Constructed Wetland Research for the Treatment of the Plant Gorgas Coal Pile Runoff

Abstract

Research was conducted to study the transport and fate of inorganic pollutants through a constructed wetland using a Reducing and Alkalinity Producing System (RAPS). RAPS have been used to successfully treat acid mine drainage (AMD). This wetland is designed to treat coal pile runoff, similar to AMD. A primary goal of this research was to evaluate an alternative design that might result in improved pollutant removal. The design was based on the partial re-circulation of treated water into a , detention basin, located immediately upstream from the RAPS, containing untreated water. This modification created a semi-passive RAPS-based system we refer to as a Recirculating RAPS (ReRAPS). To test the ReRAPS modification a full-scale RAPS-based wetland capable of recirculation was constructed, operated, and monitored. Factors that may promote improved pretreatment performance in the detention pond during the ReRAPS mode were evaluated using a series of batch tank studies. The wetland monitoring and tank studies have determined that the ReRAPS modification has the potential to enhance the basic RAPS wetland design by moderating the pH of contaminated water and reducing the contaminant loading prior to the RAPS component. The batch tank studies revealed that significant amounts of inorganic contaminants could be precipitated from mixtures of AMD and treated wetland water after 24 hours. Primary factors controlling the removal were pH, initial metal concentration and retention time.

Recirculating – Reducing and Alkalinity Producing System (Reraps) for the Treatment of Acidic Coal Pile Runoff

“…About one-third of the CPR acidity, 59 percent of the total Al, and 82 percent of the total Fe was consumed in the detention pond. These values are consistent with the previous study (Garrett et al 2001). In contrast to the previous study, no "net" Mn removal was observed in the detention pond.…”

“…The hydrological and chemical monitoring performed during this study were generally consistent with the findings of a previous study (Garrett et al 2001). In this study, sampling was much more intensive; approximately 2,300 samples (8 samples/day for 41 days at 7 nodes) were analyzed versus 98 samples (1 sample/day for 14 days @ 7 nodes) during the previous study.…”

“…The average alkalinity generation (14.0-35.9 g/d-m 2 ) during the CPR treatment events compares favorably with the rate of 23 g/d-m 2 which was measured during the winter of 2000 (Garrett et al 2001). These rates are also comparable to RAPS that receive partially treated AMD.…”

“…The previous study conducted in January 2000 by Garrett et al (2001) found that 95, 85, and 75 percent of the Fe, Al, and Mn, respectively, were pretreated prior to the RAPS component.…”

“…In a previous paper (Garrett et al 2001), we described an alternative wetland design using RAPS technology that specifically addressed the challenges associated with intermittent contaminant loading. The modification involved the partial re-circulation of treated water into a detention basin located immediately upstream from the RAPS component resulting in what we refer to as a semi-passive Recirculating Reducing and Alkalinity Producing System (ReRAPS).…”