Comparative Effects of Non-Composted and Composted Sewage Sludge from Wastewater Treatment Plants on the Physiological and Antioxidative Responses of Maize.

This study evaluated the physiological and antioxidative responses of maize to non-composted (NCSS) and composted sewage sludge (CSS) from Debrecen and Kecskemét, applied at 25%, 50%, and 75% (m/m) concentrations. Measurements were taken 21 and 35 days after sowing (DAS). Debrecen NCSS significantly enhanced plant height at all concentrations and at both sampling times, while higher doses of Kecskemét NCSS reduced growth by 35 DAS. Chlorophyll-a, chlorophyll-b, and carotenoid contents were notably enhanced by Kecskemét treatments, especially at lower concentrations, whereas Debrecen treatments showed less effect. Photosystem II (PSII) efficiency parameters varied with origin: Kecskemét NCSS notably increased minimal fluorescence (F), while Debrecen CSS occasionally reduced maximum fluorescence (F) and variable fluorescence (F) at 75% dose (21 DAS). The superoxide dismutase activity (SOD) was significantly elevated in Kecskemét treatments-by 101%, 148% and 149% at 25%, 50% and 75% CSS applications. Correlation analysis further highlighted that NCSS treatments often showed negative associations between plant height and chlorophyll content but positive correlations with antioxidant activity. In contrast, CSS treatments promoted balanced physiological responses. The results support the importance of sludge origin and application rate and suggest that composted sludge can be a safe, sustainable amendment when managed appropriately.