Particulate COD Capture in an Aerobic Granular Sludge Bed

Abstract

Aerobic granular sludge (AGS) is a revolution in the water treatment field, since it enables to simultaneously remove carbon, nitrogen, and phosphorus. Recently, the AGS studies mostly focus on the formation of granules, and the factors that influence the AGS morphology, like temperature and substrate type. In domestic wastewater, 85 % of total chemical oxygen demand (COD) are particulate COD (PCOD), which are likely to be mostly captured in anaerobic phase in AGS systems. These particles can have a negative impact on granules’ morphology. However, there are few studies about the AGS performance on particle capture in anaerobic phase. Hence, the major research objective was to investigate to what extent can particles in the influent be captured by the AGS bed in the anaerobic feeding period. There were three possible mechanisms attributing to particle capture in the anaerobic phase, which were filtering effect, adsorption, and protozoa consumption. The contribution of protozoa was investigated with a theoretical approach. Furthermore, A model was built up for studying the influence of particle transport mechanism on particle capture. A lab-scale plug-flow experiment in a column was conducted for investigation of AGS bed performance on particles in different size ranges, and the influence of duration on particle capture. The result of the laboratory work found that the particle capture efficiency was 95 %, 84 %, and 23 % for particles in the range of 45-100 μm, 10-45 μm, and 0.45-10 μm, respectively. The 1-10 μm particles were hard to be captured. Besides, the particle capture efficiency was constant with the duration of 2 hours. Anaerobic feeding duration will have limited influence on particle capture without negatively affecting the phosphorus and nitrogen removal. Towards to the role of protozoa, they are unlikely to contribute to wastewater particle capture and removal in anaerobic period. Additionally, the AGS system in anaerobic phase can act as granular filtration system and the filtration model can be applicable in AGS research. Overall, anaerobic phase most likely contributes little on particle removal for whole AGS system.