HK1035360B - Method of dewatering slurries using leaf filters (filter presses) - Google Patents

Description

The invention relates to a method for the drainage of sludge, preferably municipal sewage sludge, in the treatment of waste water by pressure filter presses, in particular chamber filter presses and membrane filter presses, using water-soluble polyelectrolytes as a flocculation aid in sludge conditioning.

In addition to agricultural recovery, the necessary disposal of sewage sludge is carried out by thermal treatment of sewage sludge by incineration or degassing and mainly by landfill.

The sludge is a highly hydrated compound, so that both during the landfill and for thermal processes the solid content of the sludge is increased by at least one mechanical drainage step, preferably by sieve presses, centrifuges or pressure filtration. In particular, to improve drainage at filter presses, it is necessary to condition the pre-concentrated sludge by further treatment by dipping.

According to EP-B-19176, the drainage can be carried out in two stages: the flocculated sludge is first drained in a sieve drum or on individual sieve strips and collected in an intermediate container before being fed to the chamber filter press via a piston membrane or eccentric scallop pump and subjected to filtration at a pressure of up to 15 bar.

In gfw-wasser/waster 126 (1985), pp. 124 - 130 V. Zees, T. Clausdorf and G. Gerardts further state that after sludge conditioning and the separation of the excess water, the drainage of the flocculated sludge in the chamber filter press can only be limited, as sufficient flocculation stability is not achieved.

According to K. J. Thomé-Kozmiensky, Water treatment of sewage sludge, TK-Verlag K. J. Thomé-K., Neuruppin, 1998, p. 266, the polymer conditioning of sewage sludge for drainage on filter presses is only advantageous if no high requirements are placed on shear strengths.

According to EP-A-151 747, a drainage process is therefore known, in which the amount of sludge produced is dosed with the flocculant depending on the density of the sludge and the sludge thus pre-treated is fed directly to the chamber filter press. At pressing times of 3 hours, 30 to 40% by weight of trollen is obtained from the dehydrated sludge in the press outlet.

This method also has the disadvantage that during pressure filtration not only the water which is difficult to remove is separated from the sludge flocs, but also the water which is already free from the floc of the floc mixture is subjected to filtration by the layer of filter which builds up and condenses under pressure.

DE-OS-38 20 110 describes a process whereby the treatment sludge is conditioned with at least two organic polymer low and high molecular weight adjuvants, allowing partial dewatering of the flocculated sludge before the chamber filter press. According to WO 88/03048, the pre-drainage is carried out on floor-shaped sieves from which the sludge is pumped into a silos without a filter.

US 4.861.492 still has a known process in which the sewage sludge is flocculated by polymer flocculation aids, sedimented and then kept in a resting phase without mechanical stress for at least 2 minutes, after which the remaining waste water is decanted and the compacted sludge is drained in the pressure filter press with further addition of flocculation aids.

In a further process, according to Chem. Ing. Tech. 66, No 9 (1994), pp. 1222, 1223, a pressure-flow-resistant flux reactor is used to flow-flow the sludge previously enriched with flotation coal and ash, the flow-flowing sludge being fed into the filter press without further mechanical stress and ensuring minimal filter resistance throughout the filling cycle.

J. T. Shah reports in the 44th Purdue Industrial Waste Conference Proceedings, 1990, Lewis Publishers, Inc., Chelsea Michigan 48118, 1989 (1990), pp. 513-518 on the possibilities of optimizing the drainage process on chamber filter presses by gradually increasing the pressure during the drainage process, which can increase the solid content of the filter cake.

DE 93 07 712 U1 describes a special design of a sludge water press in which the compressed air used for the afterpressing is used to blow out the drained sludge.

DE 93 20 903 U1 describes a filtration device for liquids, in particular swimming pool water, in which the liquid to be filtered is sucked out of a container by means of filter elements with a floated filter layer.

DE 36 17 519 A1 describes a process and device for removing residual impurities from a pre-cleared beverage liquid by using a filter press with flooded layers of filter aids. The invention is based on the construction of the regenerative layer of the filter aids, where the flooding of the filter aids layer is carried out at a certain flow rate.

