Technologies employed for carwash wastewater recovery

The discharge of wastewater from the carwash has increased with the growth of the vehicle fleet. At carwash stations, thousands of cubic meters per week of untreated wastewater are discharged, which generally contain surfactants, dust, metal, oils, organic and inorganic matter. To mitigate this problem, various technologies have been tried, however not enough attention has been paid to this very common type of wastewater. The present review summarizes the studies carried out, in the last decade, regarding treatment processes for effluents of car washing stations in different parts of the world. The foundations of biological, physicochemical, advanced oxidation and combined process that have been used to date for carwash wastewater (CWW) treatment are described and discussed here. In biological processes, the flow systems of membrane bioreactors are addressed, while, physicochemical treatments, coagulation-flocculation, sedimentation, adsorption, membrane separation and chemical oxidation processes are analyzed. For advanced oxidation processes, the assessment of their suitability to achieve environment-friendly Sustainable Development Goal 6 (SDG 6) solutions, was discussed. In addition, this work addresses combined processes such as electrocoagulation as a hybrid system with nano-filtration, chemical coagulation and biocarriers. Finally, removal efficiency, costs, parameters and operating conditions of each treatment process for CWW recovery are examined.