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Title: The mineral-electrogens-electrodes system in paddy soils and their impacts on trace elements behavior
Author: Gustave, W.
ISNI:       0000 0004 7970 4739
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2019
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Soil trace heavy metal and metalloid contamination is a serious problem that threatens humans and other organisms' well-being. Trace metal heavy contaminated rice paddy fields have become of worldwide concern since an increasing amount of paddy soils are contaminated with trace heavy metals. Rice has a high capacity to accumulate trace heavy metals and metalloids, especially arsenic, into its grains which has potential adverse effects on public health. Hence, it is essential to regulate the bioavailability of these pollutants in paddy soil if the aim is to reduce their concentration in rice grains and subsequent exposure to humans. The ability to control soil-to-solution partitioning of these trace heavy metals and metalloid from the reductive dissolution process of iron oxides has been identified as the key to limiting heavy metal uptake by rice plants. Compared to other remediation technologies, bioelectrochemical systems (BES) appear to be a promising solution to this problem. BES are able to provide an inexhaustible electrode for oxidation and the energy needed for the extraction of heavy metal to less toxic species and from the soils, respectively. In this context, the application of the sediment microbial fuel cell (sMFC) in soil remediation was investigated in this thesis. The mechanisms involved and the way the sMFC anode changes soil properties to enable heavy metal remediation were examined. The effect of the sMFC on the soil biotic and abiotic components were observed. The microbial community analysis revealed that the sMFC deployment can significantly influence the community composition within the soil profile. The results also indicate that the relic DNA generated by operating the sMFC has minimum effect on the culture independent estimates of microbial community composition. Moreover the effects of the sMFC's bioanode at different external resistance were examined. The results indicate that external resistance has a significant effects on sMFC power production, organic matter removal efficiency and microbial beta diversity. Moreover, the sMFC bioanode can significantly influence the behavior of trace element in soil. Our results showed that the sMFC was able to limit arsenic and iron reduction by creating a competition for organic substrate between sMFC bioanode and the iron- and arsenicreducing bacteria in the soils. However, we observed an increase in iron and arsenic release into the soil porewater when the sMFC was deployed in soil with high dissolve organic matter content. This was ascribed to the acidification effect of sMFC bioanode and the increase of iron reducing bacteria in the sMFC bioanode vicinity and associated bulk soil. Nevertheless, when the sMFC was coupled with wet-dry cycles to decrease dissolve organic matter, we observed a decrease in the release of iron and arsenic into the soil porewater. These results indicated that sMFC can be used to limit arsenic bioavailability in soil porewater. In addition to soil pore water iron and arsenic, the behavior of cadmium, copper, chromium and nickel was also influenced by the bioanode. Furthermore, we used the sMFC to limit the accumulation of trace metals in the rice plant parts. The results demonstrate that the sMFC can significantly reduce the total arsenic concentrations in the stems, leaves, husks, and rice grains. The total arsenic concentrations in the stems, leaves, husks, and rice grains were significantly decreased by 53.4%, 44.7%, 62.6%, and 67.9%, respectively in the plants with sMFC compared to the control. Similarly the effect of the sMFC on the accumulation of cadmium, copper, chromium and nickel in the rice plant parts were also investigated. The results showed that the sMFC can significantly limit the accumulation of cadmium, copper, chromium and nickel. The concentration of cadmium, copper, chromium and nickel in rice grains were 35.1%, 32.8%, 56.9% and 21.3% lower in the sMFC, respectively, than the control. Our work showed for the first time that operating the sMFC can significantly influence the behavior of paddy soil trace elements in soil. We also showed for the first time that the sMFC can be used as a promising technique to limit toxic trace metal bioavailability and translocation in the rice plants while simultaneously producing electricity.
Supervisor: Chen, Zheng ; Salaun, Pascal ; Raju, Sekar Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral