Surface modification of carbon fiber support by ferrous oxalate for biofilm wastewater treatment system

In order to overcome the shortcoming of poor hydrophilicity and smooth surface of carbon fiber, and to improve water treatment effect of biofilm system using carbon fiber as support, this paper employed nitric acid and ferrous oxalate to modify carbon fiber. A series tests were conducted on untreated carbon fiber, nitric acid oxidized carbon fiber, nitric acid and ferrous oxalate modified carbon fiber, namely, scanning electron microscopy-energy dispersive spectrometer, X-ray photoelectron spectroscopy, static contact angle and water treatment effect. Results showed that, hydrophilic functional group containing oxygen and nitrogen on the surface of carbon fiber increased after modification by nitric acid and ferrous oxalate, which greatly improved the hydrophilicity of carbon fiber surface. The ferrum element in ferrous oxalate modified carbon fiber existed in the form of magnetic oxide (Fe₃O₄) via FeOC to bond with carbon fiber, which noticeably enhanced the surface roughness of carbon fiber. Dry weight of biofilm per unit immobilized on ferrous oxalate modified carbon fiber support enhanced and it was 2.3 and 0.6 times bigger than that of untreated and nitric acid oxidized carbon fiber. Biofilm system with ferrous oxalate modified carbon fiber as support had better water treatment effect and stable effluent standard. The average removal efficiency of chemical oxygen demand, ammonia nitrogen and total phosphorus achieved 97%, 96% and 97%. In addition, removal efficiency of chemical oxygen demand, ammonia nitrogen and total phosphorus increased by 7.18%, 10.30%, 9.40% and 4.86%, 4.30%, 6.40%, compared to carbon fiber and nitric acid oxidized carbon fiber support biofilm system. Combination of nitric acid oxidation and ferrous oxalate deposition, which has never been developed before, is a promising carbon fiber surface modification method to improve its performance as biofilm support.