Application of the ELAN® anammox based process to treat digested blackwater in a decentralized wastewater system

Wastewater source-separation and on-site treatment systems face severe problems of wastewater availability. Therefore, the effect of repeated short-term starvation and reactivation periods on a partial nitritation-anammox (PN/AMX) based process was assessed treating digested blackwater at room temperature. First, two sequencing batch reactors (SBR) were operated in continuous mode (SBR-C, which served as control) and with repeated starvation/reactivation periods during the nights and the weekends (SBR-D), using simulated blackwater (300 mg N/L and 200 mg COD/L) as substrate. The results showed no remarkable difference in overall process performance between both reactors, achieving total nitrogen removal efficiencies (NRE) around 90 %. Furthermore, no significant variations were measured in specific activities, except for the aerobic heterotrophic one that was lower in SBR-D, presumably due to the exposure to anoxic conditions. Then, the technical feasibility of applying the PN/AMX system to treat real blackwater produced in an office building during working hours was successfully proved in a third reactor (SBR-R), with the same starvation/reactivation periods tested in SBR-D. Despite the low temperature, ranging from 14 to 21 °C, total NRE up to 95 % and total nitrogen concentration in the effluent lower than 10 mg N/L were achieved. Moreover, a good recovery of the PN/AMX process performance after a long starvation period of 15 days (simulating holidays) was observed. Results proved for the first time the feasibility and long-term stability (100 days) of the PN/AMX process for the treatment (and potential reuse) of blackwater in a decentralized system, with repeated starvation/reactivation periods and after long starvation.