A method for calculating the surface area of numerically simulated aggregates

• DEM technique was applied to simulate the aggregation of suspended particles.
• Go-chess method was developed to analytically calculate aggregate surface area.
• A correlation was proposed to relate aggregate surface area to aggregate structure.
• Aggregate surface area increased rapidly when Cn < 3.5 and Df < 1.5.
• Fractal theory was applied to convert 2D aggregate outline to 3D surface area.

The success of many industrial processes largely depends on the structural characteristics of aggregates. In intensive aerobic digestion process for wastewater treatment applications, the structural characteristics namely aggregate shape, size and therefore the aggregate surface area strongly influence the transfer of dissolved oxygen from the aeration process to aggregates of harmful contaminants/microorganisms.The aim of this study was to apply Discrete Element Modelling (DEM) techniques to the aggregation of suspended particles (microorganisms) to quantify the available surface area for convection and diffusion as a function of particles number concentration and surface charge. The simulation inputs included particle and fluid characteristics such as particle size and density, solid concentration, suspension pH and ionic strength. A post processing method based on the Go-chess concept was developed to quantify the surface area of aggregate structure. The simulation results showed that whilst an increase in connection points increases the total surface area of the aggregate, this does not necessarily translate into an increase in the surface area available for oxygen transfer as combinations of open and close pores are formed. Aggregate surface area was directly determined by aggregate structural characteristics, and increased rapidly when the coordination number was below 3.5 and the fractal dimension was less than 1.5. A correlation for prediction of aggregate external surface area was also proposed as a function of aggregate structural characteristics in terms of fractal dimension and coordination number.

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