Chemical And Toxicity Analysis-based Technical Comparison Of Biological Wastewater Treatment Processes

Conventional Activated Sludge (CAS) and Vertical Tubular Biological Reactor (VTBR) as novel biological treatment technique were set-up in lab-scale to treat the industrial coking wastewater. To evaluate their performances, both chemical indexes (e.g. COD, volatile phenol and organic compounds) and biological toxicity indexes were analyzed, Microbial community structure of the two bioreactors also was compared. Meanwhile, gas phase surface discharge plasma using liquid electrode and Fenton oxidation technologies were used to treat the bioreactor effluent, so as to choose the suitable advanced oxidation processes (AOPs).The operating results of the reactors in summer and winter revealed that VTBR performed better than CAS in the removal of conventional indexes and toxicity organic compounds, and the performance showed better in summer than in winter. In addition, the analysis of the microbial community structure by PCR-DGGE also showed VTBR had more abundance in the microbial community structure and flora diversity.The bio-toxicity tests in summer and winter showed that VTBR was more effectively in the bio-toxicity (using Photobacterium phosphoreum, Chlorella pyrenoidosa and zebra fish as test organisms) removal than CAS. The luminescent bacteria toxicity removal rate of CAS was8.1%in winter and85%in summer. While VTBR was42%in winter but almost removed in summer. The algae growth inhibiton test showed that there were no obvious differences between CAS and VTBR effluents of the algae toxicity test. The24h LD50to zebra fish of CAS effluent was33.91%(α=0.05,32.87%≤LD50≤34.97%), while VTBR had no lethal toxicity to zebra fish. But the influent, CAS and VTBR effluents all exhibited obvious behavioral toxicity effects to zebra fish.The results above explained that biological treatment could not remove the bio-toxicity absolutely, so the advanced oxidation processes were used to treat the bio-effluents and the preliminary investigation showed that Fenton oxidation technique was more effectively and affordable than plasma technique in the toxicity removal.The study concluded that VTBR had better performance in conventional indexes and bio-toxicity removal, and VTBR could remove organic compounds more completely, and also had more abundance on microbial community structure and diversity, which suggested that VTBR could be used as alternative of conventional biological treatment process aiming to reduce the potential ecological risk of effluents to the receiving water body. Meanwhile, depth treatment should be combined with biological treatment so as to achieve the toxicity totally removal.