Abstract

The development, application, and acceptance of passive treatment technologies, mainly for mining-influenced water (MIW), have advanced significantly in the past decades. With this evolution, there has been confusion and misconception about the capability and application of this technology. Like other treatment technologies, nuances exist with each water type and geographic location that give uncertainty about whether passive treatment is viable and worth pursuing for a specific project. Typically, this is resolved with field, bench, or pilot testing, but these tests can be relatively expensive, time-consuming, and inconvenient. These constraints lead to reluctance, delay, and unwarranted abandonment of passive treatment technologies.

Therefore, this study aims to demonstrate a proof-of-concept approach for passive treatment using simple procedures, readily available media, and minimal handling in a set of bench-top jar tests. The tests are designed to simulate various passive treatment mechanisms (e.g., metal sulphide formation) at the bench scale. To achieve this goal, three different MIW sources were used to demonstrate the validity of using this jar testing method to evaluate the feasibility of passive treatment technologies to improve water quality. The tested mechanisms are the building blocks of passive treatment and, when pieced together, reflect the processes occurring throughout a passive treatment system. Two additional objectives include 1) optimizing the studied processes by altering media compositions for each MIW source and 2) applying different handling protocols (i.e., stirred or shaken) to evaluate the most applicable jar test method.  

Tests were implemented over eight weeks, with handling and monitoring efforts limited to once per week. Weekly monitoring included pH, conductivity, oxidation-reduction potential, and temperature measurements. Additionally, MIW samples were sent to an analytical laboratory for metals, sulfate, and total organic carbon determinations before and after the testing period (i.e., pre- and post-treatment concentrations). A universal test set was used uniformly over the three test waters as a control (i.e., standard test media and handling method). The strength of the MIW and the potential to use locally available or cost-effective media drove the exploration of various media compositions. Further experimental control included comparing the relative importance of the handling procedures (i.e., stirring versus shaking, the addition of iron oxyhydroxide seed, and the presence or absence of light and algae) in several identical test units.

Results of the study were used to evaluate the feasibility and applicability of implementing passive technologies (i.e., biochemical reactors, iron terraces, limestone channels, and wetlands) to improve the quality of MIW. Although the data is semi-qualitative, it provides a novel, rapid, and cost-effective method of assessing the fit of passive treatment technologies for any MIW. The results also open the door early in a project for approximating acceptable ranges of system flow rate, retention time, removal rate, and cost for the applicable passive treatment processes.