DE3838864A1 - Process for precipitating out and flocculating dissolved water and waste water constituents and suspended matter in water treatment - Google Patents

Abstract

Process for precipitating out dissolved water and waste water (effluent) constituents and flocculation of suspended matter in drinking water and service water treatment, in the purification of municipal and industrial waste waters and in the conditioning of process and circulation waters, the resulting flocks being separated off from the water in a manner known per se by iron(III) salts and/or aluminium salts which contain nitrate as anion.

Description

The present invention is a process for Precipitation of dissolved water and wastewater constituents and flocculation of suspended solids during drinking and process water treatment, in the cleaning of communal and industrial wastewater and in the conditioning of Process and circulation waters and separation of the formed Precipitation and flocculation of water, in which precipitation or flocculants iron (3) - and / or aluminum nitrates used and the dosed cations and anions as far as possible be removed.

The use of iron (3) and aluminum salts as precipitators or flocculant in the water treatment is known for a long time.

According to DE-AS 19 07 359, Sp. 1, lines 54 to 65, count to the usual flocculants aluminum sulfate, iron (II) - Sulfate, Ferric Sulfate, Iron (II) Chloride, Iron (III) - chloride and aluminum chloride. These flocculants cause the coagulation of substances to be treated in the Water is suspended or dissolved and by sedimentation difficult to sell.

A disadvantage of the above flocculant is seen therein that they only have a limited effect and not can be used for all purposes.

In DE-AS 19 07 359 are still basic metal salts the formula

M _n(OH) _mX_{3 n-m}

where M is an aluminum or trivalent iron atom, n is a number between 1 and 20, X is a monovalent anion, 3n is greater than m , and M / X is between 1.5 and 200, used as the precipitating and flocculating agent to show a beneficial effect in the treatment of wastewater, especially waste water from the paper industry.

Finally, from DE-AS 19 07 359 also flocculant solutions known for water treatment, which itself from a basic metal salt of the formula

M _n(OH) _mX_{3 n-m}

in which M is a trivalent iron or aluminum atom, X is an anion from the group Cl, NO₃ and CH₃COO and 3 n is greater than m , derive the basicity of the metal salt (m / 3 n · 100) in the range of 30 to 83% and a polyvalent anion Y has been introduced into the basic salt in such an amount that the molar ratio Y / M has a value of 0.015 to 0.4.

A disadvantage of the above precipitants and flocculants is now seen therein that in the reaction of the precipitation and Flocculant in the water by hydrolysis only the cations Iron and aluminum are precipitated again, the anions but remain in the water. This has the consequence that the pH Value of the water is shifted to the acidic range. At the same time there is an undesirable Aufsalzung of Water. In low-buffered waters, the pH value can be Shift even go so far as to get one for the flocculation setting unfavorable pH value and an addition of neutralizing agents is required.

In heavily contaminated wastewater with a corresponding high precipitation requirement and in circulating waters, which are repeated can be treated with acidic metal salts, thus pH shifts and salinities can be achieved, which exceed the official limits for the discharge of waste water and concrete and metal aggressiveness.  

Nitrate ions are also used in drinking water treatment their adverse health effect undesirable. you must be removed as far as possible in the treatment of water become. Probably for this reason are in practice nitrate ions containing iron and aluminum salts as precipitates and flocculants have not been used previously.

It was therefore the task of a method for precipitation of dissolved water and wastewater constituents and Flocculation of suspended matter during drinking and process water treatment, in the cleaning of municipal and industrial Waste water and in the conditioning of process and To find circulating waters, in which the above disadvantages avoided and in addition to the dosed cations and the dosed anions are eliminated from the water.

Surprisingly, the task may be easier Be solved by iron (3) - and / or aluminum salts be dosed in dissolved form in the water, as Anion nitrate, and then these nitrate ions in the absence of oxygen dissolved in water to molecular Nitrogen can be reduced. Containing as nitrate ions Aluminum salts can be both basic and non-basic Aluminum nitrates are used. When using iron (3) - Nitrates are preferably the hydrated nitrates However, the basic iron (3) nitrates can also be used be used successfully.

The nitrate solutions to be dosed can be both saturated Solutions as well as in the form of prediluted solutions used become.

The reduction of the aluminum and / or iron salts in the water to be treated nitrate ions can with reducing agents already in the to be treated Contain water, have formed there or the Water only at or after the addition of the precipitant or flocculant have been added.  

