DK170557B1 - Process for treating sewage and other impure water by means of flocculation - Google Patents

Description

in DK 170557 B1

The present invention relates to a process for treating wastewater or other impure water.

It is known that color, turbidity, organic matter and similar impurities can be removed from water by means of coagulants, for example alum, ferric sulfate or the like. These compounds are acidic and react with all the quality of the water or with alkaline compounds, for example, lime or soda to form bulky insoluble precipitates (hydrates). The precipitates have an extremely large surface area on which the dissolved or colloidally dispersed impurities are absorbed. The suspended impurities are surrounded by the gelatinous hydrates and become part of the precipitate.

Household wastewater and industrial wastewater can be purified by the chemical precipitation process, whereby appropriate chemicals (e.g., aluminum sulfate, lime, iron chloride, polyelectrolytes or combinations thereof) are added to the wastewater, and the wastewater is directed to one or more flocculation tanks, usually equipped with rotary agitators or vanes in which colloidal solids are converted into particles of such size and weight that they will settle. The colloidal solids or flocculates are then separated from the liquid 20 by being allowed to settle in subsequent sedimentation tanks, after which the purified water is collected in a tuning structure mounted at the surface of the water, while the sediment consisting of flocculates and sludge is removed, usually by sludge scrapers and / or pumps.

The prior art, e.g. known from EP-A-0 003 327, 25 discloses the addition of various types of chemicals and combinations of chemicals to wastewater and other unclean water to remove various pollutants therefrom. In the art known from EP-A-0 003 327, the individual process steps are kept strictly separate and the flocculates produced are extremely sensitive, even to very small shear forces, so that inclined sedimentation agents must be used to separate the flocculants. from the water. By the method of the invention, on the other hand, the chemicals used are added in a mixing zone under specified conditions, and large, dense and stable flocculates are formed which are so resistant to shear forces that they are sedimented in a clearing system without the aid of inclined sediments.

Thus, the present invention overcomes, as mentioned above, and further explains a number of shortcomings of the prior art below: 1. The process of the invention, when used * to treat raw wastewater or other unclean water with very economical use, doses of three chemicals, a very large proportion of the suspended, colloidal or dissolved pollutants in the wastewater or other impure water into large, dense and stable flocculants which are so resistant to shear forces that they can be sedimented in a clarification plant without using inclined sedimentation agents and with an upward flow rate of at least eighteen to twenty meters per second. hour. This flow rate is approx. ten times higher than that recommended by professionals for clearing systems without inclined sedimentation agents.

The foregoing is a very important advantage from an economic point of view as it allows for the use of a much smaller clearing plant and reduces the area of the plot required for a treatment plant.

2. Notwithstanding the very economical doses of chemicals used and the flocculation being sedimented at an upward flow rate of 20 to 18-20 m / min without inclined sedimentation agents, the process according to the invention as described below gives rates for the removal of pollutants which are not so far has been possible.

25 30% 35 3 DK 170557 B1

Pollutant Average erosion. %

Biochemical oxygen demand 76% (BODg) dissolved BODg below 5 0.2 / n in size 32% BODjj above 0.2 / m in size 95%

Total phosphorus 97%

Turbidity 95%

Total suspended solids 92% 10 Fats, oils and lubrication 90%

Aluminum Removes all aluminum added to the wastewater or industrial effluent beyond approx.

15 70% of the small amount of aluminum contained in the input stream.

3. The process of the invention represents a considerable improvement over the prior art with respect to the removal of biochemical oxygen demand (BOD 95% of all BODg over 0.2 µm in size is removed and almost a third of BODg less than 0.2 µm in size is further removed.

This condition means that the process of the invention can be used in many places to treat raw wastewater to a standard that does not require further treatment before discharge into streams, while the effluent stream from other chemical systems requires further biological treatment.

Further, when highly polluting wastewater is treated in accordance with the method of the invention and the resulting treated effluent requires additional biological treatment, a significant reduction of the contaminant load of the subsequent biological system results in significant cost savings.

4. When wastewater or other impure water is treated by the method of the invention, the percent removal of suspended solids and turbidity is substantially greater than can be achieved by the prior art, the dose of chemicals and the flow rates through the clearing system taken into account.

This is a very important improvement over the prior art which in many cases eliminates the need for a subsequent filtration process.

In many cases, it also allows the use of additional processes such as ultraviolet disinfection, reverse osmosis, activated carbon and / or ammonia removal using Clinoptilolite ion exchange material without the use of an intermediate filtration process.

