Evaluation of Screening Level Technique in Pollutant Removal in an Engineered Ecological System
Otieno, Kennedy Omondi
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This study was based on testing Screening Level Technique (SLT) as a way of evaluating bioremediation performance of an operating horizontal wastewater flow Vegetated Submerged Bed (VSB) system with specific focus to 5 day Biochemical Oxygen Demand (BODs). BODs is a pertinent pollutant parameter in biological treatment processes such .asVSB systems. The overall objective was to establish effectiveness. and usefulness of the SLT in the assessment and design of a performing pollution abatement VSB system. The methodology applied was the estimation of the descriptive bulk loss (k) parameter from the screening level plug flow model which principally assumes steady state conditions and spatial gradients in concentrations along the main flow .axis. The screening level plug flow model was .<\0> I~ I,t chosen because of the baffling natJr~"'~f the Carnivore Resraurant VSB system. According to the concept of SLT, the amount of pollutant removal ina VSB system is quantitatively expressed in terms of the Removal Efficacy (RE). The RE basically depends on the VSB reactor's hydraulic residence time and the pollutant removal rate, k per day. The pollutant removal rate in turn depends on a number of processes and conditions such as microbial metabolism and wastewater temperature. Both the BODs Removal Efficacy and bulk loss (k) were established as . ·96% and 0.48d-1 respectively. The meaning of this is that the Carnivore VSB system does not qualify as a conventional system despite its high removal efficacy performance. This· is because evaluated k value of 0.48d-1 could not compare favourably to the typicaI1.1'04d-1 value for conventional VSB systems. In conclusion, the SLTwas validated through subjection to verification failure rather than a chance to pass by testing it for effectiveness against the relatively universally accepted Kickuth model. Statistically, the study could not conclude a chance for failure and lack of confidence in it. Consequently, the study finds that the SLT is an effective and useful technology hence can be relied on for the design of a functional VSB bioremediation system.