Computational modeling of wastewater land application treatment systems to determine strategies to improve carbon and nitrogen removal.

Land application of domestic and food processing wastewater is used due to its low cost, energy use, and maintenance. Design procedures are generally based on empirical relationships that may not account for critical site and waste-specific conditions. A mathematical model was utilized to simulate the complexity of wastewater land application. Multiple scenarios were run to determine system performance as measured by chemical oxygen demand (COD) and the nitrification/denitrification process. The modeling results showed that COD and nitrification occurred within the first 15.4 cm of a sandy loam soil. Increasing the dosing frequency slightly reduced the COD effluent concentration. Complete denitrification does not occur in a typical land application wastewater treatment system. In a domestic wastewater land application system, up to 32% of nitrate can be removed by increasing the dosing frequency and providing more organic carbon. In a food processing wastewater land application system, up to 56% of nitrate can be removed by increasing the dosing frequency and hydraulic and organic loadings. HYDRUS CW2D modeling is a valuable design tool to simulate multiple operation strategies and predict carbon degradation, nitrification, and denitrification. The model result can provide operational strategies to maximize the treatment while minimizing environmental impacts.

Evaluating the impact of field-scale management strategies on sediment transport to the watershed outlet.

Non-point source pollution from agricultural lands is a significant contributor of sediment pollution in United States lakes and streams. Therefore, quantifying the impact of individual field management strategies at the watershed-scale provides valuable information to watershed managers and conservation agencies to enhance decision-making. In this study, four methods employing some of the most cited models in field and watershed scale analysis were compared to find a practical yet accurate method for evaluating field management strategies at the watershed outlet. The models used in this study including field-scale model (the Revised Universal Soil Loss Equation 2 - RUSLE2), spatially explicit overland sediment delivery models (SEDMOD), and a watershed-scale model (Soil and Water Assessment Tool - SWAT). These models were used to develop four modeling strategies (methods) for the River Raisin watershed: Method 1) predefined field-scale subbasin and reach layers were used in SWAT model; Method 2) subbasin-scale sediment delivery ratio was employed; Method 3) results obtained from the field-scale RUSLE2 model were incorporated as point source inputs to the SWAT watershed model; and Method 4) a hybrid solution combining analyses from the RUSLE2, SEDMOD, and SWAT models. Method 4 was selected as the most accurate among the studied methods. In addition, the effectiveness of six best management practices (BMPs) in terms of the water quality improvement and associated cost were assessed. Economic analysis was performed using Method 4, and producer requested prices for BMPs were compared with prices defined by the Environmental Quality Incentives Program (EQIP). On a per unit area basis, producers requested higher prices than EQIP in four out of six BMP categories. Meanwhile, the true cost of sediment reduction at the field and watershed scales was greater than EQIP in five of six BMP categories according to producer requested prices.