use stratification to separate the media and feeds liquid saturated with bubbles inside the electrode . In the application US2014183058A1 entitled „Methods for enhanced electrocoagulation processing using membrane aeration" Wiemers Reginald, Kohlheb Robert and Zahn Peter present a a method of preparing water for treatment using membrane filtrati on . In the solution according to the invention, there is no need to use such a process to prepare the water for treatment and aerat ion is carried out using micro nano-bubbles fed inside the electrode .

In the application CN110655205A entitled „Treatment technology of high-hardness industrial wastewater" Dai Zengtao pres ents a solution based on saturating hard water with micro-nano bubbles before directing it to the electrocoagulation process so that the ions formed during the process lead to the precipitation of , among others , iron . The solution according to the invention use s only part of the puri fied water stream, which is saturated with micro- nano bubbles that are selectively fed directly into the ele ctrode and from the bottom of the chamber, reducing the energy consumption of the proces s .

The main aim of the solution according to the invention is to improve the e f ficiency and reduce the size of wastewater treatment systems using electrocoagulation and flotation with particular emphasis on improving the process , reducing its operating and investment costs . The solutions known so far use macro bubbles of 1-3 mm to clean the space between the electrodes in the electrocoagulation proces s , while in the flotation process micro bubbles >10 pm are used only to ensure flotation after adding polyelectrolyte . The solution according to the submitted invention is focused on the feeding of micro and nano bubbles at the electrocoagulation stage , with the stream divided into micro and nano bubbles separately . Micro bubbles are dosed with treated water saturated with them into the wastewater that flows into the electrocoagulation and flows between electrodes specially designed for this purpose , while nano bubbles are fed with treated water saturated with them through the electrode . The micro bubbles fed have a si ze from 10pm to 100pm and the nano bubbles from lO Onm to 500nm . Nano bubbles are responsible for the advanced exudation proces s , i . e . mainly using hydroxyl radicals formed as a result of the collapse of nano bubbles and for shortening the coagul ation process of the molecule and then , after absorbing micro bubbles , removing the colloid f rom the space between the electrod es , so that the ef ficiency of the electrode operation increases and the electrode surface area can be reduced by approximately 10 % . Absorption of macro bubbles by colloids is not possible due to their high lift velocity , which results in a short contac t time of the bubble with the molecule . The wastewater prepared i n this way is fed directly into the flotator where the sludge is r emoved by a scraper . Separating micro and nano bubbles and feedin g nano bubbles directly to the electrode makes the coagulation and flotation proces s more ef ficient .

The most significant cost in the electrocoagulation proc es s is electricity consumption and electrode wear and tear . The use of the solution according to the invention reduces elect ricity consumption by approximately 20% and al so reduces electrode wear and tear by approximately 10% . Thanks to improved ope ration efficiency of the electrodes and improved their cleaning, it is pos sible to use electrodes with up to 13% les s surface area .

The es sence of the invention is a wastewater treatment system comprising wastewater to be treated chamber and treated wastewater chamber where between the chambers there is a partition separating them from the bottom by up to 80 % of the height of the chambers and to the wastewater to be treated chamber is led at the bottom of the wall of the wastewater to be treated chamber - up to 10 % of its height - wastewater inlet pipeline and outlet pipeline of treated water is led out from the bottom part of the wall of the treated wastewater chamber and in the wastewater to be treated chamber, on the surface of the wastewater there is a s ludge scraper attached to the wall of the wastewater to be treated chamber and in the wastewater to be treated chamber there are electrodes attached to it , connected to a direct current source alternately to the positive and negative poles . From the treated water outlet pipeline there is a pipeline with installed pump led out , which is led to the micro-nano bubble generator connected to the gas source and f rom the micro-nano bubble generator there is a pipeline of water with micro bubbles Led out which is led to the wastewater to be treated chamber in tire part between the bottom and electrodes , where the part of the pipeline located inside the chamber contains perforations and the pi peline ending in the chamber is capped at the end, and from the gen erator there is a pipeline of water with nano bubbles led out , connected to each of the electrodes , which are flow electrodes .

