GB2306464A - Reducing the colour and/or odour of waste - Google Patents

Abstract

The colour and/or odour of water or soil contaminated with organic waste is reduced by addition of bromine, hypobromous acid, bromamine or any precursors which form any one of the above on addition to water. Preferably the colour/odour reducing agent is bromine, and is generated in situ from sodium bromide and sodium hypochlorite. The waste water may be a dyebath effluent, such as produced by textile dyeing operations, the dyebath containing an oxidisable contaminant such as a reactive dyestuff. The dyestuff may also be, for example, an anionic, direct, disperse or vat dye. Alternatively the contaminant may comprise pentachlorophenol.

Description

DECOLOURISING AND/OR DEODORISING CONTAMNATED WATER The present invention relates to the treatment of contaminated water or soil with certain bromine-based bleaching agents to reduce colour and/or odour. For convenience, the term "bromine" is used hereinafter to mean bromine, hypobromous acid or its water soluble salts, bromamine and their precursors.

Water used, for example in industrial processes becomes contaminated with organic substances which may impart colour and/or odour. The contaminated water may also contain other undesirable substances, including: pesticides, such as permethrin or simazine; organic solvents; biocides, such as isothiazolones and pentachlorophenol; phenols; chelants; polyaromatic hydrocarbons; aldehydes; and certain inorganic species such as hydrogen sulphide, chlorine and chlorides all of which may cause problems. Such water may cause unacceptable pollution if discharged to the environment. Industries which may experience problems with chemically contaminated water include the textile industry, paper pulp industry, chemical industry, pharmaceutical industry, oil industry and leather industry.The water may originate directly from the process itself or from an ancillary system such as a cooling water system. Contaminated water may also originate from land run-off or seepage particularly where the land has been used for waste disposal or landfill. Conversely effluent water may contaminate soil.

Particular problems have been caused in the textile industry by the presence of dyestuffs in the waste water from textile dyeing operations. Dyes such as reactive dyes, dispersed dyes, premetallised dyes and vat dyes can cause unsightly discolouration of rivers and lakes.

Conventionally, colour and/or odour has been reduced by using chlorine, usually added in the form of sodium hypochlorite, but its effectiveness has been found to be unsatisfactory and there are many coloured substances with which chlorine will not react. As a result of environmental concerns for its safety, there has been a trend away from the use of chlorine in favour of substances such as catalysed hydrogen peroxide and/or ozone.

However, the use of such substances has been found to have a number of shortcomings.

Catalysed hydrogen peroxide is effective in reducing colour and odour, but the reaction produces a troublesome sludge which fouls equipment and may block filters. The high volatility of ozone results in a high rate of loss from solution leading to a high risk of inhalation toxicity.

None of these approaches has been adequate for e.g. the textile industry which has been forced to rely on bleaches such as dithionite to meet regulatory requirements. Unfortunately the bleaching action of the latter may in certain conditions be reversible leading to a recrudescence of the colour in the water after it has been discharged.

We have now discovered that bromine is significantly more effective than any of the conventionally used substances in reducing colour and/or odour in contaminated water while being relatively free from toxicity hazards. Bromine has the added advantage of being able to control many of the other undesirable substances contained in the water, such as those referred to hereinabove. Bromine has hitherto been used as a biocide to prevent bacterial contamination of water but not as a bleaching or deodorising agent for water which is chemically contaminated. Because bromine is less reactive than chlorine, it has been assumed that it would be ineffective in such applications, in which chlorine has been found inadequate.

The present invention provides the use of bromine to reduce the colour and/or odour of water or soil containing organic contaminants.

According to a second embodiment, the present invention provides a method of treating waste water and/or process water or soil containing oxidisable coloured and/or odoriferous organic contaminants in order to reduce the colour and/or odour thereof which comprises adding thereto a treatment agent selected from one or more of bromine, hypobromous acid or its water soluble salts, bromamine or any of their precursors which form any of them on addition to water, in an amount sufficient to reduce the colour and/or odour thereof.

According to a further embodiment, the present invention provides a method of treating water containing an organic dyestuff in order to reduce the colour thereof which comprises adding thereto effective amounts of bromine, hypobromous acidor its water soluble salts, bromamine and/or any of their precursors which form any of them on addition to water. The dyestuff is preferably a reactive dye, but may alternatively be, for example, an anionic, direct, disperse or vat dye. The water is typically waste water from a textile operation.

The invention is also effective in relation to halogenated aromatic compounds such as pentachlorophenol.

The bromine may for example be added int he form of liquid elemental bromine. It is, however, usually convenient to add a mixture of sodium bromide and sodium hypochlorite (sodium hypochlorite reacts rapidly with bromide ion in solution to produce bromine). The relative proportion may typically range from 1:5 to 1.2:1 molar e.g. 1:1 to 1:2.

