Colour, turbidity and COD removal from old landfill leachate by coagulation-flocculation treatment.

The application of different coagulants and flocculants to leachate from an old landfill to determine the optimum conditions for removal of organic matter, colour and turbidity is studied. Ferric chloride, aluminium sulphate, aluminium polychloride (PAX) and polyacrylamide polyelectrolytes were tested. Higher pollutant removals (73% COD, 98% colour and 100% turbidity) were obtained using ferric chloride at pH 5.0-5.5 and for a dosage of 0.6 g Fe l(- 1). The volume of sludge generated after centrifugation represents about 4.0-4.6% when ferric chloride or aluminium sulphate is used, and 10% when employing aluminium polychloride. When flocculants were also added, the results obtained were similar to those found when adding only coagulants, although a considerable increase in the settling rate was obtained.

Coagulation-flocculation as a pretreatment process at a landfill leachate nitrification-denitrification plant.

The main aim of this research work was to study the possible application of coagulation-flocculation as a pretreatment process for young landfill leachate in order to prevent fouling in the ultrafiltration membranes employed for the separation of biomass in the biological plant. Jar-test experiments were carried out to determine the optimum conditions for the removal of turbidity colour and organic matter. The coagulants ferric chloride, aluminium sulphate and aluminium polychloride (PAX) were tested, along with different types of flocculants (anionic and cationic polyelectrolytes). Optimum pH values were around 4.0 and 6.0 for ferric chloride and aluminium sulphate, respectively. It was not necessary to alter the pH of the leachate when using PAX, as the optimum value was found to be similar to that of the leachate (around 8.3). Optimum dosages were 0.4 g Fe(3+)/L, 0.8 g Al(3+)/L and 4 g PAX/L, although there was not much difference in the results for lower dosage of PAX. The best results were found with this coagulant, obtaining 98% turbidity removal, 91% colour removal and 26% COD removal. When flocculants were also added, the results were similar to those found when adding only coagulants, although a considerable increase in the settling rate was obtained. The volume of the sludge generated represents around 4.5-5.0% when using ferric chloride or aluminium sulphate, and 15% when using aluminium polychloride.