Unraveling the role of ballast surface charge at floc growth behavior in ballasted flocculation

Abstract

This study was emphasized on unraveling the concealed role of surface charge characteristics of employed ballasts at suspended solids interaction with employed ballasts during floc formation in ballasted flocculation (BF). The purpose was to investigate possibilities in surface charge modulation of employed ballasts leading to enhanced aggregation and ballast embedment during floc growth. The ballasts with varied surface charge (-37.8 mV to + 33.6 mV) and equivalent specific gravity (SG: 5.09) were employed in BF process in this study. This Ballasted flocculation study was conducted using a static mixer device in this study, and characteristics of ballasted flocs (size and settling velocity of aggregates) were analyzed by charge coupled device camera. These image analysis investigations revealed that ballast particles and suspended solids experience attractions and repulsions during aggregation subject to ballast surface charge. However, appropriate ballast selection (surface charge characteristics) corresponding to influent characteristics, and optimization of applied ballast concentration (2gL-1) corresponding to ballast surface charge characteristics (SC: +1.23) resulted in 99% clarification (1 NTU residual turbidity) accomplished in a quick settling interval (30 s) with efficient consumption of applied ballasts compared to previous studies. The real-time velocity observations (using CCD camera) also confirmed this rapid clarification exhibiting superficial sedimentation (102.4mh−1) of the aggregated flocs. Therefore, this study concluded that appropriate ballast selection and optimalization of applied ballast concentration corresponding to surface charge characteristics and influent properties can lead to rapid clarification of micropollutants, and instantaneous sedimentation with efficient ballast consumption. This can lead to efficient treatment facility design with shorter hydraulic retention time, compact space requirements, and capability to produce high quality effluent discharge from highly turbid influent.