Experiments have indicated that, after being treated by the process of the invention and then passed directly through an ultraviolet disinfection apparatus, raw wastewater was effectively disinfected and the resulting total coli mold count was only 10 100 ml.

5. A very important advantage of the method according to the invention in relation to the prior art is its versatility. The present process can be used either as a primary and / or a secondary and / or a tertiary treatment system, and it can advantageously be combined with 20 other chemical, physical or biological processes.

6. Another important advantage of the method according to the invention is the overall speed at which the treatment process takes place. Although the total retention time required is specific to the site in question and depends on such factors as the quality of the inlet stream and / or the required quality of the outlet stream, the total retention time in wastewater treatment is typically less than thirty minutes.

The system is therefore easily automated, which will provide significant economic benefits such as controlling chemical dosages and reducing labor costs.

7. Although specific to the site in question, the quality of the sludge produced by the process of the invention is generally a very high solids content and the sludge is readily thickened shortly. The resulting thickened slurry is then easily dewatered into a high solids cake. This is a very important aspect of the invention which separates the process of the invention from the prior art in that the total volume of sludge to be disposed of is lower than usual, resulting in significant economic and environmental benefits.

The invention provides a process for treating waste water or other impure water by flocculation, by adding (A) an inorganic coagulant, (B) an anionic polymer and (C) a cationic polymer which is characterized in that 1) add A, B and C in a mixing zone, either all three in ndi vi -10 dually or at most two premixed together, with the condition that A either alone or together with B or C is not added last and that B and C are not premixed and added together, and further provided that if A, C and B are added in that order, then A and C are mixed, or mixing is avoided between the addition of A and C, 2) the flocculates separate from the liquid in a separation zone, and 3) removes the treated liquid discharge stream from the separation zone.

Further utility of the invention will become apparent from the following detailed description. It should be noted, however, that the detailed description and specific examples, although they indicate preferred embodiments of the invention, are provided by way of illustration only, as various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description.

Predefined amounts of three chemicals, one from each of the three broad generic groups, namely (A) inorganic coagulants (i.e., aluminum sulfate, ferric chloride), (B) anionic polymers, for example, polar electrolytes and (C) cationic polymers, for example, polar electrolytes. is added to wastewater or other unclean water. The three chemicals are intimately mixed with the wastewater or other impure water in a mixing / flocculation zone to form large dense flocculants from the suspended, colloidal and dissolved pollutants in the wastewater or other impure water, these flocculates being separated from the wastewater or other impure water. water in a separation zone, the treated effluent is withdrawn from the separation zone and a predetermined amount of sludge is recycled from the separation zone to the mixing / flocculation zone. The dosage of the chemicals, the order of addition, the specific chemicals used and the extent and location of the sludge recycle are specific to the plant concerned and depend on such design parameters as: 5 1. The quality of the incoming impure water to be treated .

2. The required quality of the discharge flow or economic and / or environmental and / or health criteria.

Comprehensive testing has been carried out on raw wastewater and other industrial-type waste stream using this method, and it has been found that there are certain combinations in which the three chemicals at economical dose levels can give improved and unexpected results compared to the prior art, while other combinations using the same dose levels yield highly unsatisfactory results under the same test conditions.

The following sequences of additions of the chemicals to the wastewater or impure water are those to be used to obtain the desired results: 20 1) All three chemicals are added separately in the following order: inorganic coagulant (A) anionic polymer (C) cationic polymer (B) 25 2) All three chemicals are added separately in the following order: cationic polymer (B) inorganic coagulant (A) 30 anionic polymer (C) * 3) All three chemicals are added separately in the following order: anionic polymer (C) 35 inorganic coagulant (A) cationic polymer (B) 7) 170) Inorganic coagulant (A) and cationic polymer (B) are mixed in one container and then dosed into the wastewater as a single mixture and intimately mixed with the wastewater, after which -ionic polymer (C) is dosed to the wastewater.

5) An inorganic coagulant (A) and an anionic polymer (C) are mixed in one container and then dosed into the wastewater as a single mixture and intimately mixed with the wastewater, after which cationic polymer (B) is dosed into the wastewater.

In all cases (1) to (5), the amount of inorganic coagulant used is preferably 10 to 1000 ppm, more preferably 10 to 300 ppm and most preferably 30 to 200 ppm. The amount of the anionic polymer and the cationic polymer, respectively, is preferably 0.1 to 50 ppm, more preferably 0.1 to 10 ppm and most preferably 0.1 to 5 ppm. All ppm indications are by weight relative to the impure water to be treated.

