DE19605624C2 - Process for cleaning surfactant-containing dirty water with a centrifugation stage - Google Patents

Description

The invention relates to methods for cleaning surfactant ger dirty water, especially from floor cleaning machines which the dirty water may be after a chemical and mechanical pre-treatment of a biological cleaning is pulled.

The cleaning of buildings, floors and machine parts takes off an important place in industry. The example Waste water accruing from gas stations is through streets dirt, tire and brake pad wear, oil and fuel residues as well as detergents and preservatives. Before initiation this wastewater into the public network becomes a pretreatment through oil separators, in which the specifically lighter substances too be held back.

The problem with this, however, is that it is far from sufficient oily substances are separated, since these are surfactants are emulsified and do not separate to let.  

To meet the requirements for environmental protection requirements known from the prior art several methods according to work according to the following principle:

The waste water from the washing process is in a sludge Catched and pumped into a still tank pumped.

The larger dirt particles settle there by themselves. After a sufficient calming period, the wastewater becomes in a coagulation unit is pumped. After adding a ent speaking amount of a flake and optionally a flake aid  the wastewater becomes intensive with these substances mixed, the emulsified oil droplets and above all Combine dirt particles with these substances, i.e. absorbed them will. Then these particles are cleaned with the Waste water is transferred to a filtration unit, in which one effective separation of concentrated dirt and cleaned Water takes place. The filtered out sludge becomes corresponding disposed of, while the purified water for one new washing process is available, another biolo Chemical cleaning or, if necessary, into the sewage network is initiated.

A disadvantage of these methods, however, is that flocculation and possibly flocculants are added to the wastewater to cause coagulation. These funds remain even after filtering off, partly in the filtrate and make one additional pollution for the environment or for a given if downstream biological cleaning represents. Furthermore is it is disadvantageous that these additives must be dosed quite precisely to avoid excessive stress on the filtrate.

From US 4,859,329 is a cleaning method for with oil, Known grease and fuel contaminated water where combined several methods of removing contaminants will. In a first phase, the water is settled  tank in which a flocculation of oil etc. with the help of Polypropylene strips are favored so that larger oil particles float up and with the help of a slowly rotating aluminum Remove the wheel on which the floating oil settles be animals. Pre-cleaning is supplemented by a pre-cleaning switched metallic sieve for the accumulation of oil and the like Pollutants as well as through an absorption cartridge. The so pre-cleaned water is in a second phase Vortex tank directed with pressure in which the water rotates and by centrifugal force solids to the outside and oil flakes to be transported inside. Located in the middle of the vertebra a polypropylene tube, which is the deposition process for the Oil supports.

By US 3,502,215 is a water treatment system for cars car washes known. The washing water caught in a pit This is led into settling tanks, in which the water has a high Has dwell time so that suspended solids settle can and free oil can float. The remaining one Residual solids are separated in a centrifugator. After that, the water is reused in the car wash processed.

A cleaning method is known from FR 2 690 082 A1 also intended for water contaminated with oil and grease is. The contaminated water is first drawn to a filter leads to a dry sludge. The oil phase is then separated in a centrifuge, whereby Surfactants should remain in the liquid so that the Reuse the liquid together with the added surfactants can be detected.

The known methods all have the disadvantage that they either require a large amount of equipment or not are efficient. A combination of the known methods with biological cleaning is not intended.

The invention is therefore based on the problem new cleaning that can be carried out with little equipment process for a heavily soiled surfactant Specify dirty water.

On the basis of this problem, according to the invention Method of the type mentioned in the introduction, characterized in that first the dirty liquor by sedimenting centrifugation with centrifugal acceleration above 10000 g and Tren the supernatant from the sediment is pre-cleaned so that the COD value of the dirty water drops below 15% of the initial value is lowered before biological cleaning, if necessary after chemical pretreatment.

In the method according to the invention, the surfactant-containing dirt lye sediment at least for some of the dirt particles centrifuged at high speed (≧ 10,000 g), d. that is, the norma dirt particles that do not sediment themselves surprisingly accumulate as sediment and thus a separation of the remaining liquid is possible. Then the The resulting supernatant is separated from the sediment and, if necessary subjected to biological cleaning.

