Acute toxicity and inactivation tests of CO₂ on invertebrates in drinking water treatment systems

In addition to the esthetic problem caused by invertebrates, researchers are recently starting to be more aware of their potential importance in terms of public health. However, the inactivation methods of invertebrates which could proliferate in drinking water treatment systems are not well developed. The objective of this study is to assess the acute toxicity and inactivation effects of CO₂ on familiar invertebrates in water treatment processes. The results of this study revealed that CO₂ has a definite toxicity to familiar invertebrates. The values of 24-h LC₅₀ (median lethal concentration) were calculated for each test with six groups of invertebrates. The toxicity of CO₂ was higher with increasing concentrations in solution but was lower with the increase in size of the invertebrates. Above the concentration of 1,000 mg/L for the CO₂ solution, the 100% inactivation time of all the invertebrates was less than 5 s, and in 15 min, the inactivation ratio showed a gradient descent with a decline in concentration. As seen for Mesocyclops thermocyclopoides, by dosing with a sodium bicarbonate solution first and adding a dilute hydrochloric acid solution 5 min later, it is possible to obtain a satisfactory inactivation effect in the GAC (granular activated carbon) filters.