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Title: Evaluation of Selected Wetland Plants for the Removal Efficiency of Chromium and Organic Pollutants from Tannery Wastewater in Constructed Wetlands at Modjo Tannery
Authors: Tadesse, Alemu
Advisors: Seyoum Leta(Dr.)
Keywords: Constructed wetland
Tannery wastewater treatment
Chromium uptake
Translocation factor and Chromium bioaccumulation factor
Copyright: Sep-2010
Date Added: 17-Jul-2012
Publisher: Addis Ababa University
Abstract: Wastewater from leather processing industries is very complex and leads to water pollution if discharged untreated, especially due to its high organic loading and chromium content. In this study the phytoremediation efficiency of selected wetland plant species in subsurface flow (SSF) constructed wetlands receiving tannery wastewater was investigated. Four pilot units were vegetated with C. alternifolius, T. domingensis, P. Karaka and B. aethiopium and a fifth unit was left as unvegetated (control). The treatment performance of the systems for total Cr, COD, BOD and nutrients under a 5 day hydraulic retention time were analyzed based on HACH manual. The Cr in the plant tissue was analyzed through oven dried plant tissue, milled, weighed, digested and analyzed using Atomic Absorption Spectrophotometer (AAS.) The wastewater analysis showed that Cr in the effluent was reduced up to 99.3 % for an inlet average Cr loading rate of 40 mg/L, COD was reduced by 56-80% for an inlet organic loading varying between 2202 and 8100mg/L and BOD5 was reduced by 66-77% for an inlet organic loading varying between 650 and 1950 mg/L. Nitrate removal ranges from 30% to 57% and ammonia-nitrogen removal ranges from 53% to 82%. P. karake and B. aethiopium were the plants that establish successfully and show higher BOD5, COD and nutrient removal. Despite the high removal of Cr from the influent wastewater, no significant differences in performance were observed between CW units. Plant analysis showed that Roots accumulate significantly higher Cr in all plant species compared with shoots. Roots of T. domingensis showed a high Cr accumulation capability per gram of dry weight (1848 mg/kg DW) followed by C. alteroifolius (1472mg/kg DW), B. aethiopium (180.9 mg/kg DW) and P. Karaka (62.24 mg/kg DW) and B. aethiopium and P. karaka shows higher Cr translocation factor. Constructed wetlands are cost effective and environmentally friendly treatment methods hence can be used us an alternative treatment method in developing countries.
Description: The Thesis Submitted to the School of Graduate Studies of Addis Ababa University in Partial Fulfillment of the Requirement for the Degree of Masters of Science in Environmental Sciences
URI: http://hdl.handle.net/123456789/3382
Appears in:Thesis - Environmental Sciences

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