DE 41 19 167 A1 describes a method for determining the characteristics and parameters essential for the design and dimensioning of filter presses and a device for carrying out this method: a measuring method in which a hydrostatic pressure corresponding to the previous filtration pressure is applied in the filter chamber and continuously monitored to record the pressure drop at the end of the filtration process.

US PS 5.275.740 describes a process and device for controlling the sludge pressure in a filter press, in particular to control the final pressure of the automatically occurring stepwise filtration cycles in order to optimise the filling process of the press and to maintain a constant pump pressure.

JP 07124600 A describes a process and device for the treatment of organic sludge whereby the organic sludge is first flocculated with an organic polymer flocculant and then drained on a filter press by gravity filtration, i.e. only under hydrostatic pressure of the sludge fed to the filter press.

Municipal sludge therefore has different and sometimes frequently varying properties depending on the quantity and type of its organic and mineral constituents, which have an effect on the drainage behaviour, particularly the flocculation of the dispersed solids with organic flocculation aids and on filtration. In particular, for the drainage of municipal sludge on chamber filter presses, it is therefore necessary to optimise and coordinate the individual processes of the process. The maximum selection of suitable flocculation aids and equipment will therefore be influenced by the drainage process by pressure relief systems, in particular by the flocculation of the dispersed solids with organic flocculation aids or by the absorption of flame, which will cause the flocculation to increase by 0.09 m m2 and the current flow rate of the filter will be increased by 0.30 m3 m2 per hour, so that the maximum flow rate of the filter is 0.03 m2 per hour, and the current flow rate of the filter will be increased by 0.03 m3 m3 per hour, which is the maximum flow rate of the filter during the start of the process and the current flow rate of the filter, which is 0.03 m3 m3 per hour, and the maximum flow rate of the filter will be increased by 0.03 m3 m3 m3 per hour, so that the flow rate of the filter will increase by 0.09 m3 m3 m3 per hour and the flow rate of the filter will be optimized by 0.03 m3 m3 m3 m3 m3 per hour.

The characteristic of the known drainage processes is that the sludge conveyance by the pumps in the first phase of filtration creates a settling pressure in the system which is increased by the simultaneous compaction of the filter cake resulting from this process as a result of an increase in the filtration resistance.

The known drainage processes on chamber filter presses are therefore complex combined processes or equally complex, since they are separate and multi-stage processes.

The present invention was therefore intended to find a simple method for the drainage of sewage sludge or other sludge which would meet the requirements of improved technical conditions and a reduction in costs. In particular, the task was to find a method for separating the water free of dispersed solids contained in sewage sludge after polymerization without affecting the shear stability of the flocculated sewage sludge and without the other disadvantages arising from the implementation of separate process steps. The task is supplemented by the additional aspect of improving, where appropriate, the plate filters in such a way that they are suitable for the implementation of an improved dewatering process, a procedure to improve the precision of the plate filter.

According to the ATV manual Klärschlamm, Ernst & Sohn Verlag Berlin, 4th edition 1996, pp. 357 and 358, the chamber filter presses currently used are designed to divert the solids-free filtrate through filter drain channels or collector channels in the plate pack at the bottom and towards the end of the filtration process.

The above-mentioned ATV manual also describes chamber filter presses with open filter channels, in which the filtrate drains from the individual plates by side channels, usually one-sided, and which are not used for the irrigation of sewage sludge, in particular because of the odour disturbance caused by soot or ammonia in the lime conditioning which may be required.

It has now been found that the drainage of sewage sludge can be considerably improved by the process described in claim 1, whereby the sewage sludge is conditioned using at least one organic fluxing agent and, where appropriate, other agents and the treated and flocculated sewage sludge is introduced into the plate filter, hereinafter also called the filter press, which is a chamber filter press or a membrane filter press or a frame filter press.

The invention is based on the finding that, in the case of hydrostatic filtration of the flushed sewage sludge, the free water parts of the flushed sewage sludge mixtures in the plate filter can be easily separated from the largely undispersed solid parts by introducing the flushed solid parts together with the water parts into the chamber filter press and subjecting them to the described simple filtration without an apparatus-related pressure load.

It was further shown that the quantity of flushed sludge fed into the filter press can be substantially increased in the initial phase of the filtration process, i.e. during hydrostatic filtration, compared with the conventional filtering process.

