Browsing by Author "Kimwaga, Richard Joseph"

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    Modeling of coupled dynamic roughing filters and horizontal subsurface flow constructed wetlands to tertiary treatment of waste stabilization pond effluents
    (University of Dar es Salaam, 2004) Kimwaga, Richard Joseph
    This study which was investigated in different times from May 2000 to March 2002 was conducted to determine the potential use of coupled Dynamic Roughing Filters (DyRFs) and Horizontal Subsurface Flow Constructed Wetlands (HSSFCW) as a cheaper and yet effective and appropriate alternative technology of treating domestic wastewater in tropical environments like Tanzania. Pilot set ups of coupled DyRF and HSSFCW were constructed at the outlet of the Waste Stabilisation Pond (WSP) at the University of Dar es Salaam. One set of a DyRF- HSSFCW was placed downstream the Primary Facultative WSP (PFWSP) and the other was located downstream the Maturation WSP (MWSP). The study was carried out in a 2.2-m long, 0.7-m wide and 0.7-m deep DyRF as a first stage, using three different fractions of gravel ranging from 8mm to 32mm, respectively from the top to the bottom. In the second stage, there was a HSSFCW with 0.6-m wide, 1.75-m long and 0.6-m deep planted with Phragmites mauritianus. The optimised combination of the operational and design variables yielding the highest purification efficiency of DyRF was at a filtration rate of 2 - 3m/h, a filter material size range of 8 - 25mm, and the filter media thickness of 0.7m. A further study was conducted to compare the environmental conditions, performance and first order removal rates kinetics of TSS, BOD5, COD and Faecal Coliforms (FC) for a coupled DyRF and HSSFCW placed downstream of the Primary Facultative Waste Stabilisation Ponds (PFWSP) and that after Maturation Waste Stabilisation Ponds (MWSP). The best location of DyRF - HSSFCW for the achievement of higher removal rates of 0.56 d*1 (TSS), 0.75 d'1 (BODs), 0.79 d’1 (COD) and 0.85 d'1 (FC) was found to be after the MWSP. In the final phase of the study, an ecological model was also developed to simulate the retention and removal of Total Suspended Solids (TSS) in a coupled DyRF and HSSFCW treating effluents from PFWSP system. The model was based on the application of the deep - bed filtration models for drinking water purification with an extension term that incorporates biological activities (i.e. biodegradation). The simulations were performed using STELLA™ II software. The model found out that the sedimentation process was the major removal route of the TSS in the DyRF accounting for a mean removal of 63.7% (26.67 gTSS/m2/d) of the total removal followed by the filtration process mean removal rate of 22.1% (9.25 gTSS/m2/d). However, the filtration process was the major route of removal of the TSS in the HSSFCW accounting for a mean removal of 77.4% (7.23gTSS/m2/d) followed by bio-degradation, which accounted for a mean removal of only 16.2% (1 52gTSS/m2/d).