Performance of vacuum UV (VUV) for the degradation of MC-LR, geosmin, and MIB from cyanobacteria-impacted waters

Abstract

The increasing frequency with which cyanobacterial blooms are affecting sources of drinking water is a growing concern worldwide. Such events are usually responsible for the presence of cyanotoxins as well as taste and odor (T&O) compounds. Vacuum UV (VUV) is a promising advanced oxidation process used to treat water impacted by cyanobacterial blooms, with potential applicability in small and remote communities because of its simplicity. Here, we present the performance of a VUV process, in both a collimated beam reactor (CBR) and a pilot scale flow-through reactor, using two cyanobacterial-laden Canadian source waters with different inorganic and natural organic matter contents. First, VUV performance was assessed by comparing the removal of microcystin-LR (MC-LR), 2-methylisoborneol (MIB), and geosmin (GSM). The average kinetic rates obtained in the CBR case were 2.9 × 10⁻³ cm² mJ⁻¹ for MIB and GSM and 6.6 × 10⁻³ cm² mJ⁻¹ for MC-LR. Under bloom conditions, removals of 40–60% for T&O compounds and MC-LR were achieved in the flow-through reactor. It was observed that although MC-LR, GSM, and MIB were impacted by VUV treatment, the removals achieved may not be sufficient to completely eliminate toxicity and T&O at the tested fluences (up to 400 mJ cm⁻²). In addition, we observed a 20% increase in disinfection by-products (DBPs), on average. Hence, achieving high MC-LR, MIB, and GSM removals with VUV may cause the generation of more DBPs.