| Co-treatment basins filled with inexpensive non-toxic by-products containing phosphorus (P) binding components such as iron (Fe), aluminum (Al), calcium (Ca), magnesium (Mg), organic matter or clay might increase the sustainability of P removal from wastewater by constructed wetland (CW) systems. The objective of this research was to optimize a co-treatment and CW system for P removal.;Twelve by-product materials were selected for initial evaluation with laboratory experiments. The coated-sand, Ca drinking water treatment residual (DWTR), Al, Mg, Fe-DWTR, and the humate materials exhibited the highest P removal. A column study included six substrates in co-treatment bottles paired with sand columns that were batchfed municipal or dairy wastewater for one month. The Ca, Fe, Al and humate materials were most effective. The Al material was not locally available nor a useful plant nutrient. The dried humate product had limited availability. The two optimal materials selected for further evaluation were the Ca- and Fe-DWTR.;An outdoor mesocosm study combined batch-fed 208-L co-treatment reactors (CTR) containing Ca- or Fe-DWTR (or no substrate for controls) with 567-L vertical-flow CW mesocosms (CWM), each with a 7-day HRT, planted with Schoenoplectus tabernaemontani and operated for one year. For municipal wastewater the total P (TP) concentrations (52-week means) were reduced from 1.00 to 0.72 (28%) and 0.40 mg L-1 (60%) by the Ca and Fe CTR alone compared to 0.96 mg L-1 (4%) by control CTR. These TP concentrations were reduced by the combined CTR and CWM systems from 1.00 to 0.07 and 0.05 mg L-1 (93 and 95%) by systems with Ca and Fe (compared to 0.16 mg L-1 or 84% by control systems). For dairy wastewater, TP was reduced from 48.5 to 22.5 (53%) and 22.7 (53%) mg L-1 by calcium and iron CTR and CWM systems (compared to 24.1 mg L-1 or 50% by controls). Dairy wastewater pre-treated with CW was placed in nine CTR. The post-wetland Ca and Fe CTR reduced TP concentration (57 and 71%) more than the control CTR (14%). The overall results suggest the potential for using by-product co-treatments to enhance P removal by constructed wetland systems. |
