WO2003031342A1

WO2003031342A1 - Method and apparatus for the purification of surface water

Info

Publication number: WO2003031342A1
Application number: PCT/NL2002/000637
Authority: WO
Inventors: Leo Peter Wessels; Ronaldus Cornelius Maria Jong; Bastiaan Martijn Rietman
Original assignee: Waterleiding Overijssel Nv Mij
Current assignee: Waterleiding Overijssel Nv Mij
Priority date: 2001-10-08
Filing date: 2002-10-04
Publication date: 2003-04-17
Anticipated expiration: 2004-04-08
Also published as: NL1019130C2

Abstract

The invention relates to a method for the purification of surface water or effluent from sewage purification. According to the invention floating substances, solid particles, bacteria, viruses, and dissolved substances such as salts, dissolved organic substances, pesticides and the like, are removed simultaneously. To implement this, at least one vertically disposed pressure pipe (2) is used, comprising one spiral-wound nanofiltration or hyperfiltration membrane (3) per pressure pipe. Delivery flow to the membrane is parallel, while the following steps are performed: 1) production of permeate and simultaneous and continuous discharge of concentrate and 2) flow along the membrane without the simultaneous production of permeate. The invention further relates to an apparatus for performing the method.

Description

Method and apparatus for the purification of surface water

The invention relates to a method for the purification of surface water or effluent from sewage purification, and to an apparatus for performing such a method. According to the prior art, the purification of surface water or effluent from sewage purification is mostly carried out by nanofiltration and hyperfiltration, using spiral-wound membranes. In accordance with a standard technique, such membranes are accommodated in series in horizontally disposed pressure pipes. As .a rule such pressure pipes have a length of 6 to 7 meters and comprise 6 to 7 membranes of 1 meter length each, or 4 membranes of 1.5 meter length each.

Spiral-wound membranes are known to be very susceptible to fouling due to particles, but also due to the growth of biomass, in which case one speaks of biofouling. The deposited particles cause clogging in the feed spacers, while certain nutrients in the feed water may lead to the growth of biomass. This biomass grows between the spacer and can cling to everything. One thing and another results in the biomass being very difficult to remove by, for example, flushing.

Another fact concerning the present-day application of spiral-wound membranes is that they cannot be cleaned hydraulically. In contrast with, for example, the capillary membranes which may be cleaned by means of a so- called forward flush, optionally with air, the arrangement in series makes it impossible to apply reverse flushing and flow along these membranes.

Despite these disadvantages, spiral-wound mem- branes are very popular for water purification purposes. The reasons for this are as follows:

1. High packing density (2 to 3 times the membrane surface per m² module compared with capillary membranes (1,5 mm capillaries)). 2. Standardised modules (membranes of different makes can be interchanged) and

3. Inexpensive (standardised product, several manufacturers and extensive, current market) . As already mentioned, spiral-wound membranes are very popular and they are often used for the purification of water in which hardly any particles and nutrients are left. With regard to the particles, high demands are often made of the membrane fouling index (MFI) or the Silt Den- sity Index (SDI) . With respect to the presence of nutrients, use is often made of the assimilating organic carbon (AOC) or dissolved organic carbon (DOC) . Until now, it has been shown that the treatment of surface water or effluent from sewage purification with the aid of spiral-wound mem- branes is not so simple.

In order to guarantee effectiveness, a very good pre-purification has to take place.

Such pre-purification may involve the following treatments: 1. (Microsieving) and quick-run filtration

2. (Microsieving), quick-run filtration and ultrafiltration

3. (Microsieving), quick-run filtration, activated carbon filtration and ultrafiltration. It is observed, that until now it was generally believed that microsieving in combination with quick-run filtration as pre-purification did not suffice to prevent fouling (biofouling and particle fouling) of spiral-wound membranes or to adequately combat this. Like- wise, microsieving in combination with quick-run filtration followed by ultrafiltration does not seem to adequately alleviate the problem of fouling in the spiral- wound membranes. It has been shown that this does not remove the dissolved nutrients in the feed water. An exten- sive pre-purification that includes the use of activated carbon does, however, produce good operating results. The use of activated carbon makes the process elaborate and expensive. As alternative solution, instead of spiral-wound nanofiltration or hyperfiltration membranes, capillary nanofiltration or hyperfiltration membranes may be used as discussed in WO 0029099. The present-day prior art may be summarised as follows.