Preferably, the electrodes contain two electr ically conductive , tightly connected flat layers front and back, which are tightly connected by a dielectric insert placed betwe en the layers along their outer edges and the electrodes comprise an inlet hole located between the layers in the insert . The flat layers contain perforations on the surface that is not in contact with the insert and the electrodes contain electrical conne ctions attached to the layers .

Pre ferably, at least one pipe placed between the insert s runs through the electrode inlet hole , the part of which between the layers is perforated .

Preferably, the electrode perforations are made in parallel lines running along the entire length of the layers , where the perforations of adj acent lines are arranged alternately, so that perforations in one line occur above the gap between perforations in an adj acent line .

Preferably, the outlets for the perforations of electrodes are directed towards the edge of the layers at which the inlet hole is located . Preferably, the direct current source is a photovoltaic installation .

Preferably , the gas source is an air intake or an oxyge n tank or an ozone generator or a nitrogen tank .

The essence of the invention is a method of wast ewater treatment using a system according to the invention whe re the wastewater to be treated is fed into the wastewater to be treated chamber through the inlet pipeline and at the same time the electrodes are powered with direct current so that adj acent electrodes are powered by di fferent poles and the treated water overflows the partition and enters the treated wastewater chamber from where it is discharged via a treated water pipeline a nd the scum from the upper surface of the wastewater in wastewater to be treated chamber is collected by a scraper . Up to 10% of the treated water entering the treated water pipeline is discharged by a pump through the generator supply pipeline to the micro-nano bubble generator , then the generator saturates between 40 to 60 % of the water with nano bubbles and the remaining part with micro bubbles and the water saturated with micro bubbles is pumped out through the pipeline via perforations to the lower part of the wastewater to be treated chamber and at the same time , the water saturated with nano bubbles is pumped through the pipeline to the interior of the electrodes , from where it enters the wastewater to be treated chamber .

The proposed system is a favourable solution for any wastewater containing significant amounts of suspended solids and colloids , which in a standard solution require significant amounts of chemicals or, due to the significant amounts of colloids , standard electrocoagulation is difficult . This is in particular due to the fact that the created and used 0H ° radicals have an oxidation potential of 2 . 8 [V] , for comparison , ozone has 2 . 07 [V] and chlorine 1 . 36 [V] , which makes them highly effective in the oxidation of problematic wastewater, which, combined with the electrocoagulation process in single device, gives very beneficial and non-obvious effects.

The invention in a preferred embodiment is presented in Fig. 1 showing a wastewater treatment system in which the method according to the invention was implemented; Fig. 2 shows a top view of the electrode; Fig. 3 shows a side view of the electrode; Fig. 4 shows the perforations located on the electrode.

Example 1 - implementation

The wastewater treatment system in a preferred embodiment consists of wastewater to be treated chamber (1) made of high- density polyethylene with dimensions of 2, 8m x 1,3m x 2, 5m which gives a volume of 9, 1m³ and treated wastewater chamber (2 ) made of high-density polyethylene with dimensions of 0,7m x 1,3m x 2,5m where between the chambers (1 and 2) there is a partition (3) made of high-density polyethylene, separating them from the bottom by up to 80% of the height of the chambers (1 and 2) and into the wastewater to be treated chamber (1) in the lower part of the wall of the wastewater to be treated chamber (1) , at 10% of its height, - wastewater inlet pipeline (4) made of PVC with dimension of D100 is led and from the lower part of the wall of the treated wastewater chamber (2) there is outlet pipeline (5) of treated water made of PVC with a diameter of D100 led out and in the wastewater to be treated chamber (1) on the wastewater surface there is a sludge scraper (6) attached to the wall of the wastewater to be treated chamber (1) , consisting of a gear motor with a power of 0.37 kW and a maximum speed of 135 RPM regulated by a frequency converter, on the scraper there is a chain, guides and 6 scraper blades and in the wastewater to be treated chamber (1) there are 28 electrodes (7) attached to it connected to a direct current source (8) with a voltage of 10V and an amperage of 2400A through copper busbars with a square cross-section of 4000mm², alternately to the positive and negative poles; from the outlet pipeline (5) of treated water there is pipeline (9) made of PVC with a diameter of d32 with installed pump ( 10) of centrifugal type led out, which is led to a generator ( 11) of micro-nano bubbles connected to the gas source (12) which is a gas separator and from the generator (11) of micro-nano bubbles there is led out a pipeline (13) made of PVC with the dimension d25 of water with micro bubbles, which is led to the wastewater to be treated chamber (1) in the part between the bottom and the electrodes (7) where part of the pipeline (13) located inside the chamber (1) contains perforations and the pipeline (13) ending in the chamber (1) is capped at the end with a cork, and from the generator (11) there is a pipeline (14) of water with nano bubbles made of PVC with a diameter of d25 led out, connected to each of the electrodes (7) , which are flow electrodes containing two electrically conductive, tightly connected flat layers (7.1) , front and back, made of aluminium, with a surface 80 cm² each and 2 mm thick each, which are tightly connected by a dielectric insert (7.2) made of PE100 placed between the layers (7.1) along their outer edges and the electrodes (7) contain an inlet hole (7.3) with a diameter of 100 mm located between the layers (7.1) in the insert (7.2) ; and flat layers (7.1) contain perforations