According to a particularly advantageous embodiment of the invention the reduction of nitrate ions to molecular ones takes place Nitrogen due to microbial metabolic processes during degradation of organic water ingredients, that is, by denitrification. As you know, many aerobic bacteria can contribute Absence of dissolved oxygen, the oxygen of the nitrate to cover their own oxygen demand and thus the nitrate to reduce elemental nitrogen, which is used as gas in the Atmosphere escapes.

For the denitrification of the nitrate nitrogen are suitable many of those abundant in activated sludge systems Bacteria, z. Pseudomonas, Micrococcus, Denitrobacillus, Achromobacter u. a. They can be without adjustment problems in the anoxic milieu from oxygen respiration to nitrate respiration change. Under certain conditions can Oxygen breathing and denitrification even side by side occur. Essential for the operational safety of the denitrification stage is that a sufficient amount of organic Carbon compounds in wastewater or activated sludge is available.

After a particularly favorable procedure of the invention becomes the nitrogen released in the denitrification step for the deposition of the precipitants and flocculants Flakes and existing suspended matter used under flotation. For the deposition of the flakes can also with advantage Screening machines, lamellar clarifier and / or sand filter used become.

The essence of the invention is seen in that the Water treatment and purification with precipitants and flocculants, containing nitrate as an anion, is carried out so that both the cations as well as those added with the flocculant Anions are removed, and already in two Stages.  

In the first stage, the chemicals are in the form of stable Add solutions to the water in which they are made substances to be removed from the water, for example particulate matter, COD, BOD and phosphates, precipitate or flocculate.

In the second stage, the nitration is done with the flocculant by denitrification disassembled and removed.

According to a particularly advantageous embodiment of the invention the nitration is decomposed into nitrogen and oxygen and the escaping gases are used for the separation of Suspended matter used by flotation.

Another advantage of the method is further seen in that the oxygen to avoid fermentation and decay processes can be used in the water systems. Also can for the microbial decomposition of organic water constituents be used.  

The object of the present invention is based on the following examples and the schematic drawings explained in more detail.

In Fig. 1,

1 Aussiedlerhof
2 fäkalhebeanlage and metering
3 Pipeline NW 80
4 shaft
5 channel NW 400
6 sewage treatment plant

In Fig. 2,

7 inlet
8 precipitant dosing
9 primary clarifiers
10 aeration plant
11 secondary settling tanks
12 process
13 mud circulation

In Fig. 3,
14 inlet
15 mixing containers
16 primary clarifiers
17 animation
18 secondary clarifiers
19 process

In Fig. 4,

20 inlet
21 primary clarifiers
22 animation
23 secondary clarifiers
24 mud recirculation
25 expiry

In the examples, two conventional flocculants were used and two flocculants according to the invention.

1. iron (3) chloride sulphate solution
2. aluminum sulphate
3. Iron (3) nitrate
4. Aluminum nitrate

1. iron (3) chloride sulphate solution (FeClSO₄)

Used as a 40% solution with a density of 1.5

Iron (3): 11.95 wt% = 179 g / l = 2.134 mol / kg
Chloride: 7.57% by weight = 114 g / l
Sulfate: 20.48% by weight = 307 g / l
Water: 60.0% by weight = 900 g / l

2. aluminum sulphate crystalline. Al₂ (SO₄) ₃ · x H₂O (here x = 13.5)

Aluminum: 9.23% by weight = 3.419 mol / kg
Sulfate: 49.23% by weight
Water: 41.54% by weight

3. Iron (3) nitrate Fe (NO₃) ₃ · x H₂O (here x = 7.6)

Iron (3): 15% by weight = 2.679 mol Fe / kg
Nitrate: 49.82 wt.% = Equ. 38.57 wt.% Oxygen
Water: 35.18% by weight

4. Aluminum nitrate Al (NO₃) ₃ · 9H₂O

Aluminum: 7.2% by weight = 2.667 mol Al / kg
Nitrate: 49.6% by weight = equiv. 38.4% by weight of oxygen
Water: 43.2% by weight

In all comparative experiments, product 1 was supplied (40% solution) and products 2 to 4 as solutions of the dry products. Refer to the dosage information but on the corresponding dry product.

