Disinfection is the removal, deactivation, or killing of pathogenic organisms either by physical or chemical methods. The three most common ways to disinfect wastewater are chlorination, ozonation, and ultraviolet. For onsite or smaller applications, typical disinfection of wastewater occurs through the use of chlorination or ultraviolet disinfection; thus, additional information is provided below for these two options only.
The Disinfection Question – Answers for Onsite Systems - Wastewater treatment removes pathogens and other harmful components. The final purification step for most onsite wastewater systems calls for the effluent to be filtered through a layer of soil (i.e., soil absorption system). Disinfection is generally required with onsite treatment systems when the effluent is to be surface discharged or prior to some other immediate reuse of the effluent. Onsite system disinfection options are discussed.
Chlorine is one of the most common forms of disinfection. Chlorine is used
to kill disease-causing bacteria and microorganisms in wastewater. Disinfection efficiency
depends on factors such as contact time, dosage, temperature, and pH. Tablet chlorinators
are the most common means of chlorinating domestic wastewater on a small scale. Occasionally,
when the effluent chlorine level is high enough to adversely affect receiving water,
dichlorination is necessary. Dechlorination is accomplished by the addition of chemicals
such as sulfur dioxide and activated carbon to the chlorinated effluent.
Ultraviolet (UV) disinfection occurs when radiation penetrates the cell walls of microorganisms in the effluent stream and is absorbed by the cells. This prevents cell replication and often causes cell death. For UV light to be effective and reach the bacteria, the effluent must be relatively clear and free of solids. UV light is not a chemical agent and therefore produces no toxic residuals. Once only a common large-scale application, UV light has become a cost-effective and widely used disinfection option for small-scale applications.