Granulation of biological flocs under elevated pressure: characteristics of granules.

Aerobic granules (AG) have good settling ability and are relatively insensitive to the variation of organic loading rate. When sizes of granules become bigger, substrate and oxygen become limited in the granule core, leading to cell lysis and disintegration of granules. The higher the dissolved oxygen, the deeper the oxygen penetration inside AG. AG operated under elevated pressure might be a possible way to maintain long-term stability of granules. In this study, formation and characteristics of AG in the reactor operated under elevated high pressure (HP) and ambient pressure (AP) are investigated. Results show that both systems removed an average 95% of total organic carbon. Sludge volume index at 5 and 30 min settling times under HP are 35% smaller those under AP, indicating that HP granules have a better settling ability and a denser structure than AP granules. The granule size in the HP system is very uniform, while size distribution in the AP system is broader, indicating that the AP system contains flocculent sludge. Extracellular polymeric substances and polysaccharides (PS) are almost the same for HP and AP; however, exopolymeric protein (PN) is very different. PS/PN ratio for HP sludge is four times that of AP. The result is consistent with sludge settleability, which is improved with increasing PS/PN ratio.

Comparison of high pressure and ambient pressure aerobic granulation sequential batch reactor processes.

Due to granule size, substrate and oxygen become limited in the core of granules leading to cell lysis at the core. Loss of granule stability is still a major barrier for practical application of AG. Compared to ambient pressure condition (AP), operation of AG under high pressure (HP) is a favorable condition for formation and stability of granules. Experimental results show that granulation was facilitated under HP condition. MLSS and size of granules under AP system are higher than those under HP system. However, SS of effluent in AP is higher than those in HP and is consisted mainly of flocculent sludge. Longer SRT and lower biomass yield are obtained in HP system, indicating that less sludge will be produced in HP system. HP system can operate at high nitrogen loading. Complete nitrification was observed earlier in HP, indicating that the growth of NOB was facilitated under high dissolved oxygen.

Dissolution of D2EHPA in liquid-liquid extraction process: implication on metal removal and organic content of the treated water.

Effects of pH, extractant/diluent ratios, and metal concentrations on the extent of extractant dissolution during liquid-liquid extraction were investigated. Experimental result shows that D(2)EHPA dissolution increases dramatically at pH above 4, leveling off at pH 6-7. The phenomenon is consistent with deprotonation of D(2)EHPA and the domination of negatively charged D(2)EHPA species at pH of higher than 4. Concentration of D(2)EHPA in the aqueous phase, i.e., the extent of extractant dissolution, drops after addition of metal and decreases with increasing metal concentration. The amount of D(2)EHPA 're-entering' the organic phase is calculated to be 2.04 mol per mol of Cd added, which is quite closed to the stoichiometric molar ratio of 2 between D(2)EHPA and Cd via ion exchange reaction. The effect of metal species on the extent of extractant/metal complexes re-entering is in the order of Cd ≈ Zn ＞ Ag, which might be coincident to the complexation stability of these metals with D(2)EHPA. The extent of extractant dissolution in liquid-liquid extraction process depends on the type and concentration of metal to be removed, pH of aqueous phase, and extractant/diluent ratios.