Team:UCL/Science/Bioprocessing

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.

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)

Post-module operation