Browsing by Author "Stephen, William"

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    Influence of flow velocity on the removal of faecal coliforms and soluble reactive phosphorus in horizontal subsurface flow constructed wetland
    (University of Dar es Salaam,, 2012) Stephen, William
    In order to determine the influence of flow velocity (u) on the removal of Faecal Coliform (FC) and Soluble Reactive Phosphorus (SRP) in Constructed Wetland, the removal rate constants of FC (kFc) and SRP (kp) were studied at various flow velocities (u). FC were analyzed using Membrane Filtration technique while SRP was analyzed using Spectro-photometric Ascorbic Acid method. Reed's equations for pathogen and Phosphorus removal were used to determine the overall remo-al rate constants for FC and SRP respectively; the flow equation the results were compared with Plug Influent number of FC ranged from 3,600 CFU/100 mL to 13,600 CFU/100 mL while effluent ranged from 500 CFU/100 mL to 4,300 CFU/100 mL. Using Reed's equation, the FC removal rate constants ranged from 1.6 day -1 at velocity of 4 miday to 34.5 day-1 at velocity of 42.9 m/day. On assuming plug flow equation, kFc ranged from 0.77 day-1 to 11.69 day-1. In both cases, the kFc values correlated positively with velocity Optimum FC removal rate constants were observed for the velocity ranging from 36 - 43 m/day. Influent SRP concentrations ranged from 196 mg/L to 5.42 mg/L with an average of 4.58 ± 0.44 mg/L. Effluent concentration of SRP ranged from 3.44 mg/L to 5.88 mg/L with an average of 4.39 ± 0.49 mg/L. The observed kp values from both Reed and Plug flow equation were generally poor and didn't correlate with flow velocity. Generally, it was observed that, the increase of flow velocity improved FC removal rate constants: implying that pathogens removals are influenced by diffusion of microorganisms into the biofilms on CW media where various removal mechanisms occur. On the other hand. SRP removals were uninfluenced by wastewater flow velocity. The velocity dependent approach together with Plug flow equation are therefore proposed in the design of CW as Reed's equation has a number of limitations including its dependence on temperature variations which is not the case in the tropics