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Coagulation-flocculation is commonly used in the leachate treatment. The objectives of this study were to determine the optimum conditions (dosage and pH) and to compare the performances between single coagulants (polyaluminium chloride (PAC) and tapioca starch (TS)) and dual coagulant (PAC+TS) through a series of jar test. The highest percentage removal by PAC at the optimum conditions as a single coagulant (dose 2.5 g/L at pH 7) in terms of suspended solids (SS), turbidity, colour, chemical oxygen demand (COD), and ammonia was 92 %, 77 %, 94 %, 37% and 32 %, respectively. While for TS coagulant, at the optimum conditions (dose 2.5 g/L at pH 8), the percentage removal of SS, turbidity, colour and ammonia at pH 8 was 35%, 13%, 30% and 38% removals respectively. Thus, PAC performed better than TS as a single coagulant. While in dual coagulant, the percentage removal of SS, turbidity, colour, COD and ammonia of dual coagulant at optimum condition (dose PAC 1.5 g/L and dose TS 0.2 g/L at pH 5) was 90%, 74%, 87%, 40%, and 17%, while the percentage removal of single PAC (dose 1.5 g/L at pH 5) was 69%, 31%, 85%, 28%, and 13%, respectively. The addition of TS at a dose of 0.2 g/L into 1.5 g/L of PAC at pH 5 was able to achieve more percentage removal than single PAC and TS. This showed that the dosage of chemical coagulant could be reduced by 40% (2.5 g/L to 1.5 g/L) and indirectly reduced the drawbacks without affecting its efficiency.

Physical-chemical method such as electrocoagulation (EC) and coagulation-flocculation processes work well for the treatment of stabilized leachate. This study investigated the efficiency of combined treatment (electrocoagulation and conventional coagulation) in removing colour and ammonia nitrogen (NH3-N) from stabilized leachate. For this combined treatment, the Fe and Al electrodes with the addition of composite coagulant (PAC and TF) were used. The considered factors were pH, current density, and duration of current flow. It was observed that, the highest removal of colour and NH3N were 96% and 13% at applied current density of 100 A/m2 that equal to 0.5 A and 20 minutes respectively. For single EC treatment, the highest removal was 88% for colour and 25% for NH3N at 60 minutes by 150 A/m2 that equal to 1.3A. Thus, it showed that the combined treatment performed better than single treatment in removing colour while reducing the current, and shorten the duration of current flow.