GB2338477A

GB2338477A - Adsorbent bed

Info

Publication number: GB2338477A
Application number: GB9812549A
Authority: GB
Inventors: Philip Charles Blowes; Alan John Taylor
Original assignee: ARCASORB TECHNOLOGY Ltd
Current assignee: ARCASORB TECHNOLOGY Ltd
Priority date: 1998-06-11
Filing date: 1998-06-11
Publication date: 1999-12-22
Also published as: GB9812549D0

Abstract

A decontaminating bed 2 for the removal of contaminants from water comprises a textile material such as yarn or fabric impregnated with water insoluble chitosan, and a method of constructing such a bed comprises winding a textile material impregnated with insoluble chitosan around a perforated former through which the contaminated water may be passed. A cotton or cotton/polyester fibre fabric impregnated with 3-20% w/w chitosan cross-linked using glutyraldehyde may be used. The bed may be regenerated.

Description

1 2338477 8255GB DECONTAMINATING BED -I- This invention relates to a fixed

adsorbent bed and to methods of constructing such a bed of adsorbent medium suitable for the decontamination of aqueous streams containing dilute solutions of contaminants over a range of pH 2-12 inclusive.

Water is commonly contaminated with relatively low levels of metals in solution as metallic salts, toxic compounds and other unwanted chemicals either through natural means as water passes through the atmosphere or through or over rock and detritus in the natural environment, or alternatively as a result of being used in industrial processes. Where water is to be used for human consumption contaminants such as iron (often present as Fe++ or Fe... ions in concentrations of 500 Mg/litre) impart taste and possibly a health hazard to the population and must be reduced to a satisfactory level or completely eliminated. Where the water issues as effluent from industrial processes, toxic and undesirable contaminants must be reduced to acceptable levels determined by the authorities responsible for controlling discharges to sewer or to the environment. For example, dye residue colour must be reduced to less than 0.02 absorbence units (average over six wavelengths) for discharge into rivers in the United Kingdom, whereas the effluent may have a colour in the range 1-6 absorbence units prior to any treatment.

It is known that a wide range of the contaminants occurring in natural waters and in effluents from industrial processes can be adsorbed on to chitosan.

Furthermore, it has recently been found that such adsorption is generally reversible by passing dilute aqueous solutions of acid or alkali through chitosan, whereupon the contaminants are removed from the chitosan, collected and treated for disposal or re-use.

It has now been found that chitosan can be deposited 1 8255GB on a textile substrate of yarn or fabric and rendered insoluble over a wide range of pH in conditions amicable to water treatment, and which permit the chitosan to be regenerated when it has become saturated with contaminant deposition.

The present invention therefore provides a decontaminating bed for the removal of contaminants from water comprising a textile material impregnated with water insoluble chitosan.

The present invention also provides a method of constructing a decontaminating bed for the removal of contaminants from water in which a textile material impregnated with water insoluble chitosan is wound around and retained on a perforated former through which the water may be passed.

Further, the present invention provides a method for the removal of contaminants from water in which the water is passed through a decontaminating bed.

Contaminants in the water are attached to the chitosan by adsorption, chelation, ionic bonding, absorption or other means.

The bed comprises a natural or synthetic fibre (or mixed fibre) yarn or fabric substrate. Typically, cotton, viscose, polyamide, polyester andlor polypropylene fibres may be employed. The substrate may be wound many times around a central hollow former or core in a continuous length, or in discrete parts or pieces or lengths, the whole forming a continuous thickness of bed with respect to the flow of contaminated water. This thickness is determined by the application for which the bed is used and will be decided on the basis of a combination of practical considerations such as physical handling as well as contaminant removal. The determining factors for contaminant removal may be contact time (ie. the period of time during which one molecule of water is in contact with -1 c 8255GB 1 1 o', re.

c 1 1 the bed as it passes through it), and capacity of the bed before it becomes saturated with contaminants. The length of the bed is determined by practical manufacturing and handling considerations, flow per unit length being the sizing characteristic important in performance selection.

The textile substrate is sealed across its exposed ends with, e.g. a water-proof adhesive to prevent flow bypassing the bed thickness, and after sealing the bed is bound tightly with banding tape or equivalent material to resist backward flow pressure on regeneration of the bed, for example, by use of 12mm wide flexible steel bands (5 per 2m length of bed).

Fabric substrate type and specification directly affect the performance of the bed in terms of effectiveness of removal of contaminants from the water stream.

Chitosan is solubilised by any of the methods common in the art, typically in a 2% w/w solution of acetic acid, and is padded on to the substrate and squeezed using a commercial mangle. The pressure of squeeze is adjusted to provide the amount of chitosan deposition required for ultimate performance of the bed. The chitosan is applied using several passes through the padder/mangle.

