DE1767869C - Process for the purification of fresh and used water by flocculation in the amphoteric phase - Google Patents

Description

The invention relates to a method for purifying water by flocculation using eir.es water-soluble Zinc salt, such as zinc chloride, in a weakly alkaline medium.

The treatment of the water in order to practically remove the suspended and dissolved organic substances from them has so far been carried out in the wc -ntlich.-nj ₀ by means of filter beds which mainly consisted of 14% sand. If these filter beds cannot achieve the degree of retention required for adequate cleaning, then predominantly flocculation processes are used. those using iron or aluminum salts with extensive use of kalkhy ". council to be executed.

The chemical and chemical-physical investigation the constituents of organic pollution in fresh water and household waste water results in most of the organic pollutants being those that are weakly acidic or weakly basic and in most cases amphoteric in character.

The use of flocculants with a strongly acidic or basic character appears with regard to the conditions for a strong reduction in the solubility of organic substances with amphoteric Behavior not particularly suited to being.

The means of aluminum salts, commonly used for the treatment of fresh waters a breach of the equilibrium of the phases is sufficiently complete to obtain water, the remaining ability to oxidize to potassium permanganate is considered to be satisfactory.

In the case of household wastewater, however, it is after treatment with aluminum salts determined residual oxidation ability still / u great, and for using this flocculant therefore, such amounts are required that the process is no longer appropriate. The household sewage are therefore systematically cleaned biologically. Aluminum sulfate leads furthermore, too poorly sedimentable and difficult to dewater Flakes, besides that sedimentation takes a relatively long time Without leading to positive results, flocculation viruses have also been tried, which on the use of differently modified starch products combined with other compounds are established as flocculants.

Another flocculant, which is mainly used to clean the water from phosphates (the in the form of orto- and polyphosphates) is used, is trivalent iron, in general in the form of ferric chloride. The results obtained with this remedy are better than those which are achieved with aluminum sulfate, but there are other disadvantages. like the coloring of purified water, which can be reused as drinking water resulting in the formation of very prevents voluminous sludge.

Attempts have also been made to use zinc salts, particularly zinc chloride. In this regard, LSA. Patent 1 966 733 describes an ancestor for water purification in which the water to be purified contains a water-soluble compound of cadmium. Zinc and manganese, such as a chloride, a nitrate or a sulfate, is added, the stated purpose of this addition being that. eliminate the hardness of the water / u due to the presence of dissolved silicon in the water. which is deposited in the form of insoluble silicate. Since free acid is formed in this way, it is then neutralized with an appropriate alkali.

Also in ISA.-Patent 2,074,082 is the Use of inorganic zinc salts for Flockuni: suspended substances explained which in canal water and dirty water previously subjected to biological purification would.

Finally, the USA patents 2 511 2 ^l ) -> and 2 300 693 mention the use of zinc chloride for water purification or for purifying sewer water.

However, in the processes used so far, 1 had the zinc salts and, in particular, the zinc chloride did not succeed, but were instead caused by coagulation or flocculants based on aluminum and iron are displaced.

In contrast, the method according to the invention the advantage that the effectiveness of the Zinc salt as a loosening agent g-üz significantly improved will. This is achieved by the addition of alkali borate according to the invention, which is achieved by the S'and the technology was in no way suggested. Although the buffering effect of alkali borate η is known, however, this buffering effect occurs at a pH of about 9.22, whereby it is required is. a boric acid solution of at least 0.01 molar corresponding to a boron content of 0.12 g / l should be used The amounts of alkali borate used in the process according to the invention for adjustment of the pH range are many times lower, so that a buffer effect actually can not be spoken at all and the results achieved are therefore completely surprising. Of the white tercn is the content of orthophosphates in the Method according to the invention to 0.036 mg I crnied rigt. although from the literature reference F. G. Z h a ravskiy, Trudy Komissii Anal, Khim. Akad. Naul URSS 3 (1951) s ". 486, it is known that a residue Soluble wedge at POj ions of 0.3 ιΐι ^, 'ί the actual

equivalent solubility. Also the hocheradiee Reduction in the content of protein substances in the purified water, demonstrated by the low content of residual protein nitrogen. together with the very high flocculation rate surprising and represent a significant technical advance.

