A computational fluid dynamics (CFD) model that evaluates mechanical mixing in a full-scale anaerobic digester was developed to investigate the influence of sewage sludge rheology on the steady-state digester performance. Mechanical mixing is provided through an impeller located in a draft tube. Use is made of the Multiple Reference Frame model to incorporate the rotating impeller.The non-Newtonian sludge is modeled using the Hershel-Bulkley law because of the yield stress present in the fluid. Water is also used as modeling fluid to illustrate the significant non-Newtonian effects of sewage sludge on mixing patterns. The variation of the sewage sludge rheology as a result of the digestion process is considered to determine its influence on both the required impeller torque and digester mixing patterns. It was found that when modeling the fluid with the HershelBulkley law, the high slope of the sewage stress-strain curve at high shear rates causes significant viscous torque on the impeller surface. Although the overall fluid shear stress property is reduced during digestion, this slope is increased with sludge age, causing an increase in impeller torque for digested sludge due to the high strain rates caused by the pumping impeller. Consideration should be given to using the Bingham law to deal with high strain rates. The overall mixing flow patterns of the digested sludge do however improve slightly.

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A rapid biodiversity assessment was conducted in the Republic of the Congo including a systematic biodiversity study (including a targeted study of mammals), implemented over two seasons. One hundred thirteen recce transects (250 m by 2 m) were undertaken over 34 days of fieldwork. A total of 19 species were detected (3 to genus level only). The encounter rate was 26.65 mammalian signs per km; no differences in numbers of signs between season appeared; however, the dry-season species accumulation pattern was higher than during wet season. Correlation analysis showed increasing density of mammals as distance away from villages, lakes and coast increased. The correlation result is deemed to highlight not only a substantial hunting pressure and avoidance of humans, but also preference for forested habitats noted to appear from 20 km distance from the coast. Using high numbers of relatively short recce transect proved a useful supplementary method for assessing mammalian diversity during rapid biodiversity assessments. Results suggest that 70 recce transects (with a minimum of eight per habitat type) would have been sufficient to yield this information.