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Title: Exploiting metal-organic-microbial interactions for metal recovery in engineered systems
Author: Adapa, Lakshmi Manjoosha
ISNI:       0000 0004 6495 8840
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2016
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As global populations grow and become more demanding, resource limitation and the treatment of industrially generated waste constitute an escalating dual challenge. There is, however, a growing awareness of the potential of waste streams as a resource. Metal removal and recovery employing currently available physicochemical techniques are expensive, energy intensive and often unsuitable in cases of voluminous effluents containing complexing organics and low metal concentration. Immobilised biofilms have the potential to simultaneously biodegrade organics whilst in parallel immobilising and recovering metals: the focus of this research. In this study, the maximum metal uptake was 24.60 mg/g and 5.23 mg/g for Zn (II) and Mn (II), respectively, for an initial metal concentration of 80 mg/L. The biosorption of binary system was found to be competitive in nature; Zn (II) removal decreased up to 87% whereas the Mn (II) removal decreased up to 66%. In order to improve the potential of biofilms as means of recovering resources, the mechanism by which they immobilise metals was investigated. This is the first study to investigate the potential of ultraviolet (UV) as an analytical tool for determining pollutant removal mechanisms by biofilms. A comparative assessment of chemical (sodium azide) and physical (UV) methods of cell inactivation was undertaken to determine the relative contributions of passive and metabolically active processes on organic and metal removal. Industrial effluents typically contain both organics and metals; therefore, the effect of organics on the metal removal ability of biofilms, which is poorly understood, was elucidated to help develop biologically-based treatment strategies for treating chemically mixed wastes. Chelation had by far the most inhibitory impact on the passive metal removal mechanism, reducing the zinc biosorption by 60% in fully chelated Zn-EDTA complex system. In contrast, nonionic surfactants were the only organics that increased the rate of metal removal, whilst having no detectable impact on biosorption capacity. Hence, they are potentially good candidates for reducing metal-organic competition, assisting metal recovery in the presence of organics. The recovery of biosorbed Zn (II) from microbial biofilms using sodium dodecylbenzene sulphonate (SDBS) surfactant was another novel aspect of this study. This achieved high and stable Zn (II) recovery over four successive biosorption-recovery cycles. Moreover, 94% of the Zn (II) was cumulatively recovered over six successive wash cycles, confirming that SDBS is a potential zinc recovery agent for biofilms. The findings from this study have established that the employment of biofilms to remediate chemically mixed effluents is a favourable potential alternative to energy demanding physical and chemical treatment options.
Supervisor: Porcelli, Don ; Thompson, Ian P. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available