The method of the invention is to use filter presses equipped with filter run-off channels allowing a filter flow rate of up to 1,0 m/sec. In particular, plate filters (filter presses) are used, in which the filter can be drawn by means of filter runs with large cross-sectional areas or plate filters, which have open filter runs or open filter run-off systems, consisting of single and/or multiple run-offs and, where appropriate, additional run-off elements, so that the filter can flow at a maximum flow rate of up to 1,0 m/sec. Such plate filters are known but have been used for other purposes.

In addition, plate filters with closed filter channels may be modified to have only or partially or additionally open filter channels so that the declared value of the flow rate of the filtrate is not exceeded. A further improvement of the process according to the invention is achieved, for example, by extending the filter-collection channels formed from the corner holes of the plates in the plate package, if necessary, in cross section, and/or by creating additional openings, preferably in the lower lateral area of the filter plates near the existing filter flows, on at least one part of the filter plates.

The purpose of the discontinuous drainage of sewage sludge on filter presses is to achieve short filtration times and high throughput of sewage sludge and solid-free filtrate. The method of the invention consists in the production of the flocculated sewage sludge at the filling stage with an initial discharge capacity of at least 0.3 m3 of sludge per m2 of filter area per hour, preferably in the range of 0.35-0.70 and preferably in the range of 0.40-0.60 m3 of sludge per m2 of filter area per hour. The specified power range is necessarily the result of the flocculation behaviour and filtration properties of the sewage sludge and the apparent, process-dependent, adverse effects.

The process also has the advantage of gently transporting the sludge flocs with the water into the filter press. Towards the end of the filling phase, the flocculated sludge part condenses through hydrostatic filtration in the filled chambers, creating a pressure increase throughout the filter press system. The discharge power is reduced in the subsequent phase of pressure filtration to values in the range of less than 0.3 m3 per m2 of filter area and hour to a selected lower value, the so-called closing value, with maximum pressure values in the plate filter being set in the range of 10-20 bar, preferably 10-15 bar.

The drainage method according to the invention is suitable for municipal and/or industrial sludges with solids content in the range of 0,5 to 15% by weight. The municipal sludge consists of primary, excess and residual sludge, as well as mineralized and preferably sludge and mixtures thereof. The sludges, which are usually pre-concentrated in a single indicator, are treated with organic polymer adjuvants and, where appropriate, with the addition of organic and/or organic scaffolding additives such as lime, ice salts, their asphalt, mineral dust, mineral coal and mineral proteins, such as seeds of olamine or olamine straw or mixtures thereof, conditioned in water. The organic solvents are dispersed in water, such as ammonium nitrate or ammonium nitrate, which are present in solution with at least 42-C2O2-C2O3-C2O3-C2O3-C2O2-C2O2-C2O2-C2O2-C2O2-C2O2-C2O2-C2O2-C2O2-C2O2-C2O2-C2O2-C2O2-C2O2-C2O2-C2O2-C2O2-C2O2-O2-O2-C2O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O2-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-

As an anionic polyelectrolyte, homo- and/or copolymerisates of monoethylene unsaturated carbonic acids and sulphonic acids, such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, crotonic acid and/or their alkali, preferably sodium, potassium or ammonium salts, vinyl sulphonic acid, acrylamide and methacrylamidoalkylsulphonic acids, such as 2-acrylamide-2-methylpropanolsulphonic acid, 2-sulfoethylmethacrylate and styrene sulphonic acid and/or their alkali, preferably sodium or potassium or ammonium, and/or their sodium or potassium alkylsulphonic acids, preferably vinyl phosphorus and potassium or ammonium sulphonic acid, and/or their substituents, are suitable.

Preferably, cationically active flocculant agents, such as homo- and/or copolymerisates and/or terpolymerisates of water-soluble monoethylene unsaturated vinyl compounds, such as acrylic acid and methacrylic acid esters of dialkylaminoalkylic alcohols in protonated or quaternated form, such as dimethylaminoethylacrylate, acrylic acid and methacrylic acid amides of dialkylaminoalkylamines in protonated or quaternated form, such as acrylamidopropyltrimethylammonium chloride and/or acrylamidopropylmethylamethylammonium sulphate, are used with the appropriate application, as described in the invention Copolymerisate 63-228B EP72.

