The Concentration of Organic & Ammonium Pollution and their Relationship in River Water: A Case Study

Bangladesh's largest water treatment plant sources its water from the Shitalakshya River, which is facing serious problems of organic pollution and ammonia contamination, particularly during the dry months of November to April. This study examines the extent of organic and ammonia pollution in the river and their relationship with each other. The study analyzed daily samples of raw water quality parameters, such as COD and NH3-N concentrations, from 2013 to 2018 only from the dry months, using standard laboratory methods at Dhaka's largest drinking water treatment plant. During the study period, the global average COD and ammonia concentrations in the dry months were 37.8 and 9.2 mg/L, respectively. These concentrations ranged between 10.6 to 76.3 mg/L and 0.98 to 19.54 mg/L in individual months respectively. The global yearly maximum COD and ammonia concentrations were respectively, ranging from 13 to 127 mg/L and 1.63 to 23.24 mg/L in individual months. These maximum levels occurred in March and April. The monthly minimum concentrations of COD and ammonia varied between 6-42mg/L and 0.17-15.6mg/L, respectively. It is noteworthy that the global average figures are higher than the recommended levels for drinking water sources after conventional treatment. The study found a distinct increasing trend in the maximum values of COD and ammonia concentration over time. Both the average and maximum values increased by around 0.5 mg/L every year. A statistical linear regression between the maximum COD and the ammonia concentration across the years showed an excellent strong correlation marked with an R2 value of 0.93,0.88,0.95 respectively for maximum, minimum and average values, indicating a potential common origin for these pollutants. If this trend of pollution persists, the authorities will need to modify the treatment chain to ensure that the supply of drinking water is not affected.