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Comparison of two different anaerobic feeding strategies on the treatment of municipal primary effluent using aerobic granular biomass Yu, Marcus


Aerobic granular biomass (AGB) in full-scale operations utilizes a plug-flow feeding configuration, but there has been minimal research conducted with alternative feeding configurations. An AGB study, comparing a plug-flow feeding reactor, to a completely mixed feeding reactor was suggested because converting a continuous flow system with a complete-mix anaerobic tank for an AGB system would be much easier to accommodate in a retrofit than an anaerobic cell with an upflow, plug-flow design. The primary objective of this study was to monitor the influence that completely mixed feeding has on the rate of granulation and granular stability relative to a plug-flow configuration in systems treating municipal primary effluent. A secondary objective was related to nutrient removal performance and understanding the impact that completely mixed feeding has on granulation. The plug-flow system (Reactor 1) achieved granulation on Day 185 after start up and the completely mixed system (Reactor 2) achieved granulation on Day 202. Both systems exhibited dense granular particles. However, there were distinct differences in the granular stability and morphology of the two systems. Reactor 1 had increased granular stability and maintained granular biomass from Day 185 to Day 241. The granules in Reactor 1 were larger and denser than Reactor 2. The explanation for this difference was attributed to steep substrate gradients seen in plug-flow feeding. There was a dilution of the influent feed during the completely mixed feeding in Reactor 2, which reduced the penetration of the substrate to the depths of the granules. The dilution forced Reactor 2 to lose granulation on Day 232. Although granulation was achieved in both systems, the plug-flow regime provided superior overall granulation performance. Throughout the experiment, both reactors achieved comparable nutrient removal efficiencies with respect to carbon nitrogen, and phosphorus. Both reactors lacked significant nitrification rates and Reactor 1 experienced difficulties with short-circuiting during the feeding period throughout the study. Cycle timing and apparatus modifications were implemented to counteract these issues. There was evidence that both systems were able to establish feast-famine regimes and cultivate polyphosphate accumulation organisms (PAOs), but genomic sequencing must be conducted on the biomass to confirm this finding.

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