After neutralising the bed with aqueous alkali such as caustic soda, the chitosan is cross-linked to render it insoluble for water treatment uses. The cross-linking is performed using any of the methods common in the art, for instance by contacting the bed with glutyraldehyde at a strength of 0.1 to 2% for a period of 1-24 hours at room temperature. 30 The bed is then ready to process contaminated water, but will require contacting with water at the required operating pH before it will function in the manner desired. The former, or core, 1 (see Figures 1A and 1B) on which the bed 2 (of impregnated fabric sealed across its exposed ends 3) is wound in any suitable engineering 1 8255GB material, having the strength, lack of corrosivity to acid and alkali and ability to pass water through to the hollow centre. Typical materials of constructions are perforated plastic, perforated metal, metal mesh, porous plastic and 5 wedgewire. The core is arranged so that water can pass radially through the bed, into the hollow core and pass axially along the core to the wall of the vessel containing it. Reverse direction flow is permitted. The core may be sealed at one end and at the other it passes through the end wall of the vessel in which the bed is placed, although this configuration is not intended to be limiting in the invention.

The bed assembly, comprising the bed 2 and core 1, is placed inside a vessel 4 (see Figure 2) which may be any size or shape and manufactured to good engineering practice. In this configuration one bed is placed inside a vessel designed for the purpose, in which the bed core is connected through the end cover by screwed fittings and 0 Ring seals. The opposite (sealed) end of the bed core is supported at 8. Contaminated water is pumped into the shell of the vessel at 5 (or alternatively at 7), passes through the bed 2 into the hollow core and then is piped out of the vessel at 6 in the manner described. Regeneration of the bed is performed by passing regenerants into the core and through the bed in reverse direction to water flow, and exits out of the water inlet branch. Regeneration may also be performed in the same direction as water flow. The vessel is connected with suitable valved connections to permit the water flow to be stopped whilst regeneration is being executed.

Regeneration is performed by passing a dilute aqueous solution of inorganic acid or alkali through the bed for a sufficient period of time to change the pH of the bed, as measured with reference to the pH of the water exit the bed, from acidic to alkaline, or alternatively from 8255GB is -5 alkaline to acidic, according to the mode of operation of the bed in its adsorptive state (see table 4). Acids used are hydrochloric and sulphuric and alkalis are sodium, calcium and ammonium.

The concentration of regeneration chemical (acid or alkali, as the case may be) and quantity used are dependant upon the pH of the water used in regeneration, the nature of contaminants adsorbed on to the bed, and the volume needed to achieve full desorption of the bed, within practical limits.

It has been found that between 1 and 5 bed volumes of regenerant in the concentration range 0.01 to 0.2N have been effective in achieving 98+% desorption of the bed for contaminants which have been evaluated (see examples).

After regeneration the bed may be put on line by feeding it with acidic (or alkaline, as the case may be) contaminated water, or alternatively by further cleaning the bed with water as near neutral pH and/or followed by acidic water, desirably in the range 4-5 pH (or alkaline water in the range 8-10 pH, as the case may be) in order to prevent contamination of the treated water stream with regenerant.

The bed capacity is determined from the time during which contaminated water must be in contact with the bed for the desired level of performance and for the saturation of the bed, wherein it loses the ability to remove contaminants from the water stream. The examples and performance tables illustrate these considerations, which are specific to the contaminants to be removed.

Beds are arranged in arrays to achieve the desired level of performance, with one or more beds in a vessel, beds operating in series or in parallel. Series configuration increases the removal of contaminant and parallel configuration increases throughput of water.

The following examples are intended to illustrate but 1 r- 82550B 1 1 not limit the scope of the present invention.

Example -1 - a bed of 5.7% (wlw) chitosan on a substrate of 294g of polyester/cotton woven fabric (weft 60 pickslinch, warp 94 endslinch) was wound tightly on a nominal 10 inch long 3cm internal diameter filter core and mounted in a standard filter housing. The diameter of the bed was 6. 5cm. Water at room temperature contaminated with Acid Red 44 dye was passed through the bed at 3 litres/hour. The inlet pH was 5.0. The inlet colour was 22.7 absorbence units (au) at 500 nm. Outlet colour results were as follows:

