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The disposal of residual wastewater and treatment byproducts (WTBs) generated on-site by many major industries poses environmental risks due to the elevated levels of heavy metals in WTBs and the potential release of contaminants to the environment. Solidification/stabilization (S/S) of waste is an attractive technology to address this challenge as it provides a permanent disposal strategy. S/S methods entail solidifying the waste stream by mixing combinations of additives such as lime and portland cement (OPC) with coal combustion residual byproducts, e.g., fly ash (FA). This co-disposal approach of waste liquids and waste fly ash creates a solid material that encapsulates contaminants through physical and chemical processes. However, given the variable compositions of WTBs, each solidified mixture requires a different mixture design to successfully encapsulate contaminants. Currently, the mixture design process is approached empirically and iteratively and prioritizes solidification over stabilization. Successful mixture designs are then later tested for their ability to prevent contaminants from entering the environment via leaching, which is generally done using time-intensive and expensive testing (e.g., Leaching Environmental Assessment Framework (LEAF)). This process is cumbersome and not optimized to efficiently design mixtures. 

Consequently, this work aims to fulfill two main objectives: (1) develop a method to efficiently screen mixture designs to stabilize WTBs and (2) develop a novel radial flow-through test that simultaneously assesses the leaching of heavy metals from solidified mixtures and hydraulic conductivity in less than one week. 

A small scale reactor analysis (SSRA) technique was developed to screen mixtures for stabilization. This method was successful in assessing the ability of additives to stabilize WTBs. Stabilization screening is then followed by solidification testing to determine the suitability of the mixtures for landfilling. A novel method, the rapid flow through test (RFT), was then adapted to evaluate leaching and hydraulic conductivity of the S/S specimens. RFT was able to determine the leaching behavior of heavy metals over time from different S/S mixture designs across a range of different pH values and ionic strengths and simultaneously determine the hydraulic conductivity of the S/S solid. Standard LEAF test Methods 1313 and 1315 provided complementary data to the RFT testing. The rapid screening and testing methods developed here show promise for improving and expanding the ability to successfully design mixtures that stabilize a variety of waste products.