The paper is authored by Congcong Zhang, Albert Guisasola, Juan Antonio Baeza.
Recovering energy from wastewater in addition to its treatment is a hot trend in the new concept of water resource recovery facility (WRRF). High-rate systems operating at low solid retention time (SRT) have been put forward to realize it. In this paper, the integration of Enhanced Biological Phosphorus Removal (EBPR) in an anaerobic/aerobic continuous high-rate system was evaluated. Successful P and COD removal were obtained operating at SRT 6, 5 and 4 days treating real wastewater, while a further decrease to 3 days led to biomass washout. The best steady state operational conditions were obtained at SRT = 4d, with high removal percentage of P (94.5%) and COD (96.3%), and without detecting nitrification. COD mineralization could be reduced to 30%, while 64 % of the entering carbon could be diverted as biomass to energy recovery. The nitrogen balance indicated that its loss was due to biomass growth. The whole system could be operated at low DO (0.5 mg/L), which is beneficial to decrease energy requirements. Biochemical methane potential (BMP) tests showed better productivity for the anaerobic sludge than the aerobic sludge, with an optimal BMP of 296±2 mL CH4/gVSS. FISH analysis at SRT = 4d revealed a high abundance of Accumulibacter (33±13%) and lower proportion of GAO: Competibacter (3.0±0.3%), Defluviicoccus I (0.6±0.1%) and Defluviicoccus II (4.3±1.1%).