Enhanced treatment of wastewater from the vitamin C biosynthesis industry using a UASB reactor supplemented with zero-valent iron

Abstract

The effects of zero-valent iron (Fe⁰) on the performance of a mesophilic upflow anaerobic sludge blanket (UASB) reactor treating high-strength wastewater from the vitamin C biosynthesis industry (VCW) was investigated during a 200-day period. The results showed that the chemical oxygen demand (COD) removal efficiency, CH₄ content in biogas, specific methanogenic activity of sludge, and phosphate removal efficiency were significantly improved up to 81.8–96.1%, 76.5–79.6%, 1.71–2.87 g CH₄-COD g⁻¹ VSS d⁻¹ and 68.5–85.2%, respectively, at elevated organic loading rates (OLRs) in the Fe⁰-amended reactor (R_Fe). In contrast, the corresponding values of 65.3–83.4%, 69.1–70.8%, 1.12–1.95 g CH₄-COD g⁻¹ VSS d⁻¹ and 1.4–1.6%, respectively, were recorded in the control (R₀). Elevated ferrous concentration of nearly 400 mg L⁻¹ in sludge was detected in R_Fe, whereas in the effluent of both reactors it was low (<1.0 mg L⁻¹). Batch tests further showed that Fe⁰ significantly enhanced the biodegradability of the VCW as shown by an increase in BOD/COD ratio from 0.41 to 0.65, and could serve as the electron donor for methanogenesis by anaerobic sludge, which were responsible for the differences between R_Fe and R₀. The results suggest this integrated Fe⁰-microbial system is promising in facilitating the anaerobic digestion of VCW in UASB reactors.

Keywords:

• zero-valent iron
• UASB
• high-strength wastewater
• vitamin C biosynthesis industry
• methanogenesis

Acknowledgements

This work was partly funded by the National Basic Research Program of China (No. 2004CB418505). We give special thanks to Prof. Yongfeng Jia and Prof. Guanxiong Chen for their useful discussions. We also thank Yanyuan Wang and Liying Xu for their assistance in Fe²⁺ analysis.