Example 1 ( Fig. 1)

A Aussiedlerhof ( 1 ) has a Fäkalhebe- and -zerkleinerungsanlage ( 2 ) and drained via a 2 km long pressure line NW 80 ( 3 ) in the Steinzeugkanal NW 400 ( 5 ), which leads to the municipal sewage treatment plant ( 6 ).

Because of the sometimes very long residence time of the waste water in the pipeline ( 3 ), oxygen-consuming to anaerobic degradation processes can not be avoided. For this reason, the wastewater is especially in the morning at the outlet shaft ( 4 ) in the channel NW 400 a dark, non-sedimenting suspension with a strong foul smell. The H₂S detection with lead acetate paper is positive.

A precipitation and flocculation chemical was added to the waste water in ( 2 ) in the four comparative experiments a) to d).

a) iron (3) chloride sulphate solution,
namely 165 ml / m³ = 250 g / m³
b) aluminum sulfate 155 g / m³
c) Aluminum nitrate 200 g / m³
d) iron (3) nitrate 200 g / m³

The selected dosage amounts correspond to 0.53-0.536 moles of Al or Fe (3) per m³ wastewater.

Result To a)

The dark waste water at the transfer point ( 4 ) turned deep black after metering in the iron (3) chloride sulphate solution and even colored the remaining wastewater in ( 5 ) black. There were no sedimenting flakes. The H₂S detection reaction was negative. There was only a faintly foul odor detectable.

With the flocculant, the effluent 70 mg / l of sulfate and Chloride fed.

To b)

2

Starting conditions as in a)

After addition of the aluminum sulphate solution to ( 2 ) flakes were formed at the transfer point ( 4 ) and in the entire waste water stream to the treatment plant ( 6 ).

The wastewater was compared to the untreated wastewater colored lighter. However, it had the same strong putrid Odor like untreated sewage. The H₂S detection with lead acetate paper remained strong positive.

With the flocculant, the wastewater received 76 mg sulphate / l added.

To c) Starting conditions as in a)

After metering in the aluminum nitrate solution, the wastewater took on a gray-brown color at ( 4 ). The suspended solids were largely flocculated. The wastewater no longer had a foul odor, but the typical smell of fresh sewage.

In the afternoon with more wastewater flow and shorter residence time in the NW 80-pressure line ( 3 ), even a few residual nitrate contents could be found in ( 4 ).

With the flocculant 99 mg of NO₃ / l were added to the wastewater, which corresponds to 76 mg of oxygen per liter.

To d) Starting conditions as in a)

After metered addition of the iron (3) nitrate solution, the wastewater was removed a brown color. The results were as in c).

With the flocculant 99 mg NO₃ were added to the wastewater, which corresponds to 76 mg of oxygen per liter.  

The above comparative experiments show that in a long Dwell time of the waste water under exclusion of air in the hydrogen sulphide channel can arise. In experiments a) and d) is the hydrogen sulfide formed precipitated as iron sulfide.

Prevent the precipitants and flocculants according to the invention in c) and d) the digestion processes already under anoxic conditions by oxygen separation.

Particularly effective and reliable is experiment d). This is due to the fact that the iron in the iron (3) - nitrate even in case of severe underdosing, ie in the case of oxygen deficiency, the resulting hydrogen sulfide as iron sulfide precipitates and due to the black sewage discoloration indicates the underdose.

Example 2 ( Fig. 2)

A municipal sewage treatment plant at the time of the grape harvest compared to the design data has a feed ( 7 ) with multiple overload with organic substances, especially with easily degradable compounds such as fructose and fruit acids.

The rectangular sales basin ( 9 ) for mechanical pre-treatment of this wastewater has a Längsräumer and a Schwimmstoffräumvorrichtung for the sludge discharge.

During the residence time of the waste water in ( 9 ), the organic contents begin to decompose in the absence of oxygen by fermentation. Among other things, this leads to an undesirable lowering of the pH in the wastewater.

The pH in ( 7 ) is 6.5 to 7.4. In the course of ( 9 ) it dropped to values between 4.5 and 6 due to fermentation. The process was very cloudy and smelled clearly after fermentation. The process from ( 9 ) led to bloating in ( 10 ). The sludge index in ( 10 ) as a measure of the slump behavior of activated sludge flakes was constantly greater than 400.

