Optimization of conditions for preparation of eggshell-zeolite composite as a potential surfactant adsorbent for hand-washing wastewater

Abstract

Handwashing with soap/detergent and clean water has become increasingly vital as a result of the Covid-19 pandemic. Handwashing wastewater contains high quantities of surfactants due to the use of soap and/or detergents. Handwashing with soap/detergent and clean water is vital for human hygiene and infectious disease prevention. The wastewater generated is costly to treat because of the surfactants present, which can quickly clog conventional low-cost filtration systems. As a result, the wastewater is mostly discharged into the environment leading to several detrimental effects. This study sought to develop a low-cost composite adsorbent from eggshells and zeolite for removal of surfactants from handwashing wastewater. The raw materials and the composite were characterized by X-ray fluorescence, scanning electron microscopy, Fourier-transform infrared spectroscopy, and Brunauer-Emmett-Teller (BET) surface area analyses. Preparation conditions including the percentage of eggshells in the composite (30%, 50%, 70%), calcination time (1 h, 2 h, and 3 h), and calcination temperature (300 oC, 400 oC, and 500 oC) were optimized using the Box-Behnken design of design expert software. The considered responses were Methylene blue number (MBN), BET surface area (SBET) and mean pore diameter (MPD). The optimal preparation conditions were established to be 31.57 %, 1.43 h and 310.94 oC for eggshells percentage in the composite, calcination time, and calcination temperature, respectively. This led to the maximized MBN, SBET, and MPD of 94.51 mg/g, 25.92 m2 g -1 and 10.01 nm, respectively. The calcined sample prepared at optimum conditions was subsequently applied for removal of chemical oxygen demand (COD) as an indicator of surfactants in handwashing wastewater. The COD removal percentage of 87.82%. The EZC production process was found to be viable as was established at Uganda shillings 40,800 which was low in comparison with commercial granular activated carbon.