Abstract
By modification of the operational conditions of batch reactors, a municipal wastewater treatment plant was upgraded from activated sludge to aerobic granular sludge (AGS) technology. After upgrading, the volume of the biological reactors was reduced by 30%, but the quality of the effluent substantially improved. The concentration of biomass in the reactors increased twofold; the average biomass yield was 0.6 g MLVSS/g COD, and excess granular sludge was efficiently stabilized in aerobic conditions. Canonical correspondence analysis based on the results of next-generation sequencing showed that the time of adaptation significantly influenced the microbial composition of the granules. In mature granules, the abundance of ammonium-oxidizing bacteria was very low, while the abundance of the nitrite-oxidizing bacteria Nitrospira sp. was 0.5 ± 0.1%. The core genera were Tetrasphaera, Sphingopyxis, Dechloromonas, Flavobacterium, and Ohtaekwangia. Bacteria belonging to these genera produce extracellular polymeric substances, which stabilize granule structure and accumulate phosphorus. The results of this study will be useful for designers of AGS wastewater treatment plants, and molecular data given here provide insight into the ecology of mature aerobic granules from a full-scale facility.
Highlights
Aerobic granular sludge (AGS) is one of the most intensively developed biological methods of wastewater treatment
Here we report on the process efficiency and on the microbiological and morphological structure of aerobic granules during long-term operation of a municipal wastewater treatment plant (WWTP) that was upgraded from activated sludge to aerobic granular technology by modifying the technological line and operational parameters
Despite reducing the volume of biological reactors by about 30%, the quality of the effluent improved (Table 1) and dense, spherical granules were obtained in the reactors, which were inhabited by microbial consortia able to efficiently remove carbon, nitrogen, and phosphorus in a single reactor
Summary
Aerobic granular sludge (AGS) is one of the most intensively developed biological methods of wastewater treatment. Filamentous bacteria form the basis for the creation of agglomerates upon which granulation begins. These bacteria may disappear or remain in the biomass in the later stages of granulation depending on the type of available carbon source, and their presence affects granule compactness Liu and Liu (2006). An anaerobic fill phase promotes substrate uptake and diffusion throughout the whole granule. During this period, storage polymers are formed and slow-growing organisms predominate in the granules (Pronk et al 2015a)
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