Duckbill elastomer check valve use effects on domestic wastewater discharging marine outfalls initial dilution performance improvement

Abstract

Most of the domestic wastewater discharging marine outfall diffusers have simply opened circular ports on the diffuser pipe wall. In order to protect the diffuser from seawater intrusion and clogging by sediments during lower flow rate periods, “duckbill” check valve (DBV) can be mounted on circular ports. Because of the DBV use instead circular ports at the same conditions, jet velocity at port could be increased. It was reported in some of the studies that the initial dilution was also increased in changed diffusers with DBVs. In this study, the initial dilution estimations of multiport diffusers were compared before and after DBV mounted conditions of horizontally opened circular sharp edged ports on the thin pipe wall. For Q = 0.5 m3/s design flow rate, t = 30-year lifespan, H = 20–50 m port depths and, ρa = 1,015–1,035 kg/m3 receiving water densities, 12 different diffusers with d = 150 mm diameter sized circular ports were designed. With the same total head, all diffusers were converted to 150-mm DBV nozzles. All hydraulic parameters and initial dilutions of before and after DBV usage were recalculated from the literature data for line source in this study. Dilution comparisons for the end of the project were shown that all DBV used results were lower than circular port results as ΔS (%) from −0.19 to −19.18 ranges. Except for two of the lower density values at the shallowest port depths, ΔS (%) had similar results for project start year.