Development Of A Flexible And Encapsulated Microbial Community For The Two-Stage Anaerobic Treatment Of Industrial Food And Beverage Wastewaters.

Abstract

This dissertation describes the development and use of a flexible microbial community forthe two-stage anaerobic treatment of high-strength industrial food and beverage wastewaters using encapsulation technology. The use of anaerobic treatment systems enables resource recovery from wastes, particularly high-strength industrial wastes, that would have otherwise been energy-intensive to treat aerobically. This research was a highly collaboratively work in which we investigated anaerobic treatment integrated with encapsulation technology on a lab- and pilot-scale. The feasibility of deploying a pilot two-stage anaerobic encapsulated system for the treatment of brewery WW at a local brewery in Northeast Minneapolis was assessed. It was hypothesized that the system containing encapsulated sludge would have a faster startup because of the addition of large concentrations of encapsulated biomass and would perform similarly to a parallel AnMBR because of similar long SRT values. The system consisted of a fermenting 1ststage reactor containing encapsulated hydrogen-producing organisms and a methanogenic 2nd-stage reactor containing encapsulated anaerobic sludge. A parallel 2nd-stage anaerobic membrane bioreactor (AnMBR) containing suspended anaerobic sludge was also investigated for comparison. The 1st-stage fermenting reactor produced more volatile fatty acids (VFAs) compared to the influent feed. The 2nd-stage methanogenic reactor containing encapsulated sludge started up rapidly, producing over 60% methane in the produced biogas, which took over a month for the parallel AnMBR system to achieve. Nevertheless, the performance of the 2nd-stage reactor containing encapsulated sludge subsequently declined compared to the AnMBR as a result of encapsulant breakdown and a poorly optimized initial community. The microbial dynamics and adaptation patterns in the encapsulated and suspended communities within the pilot systems were also investigated. It was hypothesized that although the encapsulated community would shift, it would not be able to adapt to the same extent as the AnMBR community, pointing to one of the reasons why the reactor employing encapsulation technology performed worse than the AnMBR. Through high-throughput 16s rRNA gene sequencing and fluorescence dye techniques, it was observed that encapsulated communities grew within the encapsulants and also adapted differently than the suspended bulk liquid. Additionally, there was no evidence of invasion of communities from the bulk into the encapsulant, though some of the encapsulated communities did leak into the bulk liquid. This pointed to the importance of the initial community encapsulated, as the organisms needed for good performance had to be present in the community that was encapsulated. To verify the importance of the initial encapsulated community and determine how to select a community capable of good COD removal from a variety of industrial wastes, additional experiments were performed. A two-stage lab-scale anaerobic system was set up with suspended cultures enriched on five types of high-strength food and beverage wastewaters and monitored to determine the influence of feed type on microbial community composition and overall performance. Here, it was hypothesized that feedstock type would strongly influence the system COD removal, fermentation, and the microbial community structure for 1st-stage fermenting communities, with identifiable “keystone” populations that signal excellent treatment potential for specific feed types. Results showed that feed type strongly impacted microbial community structure in the 1st-stage fermenting communities, but not in 2nd-stage methanogenic communities. Some of the core genera present in all of the suspended cultures, positively correlated to chemical oxygen demand removal in the different feed types, with p-values ranging from 0.004 to 0.05. Finally, cultures enriched on different feedstocks were assembled and encapsulated to evaluate how they performed, with different feeds, to determine if a single microbial community could be assembled to adapt to and degrade multiple feeds. It was hypothesized that a single community can be assembled to degrade a variety of wastes provided that the core communities needed to degrade the components of each feed type are present. A single community in the 1st-stage and another in the 2nd-stage, capable of degrading a variety of high-strength wastewaters, was developed that was able to achieve > 90% COD removal within 4 weeks of startup. The 1st-stage communities shifted with feed type while 2nd-stage communities remained relatively constant in structure regardless of the influent. Also, an HRT ≤ 2 days in the 1st-stage enhanced the overall treatment of brewery WW, highlighting the importance of the 1st-stage and fermentation performance in a two-stage digester. Overall, this work has demonstrated that encapsulation can be effectively deployed in a two-stage anaerobic system to treat a variety of high-strength industrial wastewaters, provided that the communities are enriched and tailored to specific feeds prior to encapsulation. Our findings also emphasize the important role of the 1st-stage system in the overall performance of a two-stage anaerobic system.