Abstract

Nutrient pollution from ammonium and phosphate in wastewater presents serious environmental challenges, including water eutrophication and resource inefficiency. The study aimed to analyse how magnesium-activated biochar made from temple waste could be used as a sustainable material for adsorping nutrients at the same time. The biochar was synthesized through pyrolysis and magnesium chloride activation, then applied to real wastewater from stabilization ponds in Bali. The adsorption dynamics for both ammonium and phosphate were consistent with pseudo-second-order models, suggesting that chemical absorption was the prevailing mechanism. The Freundlich isotherm model provided the best fit, suggesting heterogeneous multilayer adsorption. Results demonstrated that adsorption capacity and rate varied across different wastewater sources, with the highest adsorption rates corresponding to ponds exhibiting more favourable surface interactions. Importantly, the adsorption rate constant for phosphate surpassed that of ammonium in some cases, emphasizing the influence of ionic properties and biochar surface heterogeneity. The results confirm that biochar made from waste can effectively recover nutrients and should be included in circular approaches for managing wastewater.