Visibility Graph Analysis of Particle Size Distribution During Flocculation for Water Treatment

Abstract

Water and wastewater physicochemical treatments often rely on coagulation and flocculation to generate aggregates adequate for separation. Floc development may be assessed by particle size distribution (PSD) using dynamic light scattering techniques (DLS) available in commercial equipment. The DLS output data, however, often presents high variability, which may hinder comparisons of the aggregation time series for different conditions. The Visibility Graph (VG), a novel approach to be applied within the sanitation context, may be an alternative to disclose properties of these highly oscillatory monitoring results. In this study, after defining ideal shear rates and mixing times for the treatability of high-turbidity test water, we monitored PSD after coagulation using metallic salts (ferric chloride and ferric sulfate) and a natural coagulant (Opuntia cochenillifera). PSD data was converted to visibility networks and measurements were obtained to describe these time series by the VG technique. Although no series patterns were found, the VG approach shed some light onto the PSD through time, but no inferences were scaled to the treatability aspect. The limitations for the VG method in this study are mainly due to the small time series; thus, we endorse that visibility network analysis may be a promising technique within the environmental and sanitation context.