The copolymerisates may be formed from the above ionic monomers and non-ionic, water-soluble monoethylene unsaturated monomers such as acrylamide, methacrylamide, N-C1-C2 alkylated (meth) acrylamide, and with N-vinylamide, vinyl formamide, N-vinylacetamide, N-vinyl-N-methylacetamide, N-vinylpyrrolidone.

Similarly, the copolymers may contain to a limited extent water-soluble and/or water-insoluble ethylene unsaturated monomers such as (meth) acrylic alkyl esters and vinyl acetate, provided that the water solubility or solubility of the copolymers is maintained.

The polymerisates may also be prepared by the use of crosslinking monomers which are at least doubly reactive, preferably doubly ethylene unsaturated monomers, so that they are soluble in water or only slightly soluble, or consist of water-soluble and water-soluble polymerisates.

The amphiphilic copolymers of the invention, which are water-soluble or water-soluble, formed from cationic and anionic monomers and non-ionogenic monomers, as appropriate, may also be used.

The selection of the flocculation aids is carried out by flocculation and dehydration tests with sewage sludge on a laboratory and technical scale.

The method of the invention gives a total sludge irrigation performance of 0,1 to 0,175 m3 per m2 of filter area and hour or more than 6 m3, preferably 6 to 12 m3 per m2 of filter volume and hour.

The process of the invention is further characterized by the advantage of short loading times: a short filling time of the filter press is followed by a pressure filtration phase, which is considerably shorter in time compared to conventional processes, and the duration of which is reduced to 50 - 20% and preferably 35 - 25% in relation to the previous pressure filtration time, at comparable values of dry solids in the filter cake, which are in the range of 30 - 42% by weight when using only organic polymer flocculation aids in the invention process.

The method of the invention is preferably carried out with chamber filter presses or with membrane filter presses, whereby membrane filter presses achieve the additional advantages, in particular an additional shortened batch time and an additional increase in dry solids content. The size of the filter plates used in the method of the invention, in relation to the filter surface per plate mirror, is at least 1 m2, preferably 1 to 6 m2 and particularly preferably 1 to 4 m2, corresponding, for example, to the dimensions of the filter plates from 1,0 x 1,0 m to 2,0 x 2,0 m.

The drainage method of the invention is further characterized by the fact that the sewage sludge is flushed through the conditioning and partially drained under hydrostatic filtration in such a way that the currently largely regulated sludge discharge of the plate filter is limited or can be eliminated if necessary, since the substantial part of the sludge is introduced into the filter chambers during the hydrostatic filtration.

The invention is further explained by the following examples.

Comparison example 1

The drainage of municipal sludge with a solid content (dry matter) of about 4% by weight is carried out on a chamber filter press by Dr. Rittershaus & Blecher, type AEHIS, built in 1979, which has the following characteristics: Other

Plattengröße	1,2 x 1,2 m
Plattenwerkstoff	GGG (Grauguß)
Kammerzahl	115
Filterfläche
Gesamtpressenvolumen

The sludge was conditioned and sent to the chamber filter press using the Floctronic® system of Fa. Stockhausen GmbH & Co. KG, which was controlled by computer. The sludge was pumped into the filter press after flow measurement with the flow pump, controlled by the pressure gauge. The cationic flux aid Praestol® 853 BC was added as 0.1. At the usual water solution, the pressure and subsequent mixing energy flow were regulated by the floctrum probe. The pressure filter press started with an initial flash rate of 50 m3 bar of flux per hour, corresponding to 0.2 m3 of flux per hour. The filter was filled with a solid and after a total filter load of 32.3 kg of filter was regulated at a constant pressure of 0.3 bar per hour (maximum filter rate was maintained at 45 to 853 bar per hour) and the maximum filter flash rate was maintained at 45 to 852 m3 bar.

Example 1

The drainage of municipal sludge with a solid content of about 4% by weight was carried out on a chamber filter press of the type AEHIS, by Dr. Rittershaus & Blecher, with the characteristics mentioned in comparison example 1. The chamber filter press was fitted with an open filter run-out system. To this end, the closed filter run-out boreholes, each of which was fitted with a blind plug alternating sideways within the filter plate, were opened and extended to a nominal width of DN25 (25 mm) in the area of the lower filter run-out formed by the filter plates. The openings were further fitted with a running-out pipe of approximately 30 cm in length.

