Biological Purification of Heterogenous Car Wash Effluents: Selection of Tolerant Bacteria and Development of Microbial Consortia for Pollutant Biodegradation

Car wash wastewaters (CWW) bring growing environmental challenges due to the increasing number of vehicles worldwide and they require novel, optimized and sustainable treatment methods. They are highly heterogenous, typically containing complex mixtures of detergents, waxes, oils, petroleum derivatives, corrosion inhibitors and salts, with the composition depending on installation age, geographic location, season, and weather. This study aimed to select bacteria resistant to variable and potentially toxic CWW, capable of biodegrading organic pollutants. A total of 81 strains isolated from various environmental sites were screened for tolerance to CWW environments by performing growth inhibition tests in 20 real wastewater samples with chemical oxygen demand (COD) ranging from 122 to 2267 mg O2/dm3. Seventeen strain candidates were chosen, identified with molecular proteomics, and further evaluated for biodegradation potential. Based on the most robust isolates, six microbial consortia were developed and examined. Biodegradation experiments were conducted at ambient temperature without active pH control and nutrient supplementation to reflect real conditions occurring in wastewater treatment practice. The best-performing consortium reduced COD by 86% within 7 days. These findings should help improve the treatment of complex CWW by highlighting the potential of thoroughly selected bacteria as effective tools for bioremediation of extremely harsh environments.