Evaluation of selected wetland plants for removal of chromium from tannery wastewater in constructed wetlands, Ethiopia

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 Cyprus alternifolius, Typha domingensis, Parawaldeckia karaka and Borassus aethiopum and a fifth unit was left as unvegetated (control). The treatment performance of the systems for total Cr, chemical oxygen demand (COD), biochemical oxygen demand (BOD) and nitrogen under a 5 day hydraulic retention time were analyzed based on HACH manual. The Cr in the plant tissue was analyzed through oven dried 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 up to 80% for an inlet organic loading varying between 2202 and 8100 mg/L and BOD 5 was reduced up to 77% for an inlet organic loading varying between 650 and 1950 mg/L. NO 3 and NH 3-N removal achieved 57 and 82%, respectively. Roots accumulate significantly higher Cr in all plant species when compared with shoots. B. aethiopium and P. karaka shows higher Cr translocation factor than the others. Constructed wetlands are cost effective and environmentally friendly treatment methods in tropical climate hence can be used as an alternative treatment method in developing countries.

<b>Chromium accumulation in maize and cowpea after successive applications of composted tannery sludge

“…Interestingly, maize plants accumulated a relatively higher Cr content in the roots than cowpea plants. This may explain the low translocation to the shoots, considering that the Cr fraction bound to root cells cannot be translocated to the shoots and, therefore, could not be removed in the shoot biomass harvest (Terfie & Asfaw, 2015). Hossner, Loeppert, Newton, and Szaniszlo (1998) reported that dicotyledon species, such as cowpea, uptake and transport more Cr to shoots than monocotyledons, such as maize.…”

Artificial wetlands and floating islands: Use of macrophytes

“…93.3% 69.7 -98,.0% 94.8 -95.4% 69.2 -92.3% 85.3 -89.1% 98.5 -98.7% 92.8 -98.7% 95.5 -96% 93.1 -96.2%. AYAZ et al, 2020 Efficiency of the system, bacterial inoculation with the desired traits has appeared as an effective option (TADESSE et al, 2015) they compared the performance of four macrophytes, Brachia mutica, Typha domingensis, Phragmites australis, and Leptochala fusca, in bacterial-assisted floating treatment wetlands for the purification of five metals (Fe, Mn, Ni, Pb, and Cr) from contaminated river water.…”

“…These metals can accumulate in aquatic organisms and be magnified through food chains and eventually affect human health. The macrophage species Typha latifolia, Hydrilla verticillate and, Eichhornia crassipes have been used in surface flow wetlands, eliminating up to 23% of the Zn content TADESSE et al (2015). XIN et al (2020), SCHUCK and GREGER (2020) andWANG et al…”

Removal capacity of faecal pathogens from wastewater by four wetland vegetation: Typha latifolia, Cyperus papyrus, Cyperus alternifolius and Phragmites australis

“…Unique due to its C4 photosynthetic pathway (Mnaya et al, 2007) -->98% (Kansiime and Mwesigye, 2012;Abou-Elela et al, 2014) Kenya (Vymazal, 2013); Ethiopia (Tadesse, 2010); Uganda (Okurut et al, 1999;Kansiime and Mwesigye, 2012).…”