When using acidic metal salt solutions such as aluminum sulfate or iron (3) chloride sulphate solution, the pH in ( 9 ) dropped to values between 4.1 and 5.5. In such an acidic environment, both chemical precipitation and flocculation as well as aerobic biological processes are clearly hampered. From corresponding experiments was therefore omitted.

In the feed ( 7 ) now 250 g of aluminum nitrate per m³ wastewater were added according to the present invention. This dosage corresponds to a nitrate content of 124 g / m³ or 96 g of oxygen per m³.

With the start of dosing, the procedure in ( 9 ) became clearer. The pH in the effluent was as in the feed ( 7 ) at values of 6.5 to 7.4. The smell of fermentation was gone. The fermentation area in ( 7 ) was clearer now.

In ( 10 ), the mud index could be lowered from the original value greater than 400 to 160 within one week by the treatment according to the invention. Under the microscope, swelling filaments (Sphaerotilus natans) were only occasionally observed.

A mud shoot from ( 11 ) was no longer observed. This result significantly reduced the flooding treatment.

The above test shows several positive effects when using the flocculants according to the invention:

• 1. By flocculation in the optimum pH range, the suspended sediment in ( 9 ) is significantly improved and the overloaded biological stage ( 10 ) relieved accordingly.
• 2. The split off oxygen from the nitrate prevents one Fermentation, pH shift and a swelling sludge development.  
• 3. The split off oxygen from the nitrate is already used in ( 9 ) for the decomposition of organic compounds. This reaction relieves the biological purification stage ( 10 ). It thus increases the useful volume of ( 10 ) without additional construction measures.

Example 3 ( Fig. 3)

For a municipal sewage treatment plant with discharge ( 19 ) in a very small receiving water, the authorities demanded a phosphate precipitation. The effluent P value must be reduced to less than 2 mg P / l.

The precipitants can be dosed both into the animation ( 17 ) and into a mixing vessel ( 15 ) in front of the primary clarifier ( 16 ). In the first variant of the method one speaks of a simultaneous precipitation, in the second of a pre-precipitation. The latter method is used in the present example.

In ( 14 ), the following values (mean values) were determined in the wastewater:

BSB₅: 380 mg / l PH value 7.4 Total P-content: 11 mg / l

Without addition of precipitant and flocculant, the BOD value in the effluent from ( 16 ) was 290 mg / l. Thus, in ( 16 ), 23.7% BSB₅ was eliminated from the water.

In Examples a) to c), the amount of precipitant was adjusted to about β = 1.7. β is the stoichiometric excess precipitate, based on the measured phosphate concentration in the wastewater. Because of the very sluggish reaction in ( 17 ), the phosphate value was already measured in the course of ( 16 ). The required limit value in the sequence ( 19 ) is lower.

In the comparative experiments a), b) and c) were added:

a) iron (3) chloride sulphate solution
190 ml / l = 285 g / m³; β is 1.71

b) iron (3) nitrate
225 g / m³; β is 1.70

c) aluminum nitrate
225 g / m³; β is 1.69

Result To a)

The pH in ( 16 ) dropped to 7.0 during the precipitation period. The total P value in the effluent ( 16 ) was 1.8 mg / l, resulting in an efficiency of 83.6%.

Under the given conditions, the BOD value of ( 16 ) was 250 mg / l, the elimination thus increased from 23.7% with only mechanical sedimentation to 34.2%.

With the flocculant the wastewater 80 mg / l sulfate and Chloride added.

To b)

The pH dropped from 7.4 to 7.05 in ( 15 ). After 2.5 to 6 hours, which is the residence time of the water in ( 16 ), the pH had returned to the initial value of 7.4.

The total P value in the course from ( 16 ) was 1.6 mg / l, which corresponds to an efficiency of 85.5%.

The BOD value in ( 16 ) was 175 mg / l; the efficiency increased accordingly to 53.9%.

With the flocculant 112 mg of NO₃ / l were added to the wastewater, this corresponds to 87 mg oxygen / l.  

To c)

The course of the pH in this experiment was as in b). The total P value in the run of ( 16 ) was 1.25 mg / L, which is an increase in efficiency to 88.6%. The BOD value in the reaction from ( 16 ) was 170 mg / l, the deposition efficiency thus increased to 55.3%.

With the flocculant 112 mg of NO₃ / l were added to the wastewater, this corresponds to 86 mg oxygen / l.

