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Team:UCL/Science/Bioprocessing
From 2014.igem.org
Overview
In the textile industry today, the global production of dyestuff amounts to over millions of tonnes per year. Azodyes represent two thirds of this value, a majority of which find their way to wastewater effluent streams. Characterized by the presence of one or more azo group (more on chemistry), this type of organic colorant is also found in cosmetics, pharmaceuticals and food industries. While the desirable properties of azodyes i.e. chemical stability, high molar extinction coefficient and fastness make them a dye-class of choice, their widespread use in countries such as India and China make them a dye to die for—literally. This is because, in parallel to being aesthetically intrusive to ecosystems, azodye breakdown products have been found to be mutagenic and carcinogenic. With such a high worldwide consumption, the benefits in developing and integrating a sustainable strategy for dealing with such effluent streams is clear. It is worth to note that the ‘azodye problem’ is exacerbated by the high costs, both financial (economic) and environmental, of current physiochemical and biological methods of treatment (more on current treatment). This year, we are looking into the processing options, novel and old, that are relevant to tackling the problem of azodye discharges. In order to assess the feasibility and determine key engineering parameters for each option, the most important dyestuff sector will be used as a case study: textiles and dyeing industry.
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.
Whole-cell biocat
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.
Our Solution
Overview of the solution
Concentration
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Dyestuff industry
By considering the production of azodyes within a specific sector, it is possible to approximate a yearly production of azodyes, suited a given purpose. In this scenario, we are looking at the dyeing process of 1kg of cotton using methyl red.
Process inputs
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Reaction kinetics
Several assumptions need to be made in order to determine the basic kinetic rates for our system.
Immobilization methods
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Biofilms
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Whole-cells vs. Enzymes
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Current methods
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Other Problems
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Other Problems
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Other Problems
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Other Problems
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Other Problems
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Other Problems
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Looking into the process
Major components of treatment 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.
This versatile and simple process offers a wide range of future developments into various chemical producing sectors. It would be possible to use this technology in parallel with different industries as a form of platform technology using different synthetic biology anchors, in order to detoxify various effluent polluting chemicals.
Pre-process
In order to estimate required biomass, a functional unit will be defined: mass of azodyes required to dye 1kg of textile. Combined with information on dyeing efficiencies (i.e. fixation rates) and mass transfer kinetics, it is possible to estimate the E. coli biomass required to breakdown and detoxify this effluent stream
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 azodyes in textile factories and stoichiometric relations, we will design an optimised cell growth (fermentation) stage.
