NOVELTY - Operation of a bioreactor and filtration system (200) comprises feeding water containing contaminants into a bioreactor system containing live microorganisms (202), where bioreactor system comprises a first bioreactor; feeding a concentration of iron into the first bioreactor from 150 to 10000% above a stoichiometric requirement (204) for iron in the first bioreactor; and treating, directly or indirectly, effluent from the bioreactor system with a filtration system (206) to obtain filtration system effluent free of the contaminants.    USE - Operation of bioreactor and filtration system used for treating biodegradable waste, such as contaminated water.    ADVANTAGE - The method reduces the fouling of filtration system. The concentration of iron above the stoichiometric requirement fed into the first bioreactor results in a reduction in fouling of the filtration system when compared to utilizing the stoichiometric requirement for iron in the first bioreactor. The method improves the overall operation and efficiency of the bioreactor/filtration system. Reducing fouling or clogging of the membrane increases the efficiency and decreases the cost of operating the bioreactor and filtration system. The efficiency is increased by preventing/reducing the need to clean or replace the filter membrane and by increasing the amount of effluent that can travel from the bioreactor through the membrane of the filtration system before maintenance. Cost is reduced because more effluent can pass through the membrane of the filtration system, less time is utilized in cleaning or replacing the membrane, and the cost of cleaning or replacing the membranes is reduced/saved. The method provides for a more efficient and cost effective system for the cleaning of waste.    DESCRIPTION OF DRAWING(S) - The drawing is a flow chart illustrating the method of operating bioreactor and filtration system.    Operating bioreactor and filtration system (200)    Feeding water containing contaminants into bioreactor system containing live microorganisms (202)    Feeding concentration of iron into first bioreactor above a stoichiometric requirement (204)    Treating effluent from the bioreactor system with filtration system (206)