Step-feeding in aerobic/anoxic cycles enhanced the performance of aerobic granular sludge (AGS) systems treating effluents with low C:N ratios

Abstract

Aerobic granular sludge (AGS) systems treating effluents with a C:N:P ratio similar to real old landfill leachate were evaluated on simultaneous C, N and P removals, and to reduce the main problems encountered, such as nitrite accumulation, biomass loss, and granule disintegration. Therefore, six sequential batch reactors (SBR) were operated with different anaerobic (A), anoxic (An), and aerobic (O) configurations: A/O (R1 and R2), O/An with conventional feeding and well-defined anoxic phase (R3), O/An with step-feeding and well-defined anoxic phase (R4), and O/An (R5 and R6). The O/An with step-feeding reactor (R4) had the highest biomass retention/settleability (SVI30 < 50 mL/g), the best nitrification rates (99%), and chemical oxygen demand (COD) (97%), total nitrogen (91%) and total phosphorous (55%) removals. Furthermore, there was no nitrite accumulation, and granules’ disintegration was insignificant. The most abundant phylum in the reactors O/An was Planctomycetota, composed mainly of organisms from the Pirellulaceae and Legionellaceae families. In these reactors, the abundance of phosphorus-accumulating organisms (PAOs) and denitrifying bacteria were similar, while the abundance of glycogen-accumulating organisms was much higher than PAOs. Therefore, the type of cycle directly influences performance, granule characteristics, and system stability, being important for future investigations applying the AGS technology to leachate treatment.