Floc compaction during ballasted aggregation

Abstract

Ballasted aggregation, a process using the addition of a ballasting agent to improve the settling performance of flocs, appears particularly appropriate for the treatment of humic rich waters that leads to low-density aggregates. In that context, using an aquagenic humic acid coagulated by ferric chloride in the presence of pozzolana particles as ballasting agent, we show that the origin of improved floc settling in ballasted aggregation is not simply related to an increased specific weight of flocs, but also to a significant restructuring of flocs to a more compact structure induced by the added particles. The floc restructuring is evidenced from the increased lag time before measurable floc growth in the presence of the ballasting agent, the higher fractal dimension of flocs above the micron scale range after incorporation of the particles into the aggregates, and a much smaller sediment volume after settling. A simple model of floc compaction based on the turbulent viscous effects that act on an elastic floc, is described.

Interaction between ballasting agent and flocs in ballasted flocculation for the removal of suspended solids in water

“…5 shows that the turbidity removal decreased slightly from 90 % to 86 % with the dosage of sand. Such trend was also observed by Sieliechi et al that a slight deterioration of the residual turbidity was noted with the increased dosage of pozzolana particles as ballasting agent [12]. The increased dosage of sand resulted in the formation of smaller, isolated, and heavy flocs.…”

“…Ballasting agent such as 47 microsand typically has a high density that could significantly result in a higher settling velocity 48 compared to non-ballasted flocs [11]. According to previous work done, ballasting agent has 49 greater mass than the microflocs formed during the coagulation-flocculation process, which 50 affecting the size of flocs after the aggregation between the former and the latter and increased 51 settling velocity [12]- [14]. Also, ballasting agent has low surface charge density compared to 3 colloidal particles in water.…”

Eco‐friendly synthesis from industrial wastewater of Fe and Cu nanoparticles over NaX zeolite and activity in 4‐nitrophenol reduction

“…Up to now, metal nanoparticles (NPs) such as Cu, Al, Mg, Zn, and Fe and their oxides have been adopted for both liquid and gas phase reactions, either supported or unsupported. Examples of supports are zeolites, carbon, clay, metal oxides, graphene, etc . Their applications include dye abatement in water, organic synthesis, water gas shift, polymerization, and photocatalysis .…”

“…Examples of supports are zeolites, carbon, clay, metal oxides, graphene, etc . Their applications include dye abatement in water, organic synthesis, water gas shift, polymerization, and photocatalysis . Heavy metals in industrial wastewater represent another issue for the ecosystem, in particular for aquatic ecosystems, due to their highly carcinogenic nature and their impossibility to be biodegraded .…”

“…It causes severe consequences over 60 mg/kg . Moreover, excessive Fe in the blood damages the gastrointestinal tract …”