Study On Zero-Valent-Iron And Ferric Iron Enhanced Anaerobic Biological Treatment Of Coking Wastewater

Coking wastewater is a kind of typical lindustrial wastewater which contains plenty of refractory organic contaminants. Due to the toxicity and poor biodegradability of coking wastewater, the performance of biological treatment of actual coking wastewater is generally unsatisfied. As a high-efficient and low-cost biological treatment technology, anaerobic biological reactor has been widespreadly used for wastewater treatment. However, with respect to the treatment of actual coking wastewater, the long start-up time of traditional anaerobic reactor and the weak ability resisting the change of organic loading rate limits the performance of anaerobic reactor. Herein, zero-valent-iron (ZVI) and magnetite (Fe3O4) were added in the reactors and the enhanced performance of the reactors was investigated. Besides. The effects on microbial communities in the reactors were also studied. Our experiments provide theoretical evidences for further practical applications of ZVI enhanced anaerobic biological reactor and magnetite enhanced anaerobic biological reactor for the treatment of coking wastewater.Therefore, three reactors were operated to study on the different performance of the UASB, ZVI-UASB, and magnetite-UASB. Microbial communities of all three reactors were also investigated. The conclusions were listed as below:(1) The start-up time of the ZVI enhanced reactor was effectively reduced compared to that of UASB. The sludge acclimatization was completed in 80 days. The hydraulic retention time (HRT) was 24h. The temperature was 35±1? and the CODCr of influent was about 2000 mg/L. The CODCr removal efficiency of the ZVI-UASB effluent was 69%, which was significantly higher than that of the UASB effluent (CODCr removal efficiency was 38%). With respect to the biodegradability, the BOD5/CODCr (B/C) of influent was 0.154, which indicated the poor biodegradability of coking wastewater. The B/C of the ZVI-UASB effluent was 0.305, which was much higher than that of influent. This demonstrated that the effluent can be biodegraded easier, which would facilitate subsequent aerobic biological treatment. With respect to particular organic compounds, the concentration of phenol in the influent and effluent of coking wastewater declined from 300 mg/L to 85 mg/L detected by HPLC. ZVI-UASB reactor showed a better performance of phenol removal efficiency of 73%. High-throughput MiSeq sequencing method was used to examine the 16S rRNA genes of microbiology from ZVI-UASB reactor. Methanosaeta, which is benefit to the degradation of organic compounds, was significantly enriched in ZVI-UASB reactor. The result explained the high CODcr removal efficiency of ZVI-UASB reactor from the point of microorganism metabolize.(2) The CODcr removal efficiency of magnetite-UASB reactor was remarkably improved compared to that of UASB. Magnetite (Fe3O4) is a kind of a mixture of ferrous iron/ferric iron and added to the magnetite-UASB reactor to accelerate the electron transfer between microbial species as electron carriers. Under the same operating conditions and CODCr of influent, the CODcr removal of the reactor with magnetite is 73%, which was nearly a times higher than control UASB reactor; After 80 days of domestication, pH was stable at around 7.7, demonstrating that magnetite is helpful to maintain the reactor at a weak alkaline environment and can promote the growth of microorganisms; With respect to the removal of toxic pollutants, the phenol removal efficiency of magnetite-UASB is 76%, compared to the UASB reactor of 57%, suggesting that the addition of magnetite can improve anaerobic microbial resistance to toxic substances and degraded poor-biodegradable organic compounds. Furthermore, the operation improved the biodegradability of coking wastewater. High-throughput MiSeq sequencing results showed that:Syntrophus, which is benefit to the degradation of phenol, was significantly enriched in magnetite-UASB reactor. The experiment proved the effectiveness of magnetite in anaerobic biological treatment of actual coking wastewater, and explained the reason from the point of microbial community an alysis.