Evaluation of the integration of P recovery, polyhydroxyalkanoate production and short cut nitrogen removal in a mainstream wastewater treatment process

Wastewater treatment systems are nowadays evolving into systems where energy and resources are recovered from wastewater. This work presents the long term operation of a demo-scale pilot plant (7.8 m(3)) with a novel configuration named as mainstream SCEPPHAR (ShortCut Enhanced Phosphorus and polyhydroxyalkanoate (PHA) Recovery) and based on two sequencing batch reactors (R1-HET and R2-AUT). This is the first report of an implementation at demo scale and under relevant operational conditions of the simultaneous integration of shortcut nitrification, P recovery and production of sludge with a higher PHA content than conventional activated sludge. An operating period under full nitrification mode achieved successful removal efficiencies for total N, P and CODT (86 +/- 12%, 93 +/- 9% and 79 +/- 6%). In the following period, nitrite shortcut (with undetectable activity of nitrite oxidising bacteria) was achieved by implementing automatic control of the aerobic phase length in R2-AUT using ammonium measurement andoperating at a lower sludge retention time. Similar N, P and CODT removal efficiencies to the full nitrification period were obtained. P-recovery from the anaerobic supernatant of R1-HET was achieved in a separate precipitator by increasing pH and dosing MgCl2, recovering an average value of 45% of the P in the influent as struvite precipitate, with a peak up to 63%. These values are much higher than the typical values of sidestream P-recovery (12%). Regarding PHA, a percentage in the biomass in the range 6.9-9.2% (gPHA.g(-1)TSS) was obtained