Treatment performance of heavy metals in landfill leachate using gracilaria changii

Abstract

Leachate is a serious environmental issue due to its highly toxic contents, and it is being treated using several methods such as biological, chemical, and physical processes or the combination of these processes. However, the treated leachate somehow still needs to be refined in order to achieve the allowable standard set by the authority before it can be discharged into the environment. In this study, the leachate from Jeram Sanitary Landfill was subjected to the physico-chemical treatment method using a Gracilaria changii seaweed species to remove the heavy metals. The specific objectives of this study include the preparation and characterisation of G. changii biosorbent, the heavy metal removals (such as Fe2+, Cr6+, As5+, Ni2+ and Cd2+) performance assessments in a batch study, the investigation of heavy metal removals using a continuous fixed-bed column, and the evaluation of the adsorption kinetics and isotherms of heavy metals by G. changii. The batch study’s initial investigation showed that the optimal condition for treating landfill leachate is at the pH of 5 with the adsorbent dosage of 10 g, 50 rpm and 30 min contact time. Around 97.5%, 70.9%, 42.43%, 98% and 40% of Fe2+, Cr6+, As5+, Cd2+ and Ni2+ maximum removals were achieved respectively at 30 min, 10 g dosage, and heavy metal concentration of 100 mg/L with optimum pH and rpm. The adsorption behaviours of G. changii biosorbent were analysed using Field-Emission Scanning Electron Microscope-Energy Dispersive X-ray (FESEM-EDX) and Fourier Transform Infra-Red (FTIR) spectroscopy. The results showed visible evidence of the binding microelement ions on the surfaces of the biosorbent, and also demonstrated that the carboxyl and hydroxyl groups were found to be efficient for adsorbing the heavy metals from the landfill leachate. The investigation over the treatment performance of G. changii in a continuous fixed-bed column with leachate pH 6.5 and 3.5 mL/min flowrate using 50% fine silicone sand and 50% biosorbent indicated that the influence of fine silicone sand removal efficiency is negligible and proved via a controlled study that recorded Fe2+, Cr6+, As5+, Cd2+ and Ni2+ removals were 1%, 1.33%, 1.5%, 0.17% and 0.5%, respectively. The 1:1 packing ratio achieved the optimum removal at 24th hours, with Fe2+, Cr6+, As5+, Cd2+ and Ni2+ removals were 99.5%, 99.93%, 99.2%, 99.97% and 99.97%, respectively with an initial concentration of each heavy metal fixed at 60 mg/L. The kinetic analysis conducted over the jar test results concluded that the adsorption obeys pseudo-second order. Thus, the occupation rate of adsorption is proportional to the square of the vacant active sites numbers on the biosorbent. Meanwhile, the isotherm analysis demonstrated a higher correlation coefficient for the Freundlich isotherm, thus the biosorption was shown to be heterogeneous, multilayer and occurred on the surface. The results also established that G. changii biosorbent has active sites with different energies. In addition, the regeneration studies showed that the G. changii can be regenerated more than once, with as high as 83% of desorption percentage at 5th cycle, which verified that the regeneration of biosorbent after recovery was successful. Therefore, it can be concluded that the G. changii biosorbent successfully removed heavy metals from the leachate solution and is potentially useful for the wastewater treatment industry.