WO2014202633A1

WO2014202633A1 - Wastewater purification system

Info

Publication number: WO2014202633A1
Application number: PCT/EP2014/062762
Authority: WO
Inventors: Lars Gunnarsson; Mats HELANDER
Original assignee: Conpura Ab
Priority date: 2013-06-18
Filing date: 2014-06-17
Publication date: 2014-12-24

Abstract

A unit for wastewater treatment is provided. The unit (1) comprises a free- standing pre-assembled module on legs (2), a water inlet (4) and a water outlet (5), located in opposite sides of the unit (1). A screening compartment (6), containing a sieve (7) and a level transmitter (8) is arranged in the unit, and a grit trap compartment (13), containing a horizontal screw conveyor (14), and an inclined screw conveyor (15) is arranged downstream the screening compartment (6). Plates (22) are placed in said grit trap compartment (13) to create a vertical slit (23) after which there is a dosing point (24) for the metal salts. A polymer dosing zone (25) is located just before the outlet (26) of the grit trap compartment (13). A baffle (27) creates a gap (28) at the bottom of said grit trap compartment (13) and a weir (29) creates a horizontal barrier from the bottom of said grit trap compartment (13) followed by a mixing cavity (30) with a polymer dosing point (25) and an outlet (26). A method for operating the unit (1) is also provided.

Description

WASTEWATER PURIFICATION SYSTEM

FIELD OF THE INVENTION

The present invention relates to a compact wastewater treatment unit, capable of mechanical treatment with integrated coagulant and polymer dosing, a proprietary modular, compact and cost effective treatment concept.

BACKGROUND

Many of the small sewage treating plants are getting old with heavily worn physical components. Increased environmental awareness has also led to the connection of previously private sewers to the sewage systems, providing an increased load. Combined with higher emission standards and rapid increase of urban population, large investments are often required to sustain a high enough standard and efficiency of the sewage plants.

To face this situation, local authorities must consider if upgrading of the existing sewage treatment plants is profitable in comparison to pumping the sewage on to bigger facilities. If new capacity has to be installed or renovation / rebuilding is preferred, the plants processes and equipment has to be evaluated. In most cases a compact and cost effective device should be taken into evaluation.

Transmission lines to larger plants are in some places justified both from an economic and environmental perspective, especially in urban areas with favorable soil conditions. However, when the distance between plants increase, or when the building of transmission lines is difficult, upgrading of the smaller plants are of great interest.

The requirements for treatment plants will increase in the future and change to e.g. be able to purify wastewater from new environment foreign substances. These new requirements will require technology solutions that are more flexible than those of today.

The access to land around sewage treatment plants is also becoming more strained. Often, living areas have been constructed in the vicinity of the sewage treatment plants, making it important to be able to upgrade or convert older treatment plants without requiring more land. With increased

urbanization, there is a need for a flexible technique with a small footprint for upgrading of setting up treatment plants with a capacity for up to 50 000 people.

SUMMARY

Accordingly, the present invention preferably seeks to mitigate, alleviate or eliminate one or more of the above-identified deficiencies in the art and disadvantages singly or in any combination and solves at least the above mentioned deficiencies by providing a unit for wastewater treatment, said unit comprising: at least one free-standing pre-assembled module; a water inlet and a water outlet, located in opposite sides of the unit; a screening compartment, containing a sieve; a grit trap compartment, containing a horizontal screw conveyor, and an inclined screw conveyor; wherein at least one plate is placed in said grit trap compartment to create a vertical slit where there is a dosing point for metal salts; a polymer dosing zone is located just before the outlet of the grit trap compartment; and wherein a baffle creates a gap at the bottom of said grit trap compartment and a weir creates a horizontal barrier from the bottom of said grit trap compartment followed by a mixing cavity with a polymer dosing point.

This enables a compact system with a small footprint that can be readily installed up to replace or be combined with existing wastewater purification facilities, in a compact cost-efficient manner.

A method for operating this unit is also provided.

