Characterization and Toxicity Assessment of Wastewater from Rock Phosphate Processing in Tunisia

Phosphate ore processing wastewater (WWPP) from the Gafsa phosphate region of Tunisia was characterized. The WWPP had a very high turbidity, an almost neutral or slightly alkaline pH, and high salinity. The average chemical and biochemical oxygen demands (COD and BOD) met wastewater discharge standards, but the COD/BOD5 (4.34) significantly exceeded biodegradability values. Total nitrogen, residual phosphorus, and some others chemical constituents exceeded wastewater discharge standards. Microbiological enumeration showed that the effluents were very low in microflora. Untreated WWPP and diluted (WWPP/4) inhibited bioluminescence of Vibrio fischeri by 76 and 45%, respectively. The WWPP had a phytotoxicity rate of 20–70%, respectively, for alfalfa and tomato seeds. Adding the effluent to soil for 60 days reduced the residual phytotoxicity of the WWPP-irrigated soil to about 15 and 34%, respectively, for tomato and alfalfa seeds.