The comparative experiments show the effect known per se, namely that with a pre-precipitation phosphate can be eliminated and the efficiency of ( 16 ) can be improved.

Moreover, the significantly increased efficiency in the application of the precipitating and flocculating agents according to the invention indicates that the oxygen content in the nitrate is already used for biodegradation of the organic wastewater constituents in the mechanical clarification stage ( 16 ), thus simultaneously becoming an additional tank volume for ( 17 ).

Example 4 ( Figure 4)

For a further municipal sewage treatment plant especially a phosphate elimination is required, namely the P-value should also be reduced to less than 2 mg P / l in the wastewater. Unlike in Example 3 here the biological purification stage is oversized. The limit value for BOD in ( 25 ) is set to values less than 20 mg / l. In practice, the operating values are between 4 and 9 mg / l.

The total P value in ( 25 ) of the treatment plant without the use of flocculants was 8.5 mg P / l.

For the oxygen entry in ( 22 ) 3 submersible aerators each with 15 kW power consumption are installed, which are constantly in operation. The technical equipment of the sewage treatment plant allows a pre-precipitation and / or a simultaneous precipitation.

In the comparative experiments a), b) and c) was added:

a) aluminum sulphate
180 g / m³; β is 2.24
simultaneous precipitation

b) aluminum nitrate
230 g / m³; β is 2.24
simultaneous precipitation

c) aluminum nitrate
230 g / m³; β is 2.24
preliminary precipitate

Result To a)

The pH in ( 22 ) gradually decreased from 7.2 to 6.9. The total P value in ( 25 ) was between 0.8 and 1.2 mg / l, which is an efficiency of 85.9 to 90.6%.

In the effluent BOD ( 25 ) no significant difference to the operation without flocculant could be observed during the trial period.

With the flocculant, the effluent 89 mg sulfate / l added.

To b)

For denitrification, that is for the mining and the Use of the nitrate oxygen according to the invention Procedure had intermittently turned off the ventilation become. Optimal conditions were:

40 minutes with ventilation,
20 minutes without ventilation.

Under these conditions, the aerators' power consumption in ( 22 ) was reduced by 33%. The pH in ( 22 ) remained on average 7.2.

The results of P precipitation and elimination of BOD₅ are the same as in a).

With the flocculant 114 mg of NO₃ / l were added to the wastewater, this corresponds to 88 mg of oxygen per liter.  

To c)

As in Example 3, a considerable part of the organic substance supplied with the feed ( 20 or 4 ) should already be decomposed in the primary clarifier ( 16 or 21 ).

Under these conditions, a single aerator for the introduction of oxygen (oxygen content 1.5 to 4 mg / l) is sufficient in ( 22 ).

For a still sufficient circulation had to be installed in ( 22 ) a stirrer with 3 kW power consumption. The total P value in ( 25 ) was between 0.6 and 1.1 mg / l, which is an efficiency of 87.1 to 92.9%.

The energy consumption for oxygen entry in ( 22 ) decreased from

3 × 15 = 45 kW

1 × 15 plus 3 = 18 kW, so

by 60%.

The comparative experiments show that except those already mentioned benefits

• - no pH change -
• - no salinisation -

in the method according to the invention further improvements can be achieved. As an example, mention is made of this Make the reduction of energy needs in a generous dimensioned activation level of a sewage treatment plant.

Claims (6)

1. A method for the precipitation of dissolved water and wastewater constituents and flocculation of suspended solids in the drinking and process water treatment, in the purification of municipal and industrial wastewater and in the conditioning of process and circulating waters, the resulting flakes in a conventional manner from Water are separated, characterized in that iron (3) - and / or aluminum salts are metered in dissolved form in the water containing nitrate as an anion and these nitrate ions are then reduced in the absence of dissolved in water oxygen to molecular nitrogen. 2. The method according to claim 1, characterized in that the Reduction of nitration with reducing substances, which are in the water, arise in the water or are added to the water is performed. 3. The method according to claim 1, characterized in that the Reduction of nitration by microbial metabolic processes is carried out. 4. Process according to claims 1 to 3, characterized that the oxygen in the nitration decomposes organic Water ingredients is used. 5. Process according to Claims 1 to 4, characterized that the nitrogen formed for flotative deposition the flakes is used .. 6. Process according to Claims 1 to 5, characterized that for separating the flakes screening machines, lamella clarifier and / or sand filters are used.