For the combinations 1, 2 and 3 above, where each of the three chemicals is added separately, the following general procedure can be used.

(I) A predetermined amount of the first chemical is dosed to the wastewater or other unclean water via one or more injection points in a first portion of the mixing / occlusion zone and intimately mixed with the wastewater or other unclean water, then 25 (ii) A predetermined amount of the second chemical is dosed to the wastewater or other unclean water via one or more injection points in another part of the mixing / flocculation zone and intimately mixed with the wastewater or other unclean water, after which 30 (iii) a predetermined amount of the third chemical is dosed into the wastewater or other unclean water via one or more injection points in a third part of the mixing / flocculation zone and intimately mixed with the wastewater or other unclean water.

(Iv) A predetermined amount of the sludge removed from the solid separation zone is recycled to the mixing / flocculation zone and DK 170557 B1 is dosed into and intimately mixed with the wastewater or other unclean water. The location of the sludge recirculation point in the mixing / flocculation zone and the recycled amount is specific to the plant concerned and depends on the design parameters as described previously.

(V) The time interval between the addition of the first chemical and the second chemical or between the addition of the second chemical and the third chemical in the mixing / flocculation zone is specific to the plant concerned and depends on the design parameters 10 as previously described.

(vi) The time interval between the addition of the recycled sludge and either the preceding or subsequent chemical in the mixing / flocculation zone is specific to the plant concerned and depends on the design parameters as previously described.

(vii) The degree of mixing required in the mixing / flocculation zone is specific to the plant concerned and depends on the design parameters as described previously.

(Viii) The total retention time in the mixing / flocculation zone and separation zone is specific to the plant in question and depends on the design parameters as described previously.

25 For the above combination 1, we have found that in some cases it may be more beneficial to inject some of the chemicals or all into the unclean water in two or more places but maintaining the essential order previously described. The sludge recycle rate can range from 1-20% of the amount of the impure water stream, but 30 is preferably a flow rate of approx. 10%.

The sludge can be recycled to the incoming unclean water at various equal locations, the best location being found when testing the plant.

We have found that a total retention time (mixing and sedimentation) of approx. 30 minutes is satisfactory but can be reduced to less than 20 minutes as needed.

The time interval between successive chemical doses (various chemicals) can vary, for example from just a few seconds and up to approx. 8 minutes, but in general an interval of 5 minutes or less has proved satisfactory.

The upward velocity in the sedimentation tank can vary, for example from 10-20 meters per meter. hour.

For combinations 4 and 5 above, where an inorganic coagulant in a container is mixed with one of the polymers and then dosed to the wastewater or impure water as a homogeneous mixture, then the other polymer is dosed to the wastewater, the following general procedure 10 can be used: ) A predetermined amount of the inorganic coagulant and one of the polymers is mixed in a container and dosed as a homogeneous mixture to the wastewater or other impure water via one or more injection points in a first portion of the mixing / flocculation zone and intimately mixed with the wastewater or (ii) A predetermined amount of the second polymer (i.e., the wastewater or other impure water via one or more injection points 20 in another part of the mixing / flocculation zone and intimately mixed with the wastewater or other impure water.

(iii) A predetermined amount of the sludge removed from the separation zone is recycled to the mixing / flocculation zone and dosed to and intimately mixed with the wastewater or other unclean water. The location of the sludge recirculation point in the mixing / flocculation zone and the recycled amount is specific to the plant concerned and depends on the design parameters as described previously.

(Iv) The time interval between the addition of the homogeneous mixture of the first two chemicals (i.e., an inorganic coagulant and a polymer) and the third chemical, that is, the polymer of opposite charge to that which is mixed with the inorganic coagulant in admixture. - / flocculation zone, is specific to the particular plant and depends on the design parameters as described earlier.

(v) The time interval between the addition of the recycled sludge and either the previous or subsequent chemical dosing in the breathing / flocculation zone is specific to the site in question and depends on the design parameters as previously described. s 5 (vi) The degree of mixing required in the mixing / flocculation zone is specific to the plant concerned and depends on the design parameters as previously described.

(vii) The total retention time in the mixing / flocculation zone 10 and the separation zone is specific to the plant in question and depends on the design parameters as previously described.

