Study of Duckweed-Based Pond System for the Treatment of Domestic Wastewater
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Date
2016-06
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Addis Ababa University
Abstract
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
Description
Keywords
Duckweed, Lemna minor, Wastewater, Nutrient