title: Removal of cyanide compounds from coking wastewater by ferrous sulfate: Improvement of biodegradability.
abstract: The effect of ferrous sulfate (FeSO4) treatment on the removal of cyanide compounds and the improvement of biodegradability of coking wastewater were investigated by varying Fe:TCN molar ratios. Results suggested that the reaction between FeSO4 and coking wastewater was a two-step process. At the first step, i.e., 0≤Fe:TCN≤1.0, the reaction mechanisms were dominated by the precipitation of FeS, the complexation of CN(-), and the coagulation of organic compounds. The COD of coking wastewater decreased from 3748.1 mg/L to 3450.2 mg/L, but BOD5:COD (B/C) was improved from 0.30 to 0.51. At the second step, i.e., 1.0<Fe:TCN≤3.2, the immobilization of soluble metal-cyanide compounds by ferrous ions was the dominating mechanism. The COD showed a continuous increase to 3542.2 mg/L (Fe:TCN=3.2) due to the accumulated ferrous ions in coking wastewater. Moreover, B/C decreased progressively to 0.35, which was attributed to the negative effects of excess ferrous ions on biodegradability. To improve coking wastewater's biodegradability, a minimum ferrous dosage is required to complete the first step reaction. However, the optimum ferrous dosage should be determined to control a safe residual TCN in coking wastewater for the further biological treatment.
authors.affiliation: Faculty of Architectural, Civil Engineering and Environment, Ningbo University, Ningbo 315211, PR China. Electronic address: yxb727@gmail.com.
authors.forename: Xubiao
authors.initials: X
authors.lastname: Yu
authors.affiliation: The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, College of Environment and Energy, South China University of Technology, Guangzhou 510006, PR China.
authors.forename: Ronghua
authors.initials: R
authors.lastname: Xu
authors.affiliation: The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, College of Environment and Energy, South China University of Technology, Guangzhou 510006, PR China.
authors.forename: Chaohai
authors.initials: C
authors.lastname: Wei
authors.affiliation: School of Bioscience and Bioengineering, South China University of Technology, Guangzhou, Guangdong 510006, PR China.
authors.forename: Haizhen
authors.initials: H
authors.lastname: Wu
mesh_terms: D003486:Cyanides / Q000302:isolation & purification*; D005296:Ferrous Compounds / Q000737:chemistry*; D007220:Industrial Waste / Q000032:analysis; D014865:Waste Disposal, Fluid / Q000379:methods*; D062065:Wastewater / Q000737:chemistry
chemical_list: D003486:Cyanides; D005296:Ferrous Compounds; D007220:Industrial Waste; D062065:Wastewater; C020748:ferrous sulfate
keywords: Biodegradability; Coking wastewater; Complexation; Cyanide; Ferrous sulfate