Is Cumulative Outlet colour (au) Colour volume (litres) Removal, 1 0.017 99.9 2 0.040 99.8 3 0.153 99.3 4 0.222 99.0 5 0.785 96.5 Example 2 - a bed of 6.0% (w/w) chitosan on a substrate of 292g of polyesterjcotton woven fabric (weft 60 picks/inch, warp 94 ends/inch) was wound tightly on a nominal 10 in long 3cm, internal diameter filter core and mounted in a standard filter housing. The diameter of the bed was 6.6cm. Water at room temperature contaminated with aluminium sulphate was passed through the bed. The initial concentration of aluminium ions was 8.0 mg/litre and the pH 8.0. The following outlet concentrations of aluminium were recorded at different flowrates:

8255GB Flowrate Outlet conc. A1 % Al Removal (litres/hr) (mg/litre) 12 0.04 99.4 0.06 99.2 60 0.15 97.9 0.24 96.6 ExaMR12 3 - a bed of 5.5% chitosan on a 1.6m long x 0.15 m diameter roll of a substrate of polyester/cotton woven fabric (weft 60 pickslinch, warp 94 ends/inch) was mounted on a wedgewire core of diameter 0.05 m. The bed assembly was placed inside a stainless steel vessel and connected to external piping in the manner shown in Figure 2. Mixed effluent from a textile factory at 300C was passed through the bed at the flowrates shown in the table below and apparent colour measured at 450 nm. Inlet pH varied between 4.2-5.3 throughout. One sample of treated effluent was filtered at 0.45p (pore size) and the colour remeasured at 450 nm to determine the true colour measurement 1FlowratelInlet Colour 1 outlet 1 % Removal 1 True 1% Removall (m3/hr) (au) Colour apparent Colour true (au) colour (au) colour 0.6 0.654 0.336 49 0.6 0.678 0.335 50 - - 0.7 0.712 0.355 50 0.04 94 1.4 0.746 0.399 46 - - 2.4 0.633 0.427 32 1 8255GB Example 4 - a bed similar to example 3, but with an outside diameter increased to 0.41m and repeatedly regenerated as described above after saturation had been achieved. Textile factory effluent at 450C (mixed dye and 5 wash/scour effluent) was passed through the bed at a flowrate 28 litres/min:

Apparent (no filter in place) colour readings in absorbence units, at wavelengths Colour Sample 40Orm 450nm 50Orm 550nn 60Orm 650rm Ave. RedIn Raw 0.833 0.816 0.795 0.739 0.761 0.650 0.766 - Treated 0.040 0.041 0.022 0.015 0.020 0.016 0.026 97 True (filter in place) colour readings in absorbence units (filtered at 0.45M pore size Colour Sample 40Onm 450nm 50Onm 550nn 60Onm 65Onin Ave. RedIn Raw 0.335 0.325 0.322 0.326 0.328 0.318 0.326 Treated 0.041 0.006 0.014 0.000 0.001 0.001 0.010 97 Example 5 - a bed of 4.2% (w/w) chitosan on a substrate of 147 g of polyester/cotton woven fabric (weft 55 pickslinch, warp 72 ends/inch) was wound tightly on a nominal 10 inch long 3cm internal diameter filter core and 40 mounted in a standard f ilter housing. The diameter of the .1 - 8255GB bed was 5.8cm. Water at room temperature contaminated with humic acid and its sodium salt was passed through the bed. The concentration of contaminant was 1 gram per 20 litres of water and the pH was 4.83. Colour was measured at 80.0 5 Razen and the flowrate through bed was 3 litres/hr:

Cumulative Exit colour (Hazen) Colour volume (litres) Removal, 1 0.0 100 2 0.0 100 3 2.0 97.5 4 5.2 93.5 ExaMR12 t - a bed of 0.0058 g chitosan on a substrate of 126 g of polyester/cotton woven fabric (weft 60 picks/inch, warp 94 endslinch) was wound tightly on a nominal 10 inch long 3cm internal diameter filter core and mounted in a standard filter housing. The diameter of the bed was 5.6cm. Water at 130C contaminated with arsenic sulphate was passed through the bed at pH 7.7 at a rate of 6.4 litres/hr:

Bed volumes, Inlet Outlet Colour (cumulative) concentration, concentration, Removal, As (gg/litre) As (gg/litre) % 30 12 60 22 15 32 20 15 25 8255GB Example 7 - a bed of 5.97% (wlw) chitosan on a substrate of 146g of polyester/cotton woven fabric (weft 60 pickslinch, warp 94 endslinch) was wound tightly on a nominal 10 inch long 3cm internal diameter filter core and mounted in a standard filter housing. The diameter of the bed was 5.8cm. Tap water at room temperature contaminated with ferrous sulphate was passed through the bed. The concentration of ferrous sulphate was 0.05 g per 10 litres and the pH was 8.0:

