Imperial iGEM 2014

“To meet new environmental regulations, a step change is required in how we process water. Functionalised cellulose filtration could be a viable part of the solution.” - Dr. Michael Chipps, Principal Research Scientist at Thames Water

At a Glance

  • Ultrafiltration has many advantages for wastewater recycling
  • Limitations in current ultrafiltration technologies can be addressed by functionalised membranes for specific contaminant binding
  • The modularity underlying membrane fuctionalisation allows future targeting of any current or emerging contaminant
  • Our aqualose water treatment process offers a cost effective alternative to traditional ultrafiltration
  • The process is adaptable functioning equally as a bolt on to existing treatment facilities or as a standalone purification solution


Figure 1: Size exclusion for different grades of filter (from

Ultrafiltration (UF) membranes have a pore size of 0.1 to 0.01um (10 to 100nm) and are capable of removing particulates, bacteria and viruses. Microbial cellulose sheets naturally have pore sizes in this range (Gatenholm, P., & Klemm, D. (2010), Mautner et al 2014). Current ultrafiltration cannot remove small molecule contaminants such as pesticides and heavy metals however. Whilst nanofiltration and reverse osmosis membranes can exclude these small molecules they are expensive and energy intensive to use. Flow rates are low, they require very high pressures and the input water must be already purified by primary and secondary processes to avoid damaging the membranes.

Depending on input water quality UF systems may replace or complement existing secondary (coagulation, flocculation, sedimentation) and tertiary filtration (sand filtration and chlorination) systems in water treatment plants. Pretreatment of feed water is usually required to prevent reduce damage to the membrane units though ultrafiltration may be used in standalone systems for isolated regions. UF processes have the following advantages over traditional treatment methods:

  • Chemical free (aside from cleaning)
  • Constant output quality regardless of feed quality (excluding small molecule contaminants, changes in input water quality affect only the life of the membrane, not the quality of the flow through)
  • Compact plant size, efficient for small scale, decentralised purification
  • High quality of output water particularly with regards to pathogen removal

UF processes are currently limited by the high cost of membranes, inevitable membrane fouling means they must be regularly replaced. There use is also restricted by limitations in removal of small molecule contaminants. They can only be employed where feed water is free of these contaminants or in tandem with other (often slow or energy intensive) treatment methods for removing them.


Component Quantity Source Cost breakdown (£) Cost (£)
Water 4l London South West Water 4 liters of £5.5195 per m3 0.02
400 g granulated sugar 400g Tesco's 79p per 1 kg 0.32
Clipper green tea tea bags 4 Clipper tea 300 teabags for £9.99 0.13
Aspall organic cider vinegar 2 Aspall Suffolk 400 ml of a £2.25 500 ml bottle 1.80
Total 2.27
Component Quantity Source Price breakdown (£) Price per g (£)
Bacterial cellulose yield 60 cm by 40 cm = 0.24 m2 production from single tray 110 g/m2 x 0.24 m2 = 26.4g 0.09
Figure 2: Cost analysis of Aqualose

Microbial cellulose membranes are considerably cheaper than competitors. Whilst Polyvinylidene fluoride (PVDF) ultrafiltration membranes typically sell to the wastewater industry at upwards of $100 /m2 (Shenzhen Youber Technology Co., Ltd. no date). Current bacterial cellulose production for nata de coco costs around $1.6 /gram (Lee et al. 2014) and our cellulose with G. xylinus igem cost only £0.09 ($0.14) /g. Our thin cellulose membranes for filtration weighed around 20 g/m2 so would cost just $2.80 /m2. Whilst Our studies and existing literature (Fifield 2012) suggest bacterial cellulose is a strong and durable material however we would expect a shorter membrane life than the highly durable PVDF. Being considerably cheaper and easier to dispose of however, cellulose membranes could be more regularly replaced and still provide a more cost effective solution. This would also save on chemical washes regularly required to sustain the extended life of PVDF membranes.

Future Functionalisation

Our system for functionalising cellulose membranes is inherently modular. Proteins to bind or degrade a limitless range of contaminants can be bound to cellulose membranes. Filtration can then be adapted to the particular contaminants, altering seasonally, geographically and adapting over time to emerging threats. Metaldehyde contamination in the English home counties (Mathiesen 2013) could be addressed with specific degradation enzymes and microcystin could be removed from supplies in Ohio contaminated from algal blooms (Queally 2014).

Process Engineering

Figure 3: Schematic for dead end membrane filtration with backwash (from

We envisage functionalised bacterial cellulose membranes utilised in a plate and frame, dead end filtration setup for easy backflush cleaning and replacement when fouled. This process is particularly applicable for water recycling. Ultrafiltration combines well with activated sludge for purification when organic solids content is high and the additional membrane functionalisation can target removal of recalcitrant small molecules that can accumulate in recycled water. Current wastewater treatment plants could be easily retrofitted with the technology with dedicated facilities constructed in the longer term.

Disposal of Contaminants

Heavy metal contaminants pose a serious problem for all water processing solutions as they ultimately cannot be destroyed. To prevent escape into the environment they must be recovered and disposed of into controlled landfill (European Commission 2002). Trapping contaminants on filtration membranes concentrates them for easy recovery. To prolong filter life, contaminants could be regularly eluted and collected. When membranes are spent they could either be disposed of directly into controlled landfill or to reduce volume - incinerated and the flue scrubbed. Incineration is the most effective solution to destroy recalcitrant organic pollutants and unlike for other materials, incineration of cellulose membranes produces no harmful by products.


European Commission (2002) “Heavy Metals in Waste - Final Report” Accessed 17th October 2014 Fifield, Leonard, “Bacterial Cellulose Composites Opportunities and Challenges” PNNL Applied Materials Science Group (2012). Accessed 17th October 2014 Gatenholm, P., & Klemm, D. (2010). Bacterial nanocellulose as a renewable material for biomedical applications. MRS bulletin, 35(03), 208-213. James Queally “Toledo's tap water undrinkable for a second day; test results delayed” The LA times 3 August 2014. Accessed 17th October 2014 Karl Mathiesen “Slug poison found in one in eight of England's drinking water sources” the Guardian, Wednesday 10 July 2013. Accessed 17th October 2014 Lee, Koon‐Yang, Gizem Buldum, Athanasios Mantalaris, and Alexander Bismarck. "More than meets the eye in bacterial cellulose: Biosynthesis, bioprocessing, and applications in advanced fiber composites." Macromolecular bioscience 14, no. 1 (2014): 10-32. Mautner, A., Lee, K. Y., Lahtinen, P., Hakalahti, M., Tammelin, T., Li, K., & Bismarck, A. (2014). Nanopapers for organic solvent nanofiltration. Chemical Communications, 50(43), 5778-5781. Shenzhen Youber Technology Co., Ltd. Accessed 17th October 2014 Figure references: