Quantifying the 3D structure and function of porosity and pore space in natural sediment flocs

Abstract

Purpose Flocculated cohesive suspended sediments (flocs) play an important role in all aquatic environments, facilitating the transport and deposition of sediment and associated contaminants with consequences for aquatic health, material fluxes, and morphological evolution. Accurate modelling of the transport and behaviour of these sediments is critical for a variety of activities including fisheries, aquaculture, shipping, and waste and pollution management and this requires accurate measurement of the physical properties of flocs including porosity. Methods Despite the importance of understanding floc porosity, measurement approaches are indirect or inferential. Here, using μCT, a novel processing and analysis protocol, we directly quantify porosity in natural sediment flocs. For the first time, the complexity of floc pore spaces is observed in 3-dimensions, enabling the identification and quantification of important pore space and pore network characteristics, namely 3D pore diameter, volume, shape, tortuosity, and connectivity. Results We report on the complexity of floc pore space and differentiate effective and isolated pore space enabling new understanding of the hydraulic functioning of floc porosity. We demonstrate that current methodological approaches are overestimating floc porosity by c. 30%. Conclusion These new data have implications for our understanding of the controls on floc dynamics and the function of floc porosity and can improve the parameterisation of current cohesive sediment transport models.

Dehydration Performance of Municipal Sludge and Its Dewatering Conditioning Methods: A Review

“…The resulting sludge floc is an irregular construction with pores and holes. 35 Bacteria in sewage will gather through the hydrophobic attraction effect, forming a diameter of 100−200 μm cell cluster (or bacterial colony). The cell clusters then bind together by the interaction of their own secreted extracellular substances to compose a larger sludge granule.…”

“…The morphological characteristics of sludge indicate that the sludge is formed by the collision and adhesion of tiny particles step by step. The resulting sludge floc is an irregular construction with pores and holes . Bacteria in sewage will gather through the hydrophobic attraction effect, forming a diameter of 100–200 μm cell cluster (or bacterial colony).…”

Unveiling the Vertical Migration of Microplastics with Suspended Particulate Matter in the Estuarine Environment: Roles of Salinity, Particle Properties, and Hydrodynamics

“…The estuarine environment has long been considered an effective trap for fluvial and marine sediments, leading to high concentrations of suspended particulate matter (SPM). , In turn, in the presence of large quantities of SPM, heteroaggregation is more likely to occur, promoting the settling of MPs in the water column. On the basis of particle properties, SPM can be classified as either cohesive SPM (i.e., clay and silt) or noncohesive SPM (i.e., sand particles) depending on their differential physicochemical attractiveness. , Compared to noncohesive SPM, cohesive SPM has a greater adsorption capacity, and this has a significant impact on the adsorption, accumulation, and migration of pollutants. − Therefore, most studies in this area have focused on the interaction between pollutants and cohesive SPM. − In practice, both types of SPM are widely present in estuaries. In previous studies on MP settling with SPM, only the type of cohesive SPM, or sediments as a whole, has been employed, , while the difference in the effect of cohesive SPM versus noncohesive SPM on MP settling has received relatively little attention.…”

A novel 3D volumetric method for directly quantifying porosity and pore space morphology in flocculated suspended sediments

“…ImageJ/Fiji 40 is widely used as a package for analysing image data, as it includes a set of tools and plugins that allows 3D volumetric quantification and analysis, including MorphoLibJ [44] and BoneJ [45] . Until recently however, an approach utilizing these tools has not been developed to quantify and analyse flocculated sediments in 3D [46] . We have developed a protocol to post-process, segment, quantify and analyse 3D micro-computed tomography scan data of flocs.…”

“…This protocol has been developed, and tested, for use in flocs [46] , but could be applied to any sediment or aggregate application where structural boundaries are not clear, or where existing methods use assumptions/proxies rather than direct measurements. This is because the protocol presented here directly measures the object in question, rather than sampling the material of an object.…”