DESCRIPTION OF DRAWINGS

These and other aspects, features and advantages of which the invention is capable of will be apparent and elucidated from the following description of embodiments of the present invention, reference being made to the accompanying drawings, in which

FIG 1 shows a schematic of the purification process, according to an embodiment;

FIG 2 shows a cross-section of the purification unit, according to an embodiment, as seen from the top;

FIG 3 shows a 3D sketch of part of the unit, according to an embodiment, from inlet 1 to the outlet 15 where the polymer is added; FIG 4 shows the total phosphorus purification efficiency for a test period of 8 weeks, according to an embodiment, trying 8 different purification strategies;

FIG 5 shows the total COD purification efficiency for a test period of 8 weeks, according to an embodiment, trying 8 different purification strategies; and

FIG 6 shows the total suspended solids (SS) purification efficiency for a test period of 8 weeks, according to an embodiment, trying 8 different purification strategies.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention relates to a compact wastewater treatment unit 1, as disclosed in Figs. 1 and 2. The unit 1 is built up free-standing on legs 2. The unit 1 is built up from pre-assembled modules 3 (c.f. figure 3). The compact unit configuration enables quick installation. The compact unit configuration enables a very small footprint. The compact unit configuration enables easy service and accessibility. The compact unit configuration enables great flexibility for future changes, or upgrades, of the different modules. In one embodiment, the unit is designed for a hydraulic maximum flow rate of 20- 250 1/s. The design flow is preferably approximately 50% of the hydraulic maximum flow. The hydraulic maximum flow rate for the system may for example be 30-100 1/s, such as 30, 60, or 100 1/s.

According to an embodiment, the raw water enters a unit 1 at an inlet 4. The unit 1 is made of stainless steel and has an inlet 4 and an outlet 5 on opposing sides. The raw water enters into a first screening compartment 6, which comprises the inlet 4, a sieve 7 and a level transmitter 8. For systems with a hydraulic maximum flow rate of 20 up to 100 1/s, the sieve 7 is preferably a conveyor sieve 7. For systems with a hydraulic maximum flow rate from 100 1/s and higher, the sieve 7 is preferably a step screen. When a step screen is used, it is preferably arranged at an angle from 35 to 60 degrees, with regard to the horizontal plane of the unit 1.

The sieve 7 is for screening of the raw water. Screening at the sieve 7 removes larger debris from the water, such as fecal, paper, plastics and metals. Screening prevents damage and clogging of downstream equipment and piping. In the embodiment disclosed in FIG 1 to 3, the sieve 7 is a conveyor sieve 7. The conveyor sieve 7 is mounted along the bottom of the screening compartment 6. The conveyor sieve 7 is mounted at an angle, rising up at an angle from 20 to 35 degrees, with regard to the horizontal plane of the unit 1, in accordance with figure 1 and 3. This angle improves effective sieve area, leading to improved capacity, while maintaining an adequate clogging factor. The conveyor sieve 7 comprises a rotating screw 9 and a perforated sieve plate 10. The perforated sieve plate 10 has holes distributed over the plate. The diameter of the holes may be selected from 2 to 10 mm, such as between 3 to 8 mm, such as between 4 to 6 mm. In specific embodiments the diameter of the holes is 3, 5, or 8 mm. Water can flow through the sieve plate 10 while large debris will be caught. Caught debris will be transported from the bottom to the top of the conveyor sieve 7 by the rotating screw 9. In one embodiment, the conveyor sieve 7 transports the de-watered debris from the screen to a removable container 11. The sieve plate 10 is rinsed by brushes 12 attached to the rotating screw 9. In one embodiment, the conveyor sieve 7 can be provided with a flushing system to remove fecal matters etc. In another embodiment, a compacting unit may be installed in front of the discharge in order to reduce the volume of the screening. In one embodiment, the unit 1 is equipped with a wash press, for combined washing and pressing of the screenings. Screening from the sieve 7 is fed into the wash press. Faeces are decomposed by jets of liquid and carbon rich water is returned back to the unit 1. The remaining material is washed with water and compressed in a press zone before being discharged. The wash press reduces volume of the screenings about 2 to 4 times providing effective drainage with total solid (TS) levels of up to 45%.

The level transmitter 8 is used to start the conveyor sieve 7 at desired water levels. In one embodiment, the screw starts when the water level in the screening compartment 6 reaches the sensor of the level transmitter 8, cleaning the sieve plate 10 to lower the water level.

