A model for optimal operation of land-treatment sites for oily wastes

Land treatment as a disposal technology has been extensively used for the disposal of oily wastes. Effective management of land treatment sites require optimal operation of the system in order to achieve the fastest and most complete degradation of petroleum hydrocarbons without contamination of the environment. This paper describes a model that can be used for optimising the operation of land treatment sites for oily wastes. The model is composed of system simulator and optimisation submodels. Conceptually, the system simulation submodel is composed of a waste mixing zone, lower treatment zone and aquifer modules. The system simulation model allows for periodic waste applications and determines the spatial and temporal variation of the state variables such as phase summed (total) and aqueous phase contaminant concentrations and water content in the system. The optimisation submodel coupled with the system simulator determines the optimal values of system control variables, such as waste loading rate, infiltration rate, water content, frequency of waste application and the dimensions of the land treatment site. Optimisation of these system control variables is accomplished by maximising the hydrocarbon mass removal from the waste mixing zone under the constraint of satisfying a prespecified water quality criteria in the aquifer. Selected model applications are presented to demonstrate the applicability and utility of the model. Such model applications include determination of the optimal operating conditions for the land treatment of oily wastes under various different site and soil environmental conditions and practical waste disposal scenarios.