NL1019130C2 - Method and device for purifying surface water. - Google Patents

Description

Method and device for purifying surface water

The invention relates to a method for purifying surface water or effluent from sewage treatment or aerobic groundwater, as well as to a device for carrying out such a method.

According to the state of the art, purification of surface water or effluent from sewage treatment or aerobic groundwater often takes place using nanofiltration and hyperfiltration, wherein use is made of spiral-wound membranes. Such membranes are incorporated in series in horizontally placed pressure tubes according to a standard technique. Such pressure tubes generally have a length of 6 or 7 meters and contain 6 or 7 membranes each with a length of 1 meter or 4 membranes each with a length of 1.5 meters.

It is known that spiral wound membranes are very sensitive to contamination by particles, but also due to the growth of biomass, in which case biofouling is involved. The deposited particles cause clogging of the feedspacers, while certain nutrients in the feedwater may lead to biomass growth. This biomass grows between the spacer and can attach well anywhere. The result is that the biomass is very difficult to remove, for example by leaching.

Another fact of the current application of spiral wound membranes is that they cannot be cleaned hydraulically. Backwashing and longitudinal flushing of such membranes is not possible due to the excessive pressure drop across the series-connected membranes. This is in contrast to, for example, the capillary membranes which can be cleaned via a so-called for-wardflush, possibly with air.

Despite these disadvantages, spiral wound membranes are very popular for water purification purposes. The reasons for this are: 2 1. High packing density (2 to 3 times more membrane area per m2 module compared to capillary membranes (1.5 mm capillaries).

2. Standardized modules (interchangeability of 5 membranes from different manufacturers) and 3. Inexpensive (standardized product, multiple producers and large, current market size).

As mentioned earlier, spiral wound membranes 10 are very popular and they are often used for the purification of water, in which there are virtually no particles and nutrients anymore. With regard to the particles, high demands are often placed on the membrane fouling index (MFI) or the Silt Density Index (SDI). With regard to the presence of nutrients, the Assimilable Organic Carbon (AOC) or Dissolved Organic Carbon (DOC) is often considered. The treatment of surface water or effluent from sewage treatment plants with the aid of spiral wound membranes has so far not been found to be simple in terms of i.v.m. contamination occurring.

In order to guarantee proper operation, a very good pre-treatment must take place.

Such a pre-purification can include the following operations: 1. (Microsieve) and rapid filtration 2. (Microsieve), rapid filtration and ultrafiltration 3. (Microsieve), rapid filtration, active carbon filtration and ultrafiltration.

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It is noted that hitherto there is a general view that microsieving in combination with rapid filtration as pre-purification is insufficient to prevent contamination (biofouling and particle fouling) of the spiral-wound membranes or to sufficiently prevent them. The microsieve, in combination with rapid filtration followed by ultrafiltration, also appears to be insufficient to eliminate the problem of contamination in the spiral-wound membranes. After all, it has been found that the 3 dissolved nutrients in the feed water are not removed. However, extensive pre-treatment, including the use of activated carbon, leads to good operational results in practice. The use of active carbon makes the process extensive and expensive.

Another solution is to use capillary nanofiltration or hyperfiltration membranes instead of spiral wound nanofiltration or hyperfiltration membranes, as discussed in WO 0029099. The current state of the art can be summarized as follows.

It has been found that when spiral-wound nanofiltration and hyperfiltration membranes are used, serious contamination occurs due to the solid particles and dissolved nutrients (biofouling) present in the water to be purified, and that such membranes cannot be hydraulically cleaned in the current application. The consequence of this is that when spiral-wound nanofiltration and hyperfiltration membranes are used for purifying surface water or effluent, extensive pre-treatment must be preceded, namely microsieving, rapid filtration and ultrafiltration or (microsieving), rapid filtration, active carbon filtration and ultrafiltration. The application of a completely different technique is based on capillary nanofiltration or hyperfiltration membranes for the purification of surface water or effluent. According to this technique, the pre-purification can be limited to only the microsieve.

It is an object of the invention to provide a new method and device in which the above-mentioned disadvantages are eliminated in an effective manner. To this end, the present invention provides a method for purifying surface water or effluent from sewage treatment or aerobic groundwater, which method is characterized in that suspended solids, solid particles, bacteria, viruses, and dissolved substances such as salts, dissolved organic substances, pesticides and the like, are simultaneously removed by using at least one vertically placed pressure tube containing one spiral wound nanofiltration or hyperfiltration membrane (1 or 1.5 m length) per pressure tube, which is flowed in parallel and with which the following steps are repeated repeatedly : 1. production of permeate with simultaneous and continuous release of concentrate and 2. longitudinal flushing of the membrane, without simultaneous production of permeate.

