Restaurant wastewater as a sustainable medium for ureolytic bacteria in biocementation

Restaurant wastewater (RWW) represents an abundant yet largely unexplored nutrient source for enriching ureolytic microbial consortia applicable to microbial-induced calcite precipitation (MICP). This study characterised RWW collected from a food-service establishment in Johor, Malaysia (COD 1,341 mg/L; BOD 837 mg/L; pH 6.8), and systematically evaluated its capacity to support indigenous ureolytic bacterial enrichment across three media formulations: yeast extract-based (Medium-1), nutrient broth-based (Medium-2), and brown sugar-based (Medium-3). Medium-1 delivered the strongest performance, achieving OD₆₀₀ = 1.29 ± 0.06, urease activity = 17.42 ± 1.19 mM urea hydrolysed min^- 1, and CaCO₃ precipitation = 2.81 ± 0.17 g/L. Optimal bioactivity was recorded at pH 8 and 30 °C, conditions closely aligned with the tropical collection environment. 16 S rRNA amplicon sequencing (DADA2 pipeline; SILVA nr v138.1) yielded 101,869 quality-filtered reads across 116 amplicon sequence variants (ASVs; Shannon H = 2.79), identifying a co-dominant community of Firmicutes (50.83%) and Proteobacteria (48.36%), with Sporosarcina (6.09%), Bacillus (3.35%), Lysinibacillus (2.63%), and Raoultella (34.39%) as principal ureolytic contributors. Soil biocementation trials returned a mean surface strength of 423.3 ± 21.6 psi and a CaCO₃ content of 16.64 ± 1.72%. Heavy metal immobilisation efficiencies reached 99.60% for Cd²⁺, 81.87% for Ni²⁺, 42.47% for Cr³⁺, and 22.47% for Cu²⁺ at 10 mg/L. XRD, FTIR, TGA, and DSC collectively confirmed a thermally stable, mineralogically pure biogenic calcite (> 96.7% residue at 894 °C). Collectively, these findings establish RWW-enriched consortia as functionally capable, cost-effective biocatalysts for sustainable MICP, in support of circular economy objectives within tropical urban contexts.