Method for washing vehicles, etc. contaminated with oil, grease and particles

The recirculated water soln., before re-use, is clarified by addition of a water soln. of an easily soluble non-organic salt or salt mixt. with at least two-value anions and a water soln. of a cationic polymer. The salt soln. and the polymer soln. are fed as two separate flows to the contaminated water soln. After addition of the additives and before re-use, the water soln. is freed from slurry through sedimentation, filtration or other known appropriate process. The washing water solns., which contain heavy metals, are buffered to a pH between 8.5 and 11.5, pref. 9.5 to 10.5, by suitable addition of anion solns. The anion solns. contain small quantities of easily soluble sulphide. The non-organic anion salts are present in stoichiometric excess to the cation polymers and the other components in the washing soln. which can react with the anion salts, the excess being re-circulated with the washing soln.