Potential use of tin tetrachloride and polyacrylamide as a coagulant-coagulant aid in the treatment of highly coloured and turbid matured landfill leachate

The effectiveness of using natural coagulants as flocculants and tetravalent metal salts as coagulants in the treatment of landfill leachate remains debatable. The main aim of this study is to assess how well the polymer polyacrylamide (PAM) could interact as a coagulant, coagulant aid or flocculant with the tetravalent metal coagulant tin tetrachloride (SnCl4) in the removal of contaminants from leachate. Thus, this study examined the performance of a mix of the rare four-valence metal SnCl4 as a coagulant and compared it with the organic-based coagulant and flocculant PAM (molecular weight of 3.46 x104 Da and zeta potential of-57.9 mV). Optimal rapid/slow mixing and settling times were evaluated by performing a standard jar test. The optimal rapid mixing rates for SnCl4 and PAM were 220 rpm and 120 rpm, respectively. At these speeds, 98.4% reductions of colour and 98.7% of SS were obtained by using SnCl4 as opposed to 35.1% and 15.3% reductions for colour and SS, respectively, by using PAM. The best slow mixing speed for both coagulants was 60 rpm, with 98.4% and 98.6% reductions of colour and SS, respectively. Whereas PAM resulted in a 40.4% reduction in colour and an insig- nificant reduction in SS. SnCl4 performed better in colour and SS treatment at a faster settling time (40 min) than PAM, which required a settling time of 45 min. The optimal conditions for the application of SnCl4 as the sole coagulant were pH 8 and 10000 mg/L SnCl4. Under these conditions, SnCl4 resulted in almost complete re- ductions in colour and SS. However, PAM was ineffective when applied as the sole coagulant. When 100 mg/L PAM was introduced as a coagulant aid, the dosage of SnCl4 decreased to 6000 mg/L. At this dosage, SnCl4 caused 94.3% and 95.9% reductions in colour and SS, respectively. After treatment, the settling rate and sludge volume index also significantly increased to 0.61 cm/min and 84.2 mL/g, respectively. Therefore, SnCl4 and PAM could be used together to remove pollutants effectively.

Automated summary

The interaction between the polymer polyacrylamide (PAM) and the tetravalent metal coagulant tin tetrachloride (SnCl4) in the removal of contaminants from landfill leachate was studied. SnCl4 showed better performance as a coagulant compared to PAM, achieving higher reductions in color and suspended solids (SS). The combination of SnCl4 and PAM resulted in significant removal of pollutants.