Microalgal-bacterial aerobic granular sludge for old leachate treatment: Development, performance, and lipid production

A lab-scale photo bio sequencing batch reactor (PSBR) was used to develop microalgal-bacterial aerobic granular sludge (MB-AGS) for old leachate treatment by seeding activated sludge, while indigenous microalgae were allowed to grow naturally. Upon 100 days of experiment, mature MB-AGS was successfully developed with an average diameter of 2.5 ± 1.5 mm and excellent settling properties, with a settling velocity of 39 ± 24 m/h. The biochemical oxygen demand (BOD), chemical oxygen demand (COD), ammonia (NH₄⁺-N), total nitrogen (TN), and total phosphorus (TP) removal efficiencies were 80 ± 14%, 95 ± 2%, 88 ± 14%, 56 ± 16%, and 57 ± 14%, respectively. The shift in microbial populations were also examined, in which the abundant EPSs producing bacteria in the system could be one of the reasons behind the successful transformation of activated sludge flocs to mature MB-AGS. Furthermore, lipid was able to be extracted from the MB-AGS, in which the lipid production was 9.35 ± 1.1 mg/g-SS, accounting 0.56 ± 0.07 mg/L.d of lipid productivity.