The method according to the invention for cleaning water by flocculation using a water-soluble zinc salt, such as zinc chloride. in a weakly alkaline environment is characterized by this. that after a possible pre-adjustment of the pH value to 7.4 to 7.8 by means of a strong alkali, for example caustic soda or caustic potash, a pH range of 7.8 to vS.5 is set by means of an alkali borais. _{! 5} where the amount of alkali borate added corresponds to an increase in the pH value of at least 0.4 units.

Be. --τλτ be \ < rzug'en Xustuhrup ^ Wm des erfiniu: : nL3en Ver.j.irens are called Mkaliborat Man, r.itetra- or sodium metaSorate or a mixed,: hi-r \ on used.

{). · PH value is adjusted to 7 κ b; ·, see 2 using an alk. --hen boric acid salt divided into the lall of water · ■ ">. whose pH value is lower than" .4 ·, - :. can the '.ilischen boric acid salts da / u serve the pH-Wc ·. ^h '.s to regulate 7.x to H.5, but daK .me could be overly large applications; he go in this fa! For the regulation of the pH and a strong aifc, the acid salts are used for the control of the pH value by at least 0.4. nphoteric of boric acid and its size in the pH: 5-rich in which the flocculation is influenced Seven of the same. At the same time, an extremely strong Phcphatent'Vrnung is realized in this fan, irrespective of whether it is local phosphates or polyphosphates. The sewage holding wastewater treated by the process according to the invention has a residual DbO, value. the value for their drainage is below the value stipulated by the standard. Since interest in the process is also given, the sludge, which consists of the flakes formed by means of zinc under the conditions described, precipitates in less than 15 minutes and after it has been separated from the treated liquid can be easily thrown and thus immediately subjected to cremation.

After this sludge has been separated off by precipitation, that which is being treated becomes Filtered water by means of a fixed bed of activated carbon, in particular one in a parallel application the same applicant described bed can be used. The main task the charcoal is the one to collect the detergent, which escape any flocculation process. The filtration gives a completely clear, colorless and odorless Filtrai. The Filirat no longer produces a permanent foam when stirred, which is due to the effect of the special charcoal mentioned is due to the detergent.

The crlmdungsuemäße method was also used to F.niphosphaticrung of waters which abgege- of Haushaltungsabwasserrcinigungsanlagen Unn be that work on a biological way.

The use of zinc in amphoteric agent has been found to be better than that with trivalent one Iron achieved action, which is the best phosphate flocculant. While the iron in strong Excess of the amount of ortophosphate to be removed is used, realizes the use of zinc under the conditions according to the invention, the precipitate of its stoichiometric. Chen values in phosphoric acid and also more, after the polyphosphates have largely been suppressed are.

The process was also used for the flocculation of the active sludge, which is produced by biological means by the secondary decamation devices of cleaning plants. Sludges of this type, containing 0.5 to 1% solids, were flocculated with the aid of zinc chloride under the conditions of use of the invention. This sludge precipitated in 20 minutes.After decanting the clear liquid above, its solids content is still about 4V and after centrifuging the product obtained has a solids content that is> 4 ° ₀ and even up to 20 ° α greater is.

Flocculation in the imphoter phase is a pretreatment in the case of the purification of numerous industrial wastewater, such as wastewater from plants that produce adhesives with a protein structure or from industries that use this type of adhesive, in particular factories for the production of wood agglomerates. who work in the Naßoücr semi-wet experience. Such water decant only in extremely small form and have a very high DBCV value. which requires lengthy, costly biological cleaning. The iron and aluminum salts can never cause the intended flocculation due to the colloidal substances present. Allow the method according to the invention! it, however, to achieve an extensive flocculation, and the water can Jiit a DBO "value to be drained, which is not mg greater than 20 O ₁ 1, and which prescribed delivered standard within the public in the various countries for preventing the contamination of water by far Limits. In the case of the water which is used in factories for the production of wood agglomerate panels, the flocculation according to the invention must be supplemented by a second flocculation by means of ferric chloride, which is then possible. to knock down the substances of Osian and Polyosic character, which the flakes produced by the zinc could not carry away.

example 1

10 1 lake water, which was taken near a heavily muddy bank, were used mixed with 0.4 ml of a zinc chloride solution containing 32 Be. Then 0.3 ml of a solution were added, the per liter 1 mole of sodium metaborate and one contained the same weight of sodium tetraborate. By adding caustic soda 2 N, the pH was adjusted brought to 8.2. Flakes quickly formed, the decanted in about 20 minutes. The treated water was then filtered through activated charcoal and had a residual oxidation capacity of 2.5 mg O. 1 after this filtration.