(7.5) on the surface that is not in contact with the insert (7.2) and the electrodes (7) contain electrical connections (7.4) made in the form of a threaded hole with a screw in, attached to the layers (7.1) ; through the inlet hole (7.3) of the electrodes (7) , at least one pipe (7.6) made of PE100 with a diameter of 20 mm runs being placed between the inserts (7.1) , the part of which located between the layers (7.2) is perforated; the perforations

(7.5) of the electrodes (7) are made in parallel lines running along the entire length of the layers (7.1) where the perforations

(7.5) of the adjacent lines are arranged alternately, so that the perforations (7.5) in one line occur above the gap between the perforations in the adjacent line according to the formula where "b", i.e. the width of the perforation, is equal to three times "a", i.e. the height of the perforation and "t" and "tl" , i.e. the distances between the beginning of each perforation hole in the X and Y axes, respectively, are equal to four times ”a" and h, i.e. the depth of the perforation axis is equal to twice the thickness of the sheet and the outlets for the perforations (7.5) of the electrodes (7) are directed towards the edge of the layers (7.1) at which the inlet hole (7.3) is located.

Example 2 - Method

The wastewater treatment method in a preferred embodiment was implemented as follows: into the initially filled wastewater to be treated chamber (1) , through the inlet pipeline (4) wastewater for treatment in the amount of 20 m³/h was fed, at the same time, 28 electrodes (7) were powered with direct current with a voltage of 10 V and an amperage of 2400 A ensuring a surface current in the range of 4-25mA/cm2 so that adjacent electrodes (7) are powered by different poles - 14 pcs. are anodes and 14 pcs. are cathodes. The treated water flows by gravity through the partition (3) and enters treated wastewater chamber (2) from where it was led away by gravity through the treated water pipeline (5) . The scum from the upper surface of the wastewater in wastewater to be treated chamber (1) is collected using a scraper (6) . 5% of the treated water entering the treated water pipeline (5) was discharged using a pump (10) through the generator supply pipeline (9) to the micro-nano bubble generator (11) then the generator (11) saturated 50% of the water with nano bubbles and 50% with micro bubbles. Water saturated with micro bubbles was pumped out through a pipeline (13) made of PVC with a size of d25 using the overpressure generated by the generator (11) through perforations to the lower part of the wastewater to be treated chamber (1) . A t the same time, water saturated with nano bubbles was fed through a pipeline (14) using the overpressure generated by the generator to the interior of the electrodes (7) , from where it was entered to the wastewater to be treated chamber (1) . Thanks to the innovative design of the electrodes , the system and the use of the method according to the invention, in particular the equal distribution of nano bubbles throu gh the electrode leading to the minimization of its fouling, the electricity consumption was reduced by 1 kWh/m³ of wastewater and the need for servicing the system in the electrode area was reduced , leading to servicing costs twelve times lower than conventional solution .

