Removal of colour and suspended solids from landfill leachate using Tin tetrachloride (SnCl₄): The effects of pH, zeta potential, and particle sizes

ABSTRACT

Old landfill leachate is normally rich in colloidal particles, has low organic compound, poor biodegradability and hard to be biologically treated. The suspended particles are generally dispersed, negatively charged and do not settle by gravity due to their instability and repulsion. This paper aimed to evaluate the effectiveness of SnCl₄ as a positively charged coagulant in treating concentrated colour and suspended solids (SS) from an old leachate sampled at one of the local landfills in Malaysia (Alor Pongsu Landfill Site, Keria Perak), which may also represent other landfills with similar property. The mechanism and the effect of pH, zeta potential (ZP) and particle size of colloids on the reduction of the pollutants were evaluated through standard coagulation and flocculation experiment with ZP measurement. The standard jar test was examined at a pre-determined SnCl₄ dosage and varied from pH 3 to pH 12. The raw leachate was found negatively charged throughout pH 3 to pH 12. Adding a positively charged SnCl₄ increased the leachate surface charge to close to the point of zero charges (IEP) at pH 8 with −0.4 mV. Generally, as the pH value increase from acidic to basic condition, the raw leachate becomes more negatively charged as at higher pH values It was also found that the pH of the solution correlated with the size of the particles, where 221.3 d.nm was recorded from pH 4 to pH 11 and improved to the largest size 660 d.nm at pH 3. The highest colour and SS performance were observed at optimum pH 8 with reductions of 98.9% and 100%, respectively The reduction of repulsive forces at this pH promoted the collision of particles and thus made the aggregation possible. ZP measurement in is important as it provides an early estimation of the effective pH for the optimum coagulation and flocculation process of landfill leachate contributed by the colloidal particles.

KEYWORDS:

• Solid waste
• landfill
• leachate
• Tin tetrachloride
• hevea brasiliensis

Acknowledgments

This research was supported by the Universiti Sains Malaysia under RUI-grant (1001/PAWAM/8014081) and FRGS grant (203/PAWAM/6071412) on research related to Solid Waste Management Cluster (SWAM), Engineering Campus, Universiti Sains Malaysia. Thank you is also extended to the Majlis Daerah Kerian (MDK), Perak, for their cooperation during the study.

Author Contribution

Siti Fatihah Ramli: Data collection and conducting experiments.

Hamidi Abdul Aziz: Conceptualisation, methodology, validation and editing of the manuscript.

Fatehah Mohd Omar: Supervision, conceptualisation, methodology.

Mohd. Suffian Yusoff: Drafting the manuscript.

Herni Halim: Editing the manuscript.

Mohamad Anuar Kamaruddin: Field data collection.

Kamar Shah Ariffin: Supervision and editing the manuscript.

All authors have read and approved the final manuscript.

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.