Abstract: Sample water is introduced into a water bath in which aquatics live, and a gas sparingly soluble in water and giving no effect upon biological activities of aquatics is supplied to the water bath. The supplied gas and carbon dioxide gas generated by the biological activities of aquatics are collected, and a change in water quality of the sample water is detected from a concentration of carbon dioxide thus collected.Change in water quality of sample water can be rapidly detected thereby, which can be applied to detection of whether toxic materials are contained, for example, in river water flowing into a water purification plant, or not.

Abstract: Waste water issued from a wet type desulfurization apparatus and containing thionic acid ions is introduced into ion-exchange towers filled with weak-basic anion-exchange which has to effect anion exchange therein. The weak-basic anion-exchange resin which has adsorbed the thionic acid ions is desorbed by contacting an alkaline solution. The thionic acid ions included in the desorbing solution are decomposed by heating them in the presence of acid. A decomposed solution is issued out of the system after its neutralization.

Abstract: A waste flue gas desulfurizing method in which a waste flue gas containing sulfurous acid gas is contacted directly with sea-water, whereby the sulfurous acid gas is absorbed in the sea-water and concurrently sulfites are formed in the sea-water by the reaction between the sulfurous acid ions and metal ions present in the sea-water, and then the carbonic acid component contained in the sea-water which is then in the acidic region is released therefrom by a decarbonation operation to restore the pH value of the sea-water in the neutral region, and thereafter oxygen contained in air or from other source is introduced into the sulfite-containing sea-water to convert said sulfites into sulfates.

Abstract: There are disclosed methods for removing fluorine values from fluorine-containing waste waters, in which aluminum ions are added to fluorine-containing waste water to convert fluorine to hydroxyfluoride complexes, adding phosphoric acid or phosphate and calcium compound are added to form fluoride apatite with residual fluorine in the waste water, and the hydroxy-fluoride complex and fluoride apatite are removed from the waste water.