Successes and Challenges in Project Implementation Using Unsaturated Media Filter Systems for Onsite Wastewater Treatment in Rhode Island

Limited regulatory visits and operational constraints in Washington County, Rhode Island, requires the use of passive and resilient onsite wastewater treatment systems (OWTS). An affordable solution with a flexible design approach to meet regulatory requirements can be achieved by using a Smart Trickling Anaerobic/Aerobic Recirculation (STAAR) system for complete nitrification/denitrification. In this case study, two STAAR 6.0 systems were analyzed for BOD₅ and TSS removal, and one STAAR 4.5-N system was analyzed for TN removal. Grab samples were collected and reported to both the manufacturer’s distributor and the state official by a third-party environmental laboratory. Both STAAR 6.0 units reduced BOD₅ and TSS effluent concentrations below regulatory limits (30/30 mg/L or less). In addition, the nitrogen reducing technology (STAAR 4.5-N) achieved an average TN effluent concentration as low as 8.41 ± 0.77 mg/L which was below regulatory requirements (≤19 mg/L). STAAR systems are designed to manage the processor recirculation cycle over the filter media and to manage the sludge returns to the primary anoxic tank based on the required effluent discharge and quality. Therefore, a STAAR system designed as a BOD₅ and TSS reducing technology can be adapted to be a nitrogen reducing technology without the addition of equipment, instrumentation, and moving parts. This practice of the STAAR systems in the Washington County proved it is a reliable and affordable solution to maintain regulatory requirements for BOD₅, TSS, and TN where system monitoring is limited. Moreover, the consistency of effluent quality of the three STAAR systems assured that the STAAR integrated media allowed the growth of nitrifying bacteria without clogging the media. The hydrophobicity and surface charges of the STAAR integrated media may have contributed to this finding, and further investigations are required to understand the effect of the STAAR integrated media properties on biofilm formation.