OFlow

What it does

OFlow removes smaller-sized microplastics in water treatment plants by incorporating biofilter and bioreactor technologies. It integrates with current treatment stages to mitigate wastewater microplastic pollution before being discharged into the environment.

Your inspiration

Despite efforts to reduce microplastic pollution, 13 million tonnes of microplastic leak into the ocean every year; mainly originating from landmasses. We found that current water treatment methods are not adapted to completely filter out microplastics from domestic wastewater. Around 4.6 x 10^8 microplastic particles are discharged from treated effluents per day in medium-sized treatment plants. We saw an opportunity to nip microplastic pollution in the bud by removing these unfiltered particles before they enter the ocean. We strive towards a design that assimilates with the current water treatment process to prevent a system overhaul.

How it works

When P.fluorescens (a non-pathogenic bacteria) agglomerate, they form a protective biofilm layer comprised of polymeric matrix that binds to microplastics. Microplastics attached to the biofilm are absorbed, which results in an accumulation of microplastics in the biofilms. Using this method, we are able to filter out microplastics smaller than 200 microns. To facilitate optimal biofilm growth and efficient microplastic removal within a system with continuous flow, bacteria was grown on a scaffold, a structure with high surface area. Each scaffold is 3D printed using PLA, a biodegradable material that can be reused up to 2 years. Scaffolds can be used for a month before being saturated with microplastics. After which, scaffolds are removed and rid of microplastic filled biofilms to be reused. Flow rate data is extracted via Venturi Flow meter, which is used for calculating the nutrients injected to attain a good nutrient level balance.

Design process

53 and 25 design iterations were made to the bioreactor and to the scaffold, respectively. To capture smaller-sized microplastics, we explored unconventional technologies such as baleen filters, hydrocyclones and biofilm attachment. Biofilm methods showed the most potential in removing smaller microplastics with minimal energy consumption. We realised that biofilms can be grown on scaffolds (mainly applied in tissue engineering) to increase the surface area. Most scaffolds were designed using triply periodic minimal surfaces, taking into account flow rate changes. P. aeruginosa and P. fluorescens bacteria were tested for microplastic capture capabilities, but the latter was chosen as it is non-pathogenic. Following this, we designed a bioreactor chamber, prioritising the ease of scaffold insertion and removal for workers’ comfort. The bioreactor integrates perfectly between the 2nd and 3rd water treatment processes where water flow rate is low and oxygenated to sustain biofilms. Hence, we optimised the design under these flow conditions. CFD analysis was employed to verify an ideal flow field for nutrient flow and microplastic removal, consulting further design changes. These steps were repeated until a commercially viable and practical design was obtained.

How it is different

At present, there is no other product similar to OFlow. In small and medium-sized water treatment plants, the concept of integrating a biofilter into a bioreactor is used in trickle filters. Trickle filters stabilise wastewater using biofilm-forming microbes for biodegradation. However, the system and microbes do not remove microplastics due to design constraints. Similarly, even if these systems do, it would be difficult to clean and maintain them. OFlow embraces a semi-autonomous design that requires very little manpower to operate. The materials used are biodegradable and aimed towards long term use. The scaffolds (microplastic filters) can be easily removed, cleaned and reused for many times. Since biofilms can easily grow on almost any surface, complex surfaces can be used for biofilm culture and cleaned using an ethanol flush. A PID feedback system regulates nutrient concentration, flow rate and oxygen concentration for ideal microbial growth.

Future plans

A scaled-down version of OFlow (3D printed) is used to better understand the effects of fluid velocity, bacteria concentration, bacteria type and nutrient concentration on microplastic removal efficiency. Experiments conducted at the University of Southampton are aimed towards improving the technology for eventual commercial implementation. A proof of concept has been submitted to the National Biofilm Innovation Centre to help bring this project forward. The next step would be to seek funding and work with the Defence Science and Technology Laboratory (DSTL) UK alongside an academic staff from the University.

Awards