An excess of filamentous bacteria is a common settlement problem affecting the activated sludge process. In this study activated sludge morphology was monitored by image analysis and laser scattering. These were compared with the conventional sludge volume index. Good correlations between the two optical techniques for floc size were found when the small and interfering particles (< 50 ìm) were removed from the analysis (activated sludge size 100-500 ìm). A simpler image analysis procedure was developed using common software and equipment available in most laboratories. This should enable reproducible microbial morphology measurements to be used more widely routinely to predict the onset of poor settlement. The image analysis was used to determine the standard index of filamentinduced poor settlement, namely the total extended filament length. The results in common with some previously noted work did not show a simple link between either floc size or total extended filament length and sludge volume index. A new indicator of excess filaments is suggested, based on the frequency of occurrence of just the long extended filaments (> 100 ìm) which was shown to give better prediction of poor settlement (bulking).

The electronic structures of potassium doped ZnO have been calculated by first principles plane wave-function psuedopotential approach based on density-functional theory and local density approximation. Properties of some defects were studied in order to explicate the conductivity mechanism of p-K:ZnO, including hydrogen interstitial (Hi), oxygen vacancy (VO), zinc interstitial (Zni) and zinc vacancy (VZn). The calculated results revealed that: (1) K-doping introduced a shallow acceptor,besides increasing the system total energy simultaneously. (2) K-H:ZnO decreased the system energy and increased the system stability. (3) Although the formation of VO was more difficult than that of Zni, both of them were electronegative centers and played a role in compensating for the acceptors. (4) VZn produceda shallow acceptor approximately 0.5 eV above the maximum valence band, which was beneficial for p-type conductivity. Finally, it was proposed that the realization of p-type conductivity in K:ZnO may be due to the formation of a KZn-O-Hi-O-VZn complex.

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