Performance Evaluation of a Wetland-Type On-Site Wastewater System

Abstract

The Ridge to Reefs (R2R) Bioreactor Garden (BG) is a constructed wetland (CW) type wastewater system that was evaluated at the East Honolulu Wastewater Treatment Plant (EHWWTP). A pump, plumbing, electronic valves, dosing tank with float switch, and a programmable logic controller (the "system") were fitted to the R2R-BG. The system withdrew screened raw wastewater from the EHWWTP influent channel as influent and treated effluent was discharged into the EHWWTP sewer. The system was designed to provide a total flow of 600 gal/day to the Bioreactor Garden in a manner prescribed by the National Sanitation Foundation Standard 40 (NSF40) and 245 (NSF245) test protocols. The NSF40/245 protocols call for 35% of the daily flow to enter between 6 am and 9 am, 25% to enter between 11 am and 2 pm, and 40% to enter between 5 pm and 8 pm. The protocol calls for a sixteen-week continuous design loading period followed by a series of four stress loading tests over 7.5 weeks and a final 2.5 weeks of design loading. The R2R-BG, individual wastewater treatment system, was brought on-line for continuous operation on January 31, 2020. The sixteen-week standard performance period was completed between March 1 and June 20, 2021. The series of four stress test loadings specified by the NSF protocols were conducted between June 21 and August 11, 2021, and the final 2.5 weeks of design loading was completed on August 30, 2021. A programmable sampler (ISCO 3700) was used to collect effluent samples five-days-per-week during the period when the unit received influent, and a refrigerated programmable sampler (ISCO 5800) was used to collect 24-hour influent composite samples. Effluent samples were composited in proportion to the influent flow pattern. Influent samples were monitored for biochemical oxygen demand (BOD5), total suspended solids (TSS), nitrogen species, phosphorus species, anions and cations, pH, and alkalinity (Alk). Effluent samples were monitored for carbonaceous BOD (CBOD5), TSS, nitrogen species, phosphorus species, anions and cations, pH, and Alk. No maintenance or modifications or repairs were made during the test period. During the entire test period, the influent feed wastewater met the requirements of NSF40 and 245 and the R2R-BG system performed very well. Minimum performance for production of a NSF40 Class I effluent requires that the 30-consecutive-day mean effluent concentration of CBOD5 and TSS be no greater than 25 mg/L and 30 mg/L, respectively. At the same time, the mean values of CBOD5 and TSS for any 7-consecutive days cannot be greater than 40 mg/L and 45 mg/L, respectively. In addition, the effluent pH must always be between the limits of 6.0 and 9.0. The NSF245 standard requires that the average of all samples during the 16-week design loading period provide at least 50% removal of total nitrogen (TN). During the entire 26-week evaluation period, effluent CBOD5 averaged 19 mg/L, effluent TSS averaged 6 mg/L, and pH averaged 7.6 (minimum 7.1, maximum 8.5). During the design loading period, TN removal averaged 87%. The data presented in this report indicate that the R2R Bioreactor Garden met all of the requirements for NSF40 Class I effluent and all of the NSF245 criteria for TN removal.