Aerobic granulation of single strain oil degraders: Salt tolerance enhancing organics and nitrogen removal from high-strength refinery wastewater

The study demonstrates formation of salt tolerant aerobic granules by using Brevibacterium paucivorans, Staphylococcus hominis and Micrococcus aloeverae evaluating organics removal and nitrification efficiencies in refinery wastewater treatment. Enhanced extracellular polymeric substances (EPS) production during salinity exposure and gradual salt adaptation helped to reduce granule disintegration in all three batches maintaining 71-93 % removal of 330 mg/L total phenolic hydrocarbon (TPH). After 20 g/L salinity exposure, Brevibacterium faced partial rupture with decreasing size and volatile suspended solids (VSS) of 2.7-2.4 mm and 5-3 g/L, respectively. However, at 35 g/L salinity, the cocci abundance in Staphylococcus granules provided moderate stability with 2.5 +/- 0.09 mm granule size but Micrococcus granules achieved the smallest (0.9 +/- 0.02 mm) and strongest granules (integrity coefficient: 12 +/- 0.12 %) due to refinery sludge origin and maximum 226 mg/g VSS EPS content. High-performance liquid chromatography (HPLC) peaks suggested that Micrococcus had the fastest (12 h) complete phenolics removal efficiency among the three strains and salt tolerance improved nitrification up to 28 % by protecting nitrite-oxidizing bacteria (NOB) layers. About 330 +/- 10 mg/L of TPH and 35 g NaCl/L salt tolerance indicated Micrococcus granules to be the best fitted inoculum in hypersaline (>= 30 g/L salinity) refinery wastewater treatment.