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Introducing the wastewater biorefinery concept
Expanded Title:In this project, the wastewater biorefinery approach is explored in which we aim to use the nutrient component of partially treated domestic waste water for the production of poly (γ-glutamic acid) (γ-PGA) by enriching the microbial ecology for appropriate Bacillus species. The project considers both the specific case of PGA production as well as the broader system needs to achieve a successful biorefinery. γ-PGA, a polymer of D- and L-glutamic acid monomers connected by amide linkages, is a naturally occurring biopolymer, synthesized by a variety of micro-organisms. Most commonly, γ-PGA production has been studied in Bacillus species, such as B. subtilis and B. licheniformis. Bacillus is also associated with domestic waste water treatment and its enrichment has been associated with improved treatment processes. Potential applications of the γ-PGA are reported in the medical, food, cosmetic, waste water treatment, plastic and agricultural and textile industries. In this project, we consider the production of γ-PGA by Bacillus species for the partial treatment of domestic waste water and concomitant production of the polymer for soil improvement and water treatment. This system was selected to ensure that natural selection within the wastewater ecology was achievable. A number of isolates, 19 in total, were obtained from the Mitchell’s Plain WWTP and screened for their growth potential and potential to produce PGA. Isolates showing reproducible growth and evidence of polymer production were selected for further screening in terms of growth. The growth, substrate utilisation and PGA production of these were compared. A sub-set were selected for further research with specific emphasis on media composition in terms of C : N : P ratio and selection pressure of continuous culture under reduced substrate concentration. In parallel to this, the requirements of the waste water biorefinery were assessed and nature of wastewater as a source of nutrients described. This formed the basis for the review of reactor design and selection of appropriate reactor types. Following a broad review of bioreactor types, reactors supporting biofilm or aggregated microbial growth are selected to allow decoupling of hydraulic and biomass residence time to facilitate growth on dilute media. The fluidised bed reactor with an aerobic granular sludge (AGS) and the rotating bed contactor were selected for further study. The fluidised bed reactor with an aerobic granular sludge (AGS) and the rotating bed contactor (RBC) were designed, built and commissioned with an emphasis on simple and cheap construction. These reactors were trialled in the laboratory, using synthetic media and a pure culture of isolate 1, a Bacillus species. They were also trialled in the field at Athlone WWTP using wastewater. The latter allowed many challenges to be identified. The review of industrial ecology and the importance of this paradigm in the design of the biorefinery are reported. Further, key features of the wastewater biorefinery in terms of the process flowsheet are described as is the tension between the goals of bioprocess engineering for maximising product formation and environmental biotechnology for maximising remediation.
Date Published:01/02/2014
Document Type:Research Report
Document Subjects:Wastewater Management - Sewers
Document Keywords:Municipality
Document Format:Report
Document File Type:pdf
Research Report Type:Technical
WRC Report No:TT 587/13
ISBN No:978-1-4312-0503-5
Authors:Verster B; Madonsela Z; Minnaar S; Cohen B; Harrison STL
Project No:K5/2000
Organizations:University of Cape Town
Document Size:5 055 KB
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