Dear All, Referring to the subject above, I have found the calculation of heat load based on [Lawrence,K.W., Norman, C. P. & Yung, T. H. (2005). Advanced Air and Noise Pollution Control. Totowa: Humana Press.] My cooling pond system: 1. Purpose: cooling POME temperature from 70 to 40 degree C. 2. Medium: palm oil mill effluent (POME), 3. Surface Pond Area: 800 m2, 4. Average wind speed: 4 km/h (no shelter/open pond), 5. Humidity: 88% RH, 6. Solar radiation: 4345 kcal/(m2*d), 7. Room temperature: 30 - 35 degree C. It is using the equilibrium temperature to estimate the exit temperature of WATER from the pond. However, mine system is using POME which came after the palm oil extraction from the fresh fruit bunch (FFB). The real situation is, this created some problem due to a layer of oil on the medium as the extraction process is not that efficient. The temperature was not able to reduce after a retention time of 2 days, and the current temperature is at 45 degree C which is above the mesophilic temperature for the bacteria to be alive and active. Could anyone advice on how to calculate the exit temperature based on the situation above as the POME has a layer of oil insulating on it? Back to the calculation get from the book, it has not included the heat load for once-through cooling ponds, but only included it for completely recirculating type of cooling pond. Mine system is plug flow system, which it would be the same as once-through system. Besides, i can't find any information regarding to the density of POME. If anyone know, kindly share at here. Advance thanks, Charles CL.