Changes from adopted text to adopted text

Removed1.4. Preparation of samples

RemovedUncompounded surfactants are examined in the original state. Active content of surfactant samples must be determined in order to prepare the synthetic sewage (point 1.3).

Removed1.5. Operation of equipment

RemovedInitially, fill aeration vessel C and settling vessel D with synthetic sewage. The height of the vessel D should be so fixed that the volume contained in the aeration vessel C is three litres. Inoculation is made by introducing 3 ml of a secondary effluent of good quality, freshly collected from a treatment plant dealing with a predominantly domestic sewage. The effluent must be kept under aerobic conditions in the period between sampling and application. Then set the aerator G, air-lift E and dosing device B in operation. The synthetic sewage must pass through the aeration vessel C at a rate of one litre per hour; this gives a mean retention time of three hours.

RemovedThe rate of aeration should be so regulated that the contents of vessel C are kept constantly in suspension and the dissolved oxygen content is at least 2 mg/l. Foaming must be prevented by appropriate means. Anti-foaming agents that inhibit the activated sludge or contain surfactants must not be used. The air-lift pump E must be set so that the activated sludge from the settling vessel is continually and regularly recycled to aeration vessel C. Sludge which has accumulated around the top of the aeration vessel C, in the base of the settling vessel D, or in the circulation circuit must be returned to the circulation at least once each day by brushing or some other appropriate means. When the sludge fails to settle, its settleability may be increased by the addition of 2 ml portions of a 5 % solution of ferric chloride, repeated as necessary.

RemovedThe effluent from the settling vessel D is accumulated in vessel F for twenty-four hours, following which a sample is taken after thorough mixing. Vessel F must then be carefully cleaned.

Removed1.6. Checking measuring equipment

RemovedThe surfactant content (in mg/l) of the synthetic sewage is determined immediately before use.

RemovedThe surfactant content (in mg/l) of the effluent collected over twenty-four hours in vessel F should be determined analytically by the same method, immediately after collection: otherwise the samples must be preserved, preferably by freezing. The concentrations must be determined to the nearest 0,1 mg/l surfactant

RemovedAs a check on the efficiency of the process, the chemical oxygen demand (COD) or the dissolved organic carbon (DOC) of the glass fibre filtered effluent accumulated in vessel F and of the filtered synthetic sewage in vessel A is measured at least twice per week.

RemovedThe reduction in COD or DOC should level off when a roughly regular daily surfactant degradation is obtained at the end of the running-in period shown in Figure 3.

RemovedThe content of dry matter in the activated sludge contained in the aeration vessel should be determined twice a week in g/l. If it is more than 2,5 g/l, the excess activated sludge must be discarded.

RemovedThe degradation test is performed at room temperature; this should be steady and kept between 19-24 ° C.

Removed1.7. Calculation of biodegradability

RemovedThe percentage degradation of surfactant must be calculated every day on the basis of the surfactant content in mg/l of the synthetic sewage and of the corresponding effluent accumulated in vessel F.

RemovedThe degradability values thus obtained should be presented graphically as in Figure 3.

RemovedThe degradability of the surfactant should be calculated as the arithmetic mean of the values obtained over the twenty-one days that follow the running-in and acclimatisation period, during which degradation has been regular and the operation of the plant trouble-free. In any event the duration of the running-in period should not exceed six weeks.

RemovedThe daily degradation values are calculated to the nearest 0,1 % but the final result is given to the nearest whole number.

RemovedIn some cases it may be permissible to reduce the frequency of sampling but at least fourteen results collected over the twenty-one days which follow the running-in period should be used in calculating the average.

Removed2. Determination of anionic surfactants in biodegradability tests

Removed2.1. Principle

RemovedThe method is based on the fact that the cationic dye methylene blue forms blue salts with anionic surfactants (MBAS), which can be extracted with chloroform. To eliminate interference, the extraction is first effected from alkaline solution and the extract is then shaken with acidic methylene blue solution. The absorbency of the separated organic phase is measured photometrically at the wavelength of maximum absorption of 650 nm.

Removed2.2. Reagents and equipment

Removed2.2.1. Buffer solution pH 10

RemovedDissolve 24 g sodium bicarbonate, NaHCO3 AR, and 27 g anhydrous sodium carbonate (Na2CO3) AR in deionised water and dilute to 1000 ml.

Removed2.2.2. Neutral methylene blue solution

RemovedDissolve 0,35 g methylene blue AR in deionised water and dilute to 1000 ml. Prepare the solution at least twenty-four hours before use. The absorbency of the blank chloroform phase, measured against chloroform must not exceed 0,015 per 1 cm of layer thickness at 650 nm.

