Thesis Title: Super-fine Powdered Activated Carbon for the Removal of Microcystin-LR from Drinking Water
Cyanotoxins produced by different species of cyanobacteria are a major issue in drinking water treatment. Microcystin-LR (MC-LR) is among the most commonly detected and studied cyanotoxins, a hepatotoxin that can cause irreversible damage to liver cells and cause chronic liver and kidney diseases. Health Canada’s guidelines stipulates a maximum acceptable concentration of 1.5 µg/L for microcystins in drinking water. Powdered activated carbon (PAC) can remove extracellular cyanotoxins from drinking water and is often implemented for the control of seasonal taste and odor issues. Newly developed super-fine powdered activated carbons (SPACs) have particle sizes around 1 µm, several degrees of magnitude smaller compared to conventional PACs, and they have been shown to have faster adsorption kinetics and similar or even higher capacities than conventional (PAC) for organic contaminants. The main objective of this bench-scale study was to investigate the applicability of SPAC for the removal of MC-LR as an alternative to PAC in conventional drinking water treatment plants.
Three SPACs were prepared by pulverizing three commercially available PACs (wood-based, coconut-based, and coal-based). Bench-scale experiments established that the SPACs dosed as prewetted slurry had much faster adsorption rates for MC-LR compared to regular-size PACs. Presence of NOM in Lake Erie water reduced the adsorption rate of SPACs for MC-LR, though the SPACs still outperformed PACs under these conditions. The capacities of SPACs for MC-LR were also determined at both equilibrium and short contact times (i.e. 10, 20, 30 min up to several hours to several), the latter being more relevant to drinking water applications. It was found that SPACs also had higher capacities at both equilibrium and short contact times compared to the parent PACs, which would translate to a lower SPAC dose required for removal of MC-LR from surface water. In the last phase of the study, the removal of SPACs from treated surface water via conventional coagulation, flocculation, and sedimentation (CFS) processes was evaluated using jar tests. SPACs could be removed well from surface water spiked with SPACs using coagulant doses and coagulation regimes similar to the ones for turbidity removal in surface water without SPAC.
Overall, SPAC hold a lot of promise as an alternative to PAC for removing seasonal organic compounds, but further research is needed to explore and validate SPAC applications at pilot scale before this technology can be scaled up to full scale. At present, SPACs have not been applied at full-scale and to-date commercial SPAC products are not available for drinking water treatment applications.
A PDF copy of the thesis can be requested at UWspace and questions can be sent to Sina Golchi, Research Associate at the NSERC Chair in Water Treatemnt
