Development of a novel process to mitigate membrane fouling in a continuous sludge system by seeding aerobic granules at pilot plant

• A method was developed to mitigate membrane fouling in a continuous flow reactor.
• Granular sludge was cultivated by seeding aerobic granules at pilot-scale.
• Membrane fouling due to granular sludge was 8-fold low comparing the floc particles.
• The superior characteristics of aerobic granules lessened the membrane fouling.
• The proposed method significantly delayed the frequency of membrane cleaning.

The main goal of the current studies was to cultivate granular sludge in a continuous flow membrane bioreactor (CFMBR) to enhance the membrane performance in a pilot-scale reactor. In this regard, CFMBR was operated in two stages for 220 days; stage 1 was run without the addition of aerobic granules, while in stage 2, the aerobic granules synthesized (after a period of regulations) in a granular sludge sequencing batch reactor were seeded in the reactor. The results showed that the particle size in stage 2 was increased to nearly 625 µm and SVI5 decreased to 45 mL/g from that of 200 µm and 145 mL/g, respectively, during stage 1. The membrane fouling noted in terms of increase in transmembrane pressure values in CFMBR stage 2 was approximately 8 times lower than that of stage 1 of operation. Membrane cleaning was a regular phenomenon in stage 1, whereas no cleaning was needed during stage 2. The physicochemical analysis showed that a high PN/PS ratio (3.30) of the EPS, approximately 4-fold low soluble microbial products, a high particle size and sludge settleability were the main factors in mitigating this membrane fouling. The characterization of membrane foulants was done using FTIR spectroscopic technique.