Removed2.2.3. Acidic methylene blue solution

RemovedDissolve 0,35 g methylene blue AR in 500 ml deionised water and mix with 6,5 ml H2SO4 (d = 1,84 g/ml). Dilute to 1000 ml with deionised water. Prepare the solution at least twenty-four hours before use. The absorbency of the blank chloroform phase, measured against chloroform must not exceed 0,015 per 1 cm of layer thickness at 650 nm.

Removed2.2.4. Chloroform (trichloromethane) AR freshly distilled

Removed2.2.5. Dodecyl benzene sulphonic acid methyl ester

Removed2.2.6. Ethanolic potassium hydroxide solution, KOH 0,1 M

Removed2.2.7. Ethanol pure, C2H5OH

Removed2.2.8. sulphuric acid, H2SO4 0,5 M

Removed2.2.9. Phenolphthalein solution

RemovedDissolve 1 g phenolphthalein in 50 ml ethanol and add 50 ml deionised water while stirring continuously. Filter off any precipitate obtained.

Removed2.2.10. Methanolic hydrochloric acid: 250 ml hydrochloric acid AR and 750 ml methanol

Removed2.2.11. Separating funnel, 250 ml

Removed2.2.12. Graduated flask, 50 ml

Removed2.2.13. Graduated flask, 500 ml

Removed2.2.14. Graduated flask, 1000 ml

Removed2.2.15. Round-bottomed flask with ground glass stopper and reflux condenser, 250 ml; boiling granules

Removed2.2.16. pH meter

Removed2.2.17. Photometer for measurements at 650 nm, with 1 to 5 cm cells

Removed2.2.18. Qualitative grade filter paper

Removed2.3. Procedure

RemovedThe samples for analysis must not be taken through a layer of foam.

RemovedAfter thorough cleaning with water, the equipment used for the analysis must be thoroughly rinsed with methanolic hydrochloric acid (point 2.2.10) and then with deionised water before using.

RemovedFilter the activated sludge plant influent and effluent to be examined immediately on sampling. Discard the first 100 ml of the filtrates.

RemovedPlace a measured volume of the sample, neutralised if necessary, into a 250 ml separating funnel (point 2.2.11). The volume of sample should contain between 20 and 150 g of MBAS. At the lower MBAS content, up to 100 ml of sample may be used. When using less than 100 ml, dilute to 100 ml with deionised water. Add to the sample 10 ml of buffer solution (point 2.2.1), 5 ml of neutral methylene blue solution (point 2.2.2) and 15 ml of chloroform (point 2.2.4). Shake the mixture uniformly and not too vigorously for one minute. After phase separation, run the chloroform layer into a second separating funnel, containing 110 ml of deionised water and 5 ml of acidic methylene blue solution (point 2.2.3). Shake the mixture for one minute. Pass the chloroform layer through a cotton-wool filter previously cleaned and wetted with chloroform into a graduated flask (point 2.2.12).

RemovedExtract the alkaline and acid solutions three times, using 10 ml of chloroform for the second and third extractions. Filter the combined chloroform extracts through the same cotton wool filter and dilute to the mark in the 50 ml flask (point 2.2.12) with chloroform used for rewashing the cotton wool. Measure the absorbency of the chloroform solution with a photometer at 650 nm in 1 to 5 cm cells against chloroform. Run a blank determination through the whole procedure.

Removed2.4. Calibration curve

RemovedPrepare a calibration solution from the standard substance dodecylbenzene sulphonic acid methyl ester (tetrapropylene type mol. wt. 340) after saponification into the potassium salt. The MBAS is calculated as sodium dodecyl benzene sulphonate (mol. wt. 348).

RemovedFrom a weighing pipette, weigh 400 to 450 mg of dodecyl-benzene-sulphonic-acid-methyl-ester (point 2.2.5) to the nearest 0,1 mg in a round-bottomed flask and add 50 ml of ethanolic potassium hydroxide solution (point 2.2.6) and some boiling granules. After mounting the reflux condenser, boil for one hour. After cooling, wash the condenser and ground glass joint with about 30 ml of ethanol, and add these washings to the contents of the flask. Titrate the solution with sulphuric acid against phenolphthalein until it becomes colourless. Transfer this solution to a 1000 ml graduated flask (point 2.2.14), dilute to the mark with deionised water and mix.

RemovedPart of this surfactant stock solution is then further diluted. Withdraw 25 ml, transfer to a 500 ml graduated flask (point 2.2.13), dilute to the mark with deionised water and mix.

RemovedThis standard solution contains:

Removedwhere E is the sample weight in mg.

RemovedTo establish the calibration curve, withdraw 1, 2, 4, 6, 8 ml portions of the standard solution and dilute each to 100 ml with deionised water. Then proceed as stated under point 2.3 including a blank determination.

Removed2.5. Calculation of results

RemovedThe amount of anionic surfactant (MBAS) in the sample is read from the calibration curve (point 2.4). The MBAS content of the sample is given by: