Predicting Trihalomethanes Formation Potential (THMFP) of a Drinking Water Source in a Mega City: A Case Study

Disinfection is a very important and indispensable water treatment process for drinking water safety, as it inactivates pathogens from drinking water. In this work, 27 selected empirical THM models of 18 scientists from literature are used to investigate their reliability in real situations through their application to the Dhaka surface water treatment plant (SWTP) in Bangladesh. For each of the water samples, namely, treated, pretreated, and raw the total trihalomethanes (TTHM) concentrations were predicted using each of the 27 models and, the percentage deviation of the predicted concentrations from the measured concentrations were calculated. Two thirds of the models underestimated the THM concentration values and rest one third overestimated the concentration, even among which 34 percent deviated more than +500 percent. It is quite important that the predicted highest value of THM is nearly 150,000 times higher than the minimum value obtained for the same sample of water and 90% of the models used in this study could not estimate the THM values nearer to the actual values as determined in the laboratory. The diversified predicted concentration of TTHM for a single sample of water, from the above mentioned 27 models indicate the complexity of THM formation and in developing universally applicable THM models that can be used with diverse array of specific natural water sources. It can be seen from the studied 27 models that no model has taken into consideration the presence and its influence of ammonia which is a common pollutant in the raw water of developing countries which is also prevalent in Dhaka’s surface water during dry season. It may thus be concluded that independent THMs models should be developed to make accurate predictions for different regions.