Bio-Adsorbent Derived from Sewage Sludge Blended with Waste Coal for Nitrate and Methyl Red Removal: Synthesis, Oxidation, Performance and Environmental Consideration

Abstract

Low-cost bio-adsorbents were synthesized using two types of sewage sludge: D, which was obtained during the dissolved air flotation stage, and S, which was a mixture of primary and secondary sludge from the digestion and dewatering stages. The sewage sludge was mixed with waste coal before being activated with Potassium Hydroxide (KOH) and oxidized with ammonium persulfate (APS). The nitrate and methyl red removal capacities of the synthesized bio-adsorbents were evaluated and compared to those of industrial activated charcoal. The oxidation surface area of bio-adsorbents derived from sludge S shrank by six fold after modification, while those derived from D only varied narrowly from 312,72 m2/g to 282,22 m2/g, but surface modification had no effect on inorganic composition in either case. The adsorption of nitrate and methyl red (MR) was performed in batch mode, and the removal processes followed the pseudo second order kinetic model and the Langmuir isotherm fairly well. The adsorption capacities of nitrate and MR were higher at pH=2 and pH=4, respectively. The total nitrate Langmuir adsorption potential was DC-5-750 (26,735 mg/g) > commercial activated carbon (Com-AC) (20,61 mg/g) > DC-55-750M1 (17,06 mg/g), and for MR, Com-AC (196,07 mg/g) > DC-5-750M2 (175 mg/g).Statement of Novelty: This paper examines how the chemical structure of activated carbon derived from sewage sludge and blended with waste coal is altered during the chemical activation process to provide the optimal porous surface for nitrate and methyl red adsorptive remediation. The formation of carboxylic sites or the transformation of oxygen sites to carboxylic sites is the aim of the oxidation process of activated carbon in general. Ammonium peroxydisulfate was chosen because of its ability to oxidize the surface without significantly altering the porous structure and increase surface acidity by increasing carboxylic group presence. There are no studies that we are aware of that use ammonium peroxydisulfate to oxidize activated carbon from sewage sludge blended with waste coal