Estimating Oxygen Transfer Coefficients in the Presence of Surfactants

Abstract

Aeration process is an entity process for an aerobic system to provide oxygen for the microorganism. Oxygen transfer is the most important mechanism in the aeration process. Many factors affect the oxygen transfer rate. The presence of surfactants in the wastewater is one of the main reasons for the inferior of oxygen transfer. Over or under estimation of the oxygen transfer rate affects the process officiency and energy consumption. The optimum oxygen transfer rate is investigated in this work to find the best efficiency with a suitable power input. Laboratory scale tests of a surface aerator were performed using two sizes of three blades propeller with varying surfactant concentrations and also power inputs. Three concentrations of surfactant (0, 5, and 10 mg/L) and four values of power input (13.2, 26.3, 39.5, and 52.7 watt/m3) were varied to observe their influences on oxygen transfer. Dissolved oxygen (DO) was measured follow with ASCE standard (ASCE, 1993), and ASCE DO Parameter Estimation Program (DO_PAR) was used to determine the KLa values. From the experimental results, oxygen transfer coefficient was affected greatly by the power input. KLa values were increased with the increase of power input for both sizes of propeller linearly. The presence of surfactant influenced the oxygen transfer rate. The higher surfactant concentration affected the KLa values greater than at the lower surfactant concentration. For examples, KLa value was reduced about 57.4% from 0 mg/L to 10 mg/L of surfactant concentration, for 15 cm propeller diameter at 13.2 watts/m3 The optimum power inputs were determined using standard aeration efficiency (SAE). For 10.7 cm propeller size, the highest SAE values for each surfactant concentration were at the highest power input (52.7 watts/m3). But for 15 cm propeller diameter, the highest SAE values were at 52.7, 26.3, and 39.5 watts/m3 for 0, 5, and 10 mg/L of surfactant concentration, respectively.