Surface modification of polypropylene feed spacers typical of spiral wound membrane modules was studied by generation of crystalline ZnO nanorods. A seeding layer made by deposition of ZnO nanoparticles (20-40-60 nm diameter) from aqueous dispersions served as nucleation centers for crystallization. A uniform layer of ZnO nanorods was grown on the seeding layer by chemical bath deposition from a zinc acetate solution. Biocidal activity was estimated by antibacterial tests in static liquid culture against Escherichia coli and antibiofouling tests in flow-through/cross-flow mode against a mixture of Pseudomonas fluorescens and Bacillus subtilis. Best biocidal activity was displayed by 20 nm ZnO particles, suggesting a tradeoff between surface coverage, roughness and particle size. Although the seed layer itself displayed acceptable antibacterial activity, a marked improvement was achieved by the nanorods, proving that the morphology of the deposition layer was involved in the antibacterial mechanism. Antibiofouling activity was further improved by superhydrophobic over-coating of the nanorods with octadecyl-phosphonic acid. Modified spacers reduced permeate flux decay by at least 40% compared to controls. The enhanced antibiofouling activity of crystalline ZnO nanorods, compared with amorphous ZnO nanoparticles, can be explained by a combination of the abrasive surface of the crystalline nanorods, hydrophobic repulsion and cumulative oxidation.