The water that passes through the sieve plate 10 enters a grit trap compartment 13. The grit trap compartment 13 removes heavier particles such as sand, gravel and other heavy solid materials and suspended solids from the wastewater. In one embodiment, the unit is designed to reduce 85% of the grit larger than 0.15 mm in diameter. In another embodiment, unit is designed to reduce 85% of the grit larger than 0.2 mm in diameter. Heavier particles with setting velocities substantially greater than those of organic particles will settle at the bottom of the grip trap compartment 13. The sediment particles are transported via a horizontal screw conveyor 14 in the bottom of the grit trap compartment 13 to an inclined screw conveyor 15. The inclined screw conveyor 15 dewaters and transports the sand and grit from the unit. The inclined screw conveyor 15 is mounted at an angle, rising up at an angle from 20 to 35 degrees, with regards to the horizontal plane of the unit 1, in accordance with figure 3. In one embodiment, the inclined screw conveyor 15 transports the de- watered debris from the screen to a removable container 16. In one embodiment, the unit is equipped with a sand washer, which is installed on the top of the unit 1. The sand washer washes the sand down to a maximum of 3% organic content in the sand.

In another embodiment, an aeration system 17 is installed in the grit trap compartment 13. The air is delivered by a blower 18 which is installed on the unit's 1 framework. In another embodiment, the blower 18 is a standalone unit connected to the aeration system 17. The aeration system 17 keeps organic solids in suspension by providing aeration near the bottom of the grit trap compartment 13. The aeration system 17 system also gathers grease at the surface of the water by floatation. In on embodiment, grease removal is achieved by means of a chain driven surface scraper 19 which collects grease in pump sump 20 from where the grease is pumped with a pump 21 which is installed on the unit's 1 framework. The collected grease is pumped to the conveyor sieve 7 of the screening compartment 6. The grit trap is made of a non-corrosive material, such as stainless steel or plastics.

A coagulation stage is integrated in the unit's 1 grit trap compartment

13. Special design features are included to ensure optimal mixing of added polymers and metal salts. The design of the grit trap compartment 13 ensures a proper mixing and retention time for optimized floc-formation. To create an optimal mixing point, plates 22 have been welded on both sides of the grit trap compartment 13. The plates 22 create a narrower vertical slit 23 for the water to pass through. The arrangement of the plates 22 and the slit 23 creates a slit zone in the vicinity of the slit 23. The slit zone will have an increase in turbulence and flow rate. A dosing point 24 for the metal salt is located in the slit zone, such as right between the plates 22, downstream or upstream the plates 22, while still being in the near vicinity of the plates 22, such that the increase in flow rate and turbulence may be used to improve mixing of a metal salt. In one embodiment, the water velocity is 0.1 to 1 m/s, in another embodiment, the water velocity is 0.2 to 0.6 m/s. In a preferred embodiment, the water velocity is 0.3 m/s. Dosage may be performed with a vertical dosage tube (not shown) arranged in the water, with horizontal dosage nozzles, from which metal salts may be dosed into the water. Preferably, the lower end of the dosage tube is closed. The dosage tube may be arranged in between the plates 22, but it may also be attached, such as welded to the edge of one plate 22. In the latter case, the dosage tube will not obstruct the passage between the plates 22, such that flow characteristics, such as turbulence or flow rate, are impaired. The aforementioned plates 22 are located in the grit trap compartment 13 so that a retention time of, in one embodiment, approximately 5 to 0.5 minutes, in another embodiment, approximately 3 to 1 minutes and in the preferred embodiment, 1.5 minutes is reached after adding of a metal salt. Examples of coagulant metal salts are aluminum chloride, aluminum sulfate, sodium aluminate, aluminum chlorohydrate, poly aluminum chloride, poly aluminum sulfate chloride, poly aluminum silicate chloride, ferric sulfate, ferrous sulfate, ferric chloride, ferric chloride sulfate, poly ferric sulfate and magnesium carbonate.

A polymer dosing zone 25 is located just before the outlet 26 of the grit trap compartment 13. A baffle 27 has been welded between both sides of the grit trap compartment 13. The baffle 27 creates a horizontal barrier which the water is forced to flow under, through a gap 28, such as a horizontal slit. After the baffle 27, a weir 29, such as an outlet weir, has been welded between both sides of the grit trap compartment 13. The weir 29 creates a horizontal barrier which the water is forced to flow over. Between the baffle 27 and the weir 29. a calmer zone is created, ensuring that larger materials will sink to the bottom and not follow the water over the weir 29. The water that flows over the weir 29 forms a waterfall down to a mixing cavity 30 with a polymer dosing point 25. The waterfall created by the weir 29 ensures a water fall height of 0.1 to 0.3 meter, preferably 0.2 m. After polymer mixing, the water flows through the outlet 26. entering a flocculation tank 31 . Examples of polymers are synthetic polymers of different molecular weights. Suitable polymers are cationic polymers. Examples of suitable cationic polymers are polyacrylamide and polyamine, and emulsions of these - singly or in combination. Such polymers have been sold under the trade name Superfloc® by Kemira.

