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

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Authors

Rava, Eleonora Maria Elizabeth
Chirwa, Evans M.N.

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Publisher

IWA Publishing

Abstract

The purpose of this study was to determine the effect different biofilm carrier filling ratios would have on biofilm morphology and activity and bacterial diversity in a hybrid fixed-film bioreactor treating high strength coal gasification wastewater (CGWW) for the removal of chemical oxygen demand (COD), phenols and ammonia-nitrogen. Results showed that a carrier fill of 70% formed a ‘compact’ biofilm, a 50% fill formed a ‘rippling’ biofilm and a 30% fill formed a ‘porous’ biofilm. The highest microbial activity was obtained with a 50% carrier fill supporting a relatively 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 quality of the CGWW by removing 49% and 78% of the COD and phenols, respectively. However, no significant amount of ammonia-nitrogen was removed since nitrification did not take place due to heterotrophic bacteria out-competing autotrophic nitrifying bacteria in the biofilm. The dominant heterotrophic genera identified for all three carrier filling ratios were Thauera, Pseudaminobacter, Pseudomonas and Diaphorobacter.

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Keywords

Anox-kaldness, Biofilm, Next-generation sequencing, Nitrification, Pollutants, Thauera, Coal gasification wastewater (CGWW), Chemical oxygen demand (COD)

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Citation

Rava, E & Chirwa, E 2016, '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', Water Science and Technology, vol. 73, no. 10, pp. 2461-2467.