The process is suitable for treating wastewater or other unclean water without any further treatment, but in some cases, depending on the quality of the input stream or the required quality of the outlet stream, it may be necessary to adjust the pH or alkalinity of the input stream or outlet stream using methods well known in the art.

Many types of inorganic coagulants can be used in the practice of the invention, for example, aluminum sulfate, alum and ferric chloride, and lime. The specific type of inorganic coagulant to be used is specific to the particular plant and depends on the design parameters.

Many types of cationic polymers can be used and the following have been used successfully: 25 HERCOFLOC 885, HEROFLOC 876, HEROFLOC 849, all from Hercules, Inc. and PERCOL 763 from Allied Colloids Inc. as well as CHEMIFLOC 6350 AND 6999.

Many types of anionic polyelectrolytes can be used and the following have been used successfully: PERCOL 1011 from Allied Colloids Inc. and HERCOFLOC 831 and 847 from 30 Hercules Inc. and CHEMIFLOC 423 and 495.

A process for treating wastewater or other impure water is described in which three chemicals are added to the wastewater in the following specific sequence to generate treated effluent. *

An inorganic coagulant such as alum or ferric chloride is added to the effluent and intimately mixed thereby to produce pretreated effluent. An anionic polymer is then added to the pretreated wastewater and intimately mixed thereby to produce a preliminary DK 170557 B1 π pretreated wastewater, after which a cationic polymer is added to the pretreated wastewater and intimately mixed to produce chemically treated wastewater. The chemically treated wastewater is led [for example] to a separation zone in which the chemically treated effluent and sludge are removed separately. A predetermined amount of sludge is recycled to the mixing / flocculation zone.

In another embodiment of the process of the invention, the anionic polymer is added and intimately mixed with the wastewater to produce pretreated wastewater. Then, an inorganic coagulant such as alum is added and intimately mixed with the pretreated wastewater to produce a tentatively pretreated wastewater, after which cationic polymer is added and intimately mixed with the tentatively pretreated wastewater to produce chemically treated effluent.

The chemically treated effluent may be added to a separation zone in which the chemically treated effluent and sludge are removed separately.

A predetermined amount of sludge is recycled to the mixing / flocculation zone.

In a further embodiment of the process according to the invention, high molecular weight cationic polymer is added and intimately mixed with the wastewater to produce pretreated wastewater. Then, an inorganic coagulant such as alum is added intimately with the pretreated wastewater to produce a tentatively pretreated wastewater, after which anionic polymer is added and mixed for 25 hours with the tentatively pretreated wastewater to produce chemically treated wastewater. Then the chemically treated wastewater is added to a separation zone in which chemically treated effluent and sludge are removed separately. A predetermined amount of sludge is recycled to the mixing / flocculation zone.

In yet another embodiment of the process of the invention, the inorganic coagulant (e.g., alum or ferric chloride) is mixed with the cationic polymer in one container to form a homogeneous mixture which is then added to the wastewater and intimately mixed to produce an provisionally treated wastewater.

Then, at an later stage, an anionic polymer is added which is intimately mixed with the pre-treated wastewater to produce chemically treated wastewater. The chemically treated waste water is added to a separation zone in which the chemically treated effluent and sludge are removed separately. A predetermined amount of sludge is recycled to the mixing / flocculation zone. *

In a further embodiment of the process according to the invention, the inorganic coagulant (e.g. alum or iol ferric chloride) is mixed with the anionic polymer in one container to form a homogeneous mixture which is then added to the wastewater and intimately mixed to produce a preliminary pretreated wastewater, after which a cationic polymer is added at a later time and intimately mixed with the tentatively pretreated wastewater to produce chemically treated wastewater. The chemically treated wastewater is added to a separation zone in which the chemically treated effluent and sludge are removed separately. A predetermined amount of sludge is recycled to the mixing / flocculation zone.

In some cases, it may be advantageous to add one or more of the treatment chemicals to the water to be treated in two or more locations, provided that one of the essential sequences of the invention is maintained.

The amount of predetermined sludge recycled in the process is typically of the order of 1 to 10%, although amounts of 20% or more may be used. This percentage may vary depending on the quality of the input current and the desired output current quality. It can be recycled to the input stream or various locations, with the best location found when trying the plant.

25 Table 1 lists the results of numerous experiments conducted with a mixture of wastewater and industrial effluent using an inorganic coagulant (alum) followed by an anionic polyelectrolyte followed by a cationic polyelectrolyte.

