Investigations were conducted using four different media in large laboratory-scale anaerobic filters to show the importance of media type, size, and shape on waste treatment performance. These tests have shown that a majority of the waste treatment takes place in the lower filter heights and is associated to a large extent with the biological solids that are held loosely within the interstitial void spaces within the media matrix. Therefore, the ability of the media to retain high concentrations of biological solids either as suspended growth or by attachment to the media surfaces is an important design consideration. This solids retention characteristic seems to be as closely related to media shape and void size as to unit surface area. Media selected for full-scale anaerobic filters should permit withdrawal of biological solids to prevent accumulations that can contribute to short-circuiting and loss of treatment efficiency.

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The buildup of phosphorus (P) in the soil is a major factor limiting the operating life of a wastewater land treatment system. In this study, we evaluated changes of chemical properties, P profiles, and adsorption isotherms in the soils of a Muskegon wastewater land treatment system, which has received wastewater for ∼30 years. It was found that the pH in the 15-cm topsoil increased from ∼5−6 in 1973 to ∼7.4−7.8 in 2003; a large amount of salt (e.g., Ca, Mg) in wastewater was adsorbed by the soil; the soil Al content (either exchangeable or oxalate extractable) decreased, while the oxalate-extractable Fe content remained at the same level. Ca-bound P accounted for ≥70% of the total P adsorbed in the soil. The soil P adsorption capacity increased and was positively correlated with the concentration of exchangeable Ca in the soil. A higher concentration of exchangeable Ca was found in the 15-cm topsoil, where a higher total organic carbon was present. More P was accumulated in the upper soil than in the deeper soil. The adsorption of Ca in wastewater by the soil may extend the life expectancy of the Muskegon land treatment system.

A methodology based on fuzzy set theory is developed to incorporate imprecise parameters into steady state groundwater flow models. In this case, fuzzy numbers are used to represent parameter imprecision. As such, they are also used as a measure for the uncertainty associated with the hydraulic heads due to the imprecision in the input parameters. The imprecise input parameters may come from indirect measurements, subjective interpretation, and expert judgment of available information. In the methodology, a finite difference method is combined with level set operations to formulate the fuzzy groundwater flow model. This fuzzy modeling technique can handle imprecise parameters in a direct way without generating a large number of realizations. Two numerical solution methods are used to solve the fuzzy groundwater flow model: the groundwater model operator method proposed in this methodology and the iterative algorithm based on conventional interval arithmetics. The iterative method is simple but may overestimate the uncertainty of hydraulic heads. The groundwater model operator method not only provides the hull of the solution set for the hydraulic heads but also considers the dependence of hydraulic head coefficients which are functions of imprecise parameters. Sensitivity analysis shows that the dependence of hydraulic head coefficients has a critical impact on the model results, and neglecting this dependence may result in significant overestimation of the uncertainty of hydraulic heads. A numerical model based on the methodology is tested by comparing it with the analytical solution for a homogeneous radial flow problem. It is also applied to a simplified two‐dimensional heterogeneous flow case to demonstrate the methodology.