Biological Treatment of Car Wash Waste Waters

A Reduction Survey

Abstract

The purpose of this study was to examine how efficient a biological treatment process is in purifying car wash waste waters. Two Finnish automatic car washes having rotating bed biofilm reactors for waste water treatment were included in the study. Both of them are using 87 % of recycled water per car wash and only from 35 to 60 liters of fresh water. Samples were taken from the purified water tank every second week altogether seven times between the beginning of February and the end of May, 2012. The reduction of surfactants was at least 95 % and reduction of chemical oxygen demand (COD) between 87 and 95 % during the sampling period. Outdoor temperature seems not to have any significant effect on purification efficiency. Other water quality parameters such as conductivity, pH, oxygen concentration, total solids, and biological oxygen demand (BOD) were found to be on acceptable level based in comparison to values found in the literature. The high concentration of total nitrogen and total phosphorus in the purified water was caused by nutrients added to the bioreactor for optimal conditions for the microbes. In the studied car washes, the waste water treatment process managed to reduce input load considerably. The main challenges for the quality of purified water seems to be optimal nutrient input as well as on-line monitoring system for water quality.