Biofilms have several characteristics that ensure their survival in a range of adverse environmental conditions, including high cell numbers, close cell proximity to allow easy genetic exchange (e.g., for resistance genes), cell communication, and protection through the production of an exopolysaccharide matrix. Together, these characteristics make it difficult to kill undesirable biofilms. An elimination method that is safe, easy to deliver in physically complex environments, and not prone to microbial resistance is highly desired. Cold atmospheric plasma, a lightning-like state generated from air or other gases has recently found an extensive range of applications for biological decontamination. This is due to the unique chemical and bio-active radicals generated known collectively as reactive oxygen and nitrogen species (RONS). A plasma discharge can also be produced in water to produce plasma-activated water (PAW). We have designed new discharge electrodes to generate PAW. We demonstrate their effectiveness under different operating conditions for contaminated chicken breasts, showing that ozone, peroxides, nitrites, and nitrates affect bacterial killing but not the quality of the meat. Moreover, the use of different plasma feeding gases to eradicate Escherichia coli biofilms grown on stainless steel coupons demonstrates the importance of oxygen in the plasma to remove biofilms. Using scavengers for several reactive plasma species we show that superoxide is crucial for plasma-mediated biofilm killing. The use of PAW provides significant benefits for tackling the ubiquitous problem of biofilm contamination in food, water, and medical areas.