The Effect of Ozonation on Particle Size Distribution for Recirculating Aquacultural Seawater: Analysis of Particle Flocculation and Breakup

摘要

Solids removal is very important for water quality maintenance in recirculating aquaculture systems (RAS). Ozonation is a practical water treatment which can promote the solids removal. However, the characteristics of ozonation effects on particles are still unclear. In this study, the effect of ozonation on particle size distribution (PSD) was investigated for seawater from a RAS of Pacific white shrimp (Litopenaeus Vannamei). Both flocculation and breakup of particles were demonstrated during ozonation treatment, which resulted in changes of PSD. By using a fractal characteristic value (D-f), the flocculation process could be divided into three stages of preparation, growth and steady. Besides, the flocculation efficiency varied parabolically with contact time. A higher ozone dosage resulted in a shorter preparation stage, along with a longer growth stage (namely lasting a longer flocculation effect) and thus a relatively higher limit of parabolic flocculation efficiency. However, the limit would reach a peak and probably be accompanied with a more breakup of particles. The best flocculation efficiency was 43% at ozone dosage of 3.5 mg/L with 5 min contact time. Furthermore, a higher ozone dosage could produce more ammonia.