Design of hybrid nano-engineered bioprocesses for wastewater treatment

Ponzelli, Michele
Freshwater scarcity is a growing concern, prompting the exploration of water reuse strategies. Anaerobic wastewater treatment is gaining popularity due to its low energy requirements and the potential for resource recovery. However, its application in water reuse schemes is limited by slow interspecies electron transfer, hindering the degradation of organic materials. Additionally, the presence of organic micropollutants (OMPs) - persistent pollutants with unknown long-term effects - further complicates anaerobic treatment for water reuse. This thesis proposes a solution to overcome these challenges by introducing low-cost, conductive nanomaterials, specifically graphene oxide (GO), to enhance electron transfer and organic material degradation in anaerobic biological treatment. The research objectives include a comprehensive evaluation of previous studies on anaerobic biological systems amended with graphene-based materials, assessing the impact of GO on OMP removal and methane production through batch assays, and evaluating the effects of GO addition in long-term degradation kinetics experiments. The results demonstrate the bioreduction of GO to biologically reduced graphene oxide (bioRGO) within 24 hours using a mixed anaerobic inoculum. However, GO addition did not significantly improve the removal of selected OMPs but inhibited the formation of their transformation products. GO also caused biogas inhibition at higher concentrations. Nonetheless, further experiments using fed-batch strategies revealed that inhibitory effects on methane production were only temporary. After such initial inhibited phase, significant improvements in degradation kinetics with GO concentrations above 10 mgGO/gVS were observed. The thesis concludes that the combination of anaerobic biological treatment and GO is promising for continuously operating systems, but further research is necessary. Life cycle assessments of GO should be conducted to prevent environmental release, and the long-term effects on microbial communities and a more comprehensive range of OMPs and their transformation products should be investigated. Future hybrid nano-engineered bioprocesses should consider these aspects to develop continuously operated configurations capable of retaining GO while ensuring sustainable and effective anaerobic wastewater treatment for water reuse ​
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