Study of Duckweed-Based Pond System for the Treatment of Domestic Wastewater

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Addis Ababa University


Existing wastewater treatment technologies such as activated sludge and tertiary nutrient removal systems are too costly to provide a satisfactory solution for the increasing wastewater problems in developing regions. Besides, these technologies do not allow for re-use of valuable nutrients contained in wastewater. In the present study, an aquatic plant duckweed (Lemna minor) was investigated as an alternative cost effective biological tool for the treatment of domestic wastewater to remove concentrations of organic matter, nutrients and pathogens. Duckweed plants were inoculated into semi-batch experimental ponds to treat pretreated and untreated sewage water. The experiments were conducted under outdoor environmental conditions for a period of 21 days. Composite samples were collected under the duckweed mat every seven days. Efficiencies of duckweed for the treatment of domestic wastewater were assessed by measuring some of the physico-chemical parameters and faecal coliforms in the treated wastewater. The observations revealed mean reduction levels of 86.28% BOD5, 82.26% COD, 90.18% TSS, 66.07% NH4 +, 65.26% TKN, 68.84% PO4 3-, 70.58% TP, 97.67% FC for duckweed ponds with untreated sewage and 88.14% BOD5, 86.56% COD, 91.6% TSS, 85.84% NH4 +, 68.20% TKN, 81.01% PO4 3-, 74.21% TP, 98.95% faecal coliforms for duckweed ponds with pretreated sewage. Compared with the Provisional National Environmental Quality Standard, all parameters values of the duckweed effluents except faecal coliforms bacteria were within the standard limit values set by EEPA. However, faecal coliform values fulfilled WHO guideline set to ensure safe reuse of the effluents. The results showed that duckweed can be successfully used for treatment of domestic wastewater. Keywords: Duckweed, Lemna minor, Wastewater, Nutrient



Duckweed, Lemna minor, Wastewater, Nutrient