It has been shown that when using spiral-wound nanofiltration and hyperfiltration membranes, serious fouling occurs due to the solid particles and dissolved nutrients (biofouling) that are present in the water to be purified, and that in the current application such membranes cannot be hydraulically cleaned. The result is that when using spiral-wound nanofiltration and hyperfiltration membranes for the purification of surface water or effluent, an extensive pre-treatment has to be carried out be- forehand, namely microsieving, quick-run filtration and ultrafiltration or (microsieving) , quick-run filtration, activated carbon filtration and ultrafiltration. If applying a completely different technique, one departs from capillary nanofiltration or hyperfiltraton membranes for the purification of surface water or effluent. According to this technique, pre-purification may be restricted to just the microsieving.

It is the object of the invention to provide a new method and apparatus which effectively removes the above- mentioned drawbacks. To this end the present invention provides a method for the purification of surface water or effluent from sewage, purification, which method is characterised in that floating substances, solid particles, bacteria, viruses, and dissolved substances such as salts, dissolved organic substances, pesticides and the like, are removed simultaneously by applying at least one vertically disposed pressure pipe comprising one spiral-wound nanofiltration or hyperfiltration membrane (1 or 1.5 m length) per pressure pipe taking delivery of the flow, and wherein the following steps are repeated:

1. production of permeate and simultaneous and continuous discharge of concentrate and

2. flow along the membrane without the simultaneous production of permeate. The method according to the invention uses one or several vertically disposed pressure pipes, comprising one spiral-wound nanofiltration or hyperfiltration membrane per pressure pipe, wherein it was surprisingly shown that a minimal pre-purification suffices. This pre-purification may consist of microsieving and quick-run filtration.

It is essential that the pressure pipes filled with the spiral-wound membranes are disposed vertically, always alternating the following operation steps, to wit: 1. Production of permeate at continuous discharge of the concentrate. 2. Hydraulic flow along the membrane with water or a combination of water and gas,^" preferably air. According to the present method the direction of feed flow through the membrane during step 1. is from the top downward and during step 2. from the bottom upward.

It is remarked that during step 2. a gas is supplied to the feed in accordance with the invention, which gas is preferably compressed air. It is also possible to add chemicals to the feed during step 1. and 2.

Chemicals that according to the invention may be considered are: anti-sealants, base, acid, disinfecting chemicals, biocides, bactericides or oxygen-eliminating components such as, for example, bisulphite or hydrazine. After the addition of the chemicals -the flow along the membrane is stopped and the membrane is exposed to the chemicals for 1 to 10 minutes, after which the chemicals are flushed out of the membrane. It is observed that between step 2. and step 1. an extra flush of feed water may take place, while the feed flows through the membrane from top to bottom.

The invention also relates to an apparatus for performing a method according to the invention, which ap- paratus is characterised in that the apparatus is provided with a vertical pressure pipe, comprising a spiral-wound membrane with a top and bottom plate, which is provided with an O-ring, wherein the central permeate discharge pipe in the top plate is closed by means of a shut-off, and wherein the central permeate discharge pipe in the bottom plate is connected via interconnecter with the permeate discharge, wherein pressure pipe at the top side is connected with the feed pipe and the wash-water discharge pipe, and at the bottom side with the pipe for wash-water supply and concentrate discharge, while the feed supply is connected with an inlet for chemicals, and the wash-water inlet, which is in communication with the concentrate discharge pipe, is also connected with the gas suply/concen- trate discharge pipe, and the discharge of the first filtrate.

