Fish-Canning Wastewater Treatment by Means of Aerobic Granular Sludge for C, N and P Removal

Abstract

This research work analyses the development of aerobic granular sludge to simultaneously remove organic matter (COD), nitrogen (N) and phosphorous (P), from saline fish-canning wastewater. A 1.6 L sequencing batch reactor (SBR) with volumetric exchange ratio (VER) of 50% and a hydraulic retention time (HRT) of 0.25 d, was used. The SBR was operated in 3-hours cycles comprising: 60 min anaerobic feeding, 112 min aeration, 7–1 min settling and 1–7 min effluent discharge. The salt concentration was approximately 10.4 ± 0.8 g NaCl/L, and the applied organic loading rate (OLR) of 5.4 ± 1.9 kg COD/(m³∙d). Under these working conditions, aerobic granules were observed after 34 days of operation, although some filamentous bacteria were present on the surface of the aggregates. The granular biomass had a concentration of volatile suspended solids (VSS) of 1.34 g VSS/L, a mean diameter of 1.35 mm and a density next to 11.5 g VSS/L_granule. However, after 41 days of operation a fluffy-flocculent suspension was formed, together with granules, probably due to the salinity and the fraction of slowly biodegradable COD of the feeding (≈ 35% of total COD). Good removal efficiencies of soluble COD were observed (≈ 80%), while ammonium and phosphorous were mainly removed to cover the minimum metabolic demand of heterotrophic strains. In fact, the enrichment of the biomass with slow growing autotrophic and phosphorous accumulating bacteria, especially in a saline environment, require a longer time of operation.