Example 2

250 l of the effluent from a biologically working household sewage treatment plant was pre-filtered on activated carbon and then 5.5 g of zinc chloride were added. Then 10 ml of a solution were added which contained 1 mol of sodium metaborate and the equivalent amount by weight of sodium tetraborate per liter. The pH was adjusted to 8.2 using 2N caustic soda. A mass of very thin flakes formed, which were passed through a filter layer made of very porous activated carbon. The completely clear, foam-free filtrate contained less than 1 g of ortophosphate per cubic meter, and its oxidizing capacity was 2.5 to 3 mg O ₂ I

Example 3

1 1 sludge from a secondary decanter of a biological household sewage treatment plant 0.175 ml of a zinc chloride solution containing 32 Be was added. Socann was 1 ml Added to a molar sodium metaborate solution, and the pH was adjusted to 7.8 to 8.2 with caustic soda 2N. One came up very quickly Coagulation and flocculation of the sludge. which was reflected and a clear one about it Left water, which was practically free of urophosphates. The one subjected to a centrifugal process The sludge became considerably rich in solids. the mean content of which was 18%.

Example 4

101 household wastewater was treated with 1.3 ml of a molar sodium metaborate solution immediately after sieving. Then 1.75 ml of zinc chloride with 32 Be were added. The pH was adjusted to 8.2 with the aid of 5 to 5.5 ml of 2 N caustic soda. Abundant flakes formed immediately and _{precipitated in less than 4} hours. The precipitated flakes were subjected to a centrifugal process and heated in a porcelain container, during which they were consumed very quickly without odor and left a carbonaceous residue from which the Ζϊηκ can be recovered.

Example 5

10 liters of waste water from a factory for the production of wood agglomerate panels by the wet process were mixed with 4.8 ml of a zinc chloride solution with a titre of 32 Be. 5 ml of a molar sodium metaborate solution and about 20 ml of 2N caustic soda were added to adjust the pH to 8.2 to 8.4. Abundant flakes formed and the water was completely clear with any colloidal phase broken. The rapid precipitation of these flakes made it possible to collect a sludge which was then thrown out. The sludge exposed to the heat decomposed at a temperature of approximately 300 ^° C. and left a carbonaceous residue, from which the zinc could be recovered. The solution located above the precipitated sludge was treated with 2 ml of a ferric chloride solution which contained about 44% FeCl ₃ . After this addition, flakes formed which, through precipitation, formed ferric sludge that carried along with the osseous and polyosic components which had escaped the effect of the zinc. The water purified in this way had a residual DBO ₅ value of less than 10 mg O ₂ when it was drained,! with an initial value in the order of magnitude of 4800 mg O ₂ Zl.

In order to demonstrate the advantages achieved according to the invention even more clearly, the following are the results cited of experiments, which using the method according to the invention in association with the use of filter media on the basis of activated carbon of the kind carried out, as described in the parallel application of the same date of the applicant.

The reagents were mixed with the wastewater to be treated in a cylindrical Reaction vessel with a capacity of

200 1 by means of an agitator. The desired pH value was set using a pH meter with Glaselek '3de. after which the stirring was stopped and left alone for 1 hour. Finally the clarified liquid was siphoned off and filtered through a layer of carbon contained in a glass column. This carbonic acid had a height of 100 cm and a diameter of 3 cm, corresponding to a volume of 700 cm ³ and a weight of about 140 g (specific gravity about 0.2). The filtration rate varied between 6 and 12 m hours. The filter was periodic washed in countercurrent using from 4 to 5 ° C. of the previously purified water at a rate of from 12 to 18 m / hour

(Buffer), B (flocculant) and C (alkalizing agent) designated. Each trial was followed by a trial with a 2-1 sample to determine the most appropriate Dosage beforehand.

The sludges were collected and examined. Samples of the raw liquid, the clarified one, were also taken Water and the discharge from the carbon filter after certain volumes of water have passed through analyzed

A. Experiments with water from the Olona river

25 liters of liquid were used with the following amounts of reactant: A - 7 cm ³ , B - 9 cm ³ and C - 25 cm ³ . The liquid was

Stirred vigorously for 3 minutes and then weakly for 7 minutes and finally left to stand for 1 hour. After this case: andlung was the pH We ^r t 8.2.

