This study investigated an underwater plasma water treatment system based on a porous hydrophobic hollow ceramic tube and an alternating current (AC) voltage source, and its application to the decomposition of taste-and-odor compounds originated from algae. The taste-and-odor compounds investigated were geosmin and 2-methyl isoborneol (2-MIB), and the decomposition of algae was carried out on cyanobacteria. The features of the present atmospheric-pressure plasma system employing a porous ceramic tube are large gas liquid interfacial area due to the formation of numerous plasmatic gas bubbles and instant transfer of short-lived reactive species to water through the micro-pores of the ceramic tube right after the generation. The present plasma process was found to effectively decompose not only the taste-and-odor compounds but also the cyanobacteria algae. Both geosmin and 2-MIB were decomposed more rapidly in the raw river water than in the distilled water. The intermediate products resulting from the decomposition of the taste-and-odor compounds were identified, which showed that geosmin and 2-MIB underwent ring opening and subsequent bond cleavage at multiple sites. The specific energy inputs (SEIs) for 90% decomposition of algae ranged from 3.4 to 8.4 kJ L-1 for the initial concentration range of 129-1596 mu g L-1 The decomposition efficiencies of the taste-and-odor compounds were well correlated with the SEI. (C) 2014 Elsevier B.V. All rights reserved.