Biological anoxic phosphorus removal - the dephanox process

Abstract

Simultaneous enhanced biological phosphate uptake and biological denitrification under anoxic conditions were investigated in a modified lab-scale nutrient removal activated sludge system (DEPHANOX). The aim of the experiments was to find whether it can be technologically convenient to use the capability of poly-P bacteria of taking up phosphate under anoxic condition by utilizing nitrate as electron acceptor. An experimental comparison of removal efficiencies with a more conventional treatment flow scheme (JHB), using low influent TKN/COD ratio, was also carried out. Phosphate uptake in anoxic condition was compared to that in oxic environment in batch tests. PHB anoxic and oxic degradation was evaluated by respirometric tests. Results of the long-term operation of continuous-flow lab-scale system as well as results of batch tests showed that the anoxic phosphate uptake with simultaneous denitrification after a previous anaerobic substrate uptake could significantly reduce the extent of competition for organic substrate between poly-P bacteria and denitrifiers. A side-stream nitrification in fixed-film reactor reduced the losses of organic carbon by oxidation and stabilized the slow-growing population of nitrifiers in the system.

Effect of Particulate Biodegradable COD in a Post-Denitrification Enhanced Biological Phosphorus Removal System

“…The system is basically an A 2 process with a side nitrification biofilm stage (3). Although a small oxic zone (5) is provided after the anoxic zone (4), its sole purpose is to strip the N 2 from the sludge for optimal settling.…”

“…Bortone et al [3] previously studied a post-denitrification configuration showing the need of a high total hydraulic retention time (HRT) of 23 h when operating with a low COD/N influent. That configuration named Dephanox, exhibited steady and high P removal efficiency during those experiments.…”

Effect of basic operating parameters on biological phosphorus removal in a continuous-flow anaerobic–anoxic activated sludge system

“…nitrogen and phosphorus) could be efficiently removed from the incoming wastewater. The overall configuration, incorporating external nitrification in the basic design is widely known as the Dephanox process [45]. In this configuration a complete separation of nitrification from the mainstream line, with simultaneous phosphorus removal under anoxic conditions, is achieved.…”

Recent Advances in Biological Nutrient Removal Technology

“…Other strategies are also being evaluated (Bortone, et al, 1996). In summary, it is possible to minimize process carbon requirements in biological phosphorus and nitrogen removal processes by maximizing the growth of PAOs which are able to denitrify.…”