Étude de la formation et de la stabilité des mousses chimiques de surface de la Vienne Study of the formation and stability of chemical foam on the Vienne river between Limogesançi Confolens

Résumé

Le recensement de la charge polluante rejetée dans la rivière Vienne (France) par les usines et les stations d'épuration de Limoges à Confolens a été effectué. Des campagnes de prélèvement et d'observations visuelles ont permis de localiser les lieux d'apparition de mousses en aval d'usines de fabrication de pâte à papier et de cartons. L'étude du pouvoir moussant des mélanges des deux principaux rejets polluants (papeterie et cartonnerie) a permis de mettre en évidence des phénomènes de synergie entre certains mélanges se traduisant à la fois par une augmentation du pouvoir moussant et de la stabilité de la mousse dans le temps. L'étude par « HPLC » montre l'apparition de pics supplémentaires confirmant l'interaction entre les constituants des rejets; le principal effluent a pu être suivi à l'aide de ses caractéristiques chimiques dans la rivière et dans les mousses jusqu'à Confolens.

Mots-clés:

• Pollution rivière,
• mousses chimiques,
• pouvoir moussant,
• traceur,
• industrie papier

Abstract

The study reported here considers of the formation and stability of foam on the Vienne river. Foaming is frequently encountered in relation to the discharge of industrial effluents, especially from the paper industry (CRAIG and al., 1990). Earlier papers have investigated the consequences of such discharges (NEILSON and al., 1990; KALLQVIST and al., 1989; SRIVASTAVA and al. 1988).

The extent of foam formation is determined by a number of factors, including effluent composition, turbulence of the stream, etc. Foams stability requires the presence of long chain fatty acids, amine acids, tannins etc. Many industries discharge their effluents into the Vienne river (paper and cardboard industries, leather dressing plants and tanneries).

An inventory of the main urban and industrial discharges has been established (Map 1). The effluents from the pulp, paper and cardboard industries provide the main pollution foad in terms of volume, COD, suspended solids (SS) and anionic surfactants.

A visual survey allowed us to locus our investigations on the places where persistant foams appear, especially downstream of Saillat below the discharges from Aussedat Rey and SGPL (Picture 1), and below small waterfalls (Pont de Pilas, Chabanais, Ansac...). At Confolens, the foams are most stable and form stable drifting foam residues.

Synergistic foaming effects have been reported due to the combination of polyamides and tannins (BIKERMAN, 1953). We have chosen to analyze the main effluents (Table 1) and their mixtures in relation to foaming (foaming capacity, foaming stability and surfactant analysis). The method used for foaming capacity determination was based on the hand shaking of 250 ml bottles. The stability of the foam was defined as the time for which the height of foam persists. Anionic surfactants were present at significant concentrations, varying from 1 mg/l (as sodium dodecyl sulphate) in the Aussedat Rey effluent to 4 mg/l in the SGPL effluent and 7 mg/l in the St Junien wastewater treatment plant effluent. The maximum foaming capacity was obtained for a 70/30 Aussedat Rey/SGPL effluent mixture (Fig. 1). The foaming capacity persists river time, remaining practically unchanged for three days. After 6 days, the maximum foaming capacity appears to be reduced. Foam stability is also maximum for the same 70/30 mixture (Fig. 2). After 6 days, the 50/50 and 70/30 mixtures can still produce 3 cm of foam that persist for 2 hours (Fig. 3).

For HPLC analysis (20 µl samples), the effluents from AR and the effluents from SGPL (or the mixture of the two) were diluted in 10 times their volume of distilled water prior to analysis. Concerning the mixture 95 % AR - 5 % SGPL (95/5) the peak that characterizes the SGPL effluent starts appearing and growing at 6.76 min. With the proportions : 90/10 and 70/30, its retention time respectively diminishes from 6.34 min. to 5.58 min. Moreover an extra peak appears with the 70/30 mixture at 5.02 min. This extra peak is at its highest at 4.96 min. for a 50/50 mixture. At the same time the initial AR peak is decreasing. It is thus confirmed that one or more constituent: are formed on mixing the two effluents, as indicated by the synergistic effect described earlier for the foam capacity and stability analysis.

Anionic surfactants were analyzed in the Vienne river (Fig. 5). Their concentration dramatically increase at point (4) (Pont de Pilas), just below the discharges from AR and SGPL. When the river flow increases, dilution masks the phenomenon. A drastic decrease in pollution appears in August when the industrial activity is reduced because of holidays (Fig. 7).

The HPLC Vienne river analysis (Fig. 5) shows an important peak of pollution at point (4) (Pont de Pilas) characteristic of the AR effluent. At Chabanais point (5), the ARISGPL ratio is 95/5 and the peak of SGPL appears, perhaps, et 6.12 min (in the diluted effluents in the same ratio 95/5, it appears at 6.34 min). At Confolens (10), the intensity has diminished (after two days) and the Confolens foams are the same as those produced by a river sample without concentrated effect. No appreciable degradation has occurred, since the height of the peaks point 10 is similar as those of the chromatogram of point (5) in accord with the literature (LESZKIEWICZ and KINNER, 1988 ; COTE and OTIS, 1989).

Keywords:

• River pollution,
• chemical foams,
• foaming capacity,
• tracers,
• paper industry