The method according to the invention makes use of one or more vertically placed pressure tubes with one spiral wound nanofiltration or hyperfiltration membrane per pressure tube, wherein it has surprisingly been found that a minimum pre-purification can suffice. This pre-purification can consist of microsieving and rapid filtration.

It is essential here that the pressure tubes filled with the spiral wound membranes are arranged vertically and the following operating steps are alternated, t. w. : 1. Production of permeate with continuous release of the concentrate. 2. Hydraulic flushing of the membranes with water or a combination of water and gas, preferably air.

According to the present method, the flow direction of the feed through the membrane during step 1 is from top to bottom and during step 2 from bottom to top.

It is noted that during step 2 a gas can be supplied to the feed according to the invention, which gas is preferably compressed air.

It is also possible to add chemicals to the feed during steps 1. and 2..

Suitable chemicals according to the invention are: anti-scalants, caustic, acid, disinfecting chemicals, biocides, bacteriocides or oxygen-eliminating substances such as, for example, bisulfite or hydrazine.

After the dosing of the chemicals, the longitudinal flushing 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 noted that between step 2. and step 1. an additional flushing of feed water can take place, while the feed flows through the membrane from top to bottom.

The invention also relates to a device for performing a method according to the invention, which device is characterized in that the device is provided with a vertical pressure tube (2), which includes a spiral wound membrane (3), with respectively a top and bottom plate, which is provided with an O-ring (6), wherein the central permeate discharge tube (14) in the top plate (4) is closed with a seal (7), and wherein the central permeate discharge tube (14) in the bottom plate ( 5) is connected via interconnector (7) to the permeate discharge (9), the pressure pipe (2) being connected at the top to the supply pipe (8) and the flushing water discharge pipe (13) and connected at the bottom to the pipe for rinse water supply and concentrate drain (8 '), while the feed supply (8) is connected to a chemical supply (15), while the rinse water supply (8') in connection with concentrate drain line (10) is also connected to the gas supply / concentrate discharge line (12), and the discharge of the first filtrate (11).

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

In the drawings, figures 1, 2 and 3 represent one and the same device, wherein figure 1 illustrates the production process, figure 2 shows the flushing of the first feed water, figure 3 relates to the hydraulic cleaning or longitudinal flushing of the membrane.

The reference numerals in figures 1, 2 and 3 represent the following: 1. Device according to the invention 2. Vertical pressure tube 3. Membrane element 6 4. Top plate membrane element 5. Bottom plate membrane element 6. O-Ring 7. Closure of central permeate discharge tube (14) 5 7 'Interconnector for connecting the central permeate drain pipe (14) to the permeate drain pipe (9) 8. Supply pipe 8' Pipe for flushing water and concentrate drain 9. Pipe for the permeate 10. Pipe for the concentrate 11 Pipeline for discharge of first feed water 12. Pipeline of gas supply 15 13. Pipeline for discharge of flushing water 14. Central permeate discharge pipe 15. Pipeline of chemical supply

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

FIG. 1: Production During production, the feed is supplied either to surface water or to effluent or aerobic groundwater from sewage treatment via line (8) in the vertically arranged pressure tube (2), which is provided with a spiral wound membrane (3). After the spiral wound membrane has been traversed, the permeate is drained via the interconnector (7 ') from the central drain pipe (14), via the permeate drain line (9), while the concentrate is fed through the flushing water supply and concentrate drain (8' line). ) is discharged via the concentrate discharge line (10) to a subsequent processing step. This next processing step may consist of a further vertically placed membrane module or through a horizontal pressure tube with one or more spiral-wound membranes in series.

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The O-rings (6) of elastic material close off the top or bottom side of the vertical pressure tube (2), forcing the feed through the spiral wound membrane and thus ending up in the central discharge tube (14) ) (as permeate) or on the other outflow side of the membrane (3) (as concentrate). During production, chemicals can be supplied via the chemical supply line (15).

FIG. 2 shows the flushing of the first feed water using the same flow direction as in FIG. 1.

The first feed water is hereby discharged via line (11) without discharge of permeate.

FIG. 3 shows under step 2 namely the longitudinal rinsing of the membrane of the present process without the simultaneous production of the permeate.

Here, the flow direction of the feed is reversed with respect to Figs. 1 and 2, ie the feed is supplied via the rinse water supply and concentrate discharge line (8 ') on the underside of the vertically placed pressure tube (2), the impurities coming from the diaphragm are released and removed and discharged via line (13) at the top of the pressure tube (2) in the form of rinsing water. The permeate line (9), concentrate line (10), feed line (8) and the discharge line for the first filtrate (11) are closed by means of valves.

It is noted that via line (12) gas in the form of preferably compressed air, whether or not in combination with chemicals (15), is supplied to the feed, whereby better detachment of the contaminating or deposited components takes place and wherein moreover bacteria and biomass and the like can be killed by adding suitable chemicals.

