Algal flocculation performance of modified clay in organic matter environment and its anti-interference mechanism

The efficient management of harmful algal blooms (HABs) is a global concern. The excessive accumulation of organic matter poses a significant challenge to the HABs control. Notably, the efficiency of modified clay, widely used in coastal waters, for controlling HABs will also be affected in organic environments. In this study, the effects of four model organic compounds on the algae removal efficiency of different modified clays were systematically studied. The results show that organic matter markedly impairs the efficacy of inorganic modified clay (PAC/clay), leading to a 30-40% reduction in algae removal efficiency across various organic conditions. Conversely, composite modified clay (Al_nCTS/clay) exhibits superior resistance to interference, limiting efficiency reduction to 5-15%. Mechanism analysis indicates that organic matter substantially diminishes the flocculation performance and algae removal efficiency of modified clay through electrical double layer compression and functional group shielding. The Al_nCTS/clay, characterized by its distinctive comb-like polymer chain, maintained a stable chain structure state in organic-rich environments. Combined with its significantly enhanced surface charge density and abundant Al₁₃ and η-OH functional groups, effectively counteracts the electrical inhibition and spatial shielding effects caused by organic matter, thereby sustaining stable electrical neutralization and sweeping effects. The multi-mechanism synergy ensured the algae removal efficiency in complex organic environments. Importantly, the crucial role of the polymer chain structure and stability in resisting organic matter interference was discovered. This study provides a theoretical basis for the development of HABs control materials in organic-rich environments.