These results show that the process of the invention is suitable for producing an exceptionally high-quality discharge stream over what is heretofore known in the water treatment field in view of the low overall retention time and flocculation rate. #

The process also results in a very high level of microorganism removal level. A sample of raw wastewater was found to have a total number of coli-forming bacteria exceeding 1,800,000 per year. The treated effluent produced by the process according to the invention had a number of coliform bacteria of only 5500 per 100 ml. 100 ml, which represents a removal efficiency of over 99.7%.

When passing through a commercially available ultraviolet radiation system, the same discharge current caused the number of coliform bacteria 5 to be reduced from 5500 to 350 per gram. 100 ml. Other results have shown as low total coliform bacteria as 5 per 100 ml after irradiation of the discharge stream from the method according to the invention.

This is a very important advantage of the process according to the invention since it provides for the disinfection of waste streams a realistic alternative to chlorine, which is known to cause the formation of chlorinated hydrocarbons, some of which may be carcinogenic.

15 20 25 30 35 14 DK 170557 B1

Table 1 1 5 Inorganic Anionic Cationic Inlet-Discharge-Removal Coagulation Polymeric Polymer Current Flow Efficiency Turbidity Turbidity Tet mg / 1 mg / 1 mg / 1 NTU. NTU. % 10 195 1.00 1.46 76.2 0.91 98.8 195 0.85 1.32 77.2 0.87 98.9 162 1.06 1.28 205.0 1.04 99.5 163 1.14 1.29 126.0 0.93 99.3 15 169 1.05 1.28 99.7 0.99 99.0 179 1.24 1.24 117.5 1.01 99.1 185 1.26 1.26 107.1 1.02 99.0 162 0.94 1.01 59.7 1.24 97.9 163 0.94 1.01 58.9 1.26 97.9 20 169 1 , 03 1.10 66.8 1.05 98.4 164 0.82 1.04 83.8 1.14 98.6 165 1.17 1.17 174.6 1.34 99.2 170 0.98 1.20 114.8 1.21 98.9 171 1.06 1.22 114.2 1.50 98.7 25 176 1.07 1.22 94.7 1.47 98.4 163 1.11 0 , 82 97.4 1.09 98.9 173 1.05 0.98 68.4 0.95 98.6 191 1.11 0.96 75.5 1.24 98.4 Ψ

Claims (15)

A process for treating wastewater or other impure water by flocculation, by adding (A) an inorganic coagulant, (B) an anionic polymer, and (C) a cationic polymer, CHARACTERISTICS characterized by: 1. adding A, B and C in a mixing zone, either all three individually or at most two premixed together, provided that A is either alone or together with B or C not last added and that B and C are not premixed and added together; and further provided that if A, C and B are added in said order then A and C are premixed, or mixing is avoided between the addition of A and C, 2. the flocculates separate from the liquid in a separation zone, and 3. removes the treated liquid discharge stream from the separation zone. Process according to claim 1, characterized in that the flocculates are separated from the liquid by sedimentation as sludge. 3. A process according to claim 2, characterized in that at least some of the sludge is recycled to the mixing zone. Process according to any one of the preceding claims, characterized in that in order: 25 first adds B, then adds A and finally adds C. A process according to any one of claims 1 to 3, characterized in that one sequentially: first adds C, then adds A and finally adds B. Process according to any one of claims 1 to 3, characterized in that one sequentially: first adds A, then adds B and finally adds C. A process according to any one of claims 1 to 3, characterized in that in order: first a mixture of A and C is added and finally B. B. 170707 B1 is added. A process according to any one of claims 1 to 3, characterized in that in order: first a mixture of A and B is added and finally C. is added. Process according to any one of the preceding claims, characterized in that A is an iron or aluminum compound or salt. Process according to any one of the preceding claims, characterized in that A is alum or ferric chloride. Process according to any one of the preceding claims, characterized in that B is an anionic polyelectrolyte. A process according to claim 11, characterized in that the anionic polyelectrolyte is a polyacrylamide with negative acrylate groups. A process according to any one of the preceding claims, characterized in that C is a cationic polyelectrolyte. 20 Process according to claim 13, characterized in that the cationic polyelectrolyte is a polyamine or an acrylamide. A process according to any one of the preceding claims, characterized in that the amount of B is 0.1 - 50 ppm, that the amount of C is 0.1 - 50 ppm, and that the amount of A is 10 - 1000 ppm. %