Introduction of fiber plants to plant bed filter systems for wastewater treatment in relation to resource recycling

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Abstract
In order to develop a low-cost and energy-saving technique for wastewater treatment in combination with a resource recycling function, we constructed a plant bed filter ditch in which terrestrial and aquatic plants can be utilized for nitrogen and phosphorus removal from wastewater. The experimental ditch (4.0×0.4×0.4Hm) contained baskets filled with bed filter material (zeolite) and were planted with higher plants. Depending on the ability of the plant species to endure saturation, the height of the zeolite packed in baskets was changed. Kenaf (Hibiscus Cannabinus L.), sunn hemp (Crotalaria juncea L.), and papyrus (Cyperus papyrus L.), which are useful fiber materials, and reed (Phragmites communis Trin.) were tested to evaluate their suitability for use as plant bed filter systems. Phosphorus and nitrogen loading rate to the system during the experiment was 0.24-0.28 and 1.4-1,8 g m−2 d−1, respectively. The addition of higher plants to the ditches enhanced the removal of nitrogen and phosphorus from wastewater as the plant species considerably affected the N and P removal efficiency. Planting of papyrus and kenaf increased the N and P removal efficiency of the system remarkably. The removal of about half or more of P and N from wastewater by the plant bed filter systems depended on plant absorption. Perennial plant papyrus displayed a N and P removal efficiency of more than 50% during 7-8 months. It was observed that nitrification was accelerated in the system containing papyrus and reed in the winter season and the role of aeration by these aquatic plants was analyzed. It was concluded that papyrus was the most suitable plant for the waste-water treatment due to the considerable increase of the P and N removal efficiency of the system, and maintenance of a high removal efficiency for a long period of time. Kenaf was also suitable because of its high wastewater treatment efficiency and importance as paper source.