Innovative Decentralized Wastewater Treatment: Coupling Coagulation, nZVAl Adsorption, Sand Filtration, and ANN-Based Optimization

Abstract

Centralized wastewater treatment plants in developing countries are often overloaded, necessitating robust decentralized alternatives. This study designed and evaluated a novel decentralized system integrating coagulation-flocculation with aluminum sulfate, a tertiary treatment unit using synthesized nano zero-valent aluminum (nZVAl) for simultaneous degradation, adsorption, and disinfection, and a sand filter. The nZVAl was characterized by XRD and SEM, confirming its composition and morphology. The optimum coagulation/flocculation conditions were observed at pH 7 and 0.5 g/L of aluminum sulfate dose. For tertiary wastewater treatment using nZVAl, the optimum operating condition was observed at pH 7.5, 0.7 g/L nZVAl dose, 40 min contact time, 200 rpm stirring rate, and 35ºC temperature. The kinetic studies indicated that the adsorption data for organic carbon (COD), biodegradable organics (BOD), nutrients (TN), and total suspended solids (TSS) were best described by the Avrami kinetic model, while phosphorus (TP) removal kinetics were best described by a pseudo-second-order model. The thermodynamic results indicated that the reaction mechanisms are exothermic for COD and TSS, and endothermic for BOD, TN, and TP. The results of ANN showed that nZVAl dose is the most effective operating conditions followed by contact time. The decentralized wastewater treatment system was tested under the optimum conditions, and the results demonstrated high efficiency, with removal rates exceeding 92% for COD, BOD, TSS, and oil and grease. High removal efficiencies were also reported for TP, TN, nickel (Ni), and copper (Cu). The treated effluent complied with all limits stipulated by the Egyptian code 501/2015, confirming its suitability for reuse in agricultural applications.