Thermal sprayed ethylene methacrylic acid (EMAA) and ethylene tetrafluoroethylene (ETFE) coatings were evaluated for corrosion protection in a biochemical process to treat geothermal residues. Coupon, Atlas cell, peel strength and cathodic disbondment tests were performed in aggressive environments including geothermal sludge, hypersaline brine and sulfur oxidizing bacteria (Thiobacillus jerrooxidans) to determine coating suitability for protecting storage tanks and reaction vessels. It was found that the polymers were resistant to chemical attack and biodegradation at the test temperature of 55°C. The EMAA coatings protected 3l6L stainless steel from corrosion in coupon tests. However, corrosion of mild steel substrates coated with EMAA and ETFE occurred in Atlas cell tests that simulated a lined reactor operating environment and this resulted in decreased adhesive strength. Peel tests revealed that failure mode was dependent on exposure conditions. Cathodic disbondment tests in brine at room temperature indicated that EMAA coatings are resistant to disbondment at applied potentials of -780 to -1070 mV SCE for the test conditions and duration.