Preparation and reuse of iron and aluminum oxides activated sewage sludge based coagulants for the post-treatment of up-flow anaerobic sludge blanket reactor effluent

•Iron and aluminum oxides activation approach was used to prepare the sewage sludge based coagulants (SSCs).•XRD, TGA/DTA, FESEM/EDX and elemental mapping were used to identify the characteristics of SSCs.•SSCs were used for the post-treatment of UASB reactor effluent via coagulation-flocculation process.•Preliminary tests, response surface methodology and confirmation test analysis illustrates the activity of SSCs.

Present study proposed the iron and aluminum oxides activation approach to produce the sewage sludge derived coagulants (SSCs) through the pyrolysis of sewage sludge (SS). Characterization techniques including X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM) and elemental dispersion X-ray spectroscopy (EDX) were used to investigate the structural change in SSCs. As prepared SSCs were used for the comparative treatment study of up-flow anaerobic sludge blanket (UASB) reactor effluent via coagulation/flocculation process. Response surface methodology was used to optimize the responses namely, chemical oxygen demand (COD) and turbidity removal efficiency influenced by the variables including dose of iron oxide activated SSC, aluminum oxide activated SSC, polymeric composite coagulant ferric aluminum silicate sulfate (PFASS) from the range of 100-500 mg/L and the range of initial pH 7.0-11. Preliminary tests analysis, results of modeling and confirmation tests proved that SSCs exhibited the excellent performance for post-treatment of UASB effluent compared to polymeric coagulant PFASS because activation with pyrolysis enhanced the structures features and metal contents of sludge which favored in coagulation, precipitation, and adsorption. Additionally, sludge itself contains a higher amount of Mg, Ca and Si oxides and/or hydroxides which fairly contributes in the removal process compared to freshly prepared PAFSS. Furthermore, zeta potential study also helpful to understand the bridging of adsorption and charge neutralization during coagulation-flocculation mechanisms and played a crucial role in process optimization via decreased the colloids surface charge. The results of the present study illustrate that iron and aluminum oxides activation is an effective approach for reuse the sewage sludge as coagulants and their reuse for post-UASB reactor effluent treatment as an attractive possibility from waste to resource recovery.

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