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Team:UCL/Science/Bioprocessing
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Revision as of 23:17, 23 September 2014
Overview
How is bioprocess engineering relevant?
Why invest?
The design of a successful bioprocess requires careful analysis of the many factors that impact choice of design parameters and process variables. It is crucial to consider the cost of the process at each stage to assess it's large scale feasibility. For the problem at hand, the following interplay will affect an industry's choice to adopt a novel process:
From a conversation with an economist in the field, the chances of market success for a novel waste treatment method is dependent primarily on the financial potential of the project. It follows that potential environmental regulations could cripple a factory, just as well as general public dissatisfaction would dent a brand a name. We have the basis for a sustainable solution to discharged azodye effluents that would serve as a giant biocatalyst and sponge. Considering that dyeing is extremely water intensive (), a post-treatment step that recovers water for the potential reuse within the process, even within a heat exchanger, is financially appealing and environmentally friendly. Depending on the nature of the breakdown products obtained from the biocatalysis steps, subsequent operations could be added for more specific recovery.
What is a bioprocess?
A typical bioprocess involves the fermentation of a stock culture (e.g. E. coli) at a small scale which is subsequently scaled up to suitable production capacities. The products from the fermentative stages are then separated using a variety of techniques designed to exploit the orthogonal properties of desired products.
Stages of large scale fermentation of E. coli:
The design of a process
with azodyes
The contamination of natural habitats surrounding textile factories by coloured (azodye-rich) effluents is a real problem (more). This is because the enzymatic breakdown products of azodyes i.e. aromatic amines, are carcinogenic when ingested. These can not only build up within local ecosystems but can also be a hazard to humans through bio-accumulation in the food chain. With a large section of dyehouse effluents consisting of dyes that have half-lives spanning over decades, the latter remain in the environment for long periods of time.
Understanding the issues
with current methods
With regards to current technologies in the textile industry, exorbitant volumes of water are used for processing (around 90%), the rest being used for heat exchange purposes. Unfortunately most of the water used for processing is discharged as waste, resulting in highly diluted azodye effluent streams. Secondly, the recalcitrant nature of azodyes hikes the inherent costs of large-scale physical separation systems. As a result, industrial processes used to deal with such soluble hazardous wastes would not be a feasible option to deal with azodye effluents.
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By using whole cell biocatalysis as the workhorse for detoxification, this process will yield lucrative byproducts such as quinones, that can then be separated from the process stream and sold off.
Other Problems
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Looking into the process
The overview diagram below presents the proposed layout for the plant, using an E. coli biofilm as the ‘immobilisation method’, one of the process alternatives we are considering. The synthetic E. coli immobilisation mechanism would take the same format i.e. longitudinal plates, however, we will also consider beads of the synthetic immobilising agent in a packed bed format.
Key Features of Our System
- -Fermentation stage is where optimized growth will take place by controlling mixing and oxygen supply. At the end of this stage, viable E. coli cells expressing the enzymes of interest will be present in a broth.
- -Module- see cross section of a single system. Continuous flow system with flow rates and residence times based on mass transfer kinetics, specific to E. Coli.
- -Module 1 designed to capture the bulk of the azodyes, module 2 is a polishing step.
- -Both anaerobic and aerobic reactions take place at the same time in both the modules, design based on gas supply (nitrogen vs. oxygen).
- -Cleaning operation using biodegradable chemical at high flow rate (from holding tank 2).
- -Continuous recycle system for maximal active and diffusive uptake.
- -Filter modules- exploring the use of disposable low cost agricultural waste for filtration.
- -Further processing- based on the commercial value of the breakdown products, investments could be made into higher-tier technology such as chromatography columns to separate the breakdown products individually.
Microbial Fermentation (Stage 1)
Small-scale bioreactors are often the workhorse during process development. By experimenting at this scale, it is possible to determine the optimum growth conditions for E. coli. This will allow to assess costs at the required scale based on biomass requirements.We are using E. coli to cultivate the enzymes necessary for the biodegradation of azo dyes (azo reductase, laccase). By combining information on the production of azo dyes in textile factories and stoichiometric relations, we will design an optimised cell growth (fermentation) stage.
Module operation (Stage 2)
After the fermentation stage, the E. coli biomass is dispersed in a liquor also containing various byproducts. A concentration step could be beneficial to reduce volumes in the next stage. However, capital costs of such unit operations would not be attractive to potential dyeing companies deciding to acquire the entire system. The subsequent modules (MOD) are equipped to handle large volumes and operate in continuous-flow mode with intermittent discharges. By controlling residence time and operating flow rates, it will be possible to achieve a cell recovery deemed efficient. These will be then immobilized onto the surface of the plates within the modules. There exists a wide range of immobilization strategies used for biological wastewater treatment and this is what gives the unit its modular character. By supporting a number of immobilization methods without changing the hardware, MOD allows for the enzymatic breakdown of a wide range of recalcitrant chemicals that might be financially and environmentally costly to treat using conventional methods. (more to come)Major components of treatment process
