Treatment of an isoenzyme of potato apyrase of high adenosine triphosphatase/adenosine diphosphatase (ATPase/ADPase) ratio with iodine, N-acetylimidazole or tetranitromethane inactivates the ATPase activity of this enzyme faster than its ADPase activity. There was protection by substrates with the two last-named substances. This and the appearance of nitrotyrosine suggests the participation of tyrosyl residues in both enzymic activities of potato apyrase. The participation of thiol groups is excluded by the insensitivity of apyrase to p-chloromercuribenzoate. Also, 2-hydroxy-5-nitrobenzyl bromide or carboxymethylation produce the same rate of inactivation of ATPase and ADPase activities. Substrates protect both activities from inactivation. Hydrogen peroxide and photo-oxidation inactivate ATPase activity faster than ADPase activity. There is no protection by substrates. Analysis of pH effects on V(max.) and K(m) suggest different pK values for the amino acid residues at the ATP and ADP sites.
This study was undertaken to analyse the activated sludge of a membrane bioreactor (MBR), the behaviour of extracellular polymeric substances (EPS) and soluble microbial products (SMP) as well as their biopolymers composition, in the activated sludge of a membrane bioreactor (MBR) and their influence on membrane fouling were analysed. For the experiment an experimental fullscale MBR working with real urban wastewater at high hydraulic retention time with a variable sludge-retention time (SRT) was used. The MBR system worked in denitrification/nitrification conformation at a constant flow rate (Q = 0.45 m/h) with a recirculation flow rate of 4Q. The concentrations of SMP in the activated sludge were lower than the concentrations of EPS over the entire study, with humic substances being the main components of the two biopolymers. SMP and, more specifically, SMP carbohydrates, were the most influential biopolymers in membrane fouling, while for EPS and their components, no relation was found with fouling. The SRT and temperature were the operational variables that most influenced the SMP and EPS concentration, causing the increase of SRT and temperature a lower concentration in both biopolymers, although the effect was not the same for all the components, particularly for the EPS carbohydrates, which increased with longer SRTs. Both operational variables were also the ones most influential on the concentration of organic matter of the effluent, due to their effect on the SMP. The volatile suspended solid/total suspended solid (VSS/TSS) ratio in the activated sludge can be applied as a good indicator of the risk of membrane fouling by biopolymers in MBR systems.
Evolution of filamentous bacteria in two full-scale experimental MBR systems (microfiltration and ultrafiltration) was studied during two years. Sludge Retention Time (SRT) and Hydraulic Retention Time (HRT) were modified and acted as variables, together with temperature and variation in loading. With SRT values between 20 and 35 d and HRT between 31 and 40 h, both MBR systems presented a high density of filamentous bacteria, according to the Filamentous Index (FI) and Simplified Technique of Filamentous Count (STFC). Highest density was achieved when contaminant loads were high and temperature was low. However, the elevated presence of filamentous bacteria did not affect the quality of effluent or the permeability of the membranes. Nocardioform bacteria showed a high degree of adaptation to the characteristics of the system. Predominance of Nocardioforms gave rise to isolated episodes of massive growth at temperatures between 15 and 20°C, which in turn caused episodes of intense foaming whose most significant consequence was a loss in biomass, leading to a slight increase in transmembrane pressure. In the light of these results, FI and STFC should not be considered as suitable tools for predicting operational problems deriving from filamentous bacteria in MBR systems, which could be prevented through identification.
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