Precipitation was complete in 15 minutes and after one hour the clarified liquid became lifted and at a speed of 11 m / h. filtered through activated charcoal. The muds were chilling

4 percent by volume of the treated water, by spinning for 5 minutes at 2500 revolutions per meter ^; However, they were reduced to 0.4 percent by volume.

The results of the analyzes are given in Table 1 below, in columns 3 and 4 of which the Results of the analyzes after filtering 2 resp.

201 are given.

B. Experiment with cesspool fluids

Liquids were used in 2001 with the following amounts of reactants: A - 26 cm ³ ; B - 35 cm ³ and C - 60 cm ³ . It was stirred vigorously for 3 minutes and weakly for 7 minutes and then

then left alone for 1 hour. The pH was then 8.2. After an hour it was the clarified liquid wedge is lifted and at a speed of 10 m / h. filtered through activated charcoal. The results of the analyzes are shown in Table 2.

C. The experiment with cesspool fluids was repeated twice more, using the following amounts of reactant under otherwise identical conditions: A - 52cm ³ , B - 70cm ³ and C - 125cm ³ . The pH was found to be 8.40. The sludge made up 2 percent by volume of the

treated water, but were spun (5 minutes at 2500 rpm) to 0.4 percent by volume reduced. The slurries were also easily filtered and filtered by adding 22 g and on the When filters of air-dried sludge were calcined in a porcelain jar, 2 g of one was obtained predominantly ai's zinc oxide existing gray residue.

The results of the analyzes are given in Tables 3 and 4, the filtrations with a speed of 10 or 6 m / h. were executed.

Table 1
Try with water from the Olona River

Characteristics of the water

Olona Clarified After filtration After filtration (upon removal) after flocculation 21 201 cloudy yellow pale yellow cloudy colorless clear colorless clear nauseating easy odorless odorless Disgusting 7.5 8.2 7.9 7.9 117 37 - - 52 7th 1 '2 5.2 0.21 0.08 0.06 3.8 0,! 6 0.06 0Ό5 highly resistant pretty consistent no no

Color .
odor

PH value

Suspended Solids (per million)

A. O. 4 hours (per million)

Total phosphorus (PO 4 per million). Polyphosphates (PO 4 per million),

foam

N. B. A. O. 4 hours: residual oxidizing capacity on permanganate after 4 hours

Table 2
Experiment with sewer water

Characteristics of the liquid in the channel
(upon removal)

Clarified after flocculation

After filtration 201

color

odor

PH value

Suspended Solids (per million)

A. O. 4 hours (per million)

Total Phosphorus (PO4 per million) Polyphosphates (PO4 per million) .. Foam -

cloudy yellow
nauseating

8.1
230
82
7.8
4.7
highly resistant

pale yellow cloudy
nauseating
8.2
52
32
3.8
3.1
pretty consistent

colorless, slightly cloudy

odorless

8.1

12 1.2 1 Toil of short duration

Table 3
Experiment with sewer water

Characteristics of the liquid

color

odor

PH value

Suspended Solids (per million)

In the canal

(dcx

yellow cloudy

nauseating

8.1 272 Clarification after freezing

pale yellow cloudy

easy

nauseating
8.4

28 To Filtration

201

colorless
least

Cloudy
odorless

83

To
FU trienin?

40!

colorless
slightly cloudy

nearly

odorless
8.4

After washing the filter

colorless slightest

Cloudy odorless

After filtering

601

colorless slightest

Cloudy odorless

83

continuation

Characteristics of the liquid

In the sewer j clarification ! With removal) j after flocculation after
Filtration

: »■

To
nitration

401

After washing the filter

To

Filtration 601

A. 0.4 hours (per million) Total}; ijospbor (PO4

per million)

Polyphosphates (PO4

per million)

!Foam

98 9.2

5.4

highly resistant

A. B. S. (per million)

Ammoniacal nitrogen (N per million)

32.6

9 0.3

0.21

pretty consistent

3.7

3.2 2.6 0.12

0.11 no

0.4 0.1

3.7 0.16

0.14

of lower length of time

1.1

0.17

2.1 0.13

0.13 almost none

0.62 0.08

1.6 0.13

0.13 almost none

0.4 0.11

N. B-AB S .: Synthetic detergents.

Table 4 Experiment with sewer water

Characteristics of the liquid

Clarified in the sewer (at removal)
after flocking

To

Filtration

201

To

Filter valve 401

color

odor

PH value

Suspended Solids (Per Million) A.O. 4 Md. (Per Million)

