The present invention relates to a process for checking the saturation level of activated carbon filters for purifying waste-waters polluted with organic chemicals, and to the use thereof for purifying the waste-waters originating from animal dips, spray mixtures for treating plants, and from chemical production and laboratories.

Purifying waste-waters with activated carbon filters is a standard process in waste-water technology, the principle of which is that the organic pollutants present in the waste-water are adsorbed on activated carbon and can thus be removed from the water. This technique is particularly suitable if the waste-water contains aromatic organic compounds which are readily adsorbed on activated carbon.

Such filters can typically be used as stationary or mobile units in chemical production or for treating laboratory effluents.

In the agricultural sector, insecticides, fungicides and herbicides are used for pest and weed control in the form of aqueous spray mixtures which are not always completely used up and then have to be treated as waste-water. The purification of these waste-waters can also be effected with activated carbon filters, for example direct by the farmer or in collection stations.

The situation is similar in animal husbandry. In particular, where large flocks or herds of e.g. sheep or cattle are kept in the open it is necessary to treat the animals with dips containing organic compounds effective against animal parasites to prevent diseases and epidemics.

These animal dips containing ectoparasiticides constitute a disposal problem, as they can occur in quite remote areas and have to be brought from there by tankers to a waste-water treatment plant. This situation can arise in particular in countries like Australia and New Zealand, or in South American countries like Argentina and Chile. In these countries it has been possible tυ purify the waste-water directly on the spot, conveniently with mobile activated carbon filter units, so that the filtered water can be discharged into the environment without harm.

In the case of just such mobile units which can be used in remote areas it is especially

important to be able to carry out a simple check of the saturation level of the activated carbon filter.

The problem here is that it is necessary to determine after what concentration of waste-water the activated carbon is completely saturated and is no longer able to adsorb further pollutants. If this point is not determined exactly, then the result may be that toxic substances will escape unchecked into the environment.

Possible detection methods of identifying organics in waste- water typically include state-of-the-art analytical methods such as high-pressure liquid chromatography or gas chromatography, with which it is possible to detect direct the pollutants present in the waste- water. These methods assume, however, the availability of the electrical, water and gas connections necessary for operating the equipment and this is often not the case. In addition, the complicated equipment can only be properly operated by suitably qualified experts.

Another indirect method of detection consists in determining the total dissolved carbon in the waste-water in order to obtain information on the saturation level of the carbon filter. Here too suitable apparatus, water, power and technical knowledge are necessary.

A process developed by E. Allman, Chichester UK (®Sentinel process), comprises passing the waste-water over an activated carbon filter and using a dye (Rhodamine 6G) as indicator of the saturation level of the filter. The presumption here is that the organic pollutants migrate through the activated carbon at the same rate as Rhodamine 6G, so that the filter has to be replaced at the first appearance of coloured filtrate. This proposal too is not entirely satisfactory, as the often initially colourless waste-water becomes coloured and is held to be additionally polluted. It is also important in this process that the dye should be non-toxic and biodegradable.

The present invention solves this problem and provides a highly sensitive process, which is operable everywhere, for checking the saturation level of activated carbon filters. The problem of the coloured water is solved by adding the colourless indicator compound to the waste-water and earring out the detection of this compound by a simple spot or test-tube reaction in which a strong colouration appears. One means of colour detection is well-known in analytical chemistry as Lunge's reagent for detecting nitrite. The method is extremely inexpensive and can be carried out by anyone. From the large number of

possible coloured reactions it is possible to select those in which the reactants are held to be toxicologically and ecologically safe.

Accordingly, the invention relates to a process for checking the saturation level of activated carbon filters in the purification of waste-water containing organic chemicals, which comprises a) adding to the waste-water one or more than one colourless, water-soluble, primary aromatic amine and then passing said waste-water over the activated carbon filter, or first loading the activated carbon filter with said colourless, water-soluble, primary aromatic amine and afterwards passing the waste-water over said activated carbon filter, b) taking a portion of the filtrate, diazotising the aromatic amine and forming an azo dye with a water-soluble aromatic coupling component, and thereafter c) determining the colour of the filtrate.

