High-rate anaerobic treatment of lipid-rich wastewater

The current praxis for wastewater treatment in this era of global heating and climate emergency is linear and overly wasteful. This requires change, and while research and development towards a circular water resource recovery factories (WRRF) (rather than wastewater treatment plants) challenges remain. A suggested core of the of the future is anaerobic digestion, a microbially driven process that breaks down organics into biogas, while also making nutrients more accessible (Nitrogen and Phosphorus) for recovery. However, it still has areas that are not sufficiently developed, a primary example is lipids. To date this energy dense, macromolecule is rarely treated by AD as it has been linked to issues such as temporary inhibition. Despite being available and ubiquitous substance the praxis is to remove it from wastewater and dispose of it. This thesis aims provides an understanding of the fundamental problems, failures, and potential for lipids within wastewater all to achieve robust and directly anaerobic wastewater treatment without limitations where possible. Specifically this would allow for resource recovery, water’s redeployment to the natural environment of lipid-rich wastewater. To develop this knowledge we deconstruct the issues experienced by anaerobic treatment and experiment to add new state-of-the-art knowledge and solutions to the field from a microbiological standpoint, using microbiological methods and process/bioreactor development around the microbial communities. While significant work has been completed historically (1980s - to date), often times this work has been completed in an incomparable manner, or with wastewaters that are not reproducible for research or in industrial settings. To begin we aims to develop a strong comparison and reproducibility for both process and microbial investigations. Firstly, utilising real dairy lipid-rich wastewater and similar granular biomasses to ensure consistency in Chapter 3 we redefined the treatment of lipid-rich wastewaters by testing the traditional high-rate anaerobic treatment systems – upflow anaerobic sludge bed (UASB), expanded granular sludge bed (EGSB) and anaerobic filter (AF). Specifically, outlining their issues with treatment of (real, dairy) lipid-rich wastewater in a comparative manner. Building on this comparison, we reviewed interventions that had the potential to uncover fundamental issues and solutions in the high-rate anaerobic degradation of long chain fatty acids (LCFAs), be they physical, chemical or otherwise. Specifically we developed and tested, Trace-Element addition, hypothesising here that a limiting factor to the beta-oxidation or other biochemical pathways for the degradation of LCFAs could be assisted positively by trace element addition (Chapter 3). Building on the work of Fermoso (Thesis, 2012) and Karlsson et al (2012}, however no clear evidence was seen to support further works. Secondly lowstrength ultrasonication (US) of the granule biomass was tested, to investigate the potential positive implementation (shown by Cho et al). Particularly hypothesising it may provide greater mass transfer through granules and their surface, to bypass issues should as encapsulation. Again however, this intervention process did not offer clear results in the format (1 sec/min, 25 kWh system) that it was tested and while potential exists it was not brought further. Finally, utilising the learnings from the comparative Bioreactor Trial 1 (Chapter 3) and learnings from literature (Chapter 1 & 2) a second bioreactor trial introducing the dynamic sludge chamber – fixed film (DSC-FF) bioreactor incorporated recirculation and a fixed-film system to successfully treat dairy wastewater from 72h HRT to 24 hours and OLR up to 7.6 kgCOD/m3/d. Successful performance including high COD removal (80%) and average TSS mg/l removal of 72%. Furthermore, the trial successfully avoided issues in Trial 1 (e.g. LCFA encapsulation, biomass washout) and it was completed in comparison to Trial 1 with the same (source) of wastewater utilised. Further these successful bioreactor changes, this Thesis aims to understand and tackle the challenges through microbiology and through the fundamentals of the microbial community underpinning the degradation of LCFAs. Therefore, in Chapter 4 a variety of both granular and flocculant biomasses were tested across methanogenic, syntrophic and LCFA substrates to outline differences in their activity, further layered with 16S rRNA sequencing these combined results were utilised to pick a combination of biomasses to start up triplicate hybrid bioreactors treating synthetic LCFA-rich dairy wastewater. This novel approach of community coalescence, taking high activity biomasses for each substrate and merging them to form one matrix, with the hypothesis that the high activity may bypass previously seen inhibitory issues. The start-up of these reactors tracked again by activity testing and high-throughput sequencing showed the merging of the community through microbial 16S rRNA sequencing but also in its activity across methanogenic, syntrophic and LCFA substrate markers. Moreover, in Chapter 5 following a successful trial the microbiology was investigated over the longer-term (351 days) with in depth examination across the overall microbial community and how it evolved, how it reacted to turbulence. From a process point of view some changes were made to sparger, recirculation point and these were monitored closely but no negative impact was shown. Finally this work outlines the future possibilities that have opened up due to in depth microbiology and novel approach, further questions to truly answer the issue of temporary inhibition by LCFAs and these are described along with further in-depth propositions for future science and development in Chapter 6.

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University of Galway

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Attribution-NonCommercial-NoDerivatives 4.0 International

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University of Galway Theses (PhD Theses)