Gcääiüiphoäphäie (PO4 pTC

Million)

Polyphosphates (PO4 per million).

foam

A. B. S. (per million) Ammoniacal nitrogen (N per

Million)

yellow cloudy nauseating

8.1 272 98

9.2 5.4 highly resistant

3Z6 light yellow cloudy easy

8.4 32

0.47 0.31

resistant 3.9

- 2.8

The following Tables 5 and 6 illustrate the percent reduction in contamination by means of flocculation and by means of flocculation and subsequent filtration through activated carbon. The details of this Tables are in themselves very meaningful and confirm that the flocculant is in buffer solution is far cheaper than aluminum sulfate and ferric chloride, both in terms of the required quantities and the degree of purification that can be achieved, and finally the complete dewatering of the sludge, from which the reagent can easily be recovered.

Table 5

Percentage reduction in contamination due to flocculation

colorless almost clear odorless

1.6

0.13
0.11

almost none 0.4

0.12 Table 6

colorless almost clear

odorless

83

1.4

0.07 0.07 none 0.1

0.06

Percentage reduction in contamination by flocculation and filtration by activated carbon

Keutizcicttco

Suspended party fabrics

A. O.

Total phosphorus

SECTION

Ammoniacal nitrogen

Olona

68
86
96

liquid

the table

77 61 51

liquid

the table

45
Identification ponds Olona Liquid
the table
·> Liquid
the table Suspended Fcst
5 ° fabrics
A. O.
Total phosphorus
55 A. B. S
Ammoniacal
nitrogen 100
95
99 100
85
85 100
98
98
80 to 87
99

90 91

97

Uni the special value of the srfmdungsgemäBen The procedure for dephosphating the water is shown in the following table 7 Results of experiments reported, which with

Wastewater from the purification plant in Lausanne was carried out with the rocking agent below has been treated under the conditions described above.

11 V

Table 7 Attempt at dephosphating the wastewater from the cleaning plant

12th

in Lausanne

Days

Ortophosphale (mg / 1)

Polyphosphates (mg / 1)

Total (mg / 11

Dry matter (mg / 1)

DBO ₅

(mg Oj / 1)

Clock: 11.15

1

2

3

Clock: 3 p.m.

1

2

3

4.0 0.4

16.0 7.5 0.5

2.0 2.6

4.6 2.5 1.5

6.0 3.0

20.0 10.0 2.0

5.2

7.5 0.4 0.0

Clock: 14.15

1

2

3

Clock: 16.30

1

2

3

Clock: 13.50

1

2

3

5.0 5.0 0.5

7.5 7.5

IwI

7.5 S ₂ O 0.7

5.0 2.5 0.3

0.0 0.6

2.5 2.5 2.2

10.0 7.5 0.8

7.5 1.0

10.0 7.5 2.9

7.0 05 0.1

6.0 0.4 0.0

5.0 0.4 ÖÖ1

Clock: 2 p.m.

1

2

3

Clock: 16.45 1

3.

6.0 6.6

0.7

5.0 5.0 0.7

6.0 2.0 1.8

5.0 3.0 2.0

12.0 8.0 2.5

10.0 8.0 2.7

5.0 02 0.0

4.3 0.3

| oö

11.5

1.5

14.5 1.3

Clock: 2:20 pm

I.

2.

3

Clock: 16.00

1

2.

3

10.0 74 (oil oil

5.0 5.0

3.0 22

14.5 '0.5 2.8

2.0 1.0 0.7

Remarks

7.0 6.0 1.0

\ b \

ι Decanting equipment

: Water according to Voifittriemng through activated carbon.

: Water after flocculation and feeding through activated carbon.

4.1 0.1

Eöj

4.1 03

10.2 10.2

10.6

Claims (2)

Patent claims: 1. Process for purifying water by flocculation using a water-soluble zinc acid. such as zinc chloride, in a weakly alkaline medium, characterized in that after a possible pre-setting of the pH value to 7.4 to 7.8 by means of a strong alkali, for example Caustic soda or caustic potash, set a pH range from 7.8 to 8.5 using an alkali borais is, the amount of alkali borate added increasing the pH by at least 0.4 units. 2. The method according to claim 1, characterized in that that the alkali borate is sodium tetra- or sodium metaborate or a mixture thereof is used.