Chromium removal within constructed wetlands.
Dotro, Gabriela*,1, Palazolo, Paul1, Larsen, Daniel1, 1 The University of Memphis, Memphis, TN
ABSTRACT- Wastewaters from tanneries are notoriously difficult to treat. Because of this and their small scale of operation, many tanneries in the developing world lack the capital required to develop and operate treatment methods to produce an environmentally-friendly effluent. Constructed wetlands are being utilized to provide an alternative method of treatment for tanneries to reduce the organic loadings of the effluent. However, the fate of chromium contained in these wastewaters, a metal whose toxicity is much debated, has not been documented to date. Nine experimental wetlands were built at the University of Memphis to determine the partitioning of chromium inside laboratory scale systems. Duplicate wetlands were operated with variability in three parameters: adsorption onto media, plant effects, and intermittent feed operation. An additional set of wetlands were operated as a control. The experiment goals were to determine where the chromium accumulated in the wetland system, and if intermittent loading affected system performance. Results show organic load and chromium reductions of 95-99% and 90-99%, respectively. Chromium removal performances were statistically different for all systems (p<0.01), except when comparing the control against the intermittent feed systems (p>0.05). Analysis of plant tissues revealed that total Cr accumulated represented less than 1% of the chromium removed, and this was in decreasing order: roots > shoots > surface of roots. Scanning electron microscope analysis confirmed minimal Cr on roots and the presence of Cr and biomass on the gravel surface. The hypothesized chromium removal through sedimentation and adsorption onto media and litter matter will be further evaluated through sequential extractions from wetland media and sediments.
Key words: constructed wetlands for effluent treatment, chromium partitioning in artificial wetlands, environmental engineering for developing countries
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