The invention will now be elucidated with reference to the appended drawings.

Figures 1, 2 and 3 in the drawings represent the same apparatus, wherein Figure 1 illustrates the production process,

Figure 2 represents the flushing out of the first filtrate,

Figure 3 relates to the cleaning of, or the flow along the membrane.

The reference numbers in the Figures 1, 2 and 3 represent the following:

1. Apparatus according to the invention

2 Vertical pressure pipe 33. Membrane column 4 Top plate membrane column 5 Bottom plate membrane column 6 O-Ring 7 Shut-off central permeate discharge pipe (14) 1 ' Interconnecter for connecting the central permeate discharge pipe (14) with the permeate discharge pipe (9)

8. Feed pipe 8' Pipe for wash-water supply and concentrate discharge

9. Pipe for permeate

10. Pipe for concentrate 11, Pipe for discharge first filtrate 12. Pipe for gas supply 13. Pipe for discharge wash-water

14. Central permeate discharge pipe

15. Pipe for chemical supply

The directions of flow during production, flushing and flowing along, are in the drawing indicated by arrows.

Figure 1: Production

During production the feed, being either surface water or effluent from sewage purification, is supplied via pipe (8) into the vertically disposed pressure pipe (2) , which is provided with a spiral-wound membrane (3) . After passing through the spiral-wound membrane, the permeate is discharged via the interconnecter (! ' ) of the central discharge pipe (14) through the permeate discharge pipe (9) , while the concentrate is discharged via the supply of wash-water and concentrate discharge (8') through the concentrate discharge pipe (11) to a following processing step.

The elastic O-rings (6) seal off the top and bot- torn side of the vertical pressure pipe (2) , forcing the feed to pass through the spiral-wound membrane in order to arrive in the central discharge pipe (14) (as permeate) or at the other discharge side of the membrane (3) (as concentrate) . During the production, chemicals may be added via the chemical supply (15) .

Figure 2 shows the flushing out of t-he first filtrate using the same. flow direction as in Figure 1.

This causes the first filtrate to be discharged via pipe (11) without discharging permeate. In step 2. of Figure 3 the flow along the membrane of the present process is shown without the simultaneous production of the permeate.

The flow direction of the feed with regard to Figures 1 and 2 is now reversed, i.e. the feed is supplied via the pipe for wash-water supply and concentrate discharge (8') at the bottom side of the vertically disposed pressure pipe (2), causing the fouling to be released from the membrane and removed via pipe (13) at the top of the pressure pipe (2) in the form of wash-water. The permeate pipe (9), the concentrate pipe (10), the feed pipe (8) and the discharge pipe for the first filtrate (11) are closed off by means of valves.

It is remarked that via pipe (12) gas in the form of preferably compressed air, optionally in combination with chemicals (15), is supplied to the feed in order to aid the release of fouling components while in addition, subject to the use of suitable chemicals, bacteria, biomass and the like can be killed. It is remarked that the O-rings (6) are used as seals between the membrane module (3) and the pressure pipe (2) in order to make it possible to reverse the direction of flow (seal for both flow directions) . The vertical disposition of the pressure pipe (2) aids proper venting.

After flushing out the wash-water and before production step (1) , it is possible to flush out the first filtrate as shown in Figure 2. However, this is not required for all applications. During production step 2, the wash step (Fig. 3) , cleaning chemicals may be added.

It is remarked, that various pipes in the apparatus according to the invention are provided with regulating valves and shut-off valves (no reference numbers), for regulating or shutting off, respectively, the feed, perme- ate, concentrate and filtrate streams as well as the wash- water stream.

It is remarked that the present invention comprises the following new elements:

* The entire method, which makes it possible to automatically online and hydraulically clean operating installations by using spiral-wound membranes; the ability to reverse the flow direction.

