Salt-modified Opuntia dillenii cactus for turbidity removal in water treatment as an alternative to commercial coagulants

This study explored an eco-friendly, natural alternative to conventional chemical coagulants for treating turbid water. Opuntia dillenii cactus, commonly known as cactus, is treated with NaCl and investigated as a potential coagulant aid with alum. By analyzing the cactus using Fourier Transform Infrared Spectroscopy (FTIR), key functional groups, including carboxylic acid, methoxy, and phenolic groups, are identified, confirming the presence of galacturonic acid, a primary component of pectin in cactus. Initial experiments with cactus without adding salt revealed a modest turbidity-removal efficiency. However, when 20 mg/L cactus was treated with 6% NaCl at an initial turbidity of 400 NTU, 90% turbidity removal was achieved. These findings suggest that NaCl enhances coagulation through a combined mechanism involving improved availability of proteinaceous compounds, enhanced functionality of cactus polysaccharides, and ionic-strength-assisted destabilization of suspended colloidal particles. At lower pH levels (5–6), both commercial clay and prepared kaolinite clay turbid waters showed 80–88% turbidity removal when cactus was treated with the optimum 4% NaCl concentration. Comparative analysis demonstrated that cactus’s coagulation efficiency is comparable to established coagulants like PAC (Poly Aluminium Chloride) and alum. Specifically, cactus achieved an 89% removal efficiency, compared to 90% for PAC and alum, at a 5 mg/L dose. Furthermore, combining cactus with alum presents a promising avenue. When used together, cactus significantly enhances turbidity removal to 94% even with an alum dose as low as 4.5 mg/L. However, practical application at a water treatment facility resulted in an average turbidity removal of 61%, indicating the need for further optimization through dose adjustments or combination with alum to meet regulatory standards. In summary, this study highlights the potential of Opuntia dillenii cactus as an environmentally friendly coagulant and coagulant aid for water treatment, offering possibilities for refinement and real-world implementation.