Abstract
With the prevalence and widespread use of municipal landfills for solid waste disposal, the production and subsequent treatment of effluent leachate are ongoing management challenges for utility operators. Lowering the concentration of chemical constituents in order to prepare landfill leachate for discharge into wastewater sources can be costly. The addition of an engineered phytoremediation system may be beneficial in pre-treating leachate for disposal as a cost-effective management strategy. Development of a pilot-scale floating treatment wetland system (FTW) was analyzed through testing treatment efficiencies of a scaled-up design model based on previous findings. Refining design criteria applied projected data from bench-scale constituent removal rates to optimize the performance of selected plant species when combined in a polyculture system. Three plant treatment designs were assessed for the removal of chemical oxygen demand (COD) and ammonium from leachate, using saline-tolerant aquatic plants. Microbial communities in the soil-root matrix of each treatment were taxonomically defined through 16S rRNA metagenomic sequencing. Wet season trial data showed that two of the three pilot-scale FTW designs had comparable COD and ammonium removal. Equivalent chemical constituent removal per gram of biomass was found in both the treatment with plants growing hydroponically in leachate and the treatment constructed with a fine, fiberglass mesh containment to allow for root interaction within the provided soil. Results showed that 0.23 g of ammonium and 0.48 g of COD was removed per gram of biomass, with projected removal rates at scale to be upwards of 10.8% for each chemical constituent. Additionally, the design constructed with mesh showed to have the most diverse microbial community and retained at least one of each plant species that was originally installed in the holding ponds. Provision of the soil-matrix may benefit FTWs in retaining plant diversity while also generating a robust microbial population in the rhizosphere, further aiding in FTW longevity and the uptake of contaminants. Overall, time showed to be the significant factor when compared to treatment type in acclimating plants to leachate and sustaining biomass. The optimization of an FTW design using plant species local to Southwest Florida may provide evidence for the application of a passive and sustainable pre-treatment process for landfill leachate.