Synthesis of Sewage Sludge-based Biochar and Alum Sludge Composite Adsorbent for the Removal of Methylene Blue Dye from Industrial Wastewater

Abstract

Development of a low cost and efficient adsorbent from waste materials is a genuine practice to ensure environmental sustainability. This study investigates the synthesis and application of sewage sludge-based biochar (SSBC)-alum sludge (AlS) composite adsorbent (SSBC-AlS) on methylene blue (MB) dye removal from industrial wastewater. The synthesis is based on the idea that combining the high carbon content of SSBC with high surface area, and suitable functional groups with rough and highly porous surface properties of AlS have a synergetic to increase the composite's efficiency on MB dye removal. To this end, locally available sludges, Sewage sludge (SS) and AlS samples collected from water treatment plants were used. The samples were sun-dried and ground to a sieve size of 0.18 mm. Then, the SS samples were pyrolyzed at temperatures of 350 °C, 450 °C and 550 °C for 2 h at a heating rate of 10 °C ·min -1 to produce SSBC and labeled (SSBC350, SSBC450, and SSBC550). The SSBC, and AlS as well as SSBC-AlS composite adsorbent prepared by mixing selected SSBC with AlS, were characterized for physicochemical and thermal characteristics using FT-IR, TGA-DTA, XRD, SEM, and BET. The SSBC-AlS composite adsorbent MB removal efficiency was investigated using a batch adsorption technique, and the effect of experimental parameters such as temperature, pH of the solution, contact time, initial MB concentration, and adsorbent dosage were studied carefully. Using the optimized parameters, the kinetics and adsorption isotherm as well as reusability of the adsorbents were also investigated. The result revealed that, the adsorption efficiency reached maximum at pH 7, adsorbent dose of 1 g, contact time of 30 minutes, initial MB dye concentration of 100 mg/L and at room temperature. The maximum MB removal efficiency of the composite at optimized condition from aqueous solution and wastewater was 99.96% and 96.9%, respectively. The maximum adsorption capacity of the composite at optimized condition was found to be 19.98 (mg/g). The kinetics of the adsorption process fitted well with the Pseudo-second-order kinetic model and from the tested isotherm models, the Langmuir isotherm model was found to be the best fit. From the regeneration study, it is possible to conclude that SSBC-AlS adsorbent was recyclable and reused as MB dye adsorbent for 6 successive cycles without that much significant efficiency loss. The result clearly indicated the SSBC-AlS composite (with composition of 75wt% SSBC and 25wt% AlS) at optimized condition can be utilized to effectively remove MB dye from wastewater.