Chemical alkalinization of sewage sludge: Effects on the microbial community and antibiotic resistance associated with sulfonamides and diaminopyrimidines.

This study evaluated the fate of antibiotic resistance agents (ARAs)-including antibiotic residues, antibiotic-resistant bacteria, and antibiotic resistance genes-associated with sulfonamides and diaminopyrimidines during quicklime (CaO) alkalinization of secondary and digested sewage sludges, under different operational conditions (25%, 35%, and 45% CaO; 72 h, 30 days, and 60 days). By integrating removal performance with correlation, multivariate, and feasibility analyses, the study helps to identify key drivers of ARAs persistence after alkaline stabilization. Digested sludge was more responsive to treatment, with optimal performance at 45% CaO after 60 days, resulting in complete inactivation of sulfamethoxazole- and trimethoprim-resistant bacteria and a 4.6-log reduction in detectable sul1 abundance. Despite this reduction, residual ARAs remained significantly associated (r > 0.52; p ≤ 0.05) with biosolid physicochemical properties and microbial community profile, including sequences assigned to potentially clinically relevant taxa. These findings indicate that treatment efficiency depends only on lime dosage and contact time, but also by matrix-dependent physicochemical and microbiological interactions linked to persistence and potential co-selection. Strengths, weaknesses, opportunities, and threats (SWOT) analysis indicated that quicklime treatment may be a technically simple and potentially scalable biosafety strategy, particularly for digested sludge under stringent conditions (45% CaO). However, the persistence of ARAs suggests that alkaline stabilization alone may not fully eliminate sanitary risks. Overall, optimized chemical alkalinization represents a practical risk-reduction strategy and highlights the importance of including antibiotic resistance markers in monitoring frameworks for biosolids intended for agricultural reuse.