Nutrient removal and biomass production in land treatment systems receiving domestic effluent

Land application of pre-treated wastewater is increasingly practiced to achieve both treatment and beneficial reuse of applied effluent. Vegetation is an important component of these systems, affecting hydraulic loading and nutrient uptake and hence treatment efficiency. This work investigated the effect of plant species (Acacia cyanophylla, Eucalyptus camaldulensis, Populus nigra and Arundo donax), on water requirements, nutrient removal, water use efficiency (WUE) and biomass production in land treatment systems (LTS) in which pre-treated wastewater was applied at rates to meet crop evapotranspiration. Vegetation had a strong effect on all the parameters monitored during this trial. A. cyanophylla produced the greatest amount of biomass and showed the highest irrigation requirements and WUE, followed by E. camaldulensis, A. donax and P. nigra. In addition, A. cyanophylla and A. donax achieved a higher leaf-N content compared to other species. As a result of the differences in tissue nutrient content and biomass, A. cyanophylla accumulated 23, 20, and 70% more N in hypergeous biomass than E. camaldulensis, A. donax and P. nigra, respectively. A. cyanophylla and E. camaldulensis accumulated 57 and 53% respectively more P than did P. nigra and A. donax. Therefore substantial improvement of the performance of the LTS in terms of nutrient removal can be achieved through the selection of appropriate plant species. Despite the enhanced growth rates observed in the study nutrient recovery by vegetation did not exceed 31 and 35% of the applied N and P, respectively. The relatively low percentages of removal are attributed to increased concentration of nutrients in effluent and the high ET rates prevailing in the study area. These findings suggest that additional practices are required to mitigate environmental impacts arising from excessive nutrient loads when effluent is applied at rates to meet crop water requirements.