Enhancing natural treatment systems by utilizing water treatment residuals
Date
2008
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Abstract
The current project envisions the application of riverbank filtration (RBF) and aquifer recharge and recovery (ARR) in series as preliminary treatment steps of a multi-barrier treatment approach for the City of Aurora's Prairie Waters Project. The primary focus of the project is the removal of phosphorus, nitrogen, and carbon from the source water resulting in biologically stable water that can be stored in a terminal reservoir. In addition to nutrients, perchlorate and three commonly used pesticides, atrazine, alachlor, and metolachlor have been studied in terms of removal with the RBF and ARR systems. Aluminum based water treatment residual (WTR) was considered along with other sorbents for enhanced phosphorus removal. The experimental studies include the monitoring of an RBF field site and pilot columns that simulate RBF and ARR systems. Possible benefits of WTR as an amendment were tested by amending a column with 30% WTR under RBF and ARR conditions. Also an application scenario of RBF followed by a WTR amended ARR infiltration basin and ARR was simulated by a column study. Results of the studies indicated that the RBF and ARR systems are insufficient to provide sustainable phosphorus removal. Phosphorus removal mechanism is limited by the sorption capacity of the alluvial sand and minor biological activity. Use of the WTR amendment reduced phosphorus levels to less than the method detection limit of 0.03 mg/L with a high adsorption capacity. The ARR system in sequential RBF-ARR application suffers from the lack of labile organic carbon and therefore microbially mediated treatment processes are limited. Amending the infiltration of the ARR system with organic carbon rich WTR can promote biological activity, thus allowing further biodegradation of contaminants. Results of the study indicated that the RBF system is a sustainable barrier for nitrate removal while labile carbon limited ARR cannot achieve significant nitrate removal. To use the ARR system as a secondary barrier for nitrate, a labile carbon source should be introduced to the system. WTR was used as a supply of organic carbon to the ARR system and the experimental studies indicated that, once optimized, WTR can promote biological denitrification through the ARR system. The field and column studies also showed that both RBF and ARR can achieve perchlorate removal as long as sufficient electron donating compounds (e.g. organic carbon) are present in the environment. It has also been observed that the ability of RBF and ARR systems to remove alachlor and metolachlor is limited by the biodegradation through the alluvial sand while they achieve sustainable atrazine removal. WTR was tested as an amendment alternative the ARR infiltration basin. Concentrations of selected pesticides were reduced to the method detection limit of 0.3 μg/L during 1-foot 30% WTR amended column treatment with the residence time of 1.25 days under both abiotic and biotic conditions. The overall study suggested that once the source and type of the WTR was selected, the optimum amount of WTR can be obtained by adjusting the application ratio and the media depth for the efficient removal of all contaminants of concern.
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Subject
natural treatment systems
nitrate removal
perchlorate removal
phosphorus removal
riverbank filtration
water treatment
environmental engineering