Abstract
The aim of this study was to evaluate the removal of faecal bacteria and nutrients from domestic wastewater, in surface flow wetlands vegetated with Echinochloa pyramidalis. Horizontal surface flow (HSF) wetlands were fed with primarily treated domestic wastewater at organic loading rates varying from 20.74 to 27.15 g BOD/m2/day for two consecutive years. Water samples were collected at two weeks interval from the inflow and the outflow of the treatment wetlands for physicochemical and faecal bacteria analyses. Physicochemical parameters with highest removal rates were total suspended solids (TSS, 62-80%), Nitrates (57-73 %) and PO4-3 (57-84 %). Faecal indicators reductions of 1.4 and 0.3 log units (1st year) and 1.15 and 0.65 log units (2nd year) were respectively recorded in the vegetated and the control wetlands. Reductions of total coliforms, faecal coliforms and faecal streptococci were significantly higher in the vegetated wetland than in the non-vegetated control in both seasons of the first year. In the contrary, there was no significant difference in the removal rates of faecal indicators between vegetated wetland and the non-vegetated control during the dry season of the second year. Wetlands vegetated with E. pyramidalis was proven to be continuously efficient in the removal of faecal indicators for the two years of study, with no significant differences between the seasons of the year and between the years. Key words: Wastewater, wetlands, Echinochloa pyramidalis, faecal bacteria removal, nutrients removal
Highlights
Constructed wetlands (CWs) have been used as promising wastewater treatment alternatives to the more expensive conventional systems, especially in developing countries (Kivaisi, 2001; Song et al, 2006)
Average reductions of 1.6 and 0.35 log units were respectively observed at the outlets of the vegetated and non vegetated control wetlands during the dry season and 1.2 and 0.27 log units during the rainy season
The constructed wetland vegetated with E. pyramidalis in a horizontal surface flow configuration (HSF) was continuously efficient in the removal of faecal indicator bacteria from domestic wastewater for the two years, with no significant differences existing between the seasons of the year and between the years
Summary
Constructed wetlands (CWs) have been used as promising wastewater treatment alternatives to the more expensive conventional systems, especially in developing countries (Kivaisi, 2001; Song et al, 2006). They produce high quality effluent at low investment cost, simple operation and with very low energy dissipation (Ayaz and Akca, 2001). They help greatly to reduce the health hazards associated with the waste disposal methods in most developing countries (Gilbert et al, 1976; Mburu et al, 2008). Several studies reporting on microbial water quality improvement have shown that constructed wetlands reduce microorganism populations in wastewater at varying but significant degree of effectiveness
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