In this separate flocculation tank 31, with special design for creation of flocks suitable for the micro-screen, the water remains for between 1 to 10 minutes, preferably 2 to 6 minutes, most preferably 4 minutes to make sure the flocks are large and strong enough to be caught in a filter. In one embodiment, the tank has a special design where the water is forced to travel down, from side to side and up in order to ensure that the polymer is properly mixed. This is achieved through the position of the of the low water inlet 32 which releases the water at a low, side position in the flocculation tank 31, and the high water outlet 33, that collects the water at a high side position at the opposite side of the flocculation tank 31. In one embodiment, the flocculation tank 31 uses mechanical stirring 37 for optimum floc-formation. In one embodiment, the flocculation tank 31 is built as an integrated part of the unit. In another embodiment, the flocculation tank 31 is a stand-alone part of the unit. The resulting floes have both a size and a strength that are suitable for a drum filter unit 38 micro-screen. As disclosed in FIG 1 and 2, the flocculation tank 31 may comprise two flocculation sections in series, each of them being provided with stirring 37. In this way, the risk for water "short cutting" the flocculation tank is greatly decreased. In this arrangement, the inlet to the flocculation tank 31, just as described above, is situated at one side of the flocculation tank. The flow connection 36 between the first and the second flocculation sections is then situated on the other side of the flocculation tank, such that water will have to pass downstream and transversally of the first section 34 of the flocculation tank 31 to enter the second section 35 of the flocculation tank 31.

Then the outlet 33 is again located on the other side of the flocculation tank 31 in relation to the flow connection 36 between the first and the second sections of the flocculation tank 31, such that the water again must travel downstream and transversally of the second section 35 of the flocculation tank 31 to exit the second section 35 of the flocculation tank 31 - and thus exit the flocculation tank 31.

The surface water collected from the flocculation tank 31 is transferred to a drum filter unit 38 for filtering. The drum filter unit 8 contains a horizontally mounted drum 40 with a filter 39 mounted on the outside of the drum. The water is delivered to the center o the drum filter unit 38. where the filter 39 will start to clog up from floes in the water, casing the water level in the drum filter unit 38 to rise. At a certain level, here around 200 mm. the drum 40 will start to rotate. During rotation, a backwash system 41 uses filtered water or fresh water to rinse out and collect the flocks from the filter 39. The separated floes are rinsed off the filter into a collection trough 42. The resulting sludge will be collected separately 43 while the filtered water will continue thorough the outlet 5 of the unit 1. This careful handling of the solids prevents fragmentation of solids in the drum, enabling higher filtration efficiency. In one preferred embodiment of the invention, the drum filter unit 38 used had a drum 40 made of polyester for good chemical resistance, a filter area of 1 .8 m with a pore size of 100 μ ιπ and a backwash pressure of 7 bar.

Water quality measurements

Automated water samplers have been used to collect water samples from before and after water treatment at the testing locations. The samples have been kept cold and measured in a time proportionate manner. The samples after water treatment have been taken every 15 minutes with a volume of 25 ml per sample. Sludge samples have been collected directly from the filter cloth of the rotary drum filter.

Example 1.

Analysis of total phosphorus have been carried out using Dr. Langes test kyvett LCK348 (0.5 - 5 mg/ml limit). The analysis of total phosphorus uses unfiltered sample water, and the test results are presented in figure 4. For each week, a new water treatment method has been used. When comparing the weeks using only mechanical treatment to the weeks where the chemical addition steps used during process in the invention, the separation

improvement is increased from about 20 % to 80 - 90 %.

Example 2.

The chemical oxygen demand (COD) test is commonly used to indirectly measure the amount of organic compounds in water, making it a useful measure of water quality. Analysis of total COD have been carried out using Dr. Langes test kyvett LCK114 (150 - 1000 mg/ml limit) and LCK314 (15 - 150 mg/ml limit). The analysis of total COD uses unfiltered sample water, and the test results are presented in figure 5. For each week, a new water treatment method has been used. When comparing the weeks using only mechanical treatment to the weeks where the chemical addition steps used during process in the invention, the separation improvement is increased from about 40 % to about 60 to 80 %.

Example 3.

