Diurnal Variations in Wastewater Characteristics at Main Outfall in Lahore

Abstract

Variations in the flow and pollutants concentrations during the day were monitored at the Main Outfall disposal station of the city of Lahore. The laboratory analysis of the wastewater samples collected at 2 hour interval on 5th and 6th May, 2009 for pH, temperature, alkalinity, hardness, Biochemical Oxygen Demand (BOD5), BOD5Filtered, Total Kjeldahl Nitrogen (TKN), Ammonia Nitrogen (NH3-N), chlorides, solids, turbidity, sulphates and nitrates were carried out. Average values and standard deviations were determined to assess the type of wastewater treatment. Correlation between BOD5 and BOD5Filtered was developed through regression analysis. Diurnal variations in the Ultimate Biochemical Oxygen Demand (BODU) at the Main Outfall based on Carbonaceous Biochemical Oxygen Demand (CBODU) and Nitrogenous Biochemical Oxygen Demand (NBODU) are also estimated. The ratio between CBODU/NBODU ranges between 0.86 to 1.8 during a day at Main Outfall. This variation is primarily due to the large diurnal variation in CBODU values as a result of industrial activities in the study area. The BOD5/ TKN ratio varies between 3.3 and 6.9 and the calculated BODU (i.e., CBODU + NBODU) was found to be almost double of BOD5 during most part of the day primarily due to inclusion of NBOD. The study results reveal the importance of NBOD while designing the wastewater treatment facilities and implementing a water quality control strategy for the River Ravi.