* The novel construction and assembly (pressure pipes, pipes, valves) of a membrane installation for spiral-wound membranes, facilitating the flowing along with gas and liquid. This assembly is characterised in that:

* the pressure pipes are disposed vertically,

* membranes in the pressure pipe are not arranged in series, 1 membrane/pressure pipe,

* O-rings (6) are used at both ends of the membranes.

* the possibility is provided to supply a gas to the feed during step 2. (Fig. 3),

* the flow direction through the feed spacer during production (step 1) is counter to the flow direction during flushing (step 2) .

Some of the advantages of the present method and apparatus to be mentioned are the considerably reduced costs compared with the prior art, resulting from the fact that less pre-purification is required, the membranes can be cleaned more easily, so that the quality requirements for the feed water may be lowered. According to the inven- tion there is a reduction in the energy consumption and in the amount of chemicals used, while less pre-purification takes place. Furthermore, the use of chemicals is further restricted thanks to a better hydraulic cleaning.

The present method and apparatus are to be used in particular for the purification of liquids.

The application is the purification of liquids comprising floating substances, particles and dissolved substances (salts, organic substances, TOC, DOC, AOC, pesticides and the like) . In practice this means that with this new method salts, other dissolved substances, floating substances, particles and bacteria and viruses can be removed from surface water and effluent from sewage purification at lower costs and at lower energy consumption and with a reduction in the use of chemicals. The product water may subsequently be supplied to industry (boiler feed water and other process water applications) or purified to drinking water.

Claims

1. A method for the purification of surface water or effluent from sewage purification, characterized in that floating substances, solid particles, bacteria, viruses, and dissolved substances such as salts, dissolved organic substances, pesticides and the like, are removed simultaneously by applying at least one vertically disposed pressure pipe comprising one spiral-wound nanofiltration or hyperfiltration membrane per pressure pipe taking delivery of the parallel oriented flow, and wherein the following steps are repeated:

2. flow along the membrane without the simultaneous production of permeate. 2. A method according to claim 1, characterized in that the flow direction of the feed through the membrane during step 1. is from the top downward and during step b. from the bottom upward.

3. A method according to claim 1 or 2, charac- terized in that during step 2. a gas is supplied to the feed.

4. A method according to claim 3, characterized in that as the gas compressed air is supplied.

5. A method according to claim 1 or 2, charac- terized in that chemicals are added to the feed during step 1. or 2. β. A method according to claim 5, characterized in that anti-sealants, base, acid, disinfecting chemicals, biocides, bactericides are added to the feed. 7. A method according to claims 1-6, characterized in that chemicals are added that bind substantially all the oxygen present in the membrane such as, for example, bisulphite or hydrazine.

8. A method according to claim 1-7, character- ized in that after the addition of the chemicals during flushing (step 2.) the flow along the membrane is stopped and the membrane is exposed to the influence of the chemicals for 1 to 10 minutes, after which the chemicals are flushed out of the membrane.

9. A method according to claim 1-8, character- ized in that between step 2. and step 1. an extra flush of feed water takes place, while the feed flows through the membrane from top to bottom.

10. An apparatus for performing a method according to claims 1-9, characterized in that the apparatus (1) is provided with a vertical pressure pipe (2), comprising a spiral-wound membrane column (3) with a top plate (4) and bottom plate (5) , which are provided with an 0-ring, wherein the central permeate discharge pipe "(14) in the top plate (4) is closed by means of a shut-off (7), and wherein the central permeate discharge pipe (14) in the bottom plate (5) is connected via interconnecter (7') with the permeate discharge (9), wherein pressure pipe (2) at the top side is connected with the feed pipe (8) and the wash-water discharge pipe (13), and at the bottom side with the pipe for wash-water supply and concentrate discharge (8' ) , while the feed supply (8) is connected with an inlet for chemicals (15) , and the wash-water inlet (8' ) , which is in communication with the concentrate discharge pipe (10) , is also connected with the gas sup- ply/concentrate discharge pipe (12) , and the discharge of the first filtrate (11) .