Comparative nutrient stabilization kinetics during composting and vermicomposting of livestock manure and paper pulp sludge

Composting and vermicomposting are widely applied biological strategies for organic waste valorization; however, their comparative physicochemical stabilization kinetics across contrasting feedstocks remain insufficiently quantified. This study investigated temporal changes in physicochemical properties and total nutrient concentrations during a 120-day laboratory-scale composting and vermicomposting experiment using cattle manure, sheep manure, and paper pulp sludge. pH, electrical conductivity (EC), and total macro- (N, P, K, Ca, Mg, and Na) and micronutrients (Fe and Zn) were monitored at nine sampling times and described using a square-root parabolic kinetic model. pH increased progressively in all substrates, consistent with organic matter stabilization, whereas vermicomposting was associated with smaller transient pH fluctuations without altering the final pH values. EC exhibited a biphasic pattern, with an initial increase followed by a gradual decline, consistent with mineralization and redistribution of soluble ions. Relatively immobile nutrients (N, P, and Ca) generally showed cumulative enrichment and were adequately described by the kinetic model (R 2 > 0.75 in most treatments), whereas mobile ions (K, Na, and Mg) exhibited irregular temporal patterns and lower model performance. Manure-based vermicomposting showed comparatively higher nitrogen and soluble phosphorus concentrations during incubation, whereas composting produced more consistent temporal patterns for Ca and Mg in sheep manure. Total Fe and Zn increased across all treatments, with the highest model adequacy observed in composted manure. Overall, the results indicate that nutrient transformation patterns depended on both feedstock characteristics and nutrient mobility, suggesting that composting and vermicomposting represent complementary stabilization pathways rather than universally superior alternatives.