Use of higher plants and bed filter materials for domestic wastewater treatment in relation to resource recycling

Abstract

A bench scale experiment was conducted to compare the effectiveness of three kinds of bed filters (zeolite, zeolite + shell fossils, charcoal chips) and five plant species (Chinese water spinach (Ipomea aquatica Forskal), rice (Oryza sativa L. cv. Takanari), zinnia (Zinnia elegance L.), watercress (Nasturtium officinale R. Br.), stock (Matthiona incana R. Br.)) for use as plant-bed filter systems in order to develop low cost and energy-saving devices for wastewater treatment combined with resource recycling and amenity functions. Pots (0.05 m²) filled with bed filter materials were prepared as experimental systems.

The addition of higher plants to the bed filters enhanced the nitrogen and phosphorus removal from wastewater as plant species considerably affected the P and N removal efficiency. In the summer-autumn season (June-December), Chinese water spinach and rice were more effective than zinnia. In the winter-spring season (January-May), watercress was more effective than stock. Although the effectiveness of the addition of plants to the system on removal of total organic carbon was not conclusive, the use of zeolite and zeolite + shell fossil bed filters was superior to that of charcoal chips for P and N removal.

The system consisting of zeolite + shell fossil bed filter planted with Chinese water spinach in June-December and watercress in January-May showed the highest P and N removal efficiency, i.e. more than 80% during the experimental period. This system removed 91% of P and 90% of N in the inflow and the average removal rate of P and N was 0.11 and 0.42 g per m² per d, respectively.

Key Words:

• Chinese water spinach
• nitrogen and phosphorus removal
• plant-bed filter
• watercress
• wastewater treatment