Color Removal and Biodegradability Enhancement of Chemical Pretreatment Effluent of Eucalyptus Chemithermomechanical Pulp (CTMP) by Zero-Valent Iron

Deep color and high concentration of organic compounds are the important characteristics of Chemithermomechanical pulp (CTMP) effluent. The objectives of this study are to investigate the feasibility of removing the color of eucalyptus CTMP chemical pretreatment effluent with zero-valent iron (Fe (0)) and to examine the effect of Fe (0) treatment on biodegradability enhancement of the effluent. The effect of operating conditions, including pH, reaction time, cast- iron filings dosage and size range, on color removal rate was discussed. Results showed that under certain conditions, color removal rate of the effluent reached about 90%. It was also found that chemical oxygen demand (COD) and 5 day biochemical oxygen demand (BOD5) of the effluent decreased evidently after zero-valent iron treatment, and BOD₅ / COD increased from 0.27 to 0.42, which indicated that biodegradability of the effluent was obviously enhanced. Based on the results, it is feasible that zero- valent iron can be used for pretreatment of CTMP effluent before biological treatment processes.