Claims

Claims A wastewater treatment system comprising wastewater to be treated chamber (1) and treated wastewater chamber (2) where between the chambers (1 and 2) there is a partition (3) separating them from the bottom by up to 80% of the hehght of the chambers (1 and 2) and to the wastewater to be treated chamber (1) is led at the bottom of the wall of the wastewater to be treated chamber (1) - up to 10% of its height - wastewater inlet pipeline (4) and outlet pipeline (5) of treated water is led out from the bottom part of the wall of the treated wastewater chamber (2) and in the wastewater to be treated chamber (1) on the surface of the wastewater there is a sludge scraper (6) attached to the wall of the wastewater to be treated chamber (1) and in the wastewater to be treated chamber

(I) there are electrodes (7) attached to it, connected to a direct current source (8) alternately to the positive and negative poles characterized in that from the outlet pipeline (5) of treated water there is pipeline (9) with installed pump (10) led out, which is led to a generator (11) of micro-nano bubbles connected to the gas source (12) and from generator

(II) of micro-nano bubbles there is a pipeline (13) of water with micro bubbles led out which is led to the wastewater to be treated chamber (1) in the part between the bottom and electrodes (7) , where the part of the pipeline (13) located inside the chamber (1) contains perforations and the pipeline (13) ending in the chamber (1) is capped at the end and from the generator (11) there is a pipeline (14) of water with nano bubbles led out, connected to each of the electrodes (7) , which are flow electrodes. System for wastewater treatment according to claim 1 characterized in that the electrodes (7) contain two electrically conductive, tightly connected flat layers (7.1) , front and back, which are tightly connected by a dielectric insert (7.2) placed between the layers (7.1) along their outer edges, and the electrodes (7) contain an inlet hole (7.3) located between the layers (7.1) in the insert (7.2) ; and the flat layers (7.1) contain perforations (7.5) on the surface that is not in contact with the insert (7.

2) and the electrodes

(7) contain electrical connections (7.4) attached to the layers (7.1) .

3. System for wastewater treatment according to claim 1 or 2 characterized in that through the inlet hole (7.3) of the electrodes (7) , at least one pipe (7.6) runs being placed between the inserts (7.1) , the part of which located between the layers (7.2) is perforated.

4. System for wastewater treatment according to claim 1 ox 2 or 3 characterized in that the perforations (7.5) of the electrodes (7) are made in parallel lines running along the entire length of the layers (7.1) where the perforations (7.5) of the adjacent lines are arranged alternately, so that the perforations (7.5) in one line occur above the gap in the adjacent line.

5. System for wastewater treatment according to claim 1 or 2 or 3 or 4 characterized in that the outlets for the perforations (7.5) of electrodes (7) are directed towards the edge of the layers (7.1) at which the inlet hole (7.3) is located.

6. System for wastewater treatment according to claim 1 or 2 or 3 or 4 or 5 characterized in that the direct current source

(8) is a photovoltaic installation.

7. System for wastewater treatment according to claim 1 or 2 or

3 or 4 or 5 or 6 characterized in that the gas source (12) is an air intake or an oxygen tank or an ozone generator or a nitrogen tank.

8. A method of wastewater treatment using a system according to the invention where the wastewater to be treated is fed into the wastewater to be treated chamber (1) through the inlet pipeline (4) and at the same time the electrodes (7) are powered with direct current so that adjacent electrodes (7) are powered by different poles and the treated water overflows the partition (3) and enters the treated wastewater chamber (2) from where it is discharged via a treated water pipeline

(5) and the scum from the upper surface of the wastewater in wastewater to be treated chamber (1) is collected by a scraper

(6) , characterized in that up to 10% of the treated water entering the treated water pipeline (5) is discharged by a pump (10) through the generator supply pipeline (9) to the micro-nano bubble generator (11) , then the generator (11) saturates between 40 to 60% of the water with nano bubbles and the remaining part with micro bubbles and the water saturated with micro bubbles is pumped out through the pipeline (13) via perforations to the lower part of the wastewater to be treated chamber (1) and at the same time, the water saturated with nano bubbles is pumped through the pipeline (14) to the interior of the electrodes (7) , from where it enters the wastewater to be treated chamber (1) .