The dose rate of bromine to the contaminated water depends upon the concentration of contaminants. Typically, the dose rate may be up to 12,000 ppm, but more usually in the range of 5 to 700 ppm. Often the dose rate will be stoichiometric with respect to the contaminant. However a small excess may sometimes be desirable. Equally, a partial reduction of contamination may sometimes suffice, allowing the use of smaller amounts of bromine. Reaction times will vary depending on the temperature of the water and the nature of the substances being acted upon. It is usually observed that bromine produces an immediate alleviation of colour and odour although contaminants may require several hours to attain maximum effect.

The bromine is useful over a broad range of pH. It is useful at acid pH e.g. 1 to 6.5 but is particularly effective in neutral or alkaline water e.g. up to pH 12.

Example I A 100 ppm solution of an orange reactive dye, Cibacron Orange, was made in demineralised water and the pH value of the solution was adjusted to pH 2 by addition of 4N hydrochloric acid.

Two 100 ml conical flasks, each equipped with a magnetic stirrer, were set up and 20 ml of the prepared dye solution was added to each flask To the first flask was added sodium hypochlorite solution to give a level equivalent to 100 ppm available chlorine. To the second flask was added the same concentration of sodium hypochlorite plus 100 ppm of sodium bromide. Both solutions were then quickly readjusted to pH 2.

Visual observations were made at intervals. The hypochlorite alone gave some colour reduction of the bright orange solution after 5 minute reducing to a pale yellow after three hours. The bromide/hypochlorite gave substantially instant reduction in colour reducing to pale yellow in three hours.

Example 2 The experimental procedure as described in Example 1 was closely adhered to but, this time, the pH value was adjusted to 7 using 4N hydrochloric acid and 4N sodium hydroxide solution as necessary. The hypochlorite gave little or no reduction in colour after three hours. The bromide/hypochlorite gave an immediate colour reduction and water white solution after three hours.

Example 3 The experimental procedure as described in Example 1 was closely adhered to but, this time, the pH value was adjusted to 11 using 4N sodium hydroxide solution. The hypochlorite gave negligible colour reduction. The bromide/hypochlorite gave some immediate colour reduction proceeding slowly to a water white solution.

Example4 Examples 1 to 3 were repeated using equivalent amounts of 99% pure liquid bromine in place of bromide/hypochlorite. Substantially identical results were obtained.

Example 5 An anionic premetallised dye (Acidol Brilliant Blue) was treated with liquid bromine and with bromide/hypochlorite at pH 2, 4 and 11. Under all conditions both reagents gave complete bleaching of the deep blue dye solution.

Example 6 Bromide/hypochlorite was compared with hypochlorite alone for bleaching a direct dye (Solar Black G) at pH 2, 7.5 and 11. At pH 2 hypochlorite converted the black solution to an orange brown colour while the bromide/hypochlorite gave a pale yellow. At pH 7.5 the hypochlorite alone had no immediate effect but after a time the colour was reduced to a dark brown black. The bromide/hypochlorite produced an immediate lightening of the colour with eventual reduction to a pale yellow. At pH 11 the results were similar to pH 7.5.

Example 7 Bromide/hypochlorite was compared with hypochlorite alone for bleaching a disperse dye (Foran Brilliant Red). Hypochlorite alone had no visible effect on the dark red solution after several hours at pH 2, 7.5 or 11. Bromide/hypochlorite gave an immediate reduction in colour intensity fading to a pale pink after several days.

Example 8 A vat dye (Indanthren Blue) showed no immediate effect with hypochlorite at any pH.

Bromide/hypochlorite gave an immediate lightening of the colour.

Example 9 Samples of a 1 00ppm solution of pentachlorophenol were treated with 1 00ppm Cl2 as sodium hypochlorite and with 100ppm Br2 as 1:1.5 molar sodium bromide/sodium hypochlorite respectively. Samples were analysed by reverse phase liquid chromatography. No oxidation of the contaminant was detected with Cl2 after three hours, even when an excess of hypochlorite was added. Br2 gave substantially complete oxidation of pentachlorophenol after 15 minutes. The product was believed to be predominantly hydroquinone.

Claims (8)

1. The use of bromine to reduce the colour and/or odour of water or soil containing organic contaminants.

2. A method of treating waste water and/or process water containing coloured or oderiferous organic contaminants or soil contaminated thereby which comprises adding thereto a treatment agent selected from one or more of bromine, hypobromous acid, bromamine or any of their precursors which form any of them on addition to water, in an amount sufficient to reduce the colour or odour thereof.

3. A method according to Claim 2 for treating water containing an organic dyestuff.

4. A method according to Claim 3 wherein such water is a dyebath effluent.

5. A method according to either of Claims 3 and 4 wherein said dyestuff is a reactive dye.

6. A method according to either of Claims 3 and 4 wherein said dyestuff is an anionic, direct, disperse or vat dye.

7. A use or method according to either of Claims 1 and 2 respectively wherein said contaminant comprises pentachlorophenol.

8. A use or method according to any foregoing claim wherein the bromine is generated in situ from sodium bromide and sodium hypochlorite.