In principle it is possible to pass all waste-waters containing organic chemicals and containing no or only a minor amount of turbid matter over an activated carbon filter. The separation of turbid matter can be effected by known methods such as precipitation, filtration or flocculation in a prior purification step. It is essential that the activated carbon filter is not clogged and that the rate of flow remains as high as possible.

The provenance and outward form of the activated carbon are not crucial. Desirably it has a porous structure with an inner surface area of typically 500 to 1500m ² /g. Filter units that can be loaded with activated carbon are known per se and are used in very wide geometry for filtration operations.

The waste-water polluted with organic chemicals preferably originates from chemical production or from laboratories.

Another preferred source of the waste-water consists of animal dips or spray mixtures that contain organic chemicals for the treatment of plants or animals.

The organic chemicals are most preferably selected from:

AMITRAZ = N,N-bis(2,4-xylyliminomethyl)methylamine; BROMPHOS -ETHYL = 0-(4-bromo-2,5-dichlorophenyl)-0,0-diethyl thiophosphate; DIOXATHION = S,S'-(l,4-dioxan-2,3-diyl)-0,O,0',0'-tetraethyldithiophospha te; PROPETAMPHOS = 3-[[(ethylamino)methoxyphosphinothioyl]oxy]-2-butenoic acid 1-methylethyl ester;

CHLORPYRLFOS = phosphorothioic acid O,0-diethyl-0-(3,5,6-trichloro-2-pyridinyl) ester; DIAZINON = O,O-diethyl O-(2-isopropyl-4-methyl-6-pyrimidinyl) phosphorothioate; COUMAPHOS = phosphorothioic acid O-(3-chloro-4-mefhyl- 2-oxo-2H-l-benzopyran-7-yl) O,O-diethyl ester; ETHION = phosphorodithioic acid S,S'-rnethylene-O,O,O',O'tetraethyl ester, MALATHION = [(dimethoxyphosph.no- thioyl)thio]butanedioic acid diethyl ester, CHLORFENVINPHOS = phosphoric acid 2-chloro-l(2,4-dichlorophenyl)ethenyl diethyl ester; TOXAPHENE = chlorinated camphene; L NDANE = lα,2β,3β,4α,5α,6β-hexachlorocyclohexane; TIFATOL = N-(2,3-dihydro-3-methyl-l,3-thiazol-2-ylidene)-2,4-xylidine, or PHOXIM = O',O"-diethyl O-(α-cyanobenzylideneamino)phosphorothioate; PYROQUILON = 1,2,5,6-tetrahydropyr- rolo[3,2,l-ij]quinolin-4-one; MONOCROTOPHOS = 3-dimethoxyphosphinoyl- oxy-N-methylisocrotonamide; METOLACHLOR = 2-chloro-6'-ethyl-N-(2-methoxy- l-methylethyl)acet-o-toluidide; ATRAZINE = 2-chloro-4-ethylamino-6-isopropyl- amino-l,3,5-triazine; ISOPROTURON = 3-(4-isopropylphenyl)-l,l-dimethylurea.

The waste-water for purification can be in the pH range from 1 to 13. It is preferred to carry out filtration of the waste-water in the pH range from 4 to 8. If necessary, the pH can be adjusted beforehand to this range with a base, an acid or a buffer solution.

Suitable indicators are all primary, colourless, water-soluble aromatic amines from which a diazonium salt can be prepared with nitrite.

Particularly suitable aromatic amines of this type are naphthylamines or phenylamines which are unsubstituted or substituted by one or more identical or different members selected from the group consisting of C C ₁₂ alkyl,- S0 ₃ H, -OH, -COOH, (C ₁ -C ₆ )alkyl-COOH, and -N(C _r C ₄ alkyl) ₂ .

The alkyl group can be unbranched or branched and as C _r C ₁₂ alkyl is typically methyl, ethyl, and the different positional isomers of propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl and dodecyl.

Alkyl in (C _r C ₆ )alkyl-COOH is typically methyl, ethyl, and the different positional isomers of propyl, butyl, pentyl and hexyl.

