Sustainable waste management for lipid-rich dairy wastewater by anaerobic digestion
Liu, Yuchen
Liu, Yuchen
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Publication Date
2023-12-18
Type
Thesis
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Abstract
The efficient anaerobic degradation of long chain fatty acids (LCFA) holds the key to unlocking the energy potential of lipid-rich wastewater in the dairy industry. This study aimed to explore sustainable solutions for the treatment of LCFA-containing dairy wastewater through psychrophilic anaerobic digestion (PAD) and to optimize the management of dissolved air flotation (DAF) waste, a high-lipid byproduct generated during dairy production. The study first assessed the feasibility of PAD at 15℃ and compared it with mesophilic anaerobic treatment. Results demonstrated that psychrophilic treatment was viable, achieving high removal rates of soluble COD (>90%) and LCFA (~100%). However, long-term treatment required prior biomass acclimation to psychrophilic temperatures. Microbial community analysis revealed the significant roles of putative syntrophic fatty acid oxidizing bacteria and Methanocorpusculum in anaerobic LCFA degradation. Furthermore, fungal-bacterial biofilm was found to play an important role in psychrophilic treatment. The study then investigated the acclimation of mesophilic biomass to low temperatures as an approach to initiate psychrophilic anaerobic reactors. The acclimated biomass at 15℃ displayed efficient removal of organic matter (total COD removal >75%, soluble COD removal >88%), and LCFA (>99%). Amplicon sequencing of the 16S rRNA gene and rRNA revealed a dynamic and adaptive microbial community in response to temperature reduction. The predominant syntrophic genus identified for LCFA degradation was Smithella, supported by the expression of associated enzymes related to β-oxidation of LCFA. Synergistic partnerships among Smithella, Methanothrix, and Methanocorpusculum were found to underpin efficient LCFA removal and methane production at low temperatures. Moreover, upregulation of predicted pathways associated with the biosynthesis of unsaturated fatty acids, lipopolysaccharides, and compatible cellular solutes confirmed microbial adaptation to cold environments, enhancing membrane fluidity and maintaining osmotic balance. Additionally, the study explored novel waste management strategies for DAF waste, a high-lipid byproduct separated from dairy wastewater. The investigation assessed the effects of food to inoculum (F/I) ratio and ultrasound pre-treatment on the anaerobic digestion of DAF waste. Notably, DAF waste showed substantial methane production potential, further enhanced by ultrasound pre-treatment. The potential methane yield ranged from 436-566 mL CH4/g VSfed. However, increasing the F/I ratio led to inhibitions in methane production due to long-chain fatty acid accumulation, with high concentrations of oleate significantly inhibiting methanogenesis at F/I ratios >1.0 and delaying palmitate degradation. Ultrasound pre-treatment significantly increased soluble COD in DAF waste by 52-82%, with continuous sonication removing 38% of LCFA. Ultimately, implementing ultrasound pre-treatment and optimizing the F/I ratio offers alternative waste management strategies that mitigate environmental impacts in the dairy industry, harnessing the energy potential of DAF waste and leading to more sustainable dairy production practices. In summary, this comprehensive study sheds light on the feasibility of psychrophilic anaerobic digestion of lipid-rich dairy wastewater, highlights the crucial role of microbial communities in LCFA degradation and adaptation to low temperatures, and proposes innovative approaches for the energy-efficient management of high-lipid byproducts in the dairy industry.
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Publisher
NUI Galway