Enhancement of coagulation-flocculation using Opuntia ficus-indica mucilage for turbidity removal: Ain Zada dam (Algeria)

Surface water quality deterioration presents critical challenges for drinking water production in arid regions, where sustainable treatment solutions are essential. This study investigates Opuntia ficus-indica (OFI) mucilage as a natural coagulant aid for turbidity removal from Ain Zada dam water in northeastern Algeria. We systematically evaluated coagulation-flocculation parameters including pH (4-10), four coagulants (aluminum sulfate, aluminum chloride, ferric sulfate, ferric chloride) at 100-500 mg L-1, mixing conditions, settling time, pre-chlorination, and OFI mucilage (10-150 mL). Jar tests on water with 74-201 NTU turbidity revealed mixed organic-inorganic composition (60-70% organic colloids). A key finding is coagulant-specific compatibility with OFI mucilage: aluminum-based coagulants showed significant enhancement (aluminum sulfate improved from 57.69% to 75.77%; aluminum chloride from 68.61% to 81.85% with 10 mL mucilage per liter), while iron-based coagulants exhibited reduced efficiency (ferric sulfate decreased from 76.19% to 70.59%; ferric chloride from 79.62% to 74.43%), indicating fundamentally distinct chemical interactions between metal hydroxide surface chemistry and anionic mucilage polysaccharides. Pre-chlorination enhanced treatment to 82.85% removal while enabling 75% coagulant dose reduction. This work provides mechanistic insights into cactus-derived biopolymer integration in conventional water treatment, establishing design guidelines for sustainable implementation in arid regions where Opuntia ficus-indica is abundant.