Car Wash wastewater treatment plant
Target
Fresh water consumption can widely change according to washing methods from 400 to 100 litres per car, depending on type: manual or automatic, friction or frictionless, conveyor or in-bay.
The friction wash uses brushes or curtain strips made of cloth or other material to clean vehicles, while the frictionless uses high-pressure nozzles; in addition, a low-pressure brush may be available to assist during wash cycle.
Normally only car exterior is washed. If it’s used to wash mechanical components it’s necessary to made a specific analysis on wastewater because of high amounts of pollutants and oils.
Pollutants
In the effluent there are many dangerous pollutants like oils, grease, surfactants, heavy metals and some biological pollutants. Wastewater contains also sand, soil and residues of surfaces as particulate matter coming from floor washing.
Wastewater chemical characteristic and pollutants have to be analysed, such as pH, BOD, COD, total phosphorus, nitrous oxide, nitric nitrogen, ammonia nitrogen, chlorine (if necessary), total suspended solids TSS, total hydrocarbons, total surfactants.
System layout
Minimum system layout and nominal size (NS) calculation are specified in the European standard EN 858-2.
The treatment plant always requires a sludge trap S (or sand trap) and an oil separator (class I or II, depending on receiving body: public sewer system or surface water).
A sampling well is always required.
As well as for economic and environmental reasons, water recycling is also recommended by the norm (Annex B, table B.2).
Coalescing filters or lamellar separators are usually installed to improve effluent quality.
Washing areas must be provided with dedicated sewer system, necessary to avoid that wastewater, coming from washing operation, flows into storm drains without pass through treatment plant.
EN 858-2 describes how to calculate wastewater flow combination.
A biological section as biofiltration, pressure filter or physical-chemical plant can be added downstream of the gravity treatment. These kind of systems require oxygen, power supply and advanced control panel and sometimes, depending on pollutants characteristic, chemicals need to be added to the treatment plant. For wastewater disinfection ozonation, UV treatment, peroxide treatment or thermal treatment can be used.
In order to ensure a constant flow, a storage tank (or equalization chamber) can be added to buffer fluctuation in concentration and flow rate.
Bio-filtration is a fixed bed bioreactor and so it needs a secondary sedimentation chamber.
Car wash wastewater treatment layout
Note
Special waste as sludge must be handled and disposed in accordance with norms.
Maintenance must be carried out only by authorized company.
In advanced system treatment, to reduce transport cost, sludge can be dried, allowing water to evaporate.
