Exploring the potential use of odor-control waste carbon as a sustainable fertilizer

Circular economy principles drive the quest for sustainable solutions by reusing waste materials effectively. This study explores the potential usage of exhausted activated carbon from odor-control as a nutrient source for sustainable agriculture. The accumulation of ammonium- and sulfur-containing compounds within a porous carbon matrix was evaluated through subsequent adsorption of hydrogen sulfide (H₂S) and ammonia (NH₃) on wood-based H₃PO₄-activated carbon (BAX). Reactive adsorption outcomes were dependent on the order of gas adsorption. Ammonium sulfate and ammonium dihydrogen phosphate were formed when H₂S was adsorbed before NH₃ (BAX-SN) and the reverse sequence led to the formation of ammonium hydrogen phosphate sulfate on BAX-NS. The feasibility of this approach was evaluated by cultivation of peas at various carbon dosages. BAX-NS yielded better results than BAX-SN, likely due to its smaller ammonium content on carbon (3 and 12 mg NH₃-NH₄⁺/g carbon, respectively). Strong correlations between pea growth indices and ammonium concentration revealed that adverse effects on plant growth occurred from concentrations above 120 mg NH₃-NH₄⁺/kg mixed soil-carbon. Notably, the dosage of 30 mg NH₃-NH₄⁺/kg mixed soil-carbon increased the plant length by 11 % and dry weight by 42 %, compared to those in untreated soil, showing the positive effects of a very small dosage and thus the feasibility of this approach.