This can be done under aerobic and / or anaerobic conditions leads. Known techniques can be used will. For example, the so-called activation process be used, in which in a circuit of an animated mud-water mixture, which is in an aeration tank with after switched on secondary settling tank (settling tank) continuously fresh, constantly fresh in front of the aeration tank, Usually, pre-treated wastewater is fed in and at the secondary clarifier tank treated wastewater is withdrawn.

The activated sludge content is as constant as possible in the activation tank at a level where the secondary clarifier is able to retain entire biomass. If not too abruptly occurring changes, for example in the form of pH,  Salinity, temperature, food supply changes, is the activated sludge microcynosis is a self-regulating one System. In the case of particularly highly polluted waste water, there is a rear interconnection of two or more units possible.

To prevent insufficient biodegradation of the pollutants It is beneficial to bend when biological cleaning nutrients are added to the pre-treated wastewater to achieve a to ensure optimal microbiology. This is especially true for anaerobic degradation.

When aerobic degradation is, of course, sufficient Provide ventilation to supply oxygen.

The sewage sludge emerging from this system as well as that at The sediment obtained by centrifugation must be disposed of accordingly will.

The wastewater cleaned in this way can be released to the public sewage network initiated or, for example, floor cleaning supply machines are fed so that an almost closed Wastewater cycle is created, which is particularly ecological is imprisoned.

The centrifugation must be done with a biological cleaning linked procedures are carried out so that a large part of the Dirt particles due to multiple gravitational accelerations settles out sedimentally. This is usually the case with dirty water resulting COD content of organic components of 500,000 mg oxygen / liter should be around 90% to about 50,000 mg oxygen / liter can be reduced. This one still very much However, high COD content is essential for an optimally adjusted biolo tic cleaning level manageable, so that when passing this Usually a COD content of around 1,000 to 3,000 mg Oxygen / liter is reached.  

The sedimenting centrifugation of the dirty water and the Ab separation of the supernatant from the sediment as a whole already a process for the pre-cleaning of surfactant-containing dirt lye, whereby the pre-cleaned wastewater returns to others Process water circuits are fed in or as mentioned above can be sent to a biological or other purification.

To increase the efficiency of the separation, the centrifuga tion advantageously with ≧ 15,000 g (gravitational acceleration) carried out. Extreme separations are required for small systems even higher accelerations (around 30,000 g) have been achieved.

Furthermore, it is advantageous if the supernatant is separated from the sediment is carried out by filtration because on this way results in a particularly effective separation. In particular membrane filtrations with cellulose, for example nitrate filters with a pore size of a few micrometers particularly effective.

Furthermore, it is advantageous that biological cleaning pre-further chemical and / or physical cleaning is switched to further increase the degree of cleaning. For example, it is conceivable that lime precipitation by addition of calcium carbonate is carried out in excess, with ionic substances, including anionic surfactants, un soluble calcium salts form and precipitate. The flocculations can be filtered off or centrifuged.

Furthermore, acid precipitation as such or subsequently to be carried out on the above-mentioned lime precipitation by Acidification substances fail, their solubility with the pH decreases. These flocculations can be filtered off directly or centrifuged.

A precipitation of non-ionic surfactants is also conceivable, in which the wastewater solution pre-cleaned by centrifugation Is subjected to heat treatment. This is the solution  heated above a characteristic temperature at which the Lö solution becomes cloudy and then in two liquid phases is separated, with the addition of electrolytes of turbidity point can be shifted to lower temperatures. Ins especially the addition of sodium sulfate causes a strong turbidity exercise point depression. This special way of failing Non-ionic surfactants depend on the partial dehydration tion of the pre-hydrated hydrophilic nonionic groups the surfactants together. After the phases have been formed, the aq Rige separated from the organic phase, the latter separately must be disposed of. However, it is also conceivable that the Ent removal of the non-ionic surfactants according to the biological Reini supply takes place.

Furthermore, it is conceivable that other cleaning stages before or after the actual biological cleaning stage the waste water liquor are provided.

Devices for performing the method according to the invention (Pre-cleaning and pre-cleaning plus additional biological cleaning agents stage) have at least one centrifuging device, which in particular preceded a biological cleaning stage is.

The method according to the invention and the corresponding Vorrich are mainly intended to be quantitatively low Clean lots of dirty water containing surfactant (dirty water). For example, at a petrol station every day or Correspond to washing plant oil and surfactant-containing waste water be properly prepared and cleaned.

However, use on a large scale is also appropriate the design of the necessary centrifugation equipment conceivable.  

