Research On Refractory Wastewater Treatment Using Anaerobic Technology Enhanced By Dosing Of ZVI

Anaerobic technology has obvious advantages in the treatment of refractory and high concentration wastewaters from dyeing and pharmaceutical industries:without limitation of the dissolved oxygen, high volumetric loading, short hydraulic retention time, small power consumption, high removal efficiency, and low investment and low operation costs. Therefore, the anaerobic technology has been widely applied. However, due to the complexity of wastewaters and sensitivity of methanogenesis, the anaerobic processes are easily shocked and inhibited, accompanied with decrease of treating performance and deterioration of system. A novel anaerobic technology enhanced by dosing of zero-valent iron (ZVI) proposed in our previous studies showed that it could effectively improve methanogenesis and anaerobic performance in treatment of artifical wastewater. Therefore, this novel method needs to use treatment of actual refractory wastewaters prior to its sacle up, which was not followed in the previous works.In this study, we studied the processing capacity to treat the actual dyeing wastewater and pharmaceutical wastewater through using this ZVI-anaerobic system. The main conclusions as follows:For the actual dyeing wastewater:(1) The anaerobic reactor with dosing of ZVI had high COD removal rate, stable operation, little effect of influent water, rapid start up with a strong ability of resistance to shock load. In comparison, COD removal rate in a common anaerobic reactor without ZVI was40%lower than the ZVI-anaerobic reactor, presenting significant fluctuations with the influent.(2) ZVI played a major role in the improvement and stability of the anaerobic environment. Due to the existence of ZVI, the pH in the reactor was maintained well between7.5and8.0, creating a benefitical condition for the growth of methanogens that are sensitive to pH changes. The control anaerobic reactor was not conducive to the growth of methanogens because of pH drop with increasing of the influent loadings. The redox potential in the ZVI-anaerobic reactor maintained at below-429mV. This extremely anaerobic environment played a positive role in enhancement of the reactor.(3) Biodegradability of the effluent water of the reactor with ZVI was significantly improved. The average BOD5/COD of traditional anaerobic reactor’s effluent was0.18, while the average BOD5/COD of the anaerobic reactor’s effluent with zero-valent iron was0.31. This was of great significance for the subsequent aerobic treatment.For the actual pharmaceutical wastewater:(1) Direct treatment had the poor results, because the pharmaceutical wastewater was of complex composition, a lot of toxic substances, high COD and other characteristics and a low microbial use rate. Process of treatment pharmaceutical wastewater must be increased, such as pre-treatment before biochemical treatment.(2) With Flocculation and Fenton as a means of pre-treatment and two-phase anaerobic reactor for subsequent processing, COD of the pharmaceutical wastewater’s effluent was from40,000mg/L reduced to8740mg/L. Biodegradability was obviously improved because of increasing the ratio of BOD5/COD from0.04to0.308, which laid a solid foundation for the subsequent treatment process.For the actual dyeing wastewater:A scale-up anaerobic reactor with dosing of zero-valent iron was used for treatment of actual dyeing wastewater. The COD removal rate reached20%, which was siginificantly higher than that in the anaerobic tank of the actual treating system presently used (10%). Its effluent pH stabilized at7and the color removal rate was up to95%. This showed anaerobic technology enhanced by dosing of ZVI had obvious advantages at the treatment of dyeing wastewater, especially the treatment of chroma.