HYDROPONIC TERTIARY-TREATMENT

Three macrophytes are found to grow well in trenches filled with a sec ondary effluent of a wastewater treatment plant in the absence of any support medium: Canna, Cyperus and Paspalum. Daily concentration chang es of nutrients in the wastewater as well as evapotranspiration of the macrophytes were studied batchwise. After the vegetation had covered the trenches fully, the plants removed daily, 1.2-2.6 g of total nitro gen, 0.24-0.33 g of phosphate-phosphorus and 0.3-0.9 g of sulphate-sul phur per sq m. While ammonium and phosphate concentrations always decr eased in water, sulphate was found to increase due to evapotranspirati on. The daily water losses due to the latter was up to 20 l . m(-2) on sunny days. It was found that for extended nutrient removal under the se conditions a hydroponic tertiary treatment plant could possibly pro duce no effluent at all. After harvesting, the aerial parts of the pla nt tissue contained comparable ash contents of 0.8-0.95% on wet base. Elementary analysis showed similar N and P contents of 23-26 g/kg and 2.3-3.8 g/kg respectively and differences in some inorganic elements o f up to an order of magnitude between the three plants. Copyright (C) 1996 Elsevier Science Ltd.