No abstract

To find a biomarker for denitrification in activated sludge, five denitrifying strains isolated from three wastewater treatment plants were studied. These strains were selected from among 1500 isolates for their excellent denitrifying properties. They denitrify quickly and have no lag phase when switching from aerobic to anoxic conditions. All strains have the cd 1 -type of nitrite reductase.

Since first conceived, the concept of pedagogical content knowledge (PCK) has attracted much attention. Despite being lauded by educationalists as the unique knowledge base of teachers, research on the concept over the past 30 years has yet to result in a universally accepted definition being presented. Much of the contentions surrounding the lack of an agreed upon conception appear to have stemmed from difficulties in understanding the relationship between PCK, other areas of teacher knowledge, teacher beliefs, and enacted practice. This paper considers the application of PCK frameworks to design and technology (D&T) education, through an analysis of the nature of the discipline from an ontological and epistemological perspective and contemporary perspectives on the construct of PCK. It is theorised that the volition afforded to teachers in D&T through weakly framed subject boundaries negates the effective application of PCK frameworks, as teachers' beliefs have a greater impact on enacted practices. In an attempt to better understanding enacted practice in D&T education, the paper proposes a methodological framework centred on the interactions between teachers' beliefs and knowledge in the discipline, through synthesising the concept of amplifiers and filters of practice with the nature of D&T education. The proposed framework outlines the need to recognise individual teachers' conception of capability as a critical influence on enacted practice.

The objective of this study was to set-up a pilot plant and to evaluate its effectiveness for biological nitrogen and organic matter removal from tannery wastewater in Ethiopia. A pilot wastewater treatment plant consisting of a predenitrification-nitrification process was constructed and operated for 6 months. This was fed with a raw tannery wastewater obtained from the Modjo Tannery located 70 km south of the capital, Addis Ababa. Up to 98% total nitrogen and chemical oxygen demand, and 95% ammonium nitrogen removal efficiencies were achieved in the system. The average effluent ammonium nitrogen ranged from 8.4 mg l(-1) to 86.0 mg l(-1), whereas the average effluent for nitrate nitrogen ranged from 2.9 mg l(-1) to 4.4 mg l(-1). The average values of denitrification and nitrification rates determined by nitrate and ammonium uptake rates (NUR and AUR) were 8.0 mg NO3-N [g volatile suspended solids (VSS)](-1) h(-1) and 5.4 mg NH4-N (g VSS)(-1) h(-1), respectively, demonstrating that the treatment processes of the pilot plant were effective. Further studies of the effect of chromium III on AUR showed 50% inhibition at a concentration of 85 mg l(-1), indicating that this metal was not causing process inhibition during performance operations. Thus, the predenitrification-nitrification process was found to be efficient for simultaneous removal of nitrogen and organic substrates from tannery wastewaters.