Bioassay and use in irrigation of untreated and treated wastewaters from phosphate fertilizer industry

Abstract

Wastewater from phosphate fertilizer industry that contains essentially a significant amount of both fluoride and phosphate was treated by separative precipitation of fluoride ions with hydrated lime. Thus, a phosphate-rich effluent with low content of fluoride was obtained. The microtoxicity of the treated wastewater was then monitored by LUMIStox and its phytotoxicity was investigated on tomato ( Lycopersicon esculentum), wheat ( Triticum aestivum), maize ( Zea mays), ryegrass ( Lolium perenne), and alfalfa ( Medicago sativa) seed germination and plant growth. The cress ( Lepidium sativum) was used as a standard species for the germination index and phytotoxicity evaluation. Seedlings of four species (namely wheat, maize, ryegrass, and alfalfa) were grown in pots, which were irrigated with untreated wastewater, treated wastewater, aqueous solution of triple superphosphate fertilizer (TSP) or with tap water as control. LUMIStox tests showed that lime treatment allowed a significant toxicity removal. The treated water displayed beneficial fertilizing effect on plants. An increase in the germination index from 100% to 119% was observed. However, the untreated wastewater inhibited the species germination even when diluted 10 times. Neither plants mortality nor growth inhibition was observed after 90 days of treated wastewater application. Moreover, an improvement in plant growth, leaf number and a root development were noticed in these plants when compared with those irrigated with tap water or with fertilizer. In contrast, leaf necrosis and growth inhibition were observed in plants amended with raw wastewater. The irrigation with treated wastewater also improved soil labile P content. Indeed, soils amended with treated wastewater had more a double labile P concentration (38.15 mg kg −1) in comparison with control soil (15.53 mg kg −1).