Impact of pH on the Treatment of Artificial Textile Wastewater Containing Azo Dyes Using Pond Systems

Two controlled experiments were operated to evaluate the impact of pH on the treatment efficiency of azo dyes within artificial textile wastewater using ponds as a polishing step. The objectives were to assess the (1) inflow water quality; (2) the presence of Lemna minor and the algae Oedogonium spp. on the dye removal and the outflow water quality; and (3) suitability of applying artificial textile wastewater and the impact of this wastewater and the dye on plants. Findings indicate that the shallow ponds planted with L. minor and/or algae treated the dye Basic Red 46 (BR46) significantly (p < 0.05) higher than the control ponds without any significant (p > 0.05) impact of pH. The potential of L. minor and algae for removal of BR46 was 31% and 25%, respectively. The removal of BR46 was around 89% for ponds planted with L. minor and algae, 58% for algae ponds and 33% for control ponds. Wetlands with L. minor are successful and economic in the complete degradation of BR46 at concentrations of 10 mg L⁻¹ for any pH value between 6 and 9. The removal of ammonium-nitrogen (NH₄-N), nitrate-nitrogen (NO₃-N) and ortho-phosphate-phosphorus (PO₄-P) was higher in planted than in unplanted ponds. The mean outflow values of chemical oxygen demand, NH₄-N, NO₃-N, suspended solids and total dissolved solids were within the limits for safe discharge. The artificial wastewater constituents after dilution (1 part of artificial wastewater to 24 parts of raw water) were suitable to use within the treatment system containing L. minor. Planted ponds treat Basic Red 46 significantly better than other dyes and controls.No significant impact for systems at pH values of 6 and 9 regarding dye removal.Chemical oxygen demand and suspended/dissolved solids outflows were acceptable.Ammonium-nitrogen and nitrate-nitrogen outflows were below discharge thresholds.Diluted artificial wastewater and the presence dyes inhibited Lemna minor growth.