Evaluating the use of recycled coal combustion products in constructed wetlands: an ecologic-economic modeling approach

A simulation model was developed to couple the biogeochemistry of phosphorus removal with the potentially economical and environmentally beneficial use of a coal combustion waste product as a liner in constructed wetlands. The model includes hydrology, macrophyte and phosphorus submodels coupled to an economic accounting submodel. Data from two constructed wetlands in central Ohio, USA, the Olentangy River Wetland and the Licking County Wetland (LCW), fed by low and high nutrient loads, respectively, were used to calibrate and validate the ecologic portion of the model. The model was used to provide parameters in design of a pilot-scale treatment wetland under construction to test flue-gas-desulfurization (FGD) by-products as a liner material. Subsequent model simulations of the LCW with a liner for prediction of phosphorus retention efficiency showed enhanced phosphorus retention (≈10% by mass) and economic benefits if the wetland were lined with the FGD by-product relative to clay. Total cost saving (liner cost saving plus phosphorus treatment saving) of recycling FGD by-products predicted by the model is closely related to both wetland size and phosphorus loading. Total savings of using FGD by-products as a liner over clay in the LCW (6.4 ha) was calculated at approximately US $ 23 000 years−1 for 30 years at 8% interest rate assumed.