An Attempt to Develop Aerobic Granular Sludge in Continuous Airlift Reactors

Abstract:

Recent advancement on biological wastewater treatment is via granular sludge technology. It is widely known that, aerobic granular sludge has been developed in a batch operation since its discovery. Yet, most of the wastewater treatment plant (WWTP) is operated in continuous mode. Now, the real challenge is how to adopt the granular technology while maintaining present operation mode of WWTP. Thus, this study attempts to evaluate the feasibility of developing aerobic granular sludge in continuous airlift reactors feed with two different substrates, namely glucose and acetate. Two identical airlift reactors (6 L) were employed and operated at room temperature (30°C). Prior to the substrate feeding, both reactors were inoculated with seed sludge obtained from a palm oil mill anaerobic pond. One of the reactors was fed with 2000 mg COD L^-1 of glucose (ALR1) and the other reactor with 2000 mg COD L^-1 of acetate (ALR2). The hydraulic retention time (HRT) and organic loading rate (OLR) for both reactors were maintained at 4 days and between 0.2 to 0.5 kg m^-3day^-1 respectively. Dissolved oxygen was maintained between 5.0 and 6.0 mg O₂L^-1 and supplied by air compressor. The reactor performance was monitored based on COD removal. Aerobic granules developed throughout the study period was evaluated based on granules size and morphology, sludge volumetric index (SVI₃₀) and SVI₅/SVI₃₀ ratio analysis. Results showed that ALR1 demonstrated the formation of filamentous-type aerobic granules with most of the SVI₃₀ average at 100 to 190 mL g^-1. Ratio SVI₅/SVI₃₀ analysis was evaluated at 0.2 and 0.5. The largest granules size obtained during the experiment was about 600 μm on day-136 and average granules size obtained at 200 to 400 μm. ALR1 able to achieve 95% COD removal. For ALR2, round shaped aerobic granules were developed with average SVI₃₀ from 100 to 1000 mLg^-1. SVI₅/SVI₃₀ analysis indicated an average ratio between 0.7 and 0.9. The average granules size was between 30 to 50 μm and the largest was 78 μm on day-60. 90% of COD removal efficiency was obtained in ALR2. In conclusion, ALR fed with acetate had indicated better aerobic granules characteristics as compared to glucose fed reactor. Furthermore, the study demonstrated that to develop aerobic granules in continuous reactors is feasible.

• Periodical: Materials Science Forum (Volume 1025)
• Pages: 265-272
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.1025.265
• Online since: March 2021
• Authors: Muhammad Syafiq Mohd Shafei*, Zulkifly Jemaat
• Keywords: Activated Sludge, Aerobic Granules, Chemical Oxygen Demand (COD), Continuous Airlift Reactor, Organic Loading Rate (OLR)

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