Disinfection of Onsite Sewage Treatment and Disposal Systems: A Critical Review of U.S. State Regulations and Field Evidence

Onsite sewage treatment and disposal systems (OSTDS) serve approximately one in five U.S. households and hundreds of millions of people worldwide, yet the scientific basis for regulating onsite wastewater disinfection has not been comprehensively evaluated. This review compares statewide regulations from all 50 U.S. states with field evidence for chlorination and ultraviolet (UV) disinfection under actual OSTDS conditions. Only 24 states include specific disinfection provisions, with substantial variation in allowable technologies, certification, operational criteria, microbial standards, and maintenance requirements. Prescribed operating conditions, including chlorine residual and UV fluence, generally fall within ranges associated with successful field performance. However, available evidence is insufficient to confirm that minimum regulatory requirements consistently achieve adequate microbial reduction under routine conditions. Field studies show that treatment failures commonly result from inadequate maintenance, declining chlorine delivery or UV output, inadequate pretreatment, and failure to verify required operating conditions. These failure pathways are only partially addressed by current regulations. State policies could be strengthened through technology-specific requirements for routine performance verification, preventive maintenance, and early failure detection. Future research should prioritize long-term field validation of regulatory criteria and improved monitoring and maintenance strategies for OSTDS.