Response surface modeling and optimization of sludge activated carbon production conditions for phenolic compounds removal from water

In this study, response surface methodology was employed to study and optimize sludge based activated carbon (SBAC) production operating parameters vis-à-vis the SBAC yield and removal of catechol, phenol and resorcinol from water. The KOH activation process yielded SBACs of BET surface area of 327.42 m2/g with a corresponding yield of 83.33%. A preliminary assessment indicated that methylene blue removal efficacy of up 99.99% was achievable. The affinity of the produced SBACs towards adsorption of the phenolic compounds follows the order of catechol > resorcinol > phenol with maximum removal efficiency of 99.24, 62.23 and 26.56% with corresponding adsorption capacity of 45.57 mg/g 23.25 and 9.91 mg/g, respectively. Higher temperature and KOH-sludge ratio have greater tendency toward producing lower yield of SBAC regardless of the activation time. The optimum removal of catechol was achieved at low temperature and low KOH-sludge ratio whereas phenol and resorcinol removal increased with increasing temperature regardless of KOH ratio and activation time. The operating conditions which collectively optimized the removal of the phenolic compounds and SBAC yield were achieved at KOH-sludge ratio between 1–1.5, temperature 400°C to 700°C and activation time of 30–36.74 min with percent yield of 81.5%. Maximum removals of phenol and resorcinol were achieved at 700°C and 1.37 KOH: sludge ratio while high yield and better removal of catechol were achieved when SBAC was produced at 400°C and KOH: sludge ratio of 1.16.