ABSTRACTMODELING OXYGEN CONCENTRATION IN WASTEWATER-IRRIGATED SOILByShuai ZhangFood processing wastewater generally contains non-toxic materials and is sometimes applied to soil by irrigation as a treatment method. However, the biochemical oxygen demand (BOD) is relatively high. In an aerobic soil environment (i.e., the oxygen in soil is greater than 10% and aerobic microorganisms are active) these pollutants can be effectively assimilated with no environmental impacts. When wastewater flows through the anaerobic soil environment, metals such as Fe and Mn in soil replace the free oxygen to become electron acceptors. These metals are dissolved into the wastewater and can cause groundwater pollution. Strategic loading time, concentration, and frequency may allow for the disposal of wastewater while protecting groundwater from metal leaching. The objective was to identify the conditions in which aerobic soil environment can be maintained. Three statistical models (response surface methodology, mixed-effects model, and time series analysis) were developed to predict oxygen concentration in soil based on data from previously conducted soil column experiments. The developed models were compared using Akaike information criterion and Bayesian information criterion. Among the studied models, the mixed-effects model was the best fit model, and the conditions to keep soil aerobic were determined using response surface and contour plots.
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