Effect of carrier fill ratio on biofilm properties and performance of a hybrid fixed-film bioreactor treating coal gasification wastewater for the removal of COD, phenols and ammonia-nitrogen

摘要

The purpose of this study was to determine the effect different biofilm carrier filling ratios would have on biofilm morphology and activity andbacterial diversity in a hybrid fixed-film bioreactor treating high strength coal gasification wastewater (CGWW) for the removal of chemicaloxygen demand (COD), phenols and ammonia-nitrogen. Results showed that a carrier fill of 70% formed a ‘compact’ biofilm, a 50% fill formeda ‘rippling’ biofilm and a 30% fill formed a ‘porous’ biofilm. The highest microbial activity was obtained with a 50% carrier fill supporting arelatively thin biofilm. The highest level of biofilm bound metals were aluminium, silicon, calcium and iron in the ‘compact’ biofilm; nitrogen,magnesium, chloride, sodium and potassium in the ‘rippling’ biofilm, and copper in the ‘porous’ biofilm. The bioreactor improved the qualityof the CGWW by removing 49% and 78% of the COD and phenols, respectively. However, no significant amount of ammonia-nitrogen wasremoved since nitrification did not take place due to heterotrophic bacteria out-competing autotrophic nitrifying bacteria in the biofilm. Thedominant heterotrophic genera identified for all three carrier filling ratios were Thauera, Pseudaminobacter, Pseudomonas andDiaphorobacter.