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 mgDQOT.L-1) than phase I (211.8 mgDQOT.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.