Team:UCL/Science/Bioprocessing

Bioprocess engineering is a conglomerate of fields and is extensively employed to optimize a variety of production processes. In order to cope with market forces, industries for example the pharmaceutical, have had to considerably improve their bioprocessing tools and techniques. As a result a range of novel process alternatives have been developed to harness product-specific properties, each bearing benefits, disadvantages and costs. While these can be used to drive financial returns, biological processing is becoming a gateway to eco-friendly alternatives for the treatment of recalcitrant wastewater such as industrial effluents. 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.

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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.

Treatment strategy for cotton textile mill wastes

In their investigation of textile processing technology, both conventional and novel, Babu et al. have emphasized the importance of waste minimization in terms of pollution load and production costs.

Why invest

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.

With 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.

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.

With Immobilization The following outlines the general consensus on the benefits of using the immobilized biocatalyst format, with respect to free-floating systems.
Catalyst Retention – A huge decrease in the losses of valuable catalyst into product streams. These losses are exponential in ‘free biocatalysts’ systems, and economically unfeasible when using costly enzymes.      

Since our project involves designing a novel bioprocess using whole-cell biocatalysts, microfluidics presents us with a unique and extremely useful advantage. When it comes to identifying, developing and optimising reactor designs and reaction constraints, this can be performed with ease and with low reagent cost as all variables are scaled down to a micro-level. Most importantly, the scale-down can be carried out without losing any of the accuracy or quantification of data output; this is due the number of sensors and control mechanisms which can be integrated into the microfluidic system.

Since our project involves designing a novel bioprocess using whole-cell biocatalysts, microfluidics presents us with a unique and extremely useful advantage. When it comes to identifying, developing and optimising reactor designs and reaction constraints, this can be performed with ease and with low reagent cost as all variables are scaled down to a micro-level. Most importantly, the scale-down can be carried out without losing any of the accuracy or quantification of data output; this is due the number of sensors and control mechanisms which can be integrated into the microfluidic system.

We will use rapid polymer prototyping techniques to generate microfluidic chips that will allow us to test our reaction and aid in the construction of a realistic bioprocess, which can be successfully scaled-up for industrial use. As we optimise and change our bioprocess, we can also quickly design new microfluidic chips that can mimic its development on a micro-scale. For example, it is our goal to integrate multiple downstream steps, such as chromatography, in order to isolate potential useful products. Demonstrating this in a microfluidic system is less time-consuming and far more cost effective than doing so at a larger scale.

For our microfluidic bioreactor, we will be using a magnetic free floating bar as our mixing system. This is an effective method of mixing at a microfluidic scale, as demonstrated in the video on the right. This video is of a microfluidic chemostat bioreactor designed by Davies et al. 2014 UCL, using a free-floating bar to mix two dyes.

An example of one of our microfluidic devices designed on AutoCAD can be downloaded here. This device utilises the basic concept of mixing the cells and dyes, producing a single output stream; much alike to the bioprocessing concept. During the course of designing the microfluidic device, several key considerations must be taken into account: ability to withstand high pressure without leakage; materials of construction to be inert and transparent; size constraints of inlet and outlet piping; ability to accurately 3D-print the device.