Enhancement of a Decentralized Wastewater Treatment System by Applying a Bio-tower - A Project for Improving our Environmental Footprint

Abstract

To investigate if decentralized wastewater treatment systems impact on the environment performance can be improved, a Field Bio-tower Tank Septic system was designed, installed on an existing 1,500-gal (5678 l) decentralized wastewater treatment system. The system was started up during a 14-day start-up phase, followed by a 130-day test phase. The system was operated at an average hydraulic retention time of 16.7 days based on a 90 gal (204.4 l) daily influent wastewater flow.
 The systems recirculation flow for the bio-tower was 22.6 l/min (6 gal/min) for the start-up phase and 40.0 l/min (10.6 gal/min) for the test period with a corresponding recirculation of the entire septic tank from 5.7 to 10.1 times a day respectively.
 During the testing period a daily average temperature of 19.3°C (66.7°F) and an average rainfall of 5 l/m² was observed. The FBST system operated at an average influent pH level and temperature of 8.6 and 22.0°C. The average effluent pH and temperature was 8.5 of 20.9°C.
 The installed system reduced on average the influent TS from 79151 mg/l to 43021 mg/l and showed an average reduction of the TDS from 36424 mg/l to 21965 mf/l. The TSS and VSS was reduced on average from 94.1 mg/l to 69.9 mg/l and 89.0 mg/l to 64.9 mg/l.
 NH3-N content was reduced from 57.5 mg/l in the influent to 53.4 mg/l in the effluent. The average BOD and COD was reduced from the average influent value of 88.2 mg/l and 318.2 mg/l to 66.8 mg/l and 256.2 mg/l respectively. However, at the end of the 130-day test period BOD and COD values were the lowest at 15.5 mg/l and 56.0 mg/l respectively, indicating bacteria cultures are well established and the system operation of the FBTS system is mostly constant.
 This research showed that the FBST system can improve operations of a DWWTS system significantly reducing the effluent load over 10 times compared to the influent load of the system.