Osmotic membrane processes such as reverse osmosis (RO) are widely used in the water industry to help mitigate water scarcity (e.g., through desalination) and as a tertiary wastewater treatment. Pressure retarded osmosis (PRO) can also be used to recover or generate energy from a salinity gradient. However, biofouling is the major issue affecting the productivity and energy efficiency of osmotic membranes, leading to high energy consumption in RO and low power density in PRO. This study explores the use of iron nanoparticle (FeNP or nZVI) coatings on osmotic membranes to reduce the impact of biofouling and subsequent savings in energy consumption. Laboratory results are presented from FeNP coated (0.3 wt%) commercial membranes, biofouled with a high concentration (109 CFU ml−1) of Bacillus halotolerans MCC1, isolated from the Sea of Cortez, Mexico. The anti-biofouling effect stemming from the FeNPs is evaluated in terms of biofilm thickness, TOC, live, dead and total cells on the membrane surface after biofouling. The effect on permeation performance after biofouling in terms of the membrane hydraulic resistance, salt rejection, salt permeance and permeate flux is also analyzed. Data on RO performance and energy consumption in terms of permeate flux are then validated and used to predict the energy use and water production costs for a conventional seawater RO (SWRO) desalination plant, as well as for a hybrid RO-PRO plant, under typical operating conditions. A highly significant reduction in biofouling and higher long-term permeate flux are observed for the FeNP coated membranes compared to an uncoated membrane. The results suggest that FeNPs can help maintain permeate flux in SWRO plants despite biofouling, thereby helping reduce energy consumption. Further, decreased requirements for membrane cleaning frequency and pretreatment lead to extended membrane life, reducing the cost of desalination and water treatment.