Factorial evaluation of operational variables of a DAF process to improve PHC removal efficiency

A dissolved air flotation (DAF) process is used for removing oil from oil–water emulsions. Operational conditions that increase shearing and disturbance of liquid during the operation of large-scale DAF systems can significantly reduce oil removal efficiency. Objectives of this study were to evaluate the individual and interactive effects of the operational variables of the DAF process on removal efficiency of petroleum hydrocarbons from water sources contaminated with fuel oils. A series of batch and continuous experiments (utilizing full pressurization and effluent recirculation) were conducted using a 60-L DAF system which could be operated either in batch or continuous modes. The experiments were conducted as a factorial design to evaluate both the individual effects and the interactions of the operational variables which included oil concentration, detention time, water type (brackish and pond), coagulant use, and operational mode. The factorial analysis showed that for the batch mode of operation, oil concentration, detention time, coagulant use, and water type had a significant effect on PHC removal. However, for the continuous DAF runs, the only variable that was significant at the 95% confidence level was detention time. Coagulant use did not have a significant effect on PHC removal efficiency for the continuous runs due to shearing of the flocs.

Factorial design analysis of the operational variables of the DAF process was used to identify the variables which could be adjusted to improve PHC removal efficiency. The operational variables of the DAF process were compared for both batch and continuous modes of operation by a factorial analysis. The factorial analysis of the experimental results showed that for the batch mode of operation, all four operational variables investigated (i.e., detention time, influent PHC concentration, coagulant use, and source water type) had a significant effect on PHC removal.