BS ISO 20468-3:2020 pdf free.Guidelines for performance evaluation of treatment technologies for water reuse systems.
Depending on the water treatment efficiency and performance to be achieved, pre-treatment and/or post-treatment can be added to the ozone system. For example, sand filtration as the typical pretreatment process to remove suspended impurities including ozone scavengers and inorganic matter enhances treated water quality and reduces ineffective ozone consumption. On the other hand, posttreatment such as biological activated carbon process removes residual particles and dissolved matter which are not decomposed and/or are generated as by-products during ozonation. In order to retain bactericidal effects after ozonation, post disinfection such as chlorine disinfection can be added.The feed gas supply unit is using either air or oxygen gas to the ozone generation unit. An air-fed ozone system uses compressed air directly from the atmosphere. An oxygen-fed ozone system uses LOX or concentrated oxygen fed by an oxygen concentrator. Typically, the oxygen concentrator increases oxygen concentration by adsorbing nitrogen selectively from air.The ozone contactor is a vessel where ozone is dissolved in water and reacts with target substance(s), followed by the ozone dissolution system which dissolves ozone gas in water. Mass transfer of ozone is a critical aspect of water ozonation. Dissolution devices include bubble diffusion, down flow tube injection, venturi injection, radial diffuser, static mixers and mechanical agitation. These applicable dissolution devices should be selected depending on the space limitation for system installation, electric power charge and ozone transfer efficiency. The method of ozone gas dissolution used also depends on system design and method of ozone generation used. Since ozone is a very strong oxidant, any unreacted ozone in the off-gas can be harmful to the environment and endanger human health. Consequently, it shall be converted to oxygen and neutralized before the off-gas is released to atmosphere. The off-gas ozone treatment unit typically consists of an off-gas ozone destruction unit and an off-gas ozone suction unit. The off-gas ozone suction unit withdraws off-gas ozone from the ozone contactor and draws it into the off-gas ozone destruction unit. The off-gas ozone destruction unit converts ozone residual exhausted from the ozone contactor to oxygen by using such methods as activated carbon, catalyst media and heat, or combination of heat and catalyst media.BS ISO 20468-3 pdf download.