Show it:

Figure 1 is a schematic diagram of the biological purification of a continuously operated model clarification ge.

Fig. 2 is a process flow diagram of an exemplary design from the inventive method for cleaning surfactant-containing dirty water.

In Fig. 1, a continuously operated Mo is sketchy illustrated dell treatment plant for carrying out the biological cleaning stage of the cleaning process of the invention.

The plant has an aeration tank 4 , a secondary clarifier 7 and an activated carbon filter 10 . The total volume of aeration tank 4 and secondary clarifier 7 as well as of intermediate connections used corresponds to 1,400 ml. A peristaltic pump 12 regulates the volume flows of substrate and nutrient salt medium from the respective storage vessels 2 and 3 . The ventilation of the aeration tank 4 he follows via a stone 6 , which is operated with a pump 13 ben. The pressure is equalized via a tube 5 loosely stuffed with cotton wool. The storage vessels for substrate 2 and brine 3 and the aeration tank 4 are stirred with magnetic stirrers 1 in order to achieve optimal mixing. The secondary clarifier 7 , which is connected behind the aeration tank 4 , is intended, on the one hand, to settle the bacterial floc and, on the other hand, to enable anaerobic degradation, pressure equalization taking place via a siphon 8 in the upper opening of the secondary clarifier. The settling activated sludge is returned to the activation tank 4 via a peristaltic pump 14 . The outflow of the secondary clarifier 7 opens into an intermediate vessel 9 . From this, the sample is fed to the activated carbon filter 10 via a further peristaltic pump 15 . The outlet of the activated carbon filter 10 opens into a further collecting vessel 11 .

Waste water samples from cleaning machines contain ten side in unknown composition and concentration from the detergents used and also contaminants that were included in the course of the cleaning process.

These wastewater samples are taken at 15000 revolutions / minute (ent speaks approx. 32000 g (gravitational acceleration)) and T = 10 ° C for 15 mi centrifuged in a refrigerated centrifuge to avoid undissolved Separate components.

Then using paper filtration on pleated filters and Membrane filters with a pore size of 0.2 to 3 µm, the fixed of the liquid phase separated.

By adding calcium carbonate in excess (approx. 30 g / l) who the anionic substances, u. a. also anionic surfactants, in un soluble calcium salts transferred and precipitated. The flocculation gen are filtered off by means of pleated filters or centrifuged yaws.

After acidification with HCl, drop to a pH of approx. 2 Substances, the solubility of which decreases with the pH, from then the flocculation at 15,000 rpm for Centrifuge for 30 minutes and at T = 10 ° C in a refrigerated centrifuge gier and then filtered through pleated filters.

This treated wastewater is fed to the model sewage treatment plant shown in FIG. 1, in which the biological treatment takes place.

Then the waste water cleaned in this way becomes water by adding sodium sulfate and heating to approx. 50 ° C freed from the nonionic surfactants by precipitation of these.

This wastewater can be partially mixed with fresh water again for cleaning floors using floor cleaning machines be used.  

Table 1 shows the COD values and degrees of purification of the ver various physico-chemical treatments listed.

Table 1

COD values and degrees of cleaning of the various physical chemical treatments

This table clearly shows that only through Centrifugation of the original sample has a COD content of 467500 mg / l has been reduced to 31700 mg / l, which means a degree of purification corresponds to 93.2%.

Subsequent acid precipitation, centrifugation and paper fil tration even reduces the COD content to just 9400 mg / l, which corresponds to a degree of cleaning of 98.0%.

This 98% purified waste water is then fed to the model sewage treatment plant shown in FIG. 1.

After going through the biological cleaning process, in the course of the After clarification basin get a COD content of 3040 mg / l, which one Corresponds to a degree of purification of 98.69% (at this value the 1: 2 dilution already taken into account by the sewage treatment plant).  

After passing through the activated carbon filter, the COD content drops 717 mg / l, which corresponds to a degree of purification of 99.69% (at the 1: 2 dilution by the sewage treatment plant is already this value considered).

If one finally fails the nonionic surfactants, so a COD content of 590 mg / l is reached, which makes cleaning degree of 99.75% (this value already takes into account the 1: 2 dilution by the sewage treatment plant).

These results are summarized in Table 2.

