Economical Wastewater Treatment System for Automobile Service Stations in Sri Lanka

Abstract

Vehicle service stations use large quantities of water, oil and detergents for washing andservicing vehicles. Careful management of these effluents could minimize the ultimatedisposal of untreated wastewater to the environment. In spite of the legitimate controlsimposed by the Central Environment Authority, the disposals of untreated wastewater to theenvironment keep on increasing. It is justified by the distinctive oil spills seen in and aroundvehicle service stations in many parts of Sri Lanka.On identifying the problem the necessity of developing a suitable system for wastewatertreatment for vehicle service stations came to light. The objective was to develop aneconomical method to remove oil from wastewater and implement the developed method invehicle service stations. To start with and to get a basic idea of similar methods used in othercountries, literature survey was done. Field data collected using a questionnaire surveyfocusing vehicle service owners of Kalutara district. Wastewater effluent samples fromvehicle service stations were collected and tested for the following parameters namely pH,Temperature, TSS, BOD, Oil & Grease and COD. On analysing the results it was found thatthere were four parameters that extensively exceeded the tolerance limits specified CEA. Theanalytical method used for determining the oil contents in wastewater was APHA methodusing Benzene.The tolerance limits were exceeded by high margin due to the presence of Total SuspendedSolids (TSS), Oil and Grease in wastewater effluents. Also high values were indicated forBiological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD).A prototype system to separate oil from wastewater was developed and tested at a vehicleservice station. The system removed oil completely and directed the oil free wastewater intosecondary treatment process. In addition to the separation of oil, the separator was able tosettle suspended solids presence in the effluent. There were many methods adopted in vehicleservice stations to cater for controlling BOD and COD such as aeration. As such this paperonly concentrated on developing a suitable method for removing Oil and suspended solidsand thus relieving the load on the secondary treatment process.