The structural and hydrodynamic features for granules were characterized using settling experiments, predefined mathematical simulations and ImageJ-particle analyses. This study describes the rheological characterization of these biologically immobilized aggregates under non-Newtonian flows. The second order dimensional analysis defined as D2=1.795 for native clusters and D2=1.099 for dewatered clusters and a characteristic three-dimensional fractal dimension of 2.46 depicts that these relatively porous and differentially permeable fractals had a structural configuration in close proximity with that described for a compact sphere formed via cluster-cluster aggregation. The three-dimensional fractal dimension calculated via settling-fractal correlation, U∝l(D) to characterize immobilized granules validates the quantitative measurements used for describing its structural integrity and aggregate complexity. These results suggest that scaling relationships based on fractal geometry are vital for quantifying the effects of different laminar conditions on the aggregates' morphology and characteristics such as density, porosity, and projected surface area.
In this study, a two-stage domesticated shear-loop anaerobic contact stabilization (SLACS) system is introduced as a new reactor design to enhance methane productivity with significant reduction in hydrogen sulphide (H2S) synthesis. Due to the rich sulfate content in industrial wastewaters, the initial fermentation phase of anaerobic digestion is highly acidifying and often leads to severe performance losses, digester's instability, and even culture crash. The SLACS system functions as a dissimilatory sulfate reduction - methanogenic reactor consisting of two compartments, a shear-loop anaerobic bed (SLAB) unit and an anaerobic plug flow (APF) unit. The functional role of the SLAB unit is not limited to acidogenesis but also sulfidogenic processes, which curtails H2S generation in the APF unit (methanogenic stage). Experimental observations indicated that pH serves a critical role in the cohabitation of acidogenic and sulfidogenic microbes in the SLAB unit. Although acidogenesis was not influenced by pH within the range of 4.5-6.0, it is vital to stabilize the pH of this unit at 5.4 to establish a steady sulfate reduction of above 75%. The highest desulfurization achieved in this compartment was 88% under a hydraulic retention time (HRT) of 4 h. With an average methane productivity of 256 mL g-1 VS, the methanogenic performance of the two-stage domesticated SLACS system shows a 32% methanogenic proficiency higher than that of the one-stage digestion system. Microbial community structure within the system carried out via Next Generation Sequencing (NGS) provided qualitative data on the sludge's sulfidogenic and methanogenic performance.