It is noted that the O-rings (6) are used as a seal between the membrane module (3) and the pressure tube (2), in order to make it possible to reverse the flow direction (seal for both flow directions). By placing the 8 pressure tube (2) vertically, good venting takes place.

After rinsing the rinsing water (step 2) and before the production step (step 1), a further rinsing of the first feed water can take place, as shown in figure 2. However, this is not necessary for all applications. Cleaning chemicals can be added during operating step 2, the rinsing step (Fig. 3).

It is noted that the various lines in the device according to the invention are provided with control shut-off valves (no reference numerals), for controlling or shutting off feed, permeate, concentrate and filtrate flows, as well as flushing water flow.

It is noted that the following new elements are mentioned in the present invention: The total method in which, in practical installations, on-line and automatic hydraulic cleaning can be carried out using spiral-wound membranes; flow direction 20 can be reversed.

❖ The new construction and construction (pressure pipes, pipework, valves) of a membrane installation for spiral wound membranes, making it possible to flush along with gas and liquid. This construction is characterized by: ♦♦♦ the pressure tubes are placed vertically, ♦ J * no membranes are placed in the pressure tubes in series, 1 membrane / pressure tube, ❖ 0-rings (6) are used at both ends of the membranes, ❖ built-in possibility of supplying a gas to the feed during step 2. (fig. 3), ♦ i * The flow direction through the feed spacer during production (step 1) is opposite to the flow direction at rinsing (step 2).

The advantages of the present method and device are the considerably lower costs compared to the state of the art because less pre-purification is required, the membranes are easier to clean, so the quality requirements for the feed water can be lowered. According to the invention there is a lower energy and chemical consumption, with less pre-purification taking place. Moreover, with a better hydraulic cleaning the chemical consumption is further reduced.

The present method and device can be used in particular for the purification of liquids.

The application is the purification of liquids in which floating substances, particles and dissolved substances (salts, organic substances, TOC, DOC, AOC, pesticides and the like) may be present. In practice, this means that surface water and effluent from sewage treatment plants or aerobic groundwater can be stripped of salts, other solutes, suspended solids, particles and bacteria and viruses with this new method cheaper and with a lower energy and chemical consumption. The produced water can then be supplied to industry 20 (boiler feed water and other process water applications) or upgraded to drinking water.

Claims (10)

Process for purifying surface water or effluent from sewage treatment or aerobic groundwater, characterized in that suspended solids, solid particles, bacteria, viruses, and dissolved substances, such as salts, dissolved organic substances, pesticides and the like, simultaneously are removed using at least one vertically placed pressure tube containing one spiral wound nanofiltration or hyperfiltration membrane per pressure tube, which is flowed in parallel and the following steps 10 are repeatedly repeated: 1. production of permeate with simultaneous and continuous release of concentrate and 2 flushing the membrane without simultaneous production of permeate. Method according to claim 1, characterized in that the direction of flow of the feed through the membrane during step 1 is from top to bottom and during step b. from the bottom to the top. 3. Method according to claim 1 or 2, characterized in that a gas is supplied to the feed during step 2. Method according to claim 3, characterized in that compressed air is supplied as gas. 5. Method as claimed in claim 1 or 2, characterized in that chemicals are dosed to the feed during step 1 or 2. Method according to claim 5, characterized in that anti-scalants, lye, acid, disinfecting chemicals, biocides or bacteriocides are dosed to the feed. Method according to claims 1-6, characterized in that chemicals are metered which bind substantially all the oxygen present in the membrane, such as, for example, bisulfite or hydrazine. 8. Method according to claims 1-7, characterized in that after dosing of chemicals during rinsing (step 2.) the longitudinal rinsing is stopped and the membrane is exposed to the action of chemicals for 1-10 minutes, after which the chemicals are flushed out of the membrane. A method according to claims 1-8, characterized in that an additional flushing of feed water takes place prior to the transition from step 2. to step 1., while the feed flows through the membrane from top to bottom. Device for carrying out the method according to claims 1-9, characterized in that the device (1) is provided with a vertical pressure tube (2), in which a spiral-wound membrane column (3) is received, with respectively a top ( 4) and bottom plate (5), which are provided with an O-ring (6), wherein the central permeate discharge tube (14) in the top plate (4) is closed with a seal (7), and wherein the central permeate discharge tube ( 14) in the bottom plate (5) is connected via interconnector (7 ') to the outlet (9), the pressure pipe (2) being connected at the top to the supply pipe (8) and the flushing water discharge pipe ( 13) and is connected at the bottom to the flushing water supply and concentrate discharge line (8 '), while the feed supply (8) is connected to a chemical supply (15), while the flushing water supply (8') communicates with concentrate discharge line (8) 10) is also connected to the gas supply / concentrate drain line (12), and the drain of the first feed water (11).