Alkyl in -N(C _r C ₄ alkyl) ₂ is C _r C ₄ alkyl, typically methyl, ethyl, and the different positional isomers of propyl and butyl.

A preferred group of amines consists of primary aromatic amines which contain at least one sulfo group in the aromatic nucleus.

Particularly preferred primary aromatic amines are ortho-, meta- or para-sulfanilic acid, 2-amino-5-naphthol-7-sulfonic acid, l-amino-8-naphthol-3,6-disulfonic acid or 2-amino-8-naphthol-6-sulfonic acid.

para-Sulfanilic acid is very particularly preferred.

The primary aromatic amine is preferably used in a concentration of 0.1 mg to 1000 mg, most preferably of 5 mg to 500 mg, per litre of waste- water.

The process may be carried out by adding the amine to the waste-water direct at any time of which it is known that the activated carbon is not yet completely saturated. Another possibility consists in loading the activated carbon beforehand with a specific concentration of the amine and afterwards passing the waste-water through the activated carbon without additional amine.

It is preferred to use NaN0 ₂ or KN0 ₂ for the diazotisation.

The diazotisation reaction is carried out with an excess of acid, preferably a mineral acid or a Cι-C ₄ carboxylic acid, most preferably formic acid or acetic acid.

The aromatic coupling component for forming the dye may be any coupling component customarily used in dyestuffs chemistry.

It is preferred to use a naphthalene, a benzenoid compound or a heteroaromatic compound containing 1 to 3 aromatic rings, which compounds are each unsubstituted or substituted by one or more identical or different members selected from the goup consisting of C _r C ₁₂ alkyl,- S0 ₃ H, -OH, -COOH, C _r C ₆ alkyl-COOH, - NH ₂ , -NH(C ₁ -C ₄ alkyl) and -N(C _r C ₄ alkyl) ₂ .

Particularly preferred coupling components are: α-naphthylamine, 2-naphfhol-3,6-disulfo- nic acid, 2-naphthol-6,8-disulfonic acid, 2-amino-5-naphthol-7-sulfonic acid, l-amino-8-naphthol-3,6-disulfonic acid or 2-amino-8-naphthol-6-sulfonic acid.

cc-Naphthylamine is very particularly preferred.

The molar ratio of primary aromatic amine to coupling component is 0.5 to 2.

The coupling reaction itself may be carried out in the acid or basic pH range. It is, however, preferred to keep the reaction solution acidic and to effect coupling in the acid pH range.

The process can be carried out at any desired temperature. The preferred temperature range is from 0° to +80°C. It is most preferred to carry out the process at the prevailing ambient temperature.

Suitable utilities for the process of this invention are the purification of waste- waters originating from animal dips containing ectoparasiticides, for purifying waste-waters originating from spray mixtures containing insecticides, acaricides, microbicides or herbicides, and for purifying waste-waters originating from chemical production and labororatories.

The invention is illustrated by the following Examples.

Example 1: To a waste-water containing METOLACHLOR = 2-chloro-6'-ethyl-N-(2- methoxy-l-methylethyl)acet-o-toluidide (277 mg/1), ATRAZINE = 2-chloro-4-ethyl- amino-6-isopropylamino-l,3,5-triazine (20 mg/1) and ISOPROTURON = 3-(4-isopropyl- phenyl)-l,l-dimethylurea (20 mg/1) are added 20 mg/1 of p-sulfanilic acid. The waste-water is passed continuously over an activated carbon filter containing 25 g of activated carbon. The rate of flow is 35 rnl/h. The following detection reaction is carried out at daily intervals:

7 drops are taken from the filtrate in a test tube and acidified with acetic acid. To this solution is then added 1 drop of a 0.1 % aqueous solution of NaN0 and the mixture is shaken vigorously. Then 1 drop of a 0.135 % aqueous solution of α-naphthylamine in 30 % acetic acid is added and the mixture is shaken vigorously. A distinct red colouration is observed when p-sulfanilic acid is present. This red colouration is observed for the first time 36 days after the start of the experiment. A parallel experiment carried out to determine the total dissolved organic carbon shows from this day an increase in the carbon value.

mg/1 of p-sulfanilic acid can still be readily visualised.