In collaboration with the United States Department of Agriculture National Soil Erosion Research Laboratory (USDA-NSERL), a bioreactor was constructed to contain modified E. coli while uptaking phosphorus. This system, composed of two five-gallon buckets, tubing, 3 water filter canisters, and an aquarium pump, was designed to be as low-cost as possible as a consideration for potential future applications in developing countries.
Water flows into the reservoir bucket from where it is pumped into the reactor bucket beside it. An outflow tube in the reactor bucket leading back to the reservoir bucket keeps water level and, therefore, flow rate constant. Water exits the reactor bucket from one of three ports connected to filter canisters by flexible clear tubing. Within the canisters, space between filters and canister walls can be filled with silica beads containing immobilized bacteria. Water flows through these beads, through the filter, and out of the canisters into a holding container, completing its journey through the reactor.
The prototype experienced multiple iterations, as influenced by consultation with technicians and farmers associated with the USDA-NSERL. The earliest model featured a direct connection of the filter canisters to outflow ports in the reactor bucket, which was not conducive to easily switching or positioning the canisters. Flexible tubing was added to improve the modularity of the system. Additionally, markings were added to the dials of spigots controlling outflow to enable the user to identify the volume of water exiting the system. This is significant because, in order to maintain constant water level and flow, water must be entering and exiting at the same speed, which was difficult to gauge without definite measurements and markings.
Future iterations could feature a mechanism to recycle water through the system, allowing more phosphorus to be removed. Water filter canisters could be replaced with PVC tubes packed with silica beads, so a smaller number would need to be produced to fill the smaller space. Ultimately, the reactor could be filled with silica beads containing a variety of bacteria capable of collecting and storing phosphorus, nitrogen, and other nutrients, so the cleaning process would be comprehensive.