Application and Testing of a Laboratory Biotower Septic Tank System for Effluent Treatment - A Laboratory Study

Abstract

A laboratory biotower septic tank system was designed, installed, started up with unfiltered wastewater during a 9-day start-up phase, and operated at a hydraulic retention time of 5-, 15-, and 20 days with filtered waste water and 5-, 10-, and 15 days for liquid cow manure. The system was operated at a laboratory room temperature of 23.0±0.5°C (73.4 ± 0.9°F). The system had an influent pH of 7.5 ±0.1 and a slightly higher pH of 8.0±0.1 for the effluent for filtered wastewater, and an influent pH of 7.3 ±0.1 and a slightly increased effluent pH of 7.5  ± 0.1 for the operation with liquid cow manure. This research showed that the system is able to achieve an effluent chemical oxygen demand level between 17 ±1 mg/l, and 19 ±1 mg/l for a hydraulic retention time between 5-, and 20 days for filtered waste water, and between 23 ±1 mg/l and 32 ±3 mg/l for a hydraulic retention time between 5-, and 15 days for liquid cow manure at highly varying influent chemical oxygen demand levels between 25 ±1 mg/l and 74 ±15 mg/l and 293 ±46 mg/l to 335 ±14 mg/ for filtered wastewater and liquid cow manure respectively. The Total solids content in the effluent of the system showed an increase for the filtered wastewater and liquid cow manure influent with increasing hydraulic retention rate from of 55 mg/l to 71 mg/l and from 25 mg/l to 53 mg/l respectively. Total suspended solids for both, the filtered wastewater and the liquid cow manure was below the 4mg/l mark, except for the liquid cow manure 5-day hydraulic retention rate which had a value of 20 mg/l.