The Effect of Dewatered Sludges Obtained from Different Stabilization Systems on the Development of Strawberry Plant

Abstract

This study investigates the comparative efficacy of dewatered wastewater sludges derived from conventional treatment system followed by anaerobic digestion and extended aeration processes as organic fertilizers for strawberry (Fragaria × ananassa) cultivation. Conducted over a six-week duration in a controlled greenhouse environment, the research evaluated the vegetative and morphological development of 'Quinault' strawberry seedlings grown in sandy loam soil. The experimental design utilized a blank control group alongside five distinct mass-by-mass application rates: 1/5, 1/10, 1/20, 1/25, and 1/50. Initial results identified a clear phytotoxic threshold, as high-dosage treatments (1/5, 1/10, and 1/20) resulted in plant mortality. Conversely, optimized lower ratios significantly enhanced plant vigor. The most substantial development was recorded in the 1/50 ratio group utilizing anaerobically digested sludge, which exhibited a 244.4% increase in plant body length and a 162% increase in root length compared to initial measurements. Statistical analysis confirmed significant correlations (p<0.05) between stabilized biosolid application and improved morphological indicators. Elemental analysis revealed that anaerobic residuals possessed superior organic matter and nitrogen profiles, providing a more stable nutrient flux than the extended aeration system. The findings conclude that stabilized urban sludge is a high-efficiency organic fertilizer when applied at optimized ratios. This approach supports circular economy goals by converting wastewater residuals into valuable agricultural resources while prioritizing food safety and environmental health. However, it is emphasized that these fertilizers cannot be safely utilized without rigorous verification that they are free of heavy metal contamination.