February 2014 was considered as the end of period 1. Nutrient removal as well as a significant granule bed was present from that time onward. Performance results and operational parameters obtained between March and December 2014 are summarized in Tables 1 and 2 Monthly average nutrient concentrations are given in Fig. 5. Effluent guidelines were met for all parameters, with an average Ntot and Ptot of 6.9 and 0.9 mg L1, respectively, in the period MarcheDecember 2014. Elevated nitrogen and phosphorus concentrations in the effluent always coincided with heavy rain weather events. Due to presence of a large sewer system, heavy rain events provoke a flow rate that can be 2e5 times as high (Fig. 3a) with nutrient concentrations as occurring in dry weather flow (socalled first flush). The combination of increased flow and loading
rates leads to shorter cycle times and resulted in elevated effluent
concentrations. At these times, in accordance with the design setup
targeting an optimized installed reactor volume, metal salts
are used for the removal of phosphorus at the end of the cycle. The
Fe(III)/P molar ratio during the operational period was 0.18 with a
total P-removal efficiency of 90%. During normal rain and dry
weather flow the removal of phosphorus is completely biological.