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An Ecosystem Approach to the Treatment of Waste Waters¹

ABSTRACT

Aquatic plants such as bulrush (Scirpus spp) and cattail (Typha spp) were used to purify untreated municipal sewage in experimental tanks in a growth chamber measuring 5.5 by 3.7 by 3.7 m high. Initial concentrations of total phosphorus (TP) and total Kjeldahl nitrogen (TKN) before treatment ranged from 3.9 to 29.0 ppm for TP and from 10.3 to 44.0 ppm for TKN. Rates of removal of phosphorus and Kjeldahl nitrogen by the plants were monitored and compared with a control without plants. Generally, the concentrations of TP and TKN decreased exponentially in the treatment trays during the individual experimental runs. High rates of purification, up to 98%, were achieved in <20 days. During the 20 experimental runs lasting >500 days the plants showed unabated ability to remove nutrients while the control achieved a saturated condition.

Rates of nutrient uptake by the experimental plants increased with the ambient concentration and were much faster than the rates predicted by Michaelis-Menten kinetics. Above-water biomass obtained by periodic harvesting showed that the plants contained high levels of digestible organic matter (DOM) and crude protein comparable to the values obtainable from alfalfa. Experimental data have been used to develop equations for large-scale in situ applications. Data presented here show that aquatic plants have considerable potential in the purification of municipal waste waters within reasonably short periods.

Key Words: aquatic plants • bulrush • cattail • sewage • nutrient uptake • teritiary treatment • biomass feed value • Michaelis-Menton kinetics

¹ Contribution from the Engineering Div., Saskatchewan Research Council, 30 Campus Drive, Saskatoon, Saskatchewan, Canada, S7N OK1.

² Senior Research Scientist, Engineering Div.

Received for publication November 13, 1978.