The sludge conditioning and dispatch of the sludge filter presses was carried out using the units mentioned in comparison example 1 using the Floctronic® system. As a flocculation aid, Praestol® 853 BC was used in the form of the 0.1% by weight aqueous solution for the conditioning process. The flocculated conditioned sludge was discharged into the filter press with an initial discharge rate of 120 m3 of sludge per hour, corresponding to 0.48 m3 of sludge per m2 of filter area per hour. Under hydrostatic filtration, the main flow of 72% of the solid-free water, which was discharged to the entire water block, was treated with open flame, separated from the sludge, which was discharged from the filter at the same time by the filter filter, which was filled with the filter filter.After the chambers were fully filled with partially dewatered sludge, the controlled and progressively reduced sludge discharge, which last amounted to 10 m3 of sludge per hour, increased the pressure in the filter press to a maximum of 15 bar. After a pressure filtration time of 24 minutes and a total filtration time of 34 minutes, a total of 30 m3 of sludge containing 4.3 kg of Praestol® 853 BC was conditioned and dewatered in the chamber filter press. The sludge irrigation capacity is 10.3 m3 of sludge per m3 of filter volume per hour or 0.144 m3 of sludge per m2 of filter area per hour.2% by weight of dry matter.

The filtration process according to the invention is characterised by a significantly shortened batch time, in particular by a short pressure filtration phase.

Example 2

The drainage of municipal sludge with a solid content of about 4.6% by weight was carried out on a chamber filter press of the type AEHIS by Ritterhaus & Blecher, with the modifications described in example 1.In addition to the open lateral filtration system, the filtration system was opened over the filter channel in the plates with one filter run of DN 80 (80 mm) each and connected outside the chamber filter press to the filtration leaf tube system with a diameter of DN 300 (300 mm).

The sludge was conditioned and discharged as shown in example 1, the flocculated sludge was introduced into the chamber filter press with an initial discharge rate of 120 m3/h. After a pressure filtration time of 21 minutes and a total filtration time of 31 minutes, a total of 30 m3 of sludge containing 4.3 kg of Praestol® 853 BC was conditioned and drained in the chamber filter press.

Claims (12)

1. A process for dewatering a f locculated sewage sludge on a plate filter, which sewage sludge has been treated with at least one organic flocculation aid and optionally other auxiliary agents, characterized in that the flocculated sewage sludge is introduced into the plate filter, the major amount of water of the treated, flocculated sewage sludge is removed in the plate filter by means of hydrostatic filtration, and the partially dewatered sewage sludge subsequently is subjected to pressure filtration.
2. The process according to claim 1, characterized in that at least 50 wt.-%, preferably at least 60 wt.-%, and more preferably at least 70 wt.-% of the water of the treated, flocculated sewage sludge is removed by hydrostatic filtration.
3. The process according to any of claims 1 to 2, characterized in that the flocculated sewage sludge is introduced into the plate filter at an initial feed capacity of at least 0.3 m³ sludge per m² filter area and hour.
4. The process according to any of claims 1 to 3, characterized in that the plate filter is provided with a f iltrate outlet system permitting filtrate discharge at a flow rate of 1.0 m/s at maximum.
5. The process according to any of claims 1 to 4, characterized in that the filtrate outlet system of the plate filter is closed.
6. The process according to any of claims 1 to 4, characterized in that the filtrate is discharged from the plate filter through an open filtrate outlet system.
7. The process according to claim 6, characterized in that the open filtrate outlet system is comprised of lateral single outlets from the individual plates and/or at least one collecting channel.
8. The process according to any of claims 1 to 7, characterized in that the plate filter is a chamber filter press.
9. The process according to any of claims 1 to 7, characterized in that the plate filter is a membrane filter press.
10. The process according to any of claims 1 to 9, characterized in that the feed capacity of the plate filter during pressure filtration is less than 0.3 m³ sludge per m² filter area and hour, the maximum pressure ranging from 10 to 20 bars.
11. The process according to any of claims 1 to 10, characterized in that the filter plates of the plate filter have an area of at least 1 m².
12. The process according to any of claims 1 to 11, characterized in that municipal and/or industrial sludges having solids levels ranging from 0.5 to 15 wt.-% are employed.