Table 2

Overview of the cleaning levels of the individual treatments

In Fig. 2 is a process flow diagram is an exemplary From design of the inventive method for the purification of surfactant-containing liquor ready dirt.

The dirty liquor originating from cleaning machines is placed in a container 103 via a sieve 101 via a valve 102 . The sieve 101 serves to retain smaller objects contained in the dirty water. Via an upper and lower level indicator 104 , 105 , a pump 106 is switched on or off to ensure that a certain level is present in the container 103 during operation. A valve 107 , 108 is installed in front of and behind the pump for installation purposes. The dirty liquor is conveyed by means of the pump 106 through the valve 108 and through a 3-way valve 109 into a separator 110 in the form of a plate centrifuge. The 3-way valve 109 is used to guide the solid constituents from the following process stages to the freshly supplied dirty liquor stream into the plate centrifuge 110 , so that ultimately all precipitated and sedimented constituents from the plate centrifuge 110 via a valve 111 for disposal , for example for thermal combustion or composting, can be removed.

Via a valve 112 arranged above the valve 111 , the pre-cleaned dirty water is conveyed via a further valve 113 by a pump 114 via two further valves 115 , 116 into a precipitation stage 117 . A first precipitant is fed to a container 118 , the liquid level being displayed via a fill level indicator 119 . The first precipitation medium is conveyed into the precipitation stage 117 via a valve 120 by means of a pump 121 via a further valve 122 . In order to maintain an optimal ratio of the supplied pre-cleaned dirty water and the first precipitant, the speed of the pumps 114 and 121 is regulated in a mutual dependency with the aid of a control device 147 . The components precipitated from the precipitation stage 117 are fed back to the 3-way valve 109 via a valve 123 . The dirty liquor prepared in this way flows through a 3-way valve 124 into an activation tank 125 . The actual biological purification then takes place in the activation tank 125 . In order to maintain the microbial activity, ambient air is sucked in via a valve 127 and passed through a further valve 128 into the activation tank 125 , so that an adequate oxygen supply to the microbes is ensured, via a control device 148 and a membrane pump 126 connected to the plate centrifuge 110 . Water losses that may occur due to evaporation are compensated for by adding water accordingly. The mixture in the aeration tank 125 is passed via a valve 129 into a secondary clarifier 130 , in which, on the one hand, the bacteria flakes formed can settle and, on the other hand, an anaerobic degradation is made possible. The activated sludge which settles out is fed via a 3-way valve 131, depending on the requirements, either via the 3-way valve 109 into the plate centrifuge 110 or via a further valve 132 by means of a pump 133 again via a valve 134 and the valve 124 into the activation tank 125 leads back. The pump 133 is gel Gere via a control device 135. The supernatant liquid in the secondary clarifier 130 is passed through a valve 136 in a precipitation step 137, in which a further chemical precipitation treatment is carried out. For this purpose, another precipitant is fed into a container 138 which has a lower fill level indicator 139 . The precipitant is fed into the precipitation stage 137 via a valve 140 by means of a pump 141 via a further valve 142 . A control device 143 regulates the flow ratio of liquid originating from the clarifier 130 and supplied precipitant in order to maintain optimal precipitation conditions. The components which settle in the precipitation stage 137 are fed via a valve 144 via the 3-way valve 109 to the tel centrifuge 110 . The cleaned liquid coming from the precipitation stage 137 in this way is fed via a valve 145 to an activated carbon filter unit 146 for clarification of the cleaned liquid.

The end product highly purified by this process becomes Use in cleaning machines reused so that a close closed material cycle arises, especially under ecological aspects is desirable.

Claims (4)

1. A method for cleaning surfactant-containing dirty water, in particular from floor cleaning machines, in which the dirty water is optionally subjected to a chemical and mechanical pretreatment of a biological cleaning process, characterized in that first the dirty water is sedimented by centrifugation with egg ner centrifugal acceleration above 10,000 g and separation the supernatant from the sediment is pre-cleaned so that the COD value of the dirty water is reduced to below 15% of the initial value before the biological cleaning, if necessary after a chemical pretreatment, is carried out. 2. The method according to claim 1, characterized in that the Separation is carried out by filtration. 3. The method according to claim 1 or 2, characterized in that the COD value by sedimenting centrifugation is reduced to below 10% of the initial value.   4. The method according to any one of claims 1 to 3, characterized records that with a biological cleaning the over stood nutrients are added.