▎ 摘　　要

NOVELTY - Hydrogel comprises electrochemically active bacteria and reduced graphene oxide integrated with the outer membrane of the bacteria. USE - The hydrogel is useful in bioreactor for recovering metal. The metal is palladium (all claimed). ADVANTAGE - The hydrogel is prepared without using an inactive cross-linked material such as alginate, hence has improved mechanical properties, increased surface area or improved mass transport at the surface and improves the recovery of palladium, from electronic waste, and is environmentally-sustainable. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following: method (M1) for preparing hydrogel involves (a) culturing a precursor solution comprising electrochemically active bacteria and graphene oxide, where the step (a) reduces the graphene oxide and integrates the reduced graphene oxide with the outer membrane of the bacteria; method (M2) for recovering metal involves (i) contacting the hydrogel with a metal; a bioreactor comprising a leachate tank for holding a leachate solution, a nutrition tank for holding a nutritional solution, a mixing tank which is fluidly coupled to the leachate tank and the nutrition tank such that the leachate solution and the nutritional solution can be combined in the mixing tank to form a combined solution, the hydrogel, at least one cartridge having an inlet and an outlet, where the cartridge holds the hydrogel and the mixing tank is fluidly coupled to the inlet, and a pump, where the pump directs the combined solution to flow from the mixing tank to the inlet, through the cartridge, and exit through the outlet as an effluent; and method (M3) for removing metal species from a leachate solution involves (A) flowing the leachate and a nutritional solution into the inlet of the bioreactor cartridge and over the hydrogel to form an effluent that exits the bioreactor cartridge through the outlet.