Adaptive Pulse Cleaning Strategy Based on Scaling Behavior and Real-Time Flux Modeling for Direct Contact Membrane Distillation of Boron-Containing Low-Level Radioactive Wastewater

The scaling behavior of boric acid during direct contact membrane distillation (DCMD) treatment of boron-containing low-level radioactive wastewater was investigated, and an adaptive pulse cleaning strategy to sustain long-term performance was developed. A two-stage scaling mechanism was identified: stage I is characterized by rapid flux decline due to concentration/temperature polarization and pore blocking; stage II involves progressive scaling growth, promoted by reduced hydrophobicity and porosity. Both stages fit well with the cake filtration model. A pulse cleaning strategy was developed by periodically increasing cross-flow velocities. Fixed-interval pulse cleaning improved average flux by over 40% and reduced scaling mass by more than 83% compared with the steady-flow operation. To enable real-time cleaning initiation, a mathematical model derived from cake-layer theory was established to simulate flux decline with the instantaneous slope of the fouling coefficient kc serving as the trigger for pulse cleaning. The adaptive strategy was validated over 720 min of operation (39 cleaning cycles). By contrast, the adaptive pulse cleaning strategy maintained the average relative permeate flux above 0.72 throughout the first 240 min, substantially higher than the value of 0.58 achieved with fixed 30 min pulse cleaning. Collectively, the mechanism-guided, real-time adaptive strategy offers a practical and scalable solution for stable long-term DCMD treatment operations.