Inhibition of Acidithiobacillus thiooxidans colonisation by biocide-modified concrete: antimicrobial performance and active-substance release under wetting–drying cycles

Biogenic sulphuric acid deterioration in sewer environments involves microbial colonisation followed by acid attack. This study tests whether powder-form biostatic agents incorporated into concrete at 0.15–0.30% by dry mix mass can suppress Acidithiobacillus thiooxidans colonisation. Two agents were evaluated: a full-spectrum formulation (Type A) combining an algaecide/fungicide product (OIT and terbutryn) with the bactericide triclosan, and a bactericide-only formulation (Type B) based on triclosan, intended for sulphur-oxidising bacteria. Reference and treated concretes were characterised in fresh and hardened states. Leaching tests quantified the dosage-dependent release of OIT and terbutryn (combined Σ ≤ 3.0 mg m −2 at 0.30% odw), while impregnation-based assays showed suppression of viable recovery from > 105 to < 10 CFU after an initial activation period. A complementary screening, including a commercial antimicrobial admixture as a reference, confirmed comparable anti-colonisation performance for alternative bactericides. A Vincke-derived immersion protocol indicated reduced deterioration proxies in treated samples, although pH evolution suggests constrained bacterial activity under the adopted conditions. The results support the hypothesis that biocide-modified concrete can inhibit A. thiooxidans colonisation through leaching-mediated biostatic activity, and highlight the importance of biologically relevant accelerated protocols for interpreting antimicrobial performance under alkaline concrete conditions.