Use of coupled dynamic roughing filters and subsurface horizontal flow constructed wetland system as appropriate technology for upgrading waste stabilisation ponds effluents in Tanzania

Abstract

As a part of a comprehensive evaluation of post-treatment techniques for upgrading waste stabilization pond (WSP) effluents, coupled dynamic roughing filters (DyRF) and subsurface horizontal flow constructed wetland system (HSSFCW) system was evaluated in Tanzania. Coupled DyRF and HSSFCW were considered as cheaper and yet effective and appropriate alternative technology for upgrading WSP effluents in tropical environments like Tanzania. The main objective of the study was to determine the performance treatment of coupled DyRF and HSSFCW for upgrading WSP effluents with respect to organic compounds (TSS and BOD 5) and pathogen (FC). A pilot of coupled DyRF and HSSFCW was constructed at the outlet of the Maturation WSP at the University of Dar es Salaam, Tanzania. The study was carried out in a 2.2 m × 0.7 m × 0.7 m deep DyRF as a first stage, using three different fractions of gravel ranging from 8 mm to 32 mm, from the top to the bottom respectively. In the second stage, a HSSFCW planted with Phragmites Mauritianus with 0.6-m wide, 1.75-m long and 0.6-m deep was used. The DyRF–HSSFCW system achieved TSS load reduction by 89.35%, which is 15.97 g TSS/m 2/day, while BOD 5 load reduction by 84.47% which is 9.29 g BOD 5/m 2/day was achieved. The FC mean removal rate of 99.99% was also achieved. By achieving mean effluent TSS (12.63 ± 4.12 mg/l), BOD 5 (14.12 ± 3.84 mg/l), and mean effluent FC concentrations of 790 FC/100 ml it was concluded that application of coupled DyRF and HSSFCW in the tropics can be considered technically one of the most appropriate technology for upgrading WSP effluents.