Testing the potential of aquatic plants to treat abattoir effluent

The potential of 3 genera of emergent aquatic plant species ( Typha spp, Phragmites and Scirpus) to ameliorate effluent from a poultry abattoir was evaluated in an experimental trench system. Three plastic-lined trenches containing Typha (two species), Phragmites and Scirpus plants in a gravel substrate were constructed near the abattoir. Effluent was allowed to percolate, with retention times of 2.7–3.6 days, through the trenches. The quality of the inflowing and outflowing effluent was compared by a regular sampling program for suspended solids, conductivity, turbidity, pH, dissolved oxygen, Na, K, Cl, N and P concentrations. The importance of water loss by evapotranspiration was investigated. Comparing the inflow to outflow, each trench system successfully reduced the suspended solids (83–89%), turbidity (58–67%), total nitrogen (14–56%) and total phosphorus (37–61%) concentration of the effluent while maintaining an acceptable pH and in the case of the Phragmites and Scirpus systems oxygenating the anaerobic inflow. Conductivity increased in the Typha and Phragmites trenches. If a correction is made for water lost by evapotranspiration, the three experimental trench systems reduced the nitrogen (42–75%), phosphorus (68–79%), sodium (7–34%), potassium (9–56%) content of the effluent. The chloride content of the effluent in the Phragmites system was increased by 15% but was reduced by 31 and 53% in the Typha and Scirpus systems respectively. The results from this initial experiment give an indication of the relative abilities of the three plant systems to treat the wastewater from the abattoir. Of the three, that containing the Scirpus was superior.