Suspended solids (SS) refers to small solid particles that are in suspension in water as a colloid or due to water motion. SS are important pollutants as pathogens can be carried on the surface of the particles. Phosphor, nitrogen and organic material is strongly associated with SS. SS is commonly used as a useful measure of water quality. Total SS was determined by carefully filtering 50 ml of raw water and 100 ml of purified water respectively through pre-weighed filters, drying the filters to remove all water, after which the filters were weighed again. The water was removed by drying of the filters at 105 °C for at least 60 minutes and by storage in desiccators for at least 30 minutes. The total SS test results are presented in figure 6. For each week, a new water treatment method has been used. When comparing the weeks using only mechanical treatment to the weeks where the chemical addition steps used during process in the invention, the separation improvement generally increases from about 55 % to about 75 to 90 %.

Although the present invention has been described above with reference to (a) specific embodiment(s), it is not intended to be limited to the specific form set forth herein. Rather, the invention is limited only by the accompanying claims and, other embodiments than the specific above are equally possible within the scope of these appended claims.

In the claims, the term "comprises/comprising" does not exclude the presence of other elements or steps. Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by e.g. a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly advantageously be combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. In addition, singular references do not exclude a plurality. The terms "a", "an", "first", "second" etc do not preclude a plurality. Reference signs in the claims are provided merely as clarifying example and shall not be construed as limiting the scope of the claims in any way.

Claims

An unit for wastewater treatment, said unit (1), comprising:

at least one free-standing pre-assembled module;

a water inlet (4) and a water outlet (5), located in opposite sides of the unit (1); a screening compartment (6), containing a sieve (7) and a level transmitter (8); a grit trap compartment (13), containing a horizontal screw conveyor (14), and an inclined screw conveyor (15);

wherein at least one plate (22) is placed in said grit trap compartment (13) to create a vertical slit (23) forming a slit zone, and a dosing point (24) for metal salts in said slit zone;

a polymer dosing zone (25) is located just before the outlet (26) of the grit trap compartment (13); and

wherein a baffle (27) creates a gap (28) at the bottom of said grit trap compartment (13) for forcing water under the baffle (27), and a weir (29) creates a horizontal barrier from the bottom of said grit trap compartment (13) followed by a mi ing cavity (30) with a polymer dosing point (25).

2. The unit according to claim 1. further comprising a drum filter unit (38) downstream the screening compartment (6) and the grit trap compartment (13).

3. The unit according to claim 1, further comprising a flocculation tank (31) downstream the screening compartment (6) and the grit trap compartment (13), said flocculation tank having a water inlet (32) and water outlet (33) as well as mechanical stirring (37), wherein the water inlet (32) is arranged lower than the water outlet (33).

4. The unit according to claim 3. further comprising a drum filter unit (38) downstream the flocculation tank (31).

5. A method for waste water treatment, using a unit according to claim 1 to 4, which comprises:

(a) flowing water through the inlet (4) of the unit (1) into the screening

compartment (6); (b) screening the water from large debris by passing it through a perforated sieve plate (10) within said screening compartment (6), while said large debris is transported away by a sieve (7);

(c) flowing said screened water into the grit trap compartment (13), where grit deposit and is gathered by a horizontal screw conveyor (14) to a inclined screw conveyor (15);

(d) mixing of metal salts in the water in said grit trap compartment (13) at the dosing point (24) for the metal salts just after the vertical slit (23);

(e) flowing the water in said grit trap compartment (13) under a baffle (27) and over a weir (29) after which the water falls into a mixing cavity (30); and

(f) mixing polymers in the water in said mixing cavity (30) of said grit trap compartment (13) at a polymer dosing point (25) for mixing of polymer to increase flocculation.

6. The method according to claim 5, further comprising aerating the water in said grit trap compartment (13) with an aeration system (17), keeping organic solids in suspension and gathering grease at the surface of the water by floatation.

7. The method according to claim 5 or 6, further comprising collecting grease from the surface of the water in said grit trap compartment (13) with an a chain driven surface scraper (19) to a pump sump (20) where collected grease is pumped to said sieve (7) and on to said removable container (11).

8. The method according to any of claims 5 to 7, further comprising flocculating the water in a flocculation tank (31), wherein the water is released from a low water inlet (32), passes though the tank with mechanical stirring to the opposite side and top of the flocculation tank (31) to the high water outlet (33) into a drum filter unit (38).

9. The method according to any of claims 5 to 8, further comprising filtering the water in a drum filter unit (38), where floes are caught by a filter (39) when the drum (40) rotates.

10. The method according to claim 9, wherein the floes are rinsed filter (39) by a backwash system (41) into a collection trough (42).