Pilot-scale column experiments were conducted in this study using natural soil and river water from Ohio river to assess the removal of microbes of size ranging over 2 orders of magnitude, i.e., viruses (0.025-0.065 microm), bacteria (1-2 microm), and Cryptosporidium parvum oocysts (4-7 microm) under conditions representing normal operation and flood scour events. Among these different organisms, the bacterial indicators were transported over the longest distances and highest concentrations; whereas much greater retention was observed for smaller (i.e., viral indicators) and larger (i.e., Cryptosporidium parvum oocysts) microbes. These results are in qualitative agreement with colloid filtration theory (CFT) which predicts the least removal for micrometer size colloids, suggesting that the respective sizes of the organisms was a dominant control on their transport despite expected differences in their surface characteristics. Increased fluid velocity coupled with decreased ionic strength (representative of major flood events) decreased colloid retention, also in qualitative agreement with CFT. The retention of organisms occurred disproportionately near the source relative to the log-linear expectations of CFT, and this was true both in the presence and absence of a colmation zone, suggesting that microbial removal by the RBF system is not necessarily vulnerable to flood scour of the colmation zone.

This article addresses the state of the art of bioleaching research published in South Korean Journals. Our research team reviewed the available articles registered in the Korean Citation Index (KCI, Korean Journal Database) addressing the relevant aspects of bioleaching. We systematically categorized the target metal sources as follows: mine tailings, electronic waste, mineral ores and metal concentrates, spent catalysts, contaminated soil, and other materials. Molecular studies were also addressed in this review. The classification provided in the present manuscript details information about microbial species, parameters of operation (e.g., temperature, particle size, pH, and process length), and target metals to compare recoveries among the bioleaching processes. The findings show an increasing interest in the technology from research institutes and mineral processing-related companies over the last decade. The current research trends demonstrate that investigations are mainly focused on determining the optimum parameters of operations for different techniques and minor applications at the industrial scale, which opens the opportunity for greater technological developments. An overview of bioleaching of each metal substrate and opportunities for future research development are also included.

No abstract

Filtration: Comparison of Pilot Scale Transport with TheoryIn our introduction we considered the practical significance of microscopic particulate analysis (MPA) and the relevance of colloid filtration theory (CFT) to MPA, resulting in the statement that "The focus on larger particles by the MPA method runs counter to established theory regarding the removal of colloids during transport through porous media". To clarify this statement in a regulatory context, a public drinking water supply well is classified as groundwater under the direct influence of surface water (GWUDI) if hydrogeologic data, well proximity to surface water, and microscopic MPA results warrant this designation. Thus, we wish to clarify that the MPA is not the sole factor considered in determining GWUDI status.The MPA method focuses on Cryptosporidium parvum oocysts due to their resistance to inactivation by commonly used disinfectants (except UV); hence, coagulation and filtration are standard treatment for Cryptosporidium removal (but riverbank filtration is a potential alternative treatment). The MPA method considers a range of biological particles of varying sizes, but is empirical in nature. Effective targeting of appropriately sized biological particles based on theoretical and experimental observations would potentially improve MPA and any GWUDI determination that makes use of MPA. For example, 1 µm diameter bacteria or bacterial spores might be found to be suitable regulatory surrogates for 5 µm diameter Cryptosporidium. For this purpose, our manuscript evaluates transport of a range of biological particles of differing sizes and compares these results to expectations from theory.