Physico-Chemical Characterization and Phytotoxicity Assessment of Wastewater from Rock Phosphate Processing in Tunisia: From Seed Germination to Seedling Growth

Abstract

CPG’s wastewater from phosphate ore processing was characterized and its phytotoxicity before and after physicochemical treatment inside washing units was investigated for the first time. Mineralogical, spectral, physicochemical and microbiological characterizations showed that these wastewaters are relatively alkaline due to the high calcium and phosphorus contents. In fact, numerous minerals mainly fluorapatite, clinoptilolite and gypse were identified. In addition to its high salinity (EC = 9890 µS cm⁻¹), the BOD₅/COD ratio is equal to 0.949, which allows for the estimation that this effluent is potentially biodegradable. The microbiological characterization revealed the presence of revivable aerobic bacteria as; total coliforms (TC), fecal coliforms (FC), Pseudomonas, anaerobic sulfite bacteria (ASR), and fungi (F), whereas a complete absence of Salmonella, Vibrio cholera (CV), and Helminth egg (HE) was noted. In the second part, the influence of varying concentrations of phosphate wastewater was studied on radish, lentil, wheat and fenugreek seeds. Phosphate effluents were provided at 10%, 25%, 50%, 75% and 100%. Results were compared with a control group of the same seeds, irrigated with tap water. Based on several germination tests, plant irrigated with treated or untreated effluent exhibited a prominent reduction in growth traits at all four harvests. Except plant treated with treated effluent at 25% which generally induced no significant phytotoxicity to all species and which can play a fertilizer role. The adverse effects occurred with effluent-dose dependent manner. The high toxicity of untreated effluent compared to the treated effluent was inferred from the results. Nevertheless, the treated ffluent is still toxic, except at very low concentrations acting as a fertilizer.

Graphical Abstract

Keywords:

• Environmental pollution
• Germination tests
• Heavy metals
• Phosphate effluent
• Phytotoxicity

Acknowledgements

The authors of this research acknowledged the efforts of the laboratory staff of the regional laboratory of hygiene of Gafsa, Basic health group Gafsa, especially Mr Aderrazak Fajraoui towards the success of this work.

Disclosure statement

No potential conflict of interest was reported by the author(s).