Treatment of saline wastewater by a sequencing batch reactor with emphasis on aerobic granule formation

The formation and characteristics of aerobic granules in a sequencing batch reactor (SBR), designed to treat saline wastewater, have been investigated in this study. Granule structure was determined using scanning electron microscope (SEM), and polymerase chain reaction (PCR). Granules formed in the reactors were grouped into light brown granules and black granules that looked ‘fluffy’. The first group was more dense than the second group and consequently had a higher settling velocity. The densities of the first and the second group were 0.056 and 0.035 g/ml, respectively. While the corresponding settling velocity were 1.35 and 0.97 cm/s, respectively. The kinetic coefficients Ks, kd, k and Y in saline substrate (10 g NaCl/l) were estimated to be 195 mg s COD/l, 0.025 g VSS/g VSS d, 2.29 g s COD/g VSS d and 0.45 mg VSS/mg s COD, respectively. Analysis of granules using 16S rDNA sequences showed that the dominant microbial species was Klebsiella oxitoca. Minerals and the protozoan community in saline substrate facilitated the formation of granules. It was concluded that the fluffy granules are a variation of the light brown granules which are resistant to salt.