WRRCTR No.116 Rotating Disc Sewage Treatment System for Suburban Developments and High-Density Resorts of Hawai'i

Abstract

A large-scale pilot rotating disc treatment system was tested at the City and County of Honolulu Pacific Palisades Municipal Wastewater Treatment Facility, to evaluate its treatment effectiveness and capabilities, and to provide design and operation criteria in treating domestic waste water in Hawaiian and tropical climates. The system included primary clarification and sludge storage facilities, and a 0.55 m (1.8 ft) disc diameter, 20.9 m^2 (225 ft^2 ) four-stage rotating disc treatment unit. The test unit was tested at four hydraulic loadings of 0.09 to 0.27 m^3/day/m^2 (2.25-6.7 gpd/ft^2). Peripheral rotational disc speed was constant at 0.3 m/s (1.0 fps) and waste water temperate was 27°C to 28°C during the study. At hydraulic loadings of 0.09 to 0.27 m^3/day/m^2 (2.25-6.7 gpd/ft^2) of disc area, the test unit achieved respectively 94 to 82% overall removal of carbonaceous BOD5 and 96 to 82% overall removal of suspended solids when treating degritted raw domestic waste water. This yielded effluent concentrations of 12 to 32 mg/l BOD5 and 7 to 21 mg/l suspended solids. Sludge production from the disc section was 0.40 to 0.50 mass units sludge produced per mass unit BOD5 removed in the disc section. Low maintenance requirements, low power consumption, and resistance to the effects of hydraulic surges make the rotating disc process very attractive for package plant installations in Hawaii. In-place equipment cost for rotating disc package systems treating sewage volumes of 94.5 m^3/day (25,000 gpd) and 378 m^3/day (100,000 gpd) were estimated to be about 10% higher than for extended aeration and high-rate activated sludge package systems. However, the total annual cost over a 20-yr period was respectively about 14% and 20% lower for the rotating disc package systems than the extended aeration and high-rate activated sludge package systems.