Changes from adopted text to adopted text

Removed3.3.3. Dissolution of the precipitate

RemovedDissolve the precipitate in the filter crucible by the addition of hot ammonium tartrate solution (about 80 ° C) (point 3.2.8) in three portions of 10 ml each. Allow each portion to stand in the crucible for some minutes before being sucked through the filter into the flask.

RemovedPut the contents of the filter flask into the beaker used for the precipitation. Rinse the sides of the beaker with a further 20 ml of tartrate solution to dissolve the rest of the precipitate.

RemovedCarefully wash the crucible, adapter and filter flask with 150-200 ml water, and return the rinsing water to the beaker used for the precipitation.

Removed3.3.4. The titration

RemovedStir the solution using a magnetic stirrer (point 3.2.16), add a few drops of bromocresol purple (point 3.2.5) and add the dilute ammonia solution (point 3.2.9) until the colour turns violet (the solution is initially weakly acid from the residue of acetic acid used for rinsing).

RemovedThen add 10 ml standard acetate buffer (point 3.2.10), immerse the electrodes in the solution, and titrate potentiometrically with standard ‘carbate solution’ (point 3.2.11), the burette tip being immersed in the solution.

RemovedThe titration rate should not exceed 2 ml/min.

RemovedThe endpoint is the intersection of the tangents to the two branches of the potential curve.

RemovedIt will be observed occasionally that the inflection in the potential curve becomes flattened; this can be eliminated by carefully cleaning the platinum electrode (by polishing with emery paper).

Removed3.3.5. Blank determinations

RemovedAt the same time run a blank determination through the whole procedure with 5 ml methanol and 40 ml water, according to the instructions in point 3.3.2. The blank titration should be below 1 ml, otherwise the purity of the reagents (points 3.2.3, 3.2.7, 3.2.8, 3.2.9, 3.2.10) is suspect, especially their content of heavy metals, and they must be replaced. The blank must be taken into account in the calculation of the results.

Removed3.3.6. Control of the factor of the ‘carbate solution’

RemovedDetermine the factor for the carbate solution on the day of use. To do this, titrate 10 ml of the copper sulphate solution (point 3.2.12) with ‘carbate solution’ after the addition of 100 ml water and 10 ml standard acetate buffer (point 3.2.10). If the amount used is a ml, the factor f is:

Removedand all the results of the titration are multiplied by this factor.

Removed3.4. Calculation of results

RemovedEvery non-ionic surfactant has its own factor, depending on its composition, particularly on the length of the alkene oxide chain. The concentration of non-ionic surfactant is expressed in relation to a standard substance — a nonyl phenol with ten ethylene oxide units (NP 10) — for which the conversion factor is 0,054.

RemovedUsing this factor the amount of surfactant present in the sample is found expressed as mg of NP 10 equivalent, as follows:

Removed(b — c) xfx 0,054 = mg non-ionic surfactant as NP 10

Removedwhere:

Removed3.5. Expression of results

RemovedExpress the results in mg/l as NP 10 to the nearest 0,1.

RemovedFigure 1 Activated sludge plant: overviews

RemovedFigure 2 Activated sludge plant: detail (dimensions in millimetres)

RemovedFigure 3 Calculation of biodegradability - Confirmatory test

RemovedAnnex VIII

RemovedCORRELATION TABLE