Differential Efficacy of Citrus limon Residue Extract on the Bacterial Load and Selected Physicochemical Properties of Contaminated Water

Abstract

The growing deterioration of water quality, driven by water scarcity and microbiological contamination, demands the development of sustainable and low-environmental-impact technological alternatives. Against this background, the present study assessed the differential efficacy of an ethanolic extract obtained from Citrus limon residues (peel and residual pulp) on the bacterial load of Staphylococcus spp. and Escherichia coli, as well as its effect on pH, turbidity, and total dissolved solids (TDS) of two aqueous matrices with different initial contamination levels: one with turbidity of 100–150 NTU, bacterial load of 103–104 CFU/mL and TDS of 150 mg/L (low contamination), and another with turbidity ≥200 NTU, bacterial load ≥105 CFU/mL and TDS of 600 mg/L (high contamination). The extract was obtained by sonication (40 kHz, 480 W) and characterized by FTIR and UV-Vis spectroscopy, while its antimicrobial activity was evaluated through MIC and MBC determinations using the broth macrodilution method. Remediation assays were performed with doses of 3.12 and 6.25 mg/mL over 24 h. In the low-contamination matrix, logarithmic reductions of up to 4.28 log CFU/mL and removal percentages of ≥99.97% were achieved; in contrast, in the highly contaminated matrix, the reduction was approximately 0.9 to 1.1 log CFU/mL (82–92%). However, the addition of the extract caused a marked increase in turbidity and TDS, together with a pronounced acidification of pH. In conclusion, while the valorization of C. limon residues constitutes a promising raw material with selective antimicrobial potential, its direct application in complex waters presents substantial physicochemical limitations. This highlights the need to implement subsequent purification strategies (e.g., neutralization, filtration) or hybrid treatments to ensure successful and feasible remediation within the framework of the circular economy and sustainable water treatment.