Effect of particle size distribution on turbidity under various water quality levels during flocculation processes

• Large particles formed through combining smaller flocci and monomeric particles.
• Larger particles have prominent contribution on water turbidity.
• Fractal dimension of particles was used to evaluate smaller particle number.
• Flocculation process was divided into four stages.

The dynamic relationship between particle size distribution and water turbidity was characterized using online real-time monitoring devices to explore the impact of particle size distribution on water quality. Particle amount was proportional to water turbidity in the range of 0–40 NTU, whereas the correlation was rather poor in the range of 40–100 NTU. The number of particles smaller than 5 μm (Nd < 5) should be strictly monitored and controlled in water treatment works (WTWs) due to their complex behaviors. The fractal dimension of particles (dpf) is well suited to characterize particle size distribution under different water turbidities. The first derivative of dpf was firstly used to explain the relationship between dpf and the percentage of Nd < 5, and the turbidity and dpf values could be used together to monitor the temporal evolution of the number of smaller particles. A new block method for analyzing flocculation processes was proposed based on the change in dpf. The particle counting method was more sensitive to the evolution of particle size, which allowed a better understanding of the impact of particle size distribution on water turbidity.

Dynamic analysis on the variation of particle size distribution was characterized by the on-line particle counter. The flocculation process was divided into four different stages on the basis of the variation of dpf over the flocculation time, since the value of dpf was able to conduct real-time detection and be more extensively used in WTWs with the further improvement of fractal theory.Figure optionsDownload as PowerPoint slide