Viscous and filamentous bulking in activated sludge: Rheological and hydrodynamic modelling based on experimental data.

Although achieving good activated sludge settleability is a key requirement for meeting effluent quality criteria, wastewater treatment plants often face undesired floc structure changes. Filamentous bulking has widely been studied, however, viscous sludge formation much less investigated so far. Our main goal was to find relationship between sludge floc structure and related rheological properties, moreover, to estimate pressure loss in pipe networks through hydrodynamic modelling of the non-Newtonian flows in case of well settling (ideal-like), viscous and filamentous sludge. Severe viscous and filamentous kinds of bulking were generated separately in continuous-flow lab-scale systems initially seeded with the same reference (ideal-like) biomass and the entire evolution of viscous and filamentous bulking was monitored. The results suggested correlation between the rheological properties and the floc structure transformations, and showed the most appropriate fit for the Herschel-Bulkley model (vs. Power-law and Bingham). Validated computational fluid dynamics studies estimated the pipe pressure loss in a wide Reynolds number range for the initial well settling (reference) and the final viscous and filamentous sludge as well. A practical standard modelling protocol was developed for improving energy efficiency of sludge pumping in different floc structure scenarios.

Synthesis and amphiphilic properties of glycosyl-1,4-benzodiazepin-2,5-diones.

Glycosyl-1,4-benzodiazepin-2,5-diones were prepared by coupling polyhydroxylated groups at N-1 of the corresponding benzodiazepine. The groups include 1-deoxy-D,L-xylit-1-yl, 6-deoxy-D-glucopyranos-6-yl, and 6-deoxy-3-OR-D-glucopyranos-6-yl (R = n-CnH(2n +1); n = 8, 12, and 16). The structural variations of the sugar group allowed comparison of such amphiphilic data as water solubility (Sw), critical micelle concentration (CMC), and corresponding surface tension (gamma) values. At 25 degrees C, unsubstituted benzodiazepines have Sw values from 0.9 to 4.2 10(-3) mol L(-1), whereas xylit-1-yl and 6-deoxy-D-glucopyranos-6-yl derivatives are, respectively, 7.4-25 and 58-204 times more soluble. Also, compounds with R = n-C8H17 are more soluble than corresponding benzodiazepines (1.4-5.8 times) and give micelles with CMC from 2.7 to 5.6 10(-3) mol L(-1) and corresponding gamma from 29 to 37 mN m(-1). In contrast, compounds with R = n-C12H25 and n-C16H33 are not soluble enough to reach the critical micelle concentration.

Effects of tail alkyl chain length (n), head group structure and junction (Z) on amphiphilic properties of 1-Z-R-D,L-xylitol compounds (R = CnH2n+1).

In the family of 1-Z-R-D,L-xylitol, we have determined the main amphiphilic properties of esters (Z = OCO) as a function of alkyl chain length (R = CnH2n+1, n = 4-17). A classical decrease of critical micelle concentration with the increase in the alkyl chain has been found. With water, esters displayed lamellar phases at temperatures of 25 degrees C or higher. The extent of hydrophilic/lipophilic balance range obtained by emulsification method can be proven to be of interest for pharmaceutical applications. The results were compared with those obtained in previous investigations, i.e. for alkyl-substituted xylitol, with thioether (Z=S) and ether (Z=O) linking groups in order to discuss the role of the junction nature. Likewise, they were compiled with the results related to their D-glucose homologues, in order to put forward the effects of the head group configuration, cyclic or acyclic.