Flowrate, Inlet outlet Colour (litres/hr) concentration, concentration, Removal, FeS04 (gg/litre) FeS04 (Mgllitre) % is 3 0.28 0.10 64 6 0.30 0.01 97 9 0.26 0.01 96 12 0.29 0.01 97 18 0.22 0.01 95 Example 8 - a bed of 5.7% (wlw) chitosan on a substrate of 294g of polyester/cotton woven fabric (weft 60 pickslinch, warp 94 ends/inch) was wound tightly on a nominal 10 inch long 3cm internal diameter filter core and mounted in a standard filter housing. The diameter of the bed was 6.6cm. Water at room temperature contaminated with manganese chloride was passed through the bed. The concentration of manganese chloride was 500 gg/litre and the pH was 8.5. The flowrate was 2.44 litres/hr:

8255GB r -.

C.

-. 1 r 1 1 r ' 1 1 1 is Cumulative Volume outlet Colour (litres) Concentration Removal HnC12 (pg/litre) 1.7 100 80 2.5 300 40 3.2 300 40 5.0 300 40 6.6 300 40 TABLES

Table 1 - Shows relative performance of textile substrates for acid red dye 44 removal, flowrate 5 litres/hour, pH 5 20 at room temperature:

Substrate Weight Bed Volume % w/w % colour c.c. Chitosan Removed (after 2 litres) Cotton 260 g/m2 322 4.5 99.1 Sateen Polyester/ 300 gIm2 554 5.7 99.9 Cotton Sateen Polyester/ 123 g/m2 489 3.85 86.9 Cotton Satin Polyester/ 250 g/m2 205 6.0 62.1 Viscose (35%) Cotton yarn 2.8 g/m 579 5.3 60.0 8255GB I Table 2 - Shows relative performance of textile substrates for humic acid removal, flowrate 3 litres/hour, pH 5 at room temperature:

1Substrate 1 Weight 1Bed Volumel % w/w 1 % Colour 1 g/M2 c.c. Chitosan Removed (after 5 litres) 100% Plain 123 416 3.9 87.0 Cotton Cotton 41 567 3.9 90.7 Mousse Matting 148 440 4.0 62.9 Cotton Fine Bleach 77 514 4.2 90.5 Cotton Table 3 - Shows relative performance data for chitosan deposited on a polyester/cotton fabric substrate:

Chitosan (wlw) Removal, dye Relative Saturation Volume 5 95 1 99 1.5 15 99 1.6 8255GB Table 4 - Decontamination and regeneration pH combinations:

Decontamination Regeneration State Typical pH Chemical pH Acidic 3 - 6 Alkali (NaOH) min 8 Alkaline a - 10 Acid (HCl) max 7 '. 1 8255GB

Claims

1. A decontaminating bed for the removal of contaminants from water comprising a textile material impregnated with water insoluble chitosan.

2. A decontaminating bed as claimed in Claim 1 in which the textile material is in the form of yarn.

3. A decontaminating bed as claimed in Claim 1 in which the textile material is in the form of fabric.

4. A decontaminating bed as claimed in Claim 2 or 3 in which the textile material comprises cotton or a mixture of cotton and polyester fibres.

5. A decontaminating bed as claimed in any one of Claims 1 to 4 in which the textile material is wound on a perforated former.

6. A decontaminating bed as claimed in any one of the preceding claims in which the amount of chitosan on the textile material is 3-20% wlw.

7. A decontaminating bed as claimed in any one of the preceding claims in which the chitosan is cross-linked using glutyraldehyde.

8. A method of constructing a decontaminating bed for the removal of contaminants from water in which a textile material impregnated with water insoluble chitosan is wound around and retained on a perforated former through which the water may be passed.

9. A method of constructing a decontaminating bed as claimed in Claim 8 in which the exposed ends of the textile material are sealed.

10. A method for the removal of contaminants from water in which the water is passed through a decontaminating bed as claimed in any one of Claims 1 to 7.

11. A method for the removal of contaminants from water as claimed in claim 10 in which the pH of the contaminated water is 7 or below.

12. A method for the removal of contaminants from water as 1 I- 8255GB -Is- claimed in Claim 10 in which the pH of the contaminated water is kept above 7.

13. A method for the removal of contaminants from water as claimed in Claim 10 in which the bed is regenerated by using an acid when the pH of the contaminated water is alkaline and an alkali when the pH of the contaminated water is acid.

14. A decontaminating bed for the removal of contaminants from water substantially as hereinbefore described with reference to the accompanying drawings.

15. A method of constructing a decontaminating bed for the removal of contaminants from water substantially as hereinbefore described with reference to the accompanying drawings.

16. A method for the removal of contaminants from water substantially as hereinbefore described with reference to the accompanying drawings.