DRINKING WATER TREATMENT SLUDGE AS AN EFFECTIVE ADSORBENT FOR LINEAR ALKYLBENZENE SULFONATE FROM SYNTHETIC SOLUTIONS

Abstract

Drinking water treatment sludge, a byproduct of the coagulation process in water purification plants, offers potential for sustainable reuse in environmental remediation. This study investigates alum sludge as a cost-effective adsorbent for removing Linear Alkylbenzene Sulfonate (LAS), a common anionic surfactant in laundry wastewater. Due to its persistence and toxicity, improper discharge of LAS poses serious ecological risks. This study proposes an eco-friendly approach by repurposing waste sludge to eliminate such pollutants. Characterization studies of sludge showed a loamy sand texture with a pH of 7.42 ± 0.06, bulk density of 0.64 ± 0.1 g/cm³, particle density of 2.00 ± 0.4 g/cm³, porosity of 0.68 ± 0.1, and point of zero charge (PZC) of 6.60 ± 0.04. Batch adsorption studies were conducted using the Methylene Blue Active Substances (MBAS) method to evaluate LAS removal under varying particle sizes, sludge dosages, contact times, and pH levels. Fine particles (<0.5 mm) achieved the highest removal efficiency (47.04 ± 1.32%), while coarser particles (>3.2 mm) were less effective. Adsorption efficiency increased with higher sludge-to-solution ratios, peaking at 99.52% at a 1:2 ratio; beyond this, no significant improvement occurred. Contact time studies found optimal removal (99.49 ± 0.20%) at 60 minutes, after which equilibrium was reached. Lower pH (acidic pH) favored the adsorption process, and adsorption data fit the Langmuir isotherm model, suggesting monolayer surface coverage. These results highlight the potential of alum sludge in removing LAS from contaminated water, providing a low-cost, sustainable alternative to traditional adsorbents. The study supports waste valorization and lays the groundwork for eco-friendly surfactant removal methods using readily available industrial byproducts.