Coal Combustion Residuals Landfill Construction Runoff Treatment Using Chitosan Enhanced Filtration

Coal combustion residuals (CCR) consisting of fly ash, bottom ash, boiler slag, and FGD (flue gas desulfurization) scrubber slurry are byproduct solids from the generation of electricity at coal-fired steam electric generating stations. Waste management options for these solids typically involve reuse (e.g., as additives in various construction materials and in the manufacture of gypsum wallboard and surface abrasion/blasting grit) and disposal in a secure, lined landfill. The landfilling option involves a long term construction project encompassing excavation of disposal cells, installation of leachate collection systems, lining of cells and installation of leachate monitoring systems, landfilling and grading of CCR materials, and capping/stabilization of CCR materials. Landfill construction is a continuous process of preparing new disposal cells as constructed cells are filled, capped, and vegetated.Precipitation runoff from landfill construction activities (i.e., runoff that has not contacted CCR material) requires management to minimize erosion and associated sediment transport into surface waters to comply with construction stormwater discharge and/or solid waste NPDES (National Pollutant Discharge Elimination System) permit requirements, which may include, but not necessarily be limited to Total Suspended Solid (TSS), pH, turbidity, and metals (e.g., iron. depending on native soil characteristics). Passive erosion and sediment control measures are typically employed at landfill construction sites and include:Minimizing disturbed acreage exposed to precipitation,construction season planning,coir filtration baffles,check dams with and without flocculant chemistry socks and impregnated filter fabric, andsettling basins.In the event that active treatment is needed to supplement passive treatment, active physical/chemical treatment (coagulant enhanced filtration) is considered as a component of the site’s overall erosion and sediment control plan.This paper presents a project recently completed by AECOM for a confidential client at their coal fired steam electric generating plant CCR landfill site. A feasibility study was initially completed, evaluating several erosion and sediment control/precipitation runoff management options for the site to supplement existing passive control measures, including active physical/chemical treatment for landfill construction activities to meet the site’s permitted TSS and turbidity discharge limits and TMDL (Total maximum Daily Load) requirements for iron in the receiving water. The feasibility study concluded that active treatment would be the most cost effective solution for supplementing existing passive erosion and sediment/precipitation runoff management measures. Treatability testing demonstrated that active treatment using chitosan enhanced filtration (chitosan is a biopolymer derived from the exoskeleton of marine organisms) as the most technically feasible/cost effective supplemental treatment for post-treating passively treated precipitation runoff during events generating high solids loadings in runoff streams. The presentation includes discussion of the feasibility study; treatability study; active treatment system design, procurement, commissioning/operation; and performance data from a range of precipitation events and solids loadings to the active treatment system. The presentation will conclude with a discussion of the potential application of active treatment in the management of free water and ash entrained water for CCR basin closure dewatering projects.