Sekiranda, S.B.K.

National Agricultural Research Organisation (NARO), Fisheries Resources Research Institute (FIRRI), P.O. Box 343, Jinja, Uganda. E-mail: firi@infocom.co.ug

Efficiency of Phragmites mauritianus in removal of nutrients to improve water quality.

Wetland plants can be utilised to improve water quality, including wastewater purification. The feasibility of using artificial wetlands to improve pre-settled wastewater quality, which has yet to be used in Uganda, was tested using 40 L experimental buckets (mesocosms). The aim of this study was to examine the use of Phragmites mauritianus to treat pre-settled wastewater for Phosphorus (P) and nitrogen (N). Changes in P and N loads of settled wastewater applied to and outflows from potted P. mauritianus were evaluated. The experimental buckets were operated in an intermittent, vertical flow mode. Removal efficiencies were calculated as (inlet load-outlet load\inlet load) X 100%.

Results showed that laterite-gravel rooted Phragmites buckets were more efficient (5% N and 8% P in the outflow) than ones with floating plants (12% N and 25% P in the outflow) for wastewater upgrading. The laterite-gravel rooted Phragmites buckets improved wastewater quality to excellent secondary or tertiary water quality levels. These buckets achieved a reduction efficiency of over 90 % for P and over 60% for N after a 5- day water retention time. Furthermore, the mass balances of N and P over the reactors indicated a higher P uptake rate by the plant than for N (i.e. P (54%) N (29%)) plant uptake for Laterite-gravel rooted Phragmites. This study proved that the treatment method using Phragmites mauritianus when rooted in a suitable substrate is an effective way of improving wastewater quality.