EFFECTIVENESS OF PHOSPHORUS REMOVAL IN AN SBR USING CO-PRECIPITATION WITH FERRIC CHLORIDE, AND ITS EFFECTS ON MICROBIAL ACTIVITY

Abstract

The present study evaluated the phosphorus removal in a Sequencing Batch Reactor (SBR - 2,500L) used to treat the wastewater from an office building in two steps: phase I-Enhanced biological phosphorus removal (EBPR) and phase II-co-precipitation using FeCl₃ as precipitant. The raw sewage presented a high organic load variation ranging from 0.11 (phase I) to 0.66 (phase II) kgCOD.m^-3.d^-1. A better phosphorus removal performance was obtained during co-precipitation (from 19.0 to 1.2 mg.L^-1 = 93% of efficiency) compared with biological removal (from 15.6 to 9.0 mgL^-1 = 42% of efficiency). FISH analyses did not demonstrate a strong PAO inhibition; however, nitrifying and denitrifying organisms (NSO and PAE) showed a significant activity reduction during phase II. Therefore, the bench tests made to obtain the oxygen uptake rate (OUR) revealed a heterotrophic organisms activity significantly lower in phase II (46.8 mgDQO_T.L^-1) than phase I (211.8 mgDQO_T.L^-1), indicating metabolic inhibition. The co-precipitation processes enhanced phosphorus removal, bringing the SBR effluent into accord with state law requirements; however, the inhibitory effect of ferric chloride on microorganism activity was highlighted.

Keywords:
Phosphorus removal; Co-precipitation; SBR; Ferric chloride; Microbial activity