Browsing by Author "Manyama, Mkama"

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    Effect of pretreatment on nitrogen transformation and removal in subsurface gravel bed constructed wetland
    (University of Dar es Salaam, 2005) Manyama, Mkama
    This study discusses the effect of pre-treatment on nitrogen transformation and removal mechanisms in gravel bed SSCW and a coupled HRP-SSCW gravel bed located at University of Dar es Salaam. The study was conducted at two different settings. In Phase I, effluent from primary facultative pond was fed directly to unplanted gravel bed SSCW, with a discharge of 0.69 m3/d. During Phase II, the HRP with 0.6 m depth, received effluent from primary facultative pond at a flow rate of 1.2 m3/d and discharged it to unplanted gravel bed SSCW with 0.8 m deep, filled to 10 cm above water level with 20 mm diameter aggregates, at a flow rate of 0.69 m3/d. Both HRP and SSCW were operated at a retention time of 5 days. The results showed that improved nitrogen removal occurred with inclusion of HRP unit. While a direct system achieved nitrogen removal by 41.3%, a coupled system (Phase II) improved to 60.2%. These results show the significance of pre treatment (HRP) for better performance of nitrogen removal in gravel bed SSCW. Based on the model results, nitrification - denitrification process was higher in a coupled SSCW system accounting for 34% - 39%, compared to 24% - 26% observed in the direct system. Hence this research proved that provided the influent is fully nitrified in the pre- treatment system such as HRP, denitrification becomes the major contributor to the nitrogen removal process in SSCW. The model also revealed the significance of attached biomass on nitrogen removal, whereby 41.5% and 31.1% total nitrogen removal were achieved in direct system when biofilm was included and rejected, respectively. In a coupled SSCW